BEP-049 M1–M4: backtick strings, interpolation, control flow, tagged templates

[codeshaunted]

Implements BEP-049 (String Interpolation) milestones M1 through M4.

What's in this PR

M1 — backtick string literals `...`: new BACKTICK token, multi-tick delimiter ladders, escapes, multi-line auto-dedent (§12), usable in any expression position.

M2 — ${expr} interpolation: ${...} as a block expression (§4), implicit .to_string() for non-string values (§11), and strict typing (§7/§11) — interpolating a nullable or non-stringable value is a compile-time error.

M3 — block control flow: ${for (let x in xs)}…${endfor}, ${if (c)}…${else if}…${else}…${endif} using host syntax, with §13 whitespace control.

M4 — tagged templates (§10): tag`...` with the //baml:tagged_string marker, TaggedString { parts, values }, tag resolution + signature validation, body-lambda params scoping into ${…}, and full VM execution — static layouts (M4e.1a) and ${for}/${if} runtime flattening (M4e.1b).

Architecture: check-then-lower (clean diagnostics)

Both backtick forms are unified behind a first-class Expr::Template { tag: Default { elaborated } | Custom { tag, body }, segments } node that survives through TIR. Untagged backticks no longer desugar early — interpolation diagnostics point at the original ${…} span instead of leaking a synthetic .to_string() call. This matches how tagged templates (and TypeScript) check the structured node and lower late.

Testing

Full workspace suite green. Adds unit + runtime coverage for backtick literals, interpolation, strict-type diagnostics, control flow, and tagged-template execution (static, ${for}/${if}, nested, mixed, captures, body-param injection, nested lambdas capturing loop-locals).

Not in this PR

M5 (built-in prompt tag), M6 (legacy #"..."# interop + migrator), M7 (drop minijinja).

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • BEP-049 backtick string literals with ${} interpolation, including ${for} / ${if} control-flow.
  • Tagged templates with custom tag expressions and structured TaggedString template metadata.
  • Backtick-aware LLM prompts using prompt closures, plus typed prompt/context helpers in the standard library.
• Improvements
  • BEP-049 dedentation and block-tag trimming for multiline literals.
  • Extended escape decoding with backtick-specific line-ending normalization.
  • Formatter/lexer/parser now properly recognize and preserve backtick delimiter/interpolation syntax.
• Bug Fixes
  • More precise template diagnostics and improved diagnostic span stability.

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Project	Deployment	Actions	Updated (UTC)
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📝 Walkthrough

Walkthrough

Implements BEP-049 backtick interpolated string literals and tagged-template expressions end-to-end: shared dedent/escape utilities with Unicode-safe processing, a new Backtick lexer token with multi-tick delimiter parsing, backtick AST wrappers with dedent and segment building, compiler AST Expr::Template nodes with tagged/untagged variants, CST-to-AST lowering with prompt-closure synthesis, HIR/MIR/TIR pipeline extensions for capture analysis and type inference, LLM runtime integration with per-attempt prompt compilation, formatter support for verbatim backtick output, comprehensive fixture coverage, and binary size-gate refresh.

Changes

BEP-049 End-to-end Implementation

Layer / File(s)	Summary
Template preprocessing, escape utilities, and TaggedString runtime struct baml_language/crates/baml_base/src/dedent.rs, baml_language/crates/baml_base/src/escape.rs, baml_language/crates/baml_base/src/lib.rs, baml_language/crates/baml_builtins2/baml_std/baml/core.baml	Exports preprocess_template computing longest-common leading-whitespace prefix across non-blank lines with UTF-8 byte-safe stripping, unescape_string_literal and unescape_backtick_string_literal for flavor-specific escape decoding (backtick includes \`` / $recognition and CRLF normalization), registers both as public crate modules, and definesTaggedString { parts: string[], values: unknown[] }runtime struct withparts.length == values.length + 1` invariant.
Backtick lexical tokenization and parser grammar baml_language/crates/baml_compiler_lexer/src/tokens.rs, baml_language/crates/baml_compiler_syntax/src/syntax_kind.rs, baml_language/crates/baml_compiler_parser/src/parser.rs	Adds TokenKind::Backtick, syntax kinds for BACKTICK_STRING_LITERAL and ${...} block-tag markers (BACKTICK_FOR_OPEN/ENDFOR/IF_OPEN/ELSE_IF/ELSE/ENDIF), implements multi-tick delimiter-ladder backtick parsing with anchored close and escaped character handling, routes ${...} into block-tag vs expression forms, adds Pratt-postfix tagged-template wrapping when backtick follows expression with no newline, makes match scrutinee parentheses optional (: Type only in paren form), accepts client in field/member contexts with disambiguation, restricts Word regex to reject trailing $ so interpolation operators lex separately, and extends parser test coverage.
CST/AST wrappers for backtick literals baml_language/crates/baml_compiler_syntax/Cargo.toml, baml_language/crates/baml_compiler_syntax/src/ast.rs	Imports baml_base dependency and shared unescape helpers, adds typed BacktickStringLiteral/BacktickText/BacktickInterpolation wrappers, implements full API with full_text(), delimiter_count(), raw_inner(), is_multiline(), value(), segments(), segments_with_errors(), builds two-pass flat-part stream from CST tokens/nodes and reconstructs segments with escape decoding and dedent via placeholder strategy, applies BEP §13 "alone-on-line" whitespace trimming for block tags while excluding inline ${expr}, validates block structure with stack-based error detection for unclosed/mismatched/stray tags, and wires backtick/tagged-template nodes into PromptField.backtick_string(), LetStmt.initializer(), BlockExpr.elements(), and Field.name() accessors.
Compiler AST template model and lowering diagnostics baml_language/crates/baml_compiler2_ast/src/ast.rs, baml_language/crates/baml_compiler2_ast/src/lowering_diagnostic.rs, baml_language/crates/baml_compiler2_ast/src/docstring.rs, baml_language/crates/baml_compiler2_ast/src/auto_derive_json.rs, baml_language/crates/baml_compiler2_ast/src/lib.rs	Adds Expr::Template with TemplateTag::Default { elaborated: ExprId } (default realization) and TemplateTag::Custom { tag, body }, TemplateSegment tree including Text/Interp/For (iterator and C-style) / If with branches and optional else, FunctionDef::is_tagged_template_tag field to mark tagged-string tags with //baml:tagged_string marker, LlmBodyDef::stream_body: Option<(ExprBody, AstSourceMap)> for pre-lowered $stream companion, introduces has_baml_marker helper for directive detection, adds LoweringDiagnostic::MalformedTemplateBlock (error) and EmptyInterpolation (warning) variants, renames maybe_synthesize_json_methods to maybe_synthesize_derived_methods, re-exports shared unescape, and extends AST tests with backtick/tagged-template lowering and interpolation-chain validation.
CST-to-AST template lowering and LLM prompt closure synthesis baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs, baml_language/crates/baml_compiler2_ast/src/lower_cst.rs, baml_language/crates/baml_compiler2_ast/src/companions.rs	Dispatches BACKTICK_STRING_LITERAL to lower_backtick_string_literal producing Expr::Template with default realization via elaborate_default_segments, dispatches TAGGED_TEMPLATE_EXPR to lower_tagged_template_expr producing custom tag closure, implements untagged elaboration with accumulator loops for text segments and implicit .to_string() coercions for ${expr}, supports iterator and C-style ${for} (translated to accumulator while), builds ${if} as inside-out host if-chain with empty string for missing else, implements tagged templates via build_prompt_tag_closure constructing baml.TaggedString { parts, values }, adds synthesize_llm_call_with_prompt for new-mode LLM function bodies with prompt_closure parameter, pre-computes stream_body and companion bodies from backtick prompts in lower_function, derives is_tagged_template_tag via has_baml_marker(..., "tagged_string"), sets is_tagged_template_tag: false on all synthesized lambdas, and propagates flag through llm_parse/make_llm_companion into generated companion function defs.
HIR scope/capture tracking and MIR custom template lowering baml_language/crates/baml_compiler2_hir/src/item_tree.rs, baml_language/crates/baml_compiler2_hir/src/scope.rs, baml_language/crates/baml_compiler2_hir/src/builder.rs, baml_language/crates/baml_compiler2_mir/src/lower.rs	Adds Function::is_tagged_template_tag to HIR and propagates from AST during allocation, introduces Scope::is_template_body to mark synthetic template-body lambda scopes as transparent for inference ownership, implements walk_template_lambda_body that pushes synthetic lambda scope, walks flattened body, computes captures via analyze_lambda_captures, and performs transitive capture re-recording when nested, lowers custom templates in MIR via lower_tagged_template that resolves tag function and constructs hand-rolled body closure producing baml.TaggedString, implements tagged_body_param_bindings map for MIR-only closure parameters, supports static (text+interps) and dynamic (with control flow) paths, adds ensure_transitive_capture for nested lambda parameter forwarding, handles IO sys-op omitted-default materialization at call sites via sys_op_callee detection, and extends lower_path_expr to resolve tagged-body parameters as locals or transitive captures.
TIR type inference, tagged-tag validation, and diagnostic span stabilization baml_language/crates/baml_compiler2_tir/src/builder.rs, baml_language/crates/baml_compiler2_tir/src/inference.rs, baml_language/crates/baml_compiler2_tir/src/infer_context.rs, baml_language/crates/baml_compiler2_tir/src/throws_analysis.rs, baml_language/crates/baml_compiler2_tir/src/normalize.rs, baml_language/crates/baml_compiler2_visualization/src/control_flow/from_ast.rs, baml_language/crates/baml_lsp2_actions/src/check.rs, baml_language/crates/baml_lsp2_actions/src/completions.rs	Extends TypeInferenceBuilder with template_body_params map to track synthetic parameter types per FileScopeId, threads params through ScopeInference with seed_template_body_params lambda inference helper, validates tagged-template tag function shape via validate_tagged_tag checking first parameter is body: (...) -> baml.TaggedString, implements Expr::Template synthesis for tagged (infers tag, binds/records body params, types body) and untagged (types elaboration, retains user diagnostics, enforces nullability/stringability of ${expr}), adds interpolation helpers (check_template_interps_stringable, check_interp_stringable, is_unit_tail) to enforce non-nullable and .to_string()-convertible values, extends throws analysis with recursive template-segment walking, refactors unknown-like detection via ty_contains_unknown_like with builtin-unknown toggle, adds type errors for invalid tags (TaggedTagNotAFunction, TaggedTagNotMarked, TaggedTagBadBodyParam) and invalid interpolations (InterpolatedValueMaybeNull, TypeNotInterpolatable), implements diagnostic span freezing via freeze_diagnostic_spans_from to preserve nested lambda error locations, stabilizes lambda diagnostic handling with lambda_diag_start capture, updates try_resolve_member_on_ty so union members must resolve on all arms, extends default-parameter forward-reference and throws fact collection for template segments, updates LSP completion detection to require annotation context check, and maps new type error variants to diagnostic IDs.
Compiler emission, PPIR companion reuse, and LLM prompt-closure runtime baml_language/crates/baml_compiler2_emit/src/lib.rs, baml_language/crates/baml_compiler2_ppir/src/lib.rs, baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm.baml, baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm_types.baml	Refactors emit metadata to construct FunctionMeta::Llm when client is present (regardless of prompt), sets prompt_template from llm_meta.prompt when available or empty string otherwise, updates PPIR companion generation to prefer pre-lowered stream_body from DeclarativeMeta::Llm and propagate is_tagged_template_tag, adds prompt_closure: ((Context) -> PromptAst)? parameter to ExecutionContext and LLM function signatures, introduces OutputFormat/Role/ContextClient/Context typed prompt model classes, adds assembly helper assemble_prompt_ast(parts, values) and schema helpers render_output_format/build_output_format, implements PrimitiveClient.render_specialized_prompt branching on closure presence (legacy render_prompt vs closure invocation with per-attempt Context), updates call_llm_function and stream_llm_function to accept and pass prompt_closure to ExecutionContext, and extends execute_once_stream/execute_once_oneshot to use unified render_specialized_prompt path.
Formatter expression rendering for backtick literals baml_language/crates/baml_fmt/src/ast/tokens.rs, baml_language/crates/baml_fmt/src/ast/expressions.rs, baml_language/crates/baml_fmt/src/lib.rs	Adds BacktickString formatter token with token_span construction from opening backtick through node end, implements Token/KnownKind/Printable traits with raw-text output via print_raw_token, multiline width detection via newline presence in span, and leftmost/rightmost token helpers returning backtick characters, adds Expression::BacktickString variant with FromCST construction and delegation to token methods, and includes round-trip and idempotence formatter tests.
Compile fixtures, diagnostic validation, and TIR regression tests baml_language/crates/baml_tests/projects/compiles/backtick_strings/main.baml, baml_language/crates/baml_tests/projects/diagnostic_errors/backtick_strict_types/main.baml, baml_language/crates/baml_tests/projects/diagnostic_errors/control_flow/main.baml, baml_language/crates/baml_tests/src/compiler2_tir/phase3a.rs	Adds M1/M2/M3 backtick compile fixtures covering non-interpolated literals with escapes/multiline/multi-tick, ${expr} interpolation for primitives and function calls, and ${for}/${if} block control-flow, pins strict-type diagnostic fixtures for nullable interpolation scenarios, adjusts control-flow snapshot to use guaranteed-missing method call, adds phase3a gap tests verifying clean prompt-closure compilation, non-zero diagnostic spans for user-facing errors, and correct list element type pinning behavior.

CI Size-gate Updates

Layer / File(s)	Summary
aarch64-apple-darwin size threshold and measurement refresh baml_language/.cargo/size-gate.toml, baml_language/.ci/size-gate/aarch64-apple-darwin.toml	Raises baml-cli and packed-program macOS arm64 max_file_bytes ceilings in the gate config and updates recorded timestamp, git SHA, and binary artifact byte metrics in the CI size-gate snapshot to the 2026-06-17 build baseline.

Sequence Diagram(s)

sequenceDiagram
  rect rgba(135, 206, 250, 0.5)
    note over BAML Source,Lexer: Lexing
    BAML Source->>Lexer: backtick literal or tag`...`
    Lexer->>Parser: Backtick, Dollar, LBrace, Word, RBrace tokens
  end
  rect rgba(144, 238, 144, 0.5)
    note over Parser,SyntaxAST: Parsing & Syntax
    Parser->>Parser: parse_backtick_string (delimiter ladder, ${for}/${if}/${expr})
    Parser->>SyntaxAST: BACKTICK_STRING_LITERAL or TAGGED_TEMPLATE_EXPR node
    SyntaxAST->>SyntaxAST: BacktickStringLiteral API — dedent, escape decode, segments
  end
  rect rgba(255, 218, 185, 0.5)
    note over lower_cst,TIR: Lowering & Typing
    lower_cst->>lower_expr_body: detect backtick prompt in llm.prompt_field()
    lower_expr_body->>CompilerAST: produce Expr::Template (TemplateTag::Default or Custom)
    lower_cst->>lower_expr_body: synthesize_llm_call_with_prompt → stores stream_body
    TIR->>TIR: validate_tagged_tag, seed template_body_params, check interp nullability
  end
  rect rgba(221, 160, 221, 0.5)
    note over PPIR,LLM Runtime: Execution
    PPIR->>PPIR: prefer pre-lowered stream_body over synthesized fallback
    LLM Runtime->>LLM Runtime: call_llm_function with prompt_closure parameter
    LLM Runtime->>LLM Runtime: branch on prompt_closure — closure vs legacy Jinja
  end

Loading

Estimated code review effort

🎯 5 (Critical) | ⏱️ ~150 minutes

Possibly related PRs

• BoundaryML/baml#3094: Both PRs add new LLM function body lowering paths that ultimately call baml.llm.call_llm_function for bytecode execution; main PR adds backtick prompt closure variant while retrieved PR synthesizes generic LLM function bodies.
• BoundaryML/baml#3096: Both PRs extend the template-string preprocessing pipeline; main PR introduces preprocess_template in baml_base::dedent, while retrieved PR uses this new function in sys_llm Jinja prompt template construction.
• BoundaryML/baml#3311: Both PRs modify the LLM prompt-rendering pipeline (baml_std/ns_llm/llm.baml), particularly render_prompt and PrimitiveClient::render_prompt flow; main PR adds backtick/tagged-template closure-based rendering, retrieved PR adds early return_type resolution for output format rendering.

Poem

🐰 Hop, hop, the backtick lands!
With ${expr} in my paws and plans,
Tagged templates bloom from dedented strings,
The prompt closure flows on compiler wings.
No more Jinja—new-mode reigns!
`Hello, ${world}` 🎉 the rabbit explains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title 'BEP-049 M1–M4: backtick strings, interpolation, control flow, tagged templates' clearly and concisely summarizes the main changes: implementation of BEP-049 milestones M1 through M4 covering backtick string literals, ${expr} interpolation, block control flow, and tagged templates. It is specific, descriptive, and accurately reflects the primary objective of this comprehensive feature implementation.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch avery/string-interpolation

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (2)

baml_language/crates/baml_compiler_syntax/src/ast.rs (1)

1063-1073: 💤 Low value

Dedent condition checks decoded content instead of source multiline status.

The condition decoded.contains('\n') determines whether to apply dedent based on the decoded content having newlines. This differs from is_multiline() which correctly checks whether the source spans multiple lines. Per BEP-049, dedent should apply only to source-level multiline strings, not to single-line sources containing \n escape sequences.

Practically, preprocess_template on single-line content with embedded newlines produces the same result, so tests pass. However, the semantic intent is clearer with is_multiline().

♻️ Suggested fix for clarity

     pub fn value(&self) -> String {
         let Some(inner) = self.raw_inner() else {
             return String::new();
         };
         let decoded = unescape_backtick_string_literal(&inner);
-        if decoded.contains('\n') {
+        if self.is_multiline() {
             baml_base::dedent::preprocess_template(&decoded)
         } else {
             decoded
         }
     }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler_syntax/src/ast.rs` around lines 1063 -
1073, The value() method currently decides to call
baml_base::dedent::preprocess_template based on decoded.contains('\n'); change
it to use the source-level multiline check by calling is_multiline() instead
(i.e., replace the decoded.contains('\n') condition with self.is_multiline()).
Keep the rest of the logic (unescape_backtick_string_literal(&inner) and
returning either preprocess_template(&decoded) or decoded) unchanged so dedent
runs only for source multiline strings.

baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs (1)

2300-2301: 💤 Low value

Remove redundant import.

rowan::ast::AstNode is already imported at line 10, so the local use statement on line 2301 is unnecessary.

♻️ Remove redundant import

 fn lower_backtick_string_literal(&mut self, node: &SyntaxNode) -> ExprId {
     use baml_compiler_syntax::BacktickStringLiteral;
-    use rowan::ast::AstNode;

     let value = BacktickStringLiteral::cast(node.clone())

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs` around lines
2300 - 2301, Remove the redundant import of rowan::ast::AstNode in
lower_expr_body.rs: delete the duplicate `use rowan::ast::AstNode;` line (the
file already imports AstNode earlier), leaving only the single existing import
to avoid duplicate imports and clippy/warning noise; locate the extra `use` near
the block that also imports `baml_compiler_syntax::BacktickStringLiteral` and
remove it.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@baml_language/crates/baml_compiler_parser/src/parser.rs`:
- Around line 1840-1849: The helper find_first_backtick_pos (and the similar
helper at the other location) only skips basic trivia via is_basic_trivia, but
parse_backtick_string is entered via self.at(TokenKind::Backtick) which skips
full trivia (including comments), so these helpers can miss an opening backtick
when comments lie between current and the backtick. Fix both helpers to skip the
same set of trivia that self.at uses (i.e., include comments) — replace the
is_basic_trivia check with the broader trivia predicate used by self.at (or
reuse the same utility method used by self.at, or add a small wrapper like
is_full_trivia/is_trivia_including_comments) so the loop advances past comments
as well and then checks for TokenKind::Backtick; update both occurrences
(find_first_backtick_pos and the other helper around the parse_backtick_string
flow) to use this corrected trivia-skipping logic.

---

Nitpick comments:
In `@baml_language/crates/baml_compiler_syntax/src/ast.rs`:
- Around line 1063-1073: The value() method currently decides to call
baml_base::dedent::preprocess_template based on decoded.contains('\n'); change
it to use the source-level multiline check by calling is_multiline() instead
(i.e., replace the decoded.contains('\n') condition with self.is_multiline()).
Keep the rest of the logic (unescape_backtick_string_literal(&inner) and
returning either preprocess_template(&decoded) or decoded) unchanged so dedent
runs only for source multiline strings.

In `@baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs`:
- Around line 2300-2301: Remove the redundant import of rowan::ast::AstNode in
lower_expr_body.rs: delete the duplicate `use rowan::ast::AstNode;` line (the
file already imports AstNode earlier), leaving only the single existing import
to avoid duplicate imports and clippy/warning noise; locate the extra `use` near
the block that also imports `baml_compiler_syntax::BacktickStringLiteral` and
remove it.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: e5e898f2-8a4b-4eaf-afda-5b333e80befe

📥 Commits

Reviewing files that changed from the base of the PR and between 763fa16 and 3ab9197.

⛔ Files ignored due to path filters (55)

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📒 Files selected for processing (15)

• baml_language/crates/baml_base/src/dedent.rs
• baml_language/crates/baml_base/src/escape.rs
• baml_language/crates/baml_base/src/lib.rs
• baml_language/crates/baml_compiler2_ast/src/lib.rs
• baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs
• baml_language/crates/baml_compiler_lexer/src/tokens.rs
• baml_language/crates/baml_compiler_parser/src/parser.rs
• baml_language/crates/baml_compiler_syntax/Cargo.toml
• baml_language/crates/baml_compiler_syntax/src/ast.rs
• baml_language/crates/baml_compiler_syntax/src/syntax_kind.rs
• baml_language/crates/baml_fmt/src/ast/expressions.rs
• baml_language/crates/baml_fmt/src/ast/tokens.rs
• baml_language/crates/baml_fmt/src/lib.rs
• baml_language/crates/baml_tests/projects/compiles/backtick_strings/main.baml
• baml_language/crates/bex_engine/tests/backtick_strings.rs

[coderabbitai]

Actionable comments posted: 2

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

baml_language/crates/baml_compiler_parser/src/parser.rs (1)

1919-1923: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Consume only the immediate raw token after \.

The second bump_raw() skips intervening whitespace/newlines, so inputs like `\ ${name}` or `\ ` can swallow the later $/` and suppress interpolation or the closing delimiter. After consuming the backslash, this path needs to emit exactly one raw token, not “next non-trivia token.”

Proposed fix

+    /// Consume exactly one raw token at `self.current` without skipping trivia.
+    fn bump_exact_raw(&mut self) -> bool {
+        let Some(token) = self.tokens.get(self.current) else {
+            return false;
+        };
+        self.events.push(Event::Token {
+            kind: token_kind_to_syntax_kind(token.kind),
+            text: token.text.clone(),
+        });
+        self.current += 1;
+        true
+    }
+
     fn parse_backtick_content(&mut self, opening_ticks: usize) {
         let mut loop_counter = 0;
         loop {
@@
             if self.at_raw(TokenKind::Backslash) {
                 self.bump_raw();
                 if self.current < self.tokens.len() {
-                    self.bump_raw();
+                    self.bump_exact_raw();
                 }
                 continue;
             }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler_parser/src/parser.rs` around lines 1919 -
1923, After detecting a raw backslash (self.at_raw(TokenKind::Backslash)) we
should consume exactly one immediate token (the token directly following the
backslash) instead of calling bump_raw which advances to the next non-trivia
token; change the second consume to advance/consume only the next token in the
token stream (the token at self.current, after the backslash bump) so
interpolation delimiters or closing backticks aren't skipped. Update the logic
around self.bump_raw(), self.current and self.tokens so the backslash path
consumes exactly one following token (the immediate token) rather than “next
non-trivia token.”

🧹 Nitpick comments (1)

baml_language/crates/baml_compiler_lexer/src/tokens.rs (1)

853-873: ⚡ Quick win

Add a regression case for before-${x} token splitting.

Line 856 validates ${...} tokenization, but it doesn’t cover the specific guard documented in Lines 112-116 (preventing Word("before-$")). Please add a case asserting Word("before-"), Dollar, LBrace, Word("x"), RBrace for `before-${x}`.

Proposed test addition

     #[test]
     fn test_backtick_with_interpolation_tokens() {
         // ${...} inside backtick — lexer emits the raw tokens; parser assembles
         let source = "`Hello ${name}`";
         let tokens = lex_no_whitespace(source);

         assert_eq!(
             tokens,
             vec![
                 TokenKind::Backtick,
                 TokenKind::Word, // Hello
                 TokenKind::Dollar,
                 TokenKind::LBrace,
                 TokenKind::Word, // name
                 TokenKind::RBrace,
                 TokenKind::Backtick,
             ]
         );

         assert_eq!(reconstruct_source(&lex(source)), source);
+
+        // Regression: `${` must not be absorbed into a trailing-$ word segment.
+        let source2 = "`before-${x}`";
+        let tokens2 = lex_no_whitespace(source2);
+        assert_eq!(
+            tokens2,
+            vec![
+                TokenKind::Backtick,
+                TokenKind::Word, // before-
+                TokenKind::Dollar,
+                TokenKind::LBrace,
+                TokenKind::Word, // x
+                TokenKind::RBrace,
+                TokenKind::Backtick,
+            ]
+        );
+        assert_eq!(reconstruct_source(&lex(source2)), source2);
     }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler_lexer/src/tokens.rs` around lines 853 -
873, Update the backtick interpolation test to cover the guard that prevents
combining a trailing '$' into a Word token: inside the
test_backtick_with_interpolation_tokens (which uses lex_no_whitespace and
lex/reconstruct_source), add an assertion for the source "`before-${x}`" that
expects tokens [TokenKind::Backtick, TokenKind::Word (with text "before-"),
TokenKind::Dollar, TokenKind::LBrace, TokenKind::Word (with text "x"),
TokenKind::RBrace, TokenKind::Backtick] and also assert
reconstruct_source(&lex(source)) == source to ensure round-trip correctness;
locate uses of lex_no_whitespace, lex, and reconstruct_source in the test to add
this new case.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@baml_language/crates/baml_compiler_syntax/src/ast.rs`:
- Around line 1168-1196: The dedent remapping in BacktickStringLiteral::segments
misaligns when the first decoded part is RawPart::Interp because the current
loop only advances the split iterator for RawPart::Text; fix by changing the
remapping loop that walks decoded (the for p in &mut decoded after
dedented.split(PLACEHOLDER)) so that it consumes iter.next() for every part
(call iter.next() and ignore its value for RawPart::Interp, assign it to
RawPart::Text for Text parts) thereby preserving split positions, keep the
existing tail-handling logic that appends any leftover rest to the last
RawPart::Text, and add a new test covering a multiline template that starts with
an interpolation to prevent regressions.

In `@baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs`:
- Around line 2300-2302: The doc comment on lower_backtick_string_literal is
stale: update the sentence "Implicit `.to_string()` for non-string types is task
`#13`" to state that lowering now performs implicit `.to_string()` on non-string
interpolations (reflecting the conversion logic in the interpolation-handling
block that forces non-string child expressions to strings), so the comment
matches the implemented behavior in lower_backtick_string_literal and the
adjacent interpolation-lowering code paths.

---

Outside diff comments:
In `@baml_language/crates/baml_compiler_parser/src/parser.rs`:
- Around line 1919-1923: After detecting a raw backslash
(self.at_raw(TokenKind::Backslash)) we should consume exactly one immediate
token (the token directly following the backslash) instead of calling bump_raw
which advances to the next non-trivia token; change the second consume to
advance/consume only the next token in the token stream (the token at
self.current, after the backslash bump) so interpolation delimiters or closing
backticks aren't skipped. Update the logic around self.bump_raw(), self.current
and self.tokens so the backslash path consumes exactly one following token (the
immediate token) rather than “next non-trivia token.”

---

Nitpick comments:
In `@baml_language/crates/baml_compiler_lexer/src/tokens.rs`:
- Around line 853-873: Update the backtick interpolation test to cover the guard
that prevents combining a trailing '$' into a Word token: inside the
test_backtick_with_interpolation_tokens (which uses lex_no_whitespace and
lex/reconstruct_source), add an assertion for the source "`before-${x}`" that
expects tokens [TokenKind::Backtick, TokenKind::Word (with text "before-"),
TokenKind::Dollar, TokenKind::LBrace, TokenKind::Word (with text "x"),
TokenKind::RBrace, TokenKind::Backtick] and also assert
reconstruct_source(&lex(source)) == source to ensure round-trip correctness;
locate uses of lex_no_whitespace, lex, and reconstruct_source in the test to add
this new case.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 47ec80ea-80ac-4bcb-af3d-65b1627839d4

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Reviewing files that changed from the base of the PR and between 3ab9197 and c59c46a.

⛔ Files ignored due to path filters (27)

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• baml_language/crates/baml_tests/snapshots/diagnostic_errors/null_handling/baml_tests__diagnostic_errors__null_handling__05_diagnostics.snap is excluded by !**/*.snap

📒 Files selected for processing (18)

• baml_language/crates/baml_base/src/escape.rs
• baml_language/crates/baml_builtins2/baml_std/baml/bool.baml
• baml_language/crates/baml_builtins2/baml_std/baml/float.baml
• baml_language/crates/baml_builtins2/baml_std/baml/int.baml
• baml_language/crates/baml_builtins2/baml_std/baml/string.baml
• baml_language/crates/baml_compiler2_ast/src/lib.rs
• baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs
• baml_language/crates/baml_compiler_lexer/src/tokens.rs
• baml_language/crates/baml_compiler_parser/src/parser.rs
• baml_language/crates/baml_compiler_syntax/src/ast.rs
• baml_language/crates/baml_tests/projects/compiles/backtick_strings/main.baml
• baml_language/crates/baml_tests/projects/diagnostic_errors/backtick_strict_types/main.baml
• baml_language/crates/baml_tests/projects/diagnostic_errors/control_flow/main.baml
• baml_language/crates/bex_engine/tests/backtick_strings.rs
• baml_language/crates/bex_vm/src/package_baml/float.rs
• baml_language/crates/bex_vm/src/package_baml/int.rs
• baml_language/crates/bex_vm/src/package_baml/primitives.rs
• baml_language/crates/bex_vm/src/package_baml/string.rs

✅ Files skipped from review due to trivial changes (1)

• baml_language/crates/baml_tests/projects/diagnostic_errors/backtick_strict_types/main.baml

[coderabbitai]

🧹 Nitpick comments (1)

baml_language/crates/baml_compiler_parser/src/parser.rs (1)

7772-7785: ⚡ Quick win

Add a negative test for unparenthesized type-ascribed scrutinees.

You’ve documented : Type as parenthesized-only, but current additions only assert positive forms. Add a match x: int { ... } test that expects diagnostics to lock that contract.

Suggested test

+    #[test]
+    fn match_scrutinee_type_annotation_requires_parens() {
+        let source = "
+function Demo(x: int) -> int {
+    match x: int {
+        _ => 0,
+    }
+}
+";
+        let (_root, errors) = parse_source(source);
+        assert!(
+            !errors.is_empty(),
+            "expected parse errors for unparenthesized type-ascribed scrutinee"
+        );
+    }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler_parser/src/parser.rs` around lines 7772 -
7785, Add a negative test that ensures unparenthesized type-ascribed scrutinees
(e.g., `match x: int { ... }`) produce diagnostics: create a new test function
(e.g., match_scrutinee_with_type_annotation_unparenthesized) that calls
parse_source with a source containing `match x: int { _ => 0, }`, then assert
that the returned errors are non-empty (e.g., assert!(errors.len() > 0)) or
otherwise verify the expected diagnostic appears; use the same helpers seen in
the file (parse_source and the errors variable) to locate and validate the
failure.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@baml_language/crates/baml_compiler_parser/src/parser.rs`:
- Around line 7772-7785: Add a negative test that ensures unparenthesized
type-ascribed scrutinees (e.g., `match x: int { ... }`) produce diagnostics:
create a new test function (e.g.,
match_scrutinee_with_type_annotation_unparenthesized) that calls parse_source
with a source containing `match x: int { _ => 0, }`, then assert that the
returned errors are non-empty (e.g., assert!(errors.len() > 0)) or otherwise
verify the expected diagnostic appears; use the same helpers seen in the file
(parse_source and the errors variable) to locate and validate the failure.

---

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Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

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• baml_language/crates/baml_compiler_parser/src/parser.rs

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Actionable comments posted: 12

Caution

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⚠️ Outside diff range comments (1)

baml_language/crates/baml_compiler_parser/src/parser.rs (1)

7249-7251: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Route backtick config values through expression parsing.

looks_like_config_expression() treats quoted/raw strings as expressions but omits TokenKind::Backtick, so a config value starting with a backtick falls through to expect(TokenKind::Word) instead of parse_expr().

Proposed fix

         // Regular string literals are always expressions
-        if self.at(TokenKind::Quote) {
+        if self.at(TokenKind::Quote) || self.at(TokenKind::Backtick) {
             return true;
         }

Also applies to: 7261-7274

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler_parser/src/parser.rs` around lines 7249 -
7251, The `looks_like_config_expression()` function is missing a check for
`TokenKind::Backtick`, causing backtick-prefixed config values to not be routed
through `parse_expr()` as intended. Update the `looks_like_config_expression()`
function to include `TokenKind::Backtick` alongside the existing checks for
quoted and raw strings, ensuring that backtick expressions are handled
consistently with other expression types in config value parsing.

🧹 Nitpick comments (1)

baml_language/crates/baml_tests/tests/backtick_block_diagnostics.rs (1)

60-75: ⚡ Quick win

Add untagged-path assertions for the remaining structural cases.

mismatched_if_close_diagnoses and stray_endif_diagnoses currently validate only the prompt path, while this suite otherwise targets both prompt + untagged behavior of the shared segment builder.

Suggested test additions

 #[test]
 fn mismatched_if_close_diagnoses() {
     // ${if} closed by ${endfor}
     assert_has(&prompt("${if (true)}a${endfor}"), "${endif}");
+    assert_has(&untagged("${if (true)}a${endfor}"), "${endif}");
 }

 #[test]
 fn stray_endif_diagnoses() {
     assert_has(&prompt("a${endif}b"), "stray ${endif}");
+    assert_has(&untagged("a${endif}b"), "stray ${endif}");
 }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_tests/tests/backtick_block_diagnostics.rs` around
lines 60 - 75, Add untagged-path assertions to the mismatched_if_close_diagnoses
and stray_endif_diagnoses test functions to ensure consistency with the rest of
the test suite. Both functions currently only assert on the prompt path using
assert_has with prompt(), but should also include corresponding assertions using
the untagged() function with the same test inputs and expected diagnostic
messages, following the pattern already established in stray_endfor_diagnoses.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@baml_language/crates/baml_compiler_parser/src/parser.rs`:
- Around line 2198-2218: The function `has_backtick_close_ahead_from`
prematurely stops searching for closing backticks when it encounters keyword
tokens like `TokenKind::Function`, even if those keywords appear inside the
backtick literal itself (e.g., ````function keyword````). Instead of using these
token kinds as unconditional item boundaries, refine the boundary detection
logic to only return false when a keyword token is confirmed to be outside the
backtick literal being scanned. Track the nesting depth or structure of the
backtick literal to distinguish between tokens that are actual item boundaries
versus tokens that are legitimate content within the backtick delimiters, so
that keywords appearing inside multi-tick literals do not prematurely terminate
the search for the closing delimiter.
- Around line 2450-2458: The block-tag classification in the parser uses
is_basic_trivia() to skip trivia when lookahead-checking for the If token after
else, but basic trivia does not include block comments. This causes block
comments between else and if (or between if and opening braces) to break the
lookahead logic, resulting in incorrect tag classification. Replace the
is_basic_trivia() call used during the lookahead skip loops with a method that
skips all trivia including block comments (or introduce such a helper if it does
not exist), ensuring consistent trivia handling at all block-tag classification
points including the else-if check around the given location and the similar
checks mentioned to also apply at lines 2479-2493.
- Around line 2577-2593: The condition in the parenthesized template for-loop
parsing only checks for TokenKind::Let but should also accept contextual const
keywords. Update the condition that currently checks if self.at(TokenKind::Let)
to also allow contextual const (look at how the host for parser handles this
contextual keyword check), so that expressions like ${for (const x in xs)} route
to parse_for_in_pattern instead of falling through to the C-style for loop path
and erroring.
- Around line 5680-5697: The `has_newline_ahead()` function skips over block
comments without checking if they contain newline tokens inside them, causing
tagged templates to be incorrectly parsed when there is a line break within an
intervening block comment. Modify the `has_newline_ahead()` function to treat
any newline tokens found within block comments as line terminators for the
purpose of tagged template parsing, ensuring that constructs like `tag /*\n*/
`body`` are not misparsed as tagged templates.

In `@baml_language/crates/baml_compiler_syntax/src/ast.rs`:
- Around line 1709-1717: The validation for FlatPart::Else and FlatPart::ElseIf
only checks if the immediate stack frame is Open::If, but does not validate
branch ordering within an if-chain. This allows invalid sequences like multiple
${else} blocks or ${else if} after ${else} to pass validation. Enhance the
validation by tracking the last branch type seen within the current if-chain
(initial, else-if, or else) in the stack state, then add checks to reject ${else
if} when the last branch was ${else}, reject ${else} when it already appeared,
and create corresponding error kind variants and diagnostic mappings for these
new invalid-order cases.

In `@baml_language/crates/baml_compiler2_hir/src/builder.rs`:
- Around line 689-693: The if branch that handles Expr::Block only calls
walk_block_contents on the block's statements and tail expression, which skips
recording the block's ExprId itself in expr_scopes. This causes MIR/TIR scope
lookups for the synthetic body to fail. Add a call to walk_expr for the
flatten_body ExprId with push_block_scope set to false (to avoid duplicating the
scope already created by walk_block_contents) so that the block expression is
properly recorded in expr_scopes, matching the behavior of the else branch that
already calls walk_expr.

In `@baml_language/crates/baml_compiler2_mir/src/lower.rs`:
- Around line 4689-4691: The issue is that `tagged_body_param_names` only
resolves body params when they exist in `self.locals`, but when a nested lambda
inside `${...}` references one of these params, `lower_lambda` clears
`self.locals`, preventing the nested lambda from capturing the param since HIR
has no `BindingId` for it. Fix this by either threading the synthetic body
params through the lambda capture path so nested lambdas can access them even
after `self.locals` is cleared, or by converting these params into real scoped
bindings with proper `BindingId`s before MIR lowering so they are available in
the HIR binding system. This fix should be applied wherever
`tagged_body_param_names` is set and wherever nested lambdas are lowered to
ensure consistent param resolution across all interpolation contexts.
- Around line 6451-6455: When handling ParamBinding::OmittedDefault with a
Some(callee_loc) for a method sys-op call, the param_index is receiver-relative
(self parameter excluded) but sysop_default_operand passes it directly to
defaults.param_default which indexes the full signature including self. Adjust
param_index by adding 1 to account for the self parameter when the callee is a
method, before passing it to self.sysop_default_operand(callee_loc,
param_index). Check if the callee_loc refers to a method and only apply the
adjustment in that case.

In `@baml_language/crates/baml_compiler2_tir/src/builder.rs`:
- Around line 8145-8150: The CStyleFor case in the throws analysis for
ast::TemplateSegment::CStyleFor is missing extraction and processing of throw
facts from the init statement's initializer. Currently it only processes cond
and body, but ignores init. Extract the initializer from the init statement
using the same approach shown in lines 2947-2955 (the forward-reference walker),
and call self.collect_throw_facts_from_expr on that extracted initializer with
the appropriate body parameter before processing cond and body.
- Around line 2939-2967: The condition expression in the C-style for loop is
being processed before the loop variable's pattern is pushed onto the shadowed
list, which causes references to the loop variable in the condition to be
incorrectly treated as forward references. Move the pattern shadowing operations
earlier in the sequence: call Self::push_pattern_bindings(p, body, shadowed)
before processing the condition via
Self::collect_default_expr_forward_references(*cond, ...), so that the loop
variable binding is visible when evaluating the condition expression, while
preserving the correct order where the initializer is processed before shadowing
and the inner content is processed after.

In `@baml_language/crates/baml_compiler2_tir/src/throws_analysis.rs`:
- Around line 422-427: The CStyleFor arm in the throws analysis is missing
traversal of the init and step statements, which can throw exceptions but are
currently ignored. Modify the pattern match for ast::TemplateSegment::CStyleFor
to destructure the init and step fields (currently captured by the .. wildcard).
Add calls to collect_from_expr or collect_from_template_segments (whichever is
appropriate for the statement types) for both the init and step fields, ensuring
they are analyzed before collecting from cond and the body segments.
- Around line 384-389: The custom tag template handling in the Expr::Template
match arm collects throws from the tag expression and segments, but omits the
throws that originate from invoking the tag function itself. In the block
starting at Line 384 where Expr::Template with ast::TemplateTag::Custom is
handled, after calling collect_from_expr for the tag and
collect_from_template_segments for the segments, add a call to collect the
throws that result from calling the tag function (similar to how function call
throws would be collected elsewhere in the codebase). This ensures that escaping
throws from tagged template invocations are fully reported.

---

Outside diff comments:
In `@baml_language/crates/baml_compiler_parser/src/parser.rs`:
- Around line 7249-7251: The `looks_like_config_expression()` function is
missing a check for `TokenKind::Backtick`, causing backtick-prefixed config
values to not be routed through `parse_expr()` as intended. Update the
`looks_like_config_expression()` function to include `TokenKind::Backtick`
alongside the existing checks for quoted and raw strings, ensuring that backtick
expressions are handled consistently with other expression types in config value
parsing.

---

Nitpick comments:
In `@baml_language/crates/baml_tests/tests/backtick_block_diagnostics.rs`:
- Around line 60-75: Add untagged-path assertions to the
mismatched_if_close_diagnoses and stray_endif_diagnoses test functions to ensure
consistency with the rest of the test suite. Both functions currently only
assert on the prompt path using assert_has with prompt(), but should also
include corresponding assertions using the untagged() function with the same
test inputs and expected diagnostic messages, following the pattern already
established in stray_endfor_diagnoses.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: cf8929ab-afd2-4b73-a967-7663aa0a95f3

📥 Commits

Reviewing files that changed from the base of the PR and between 36dc05b and ccc0451.

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• baml_language/crates/baml_tests/snapshots/diagnostic_errors/is_pattern_negative/baml_tests__diagnostic_errors__is_pattern_negative__01_lexer__main.snap is excluded by !**/*.snap
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📒 Files selected for processing (61)

• baml_language/crates/baml_base/src/dedent.rs
• baml_language/crates/baml_base/src/escape.rs
• baml_language/crates/baml_base/src/lib.rs
• baml_language/crates/baml_builtins2/baml_std/baml/bool.baml
• baml_language/crates/baml_builtins2/baml_std/baml/core.baml
• baml_language/crates/baml_builtins2/baml_std/baml/float.baml
• baml_language/crates/baml_builtins2/baml_std/baml/int.baml
• baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm.baml
• baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm_types.baml
• baml_language/crates/baml_builtins2/baml_std/baml/string.baml
• baml_language/crates/baml_compiler2_ast/src/ast.rs
• baml_language/crates/baml_compiler2_ast/src/auto_derive_json.rs
• baml_language/crates/baml_compiler2_ast/src/companions.rs
• baml_language/crates/baml_compiler2_ast/src/docstring.rs
• baml_language/crates/baml_compiler2_ast/src/lib.rs
• baml_language/crates/baml_compiler2_ast/src/lower_cst.rs
• baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs
• baml_language/crates/baml_compiler2_ast/src/lower_type_expr.rs
• baml_language/crates/baml_compiler2_ast/src/lowering_diagnostic.rs
• baml_language/crates/baml_compiler2_emit/src/lib.rs
• baml_language/crates/baml_compiler2_hir/src/builder.rs
• baml_language/crates/baml_compiler2_hir/src/item_tree.rs
• baml_language/crates/baml_compiler2_hir/src/scope.rs
• baml_language/crates/baml_compiler2_mir/src/lower.rs
• baml_language/crates/baml_compiler2_ppir/src/lib.rs
• baml_language/crates/baml_compiler2_tir/src/builder.rs
• baml_language/crates/baml_compiler2_tir/src/infer_context.rs
• baml_language/crates/baml_compiler2_tir/src/inference.rs
• baml_language/crates/baml_compiler2_tir/src/normalize.rs
• baml_language/crates/baml_compiler2_tir/src/throws_analysis.rs
• baml_language/crates/baml_compiler2_visualization/src/control_flow/from_ast.rs
• baml_language/crates/baml_compiler_lexer/src/tokens.rs
• baml_language/crates/baml_compiler_parser/src/parser.rs
• baml_language/crates/baml_compiler_syntax/Cargo.toml
• baml_language/crates/baml_compiler_syntax/src/ast.rs
• baml_language/crates/baml_compiler_syntax/src/syntax_kind.rs
• baml_language/crates/baml_fmt/src/ast/expressions.rs
• baml_language/crates/baml_fmt/src/ast/tokens.rs
• baml_language/crates/baml_fmt/src/lib.rs
• baml_language/crates/baml_lsp2_actions/src/check.rs
• baml_language/crates/baml_lsp2_actions/src/completions.rs
• baml_language/crates/baml_tests/projects/compiles/backtick_strings/main.baml
• baml_language/crates/baml_tests/projects/diagnostic_errors/backtick_strict_types/main.baml
• baml_language/crates/baml_tests/projects/diagnostic_errors/control_flow/main.baml
• baml_language/crates/baml_tests/src/compiler2_tir/mod.rs
• baml_language/crates/baml_tests/src/compiler2_tir/phase3a.rs
• baml_language/crates/baml_tests/tests/backtick_block_diagnostics.rs
• baml_language/crates/baml_tests/tests/prompt_tag_e2e.rs
• baml_language/crates/baml_tests/tests/prompt_tag_runtime.rs
• baml_language/crates/baml_tests/tests/tagged_template_lowering.rs
• baml_language/crates/baml_tests/tests/tagged_template_runtime.rs
• baml_language/crates/bex_engine/tests/backtick_strings.rs
• baml_language/crates/bex_vm/src/package_baml/float.rs
• baml_language/crates/bex_vm/src/package_baml/int.rs
• baml_language/crates/bex_vm/src/package_baml/primitives.rs
• baml_language/crates/bex_vm/src/package_baml/string.rs
• baml_language/crates/sys_llm/src/lib.rs
• baml_language/crates/sys_ops/src/lib.rs
• baml_language/crates/tools_onionskin/src/app.rs
• baml_language/crates/tools_onionskin/src/compiler.rs
• baml_language/sdks/nodejs/bridge_nodejs/typescript_src/proto/baml_cffi.js

[coderabbitai]

Actionable comments posted: 1

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

baml_language/crates/baml_compiler2_mir/src/lower.rs (1)

5638-5682: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Resolve tagged-body params before falling back to HIR locals/captures.

The ResolvedName::Unknown branch only works when no outer binding has the same name. Because body params are MIR-only, resolve_name_at_in_scope can still return an enclosing ResolvedName::Local for a same-named outer variable, so a nested interpolation lambda captures the outer local instead of the tag body param. The same gap affects multi-segment roots like ctx.name/ctx.method() because the root path logic never consults tagged_body_param_bindings.

Centralize a helper that resolves a tagged-body param to Place::Local or Place::Capture(self.ensure_transitive_capture(...)), and use it before HIR-capture fallback for single-segment and multi-segment roots.

Suggested shape

+    fn tagged_body_param_place(&mut self, name: &Name) -> Option<Place> {
+        let binding_id = *self.tagged_body_param_bindings.get(name)?;
+        if let Some(&local) = self.locals.get(name) {
+            Some(Place::Local(local))
+        } else {
+            Some(Place::Capture(self.ensure_transitive_capture(binding_id)))
+        }
+    }

Use this helper before capture_index_for_name_at(...) in the single-name path branch, and as another root case in lower_multi_segment_path_as_field_chain.

Also applies to: 5713-5741

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler2_mir/src/lower.rs` around lines 5638 -
5682, The current implementation checks for tagged-body params only in the
ResolvedName::Unknown branch, but this misses cases where
resolve_name_at_in_scope returns a ResolvedName::Local for an outer binding with
the same name, causing nested interpolation lambdas to capture the wrong
variable. Create a centralized helper method that checks
tagged_body_param_bindings and returns the appropriate Place (either
Place::Local or Place::Capture with ensure_transitive_capture), then call this
helper in the ResolvedName::Local branch before falling back to
capture_index_for_name_at, and also apply the same pattern to multi-segment root
path resolution in lower_multi_segment_path_as_field_chain to ensure tagged-body
params are prioritized over HIR-based captures for both single-segment and
multi-segment roots.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@baml_language/crates/baml_compiler2_tir/src/inference.rs`:
- Around line 1061-1086: The doc comment describing "Search for a `Lambda`
expression..." currently precedes the `seed_template_body_params` function, but
it was originally intended to document the `find_lambda_by_span` function. In
Rust, doc comments attach to the immediately following item, so this comment is
now incorrectly documenting `seed_template_body_params` and leaving
`find_lambda_by_span` undocumented. Move the doc comment that currently appears
above `seed_template_body_params` to immediately precede the
`find_lambda_by_span` function instead.

---

Outside diff comments:
In `@baml_language/crates/baml_compiler2_mir/src/lower.rs`:
- Around line 5638-5682: The current implementation checks for tagged-body
params only in the ResolvedName::Unknown branch, but this misses cases where
resolve_name_at_in_scope returns a ResolvedName::Local for an outer binding with
the same name, causing nested interpolation lambdas to capture the wrong
variable. Create a centralized helper method that checks
tagged_body_param_bindings and returns the appropriate Place (either
Place::Local or Place::Capture with ensure_transitive_capture), then call this
helper in the ResolvedName::Local branch before falling back to
capture_index_for_name_at, and also apply the same pattern to multi-segment root
path resolution in lower_multi_segment_path_as_field_chain to ensure tagged-body
params are prioritized over HIR-based captures for both single-segment and
multi-segment roots.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 6441f242-8139-48c3-81be-b05e156ea55d

📥 Commits

Reviewing files that changed from the base of the PR and between 7df24eb and 4796a2b.

📒 Files selected for processing (11)

• baml_language/crates/baml_compiler2_ast/src/lowering_diagnostic.rs
• baml_language/crates/baml_compiler2_hir/src/builder.rs
• baml_language/crates/baml_compiler2_mir/src/lower.rs
• baml_language/crates/baml_compiler2_tir/src/builder.rs
• baml_language/crates/baml_compiler2_tir/src/inference.rs
• baml_language/crates/baml_compiler2_tir/src/throws_analysis.rs
• baml_language/crates/baml_compiler_parser/src/parser.rs
• baml_language/crates/baml_compiler_syntax/src/ast.rs
• baml_language/crates/baml_fmt/src/ast/expressions.rs
• baml_language/crates/baml_fmt/src/lib.rs
• baml_language/crates/baml_lsp2_actions/src/check.rs

🚧 Files skipped from review as they are similar to previous changes (8)

• baml_language/crates/baml_fmt/src/lib.rs
• baml_language/crates/baml_lsp2_actions/src/check.rs
• baml_language/crates/baml_compiler2_hir/src/builder.rs
• baml_language/crates/baml_compiler2_ast/src/lowering_diagnostic.rs
• baml_language/crates/baml_compiler2_tir/src/throws_analysis.rs
• baml_language/crates/baml_fmt/src/ast/expressions.rs
• baml_language/crates/baml_compiler_syntax/src/ast.rs
• baml_language/crates/baml_compiler_parser/src/parser.rs

[coderabbitai]

Actionable comments posted: 1

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

baml_language/crates/baml_compiler2_mir/src/lower.rs (1)

6327-6383: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Reuse the null-checked base operand for ?.[].

Line 6328 lowers base for the null guard, but Line 6383 lowers it again for the actual access. A side-effectful base can pass the guard on the first evaluation and then index a different value on the second. Materialize the checked base once and pass it into the access helper.

🐛 Proposed fix

-    fn lower_optional_index(&mut self, base: AstExprId, index: AstExprId, dest: Place) {
-        let base_op = self.lower_to_operand(base);
+    fn lower_optional_index(&mut self, base: AstExprId, index: AstExprId, dest: Place) {
+        let base_ty = self.expr_ty(base);
+        let base_op = self.lower_to_operand(base);
+        let base_local = self.operand_to_local(base_op, base_ty.clone());

         let is_null = Rvalue::BinaryOp {
             op: BinOp::Eq,
-            left: base_op,
+            left: Operand::Copy(Place::Local(base_local)),
             right: Operand::Constant(Constant::Null),
         };
@@
             self.builder.set_current_block(bb_access);
-            self.lower_optional_index_access(base, index, dest, bb_null);
+            self.lower_optional_index_access(
+                Operand::Copy(Place::Local(base_local)),
+                base_ty,
+                index,
+                dest,
+                bb_null,
+            );
         } else {
@@
             self.builder.set_current_block(bb_access);
-            self.lower_optional_index_access(base, index, dest.clone(), bb_null);
+            self.lower_optional_index_access(
+                Operand::Copy(Place::Local(base_local)),
+                base_ty,
+                index,
+                dest.clone(),
+                bb_null,
+            );
@@
     fn lower_optional_index_access(
         &mut self,
-        base: AstExprId,
+        base_op: Operand,
+        base_ty: RuntimeTy,
         index: AstExprId,
         dest: Place,
         bb_null: BlockId,
     ) {
-        let base_ty = self.expr_ty(base);
-        let base_op = self.lower_to_operand(base);
         let index_ty = self.expr_ty(index);

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler2_mir/src/lower.rs` around lines 6327 -
6383, The `lower_optional_index` function lowers the base expression once to
check for null (line 6328), but then passes the original AstExprId to
`lower_optional_index_access` which lowers it again (line 6383). This causes
side-effectful bases to be evaluated twice, potentially yielding different
values. Fix this by modifying the `lower_optional_index_access` method signature
to accept the already-lowered Operand instead of the AstExprId, then pass the
base_op operand from `lower_optional_index` and remove the duplicate lowering
inside `lower_optional_index_access`.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@baml_language/crates/baml_compiler2_tir/src/builder.rs`:
- Around line 4703-4755: The check_index_key_type method conditionally strips
null from index types when allow_null is true (lines 4722-4726), assuming
indices in optional chains are non-null in the narrowed context, but no
narrowing analysis is actually performed on index expressions. This allows null
indices to pass compile-time checks and fail at runtime. Either remove the
allow_null conditional logic entirely and always validate the index_ty directly
against the expected_key type without stripping null, or implement actual
narrowing analysis for indices in optional indexing chains (in
infer_optional_index_expr or similar) to guarantee non-null indices before
passing allow_null as true to check_index_key_type.

---

Outside diff comments:
In `@baml_language/crates/baml_compiler2_mir/src/lower.rs`:
- Around line 6327-6383: The `lower_optional_index` function lowers the base
expression once to check for null (line 6328), but then passes the original
AstExprId to `lower_optional_index_access` which lowers it again (line 6383).
This causes side-effectful bases to be evaluated twice, potentially yielding
different values. Fix this by modifying the `lower_optional_index_access` method
signature to accept the already-lowered Operand instead of the AstExprId, then
pass the base_op operand from `lower_optional_index` and remove the duplicate
lowering inside `lower_optional_index_access`.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: a9e79bcf-2a9a-4e37-b1a8-4d0eb50ce794

📥 Commits

Reviewing files that changed from the base of the PR and between 4796a2b and b49b605.

⛔ Files ignored due to path filters (9)

• baml_language/Cargo.lock is excluded by !**/*.lock
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_builtin_package_listing.snap is excluded by !**/*.snap
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_describe_alias_string.snap is excluded by !**/*.snap
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_describe_builtin_item_by_definition.snap is excluded by !**/*.snap
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_describe_builtin_string.snap is excluded by !**/*.snap
• baml_language/crates/baml_lsp2_actions/src/snapshots/baml_lsp2_actions__describe_tests__describe_builtin_string_with_compiler2_visible_files.snap is excluded by !**/*.snap
• baml_language/crates/baml_tests/snapshots/compiles/__baml_std__/baml_tests__compiles____baml_std____03_hir.snap is excluded by !**/*.snap
• baml_language/crates/baml_tests/snapshots/compiles/__baml_std__/baml_tests__compiles____baml_std____04_5_mir.snap is excluded by !**/*.snap
• baml_language/crates/baml_tests/snapshots/compiles/__baml_std__/baml_tests__compiles____baml_std____06_codegen.snap is excluded by !**/*.snap

📒 Files selected for processing (4)

• baml_language/crates/baml_builtins2/baml_std/baml/string.baml
• baml_language/crates/baml_compiler2_mir/src/lower.rs
• baml_language/crates/baml_compiler2_tir/src/builder.rs
• baml_language/crates/baml_compiler2_tir/src/inference.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• baml_language/crates/baml_builtins2/baml_std/baml/string.baml
• baml_language/crates/baml_compiler2_tir/src/inference.rs

[coderabbitai]

Caution

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Actionable comments posted: 1

Caution

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⚠️ Outside diff range comments (1)

baml_language/crates/baml_compiler2_mir/src/lower.rs (1)

6327-6383: ⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Reuse the null-checked base operand for ?.[].

Line 6328 lowers base for the null guard, but Line 6383 lowers it again for the actual access. A side-effectful base can pass the guard on the first evaluation and then index a different value on the second. Materialize the checked base once and pass it into the access helper.

🐛 Proposed fix

-    fn lower_optional_index(&mut self, base: AstExprId, index: AstExprId, dest: Place) {
-        let base_op = self.lower_to_operand(base);
+    fn lower_optional_index(&mut self, base: AstExprId, index: AstExprId, dest: Place) {
+        let base_ty = self.expr_ty(base);
+        let base_op = self.lower_to_operand(base);
+        let base_local = self.operand_to_local(base_op, base_ty.clone());

         let is_null = Rvalue::BinaryOp {
             op: BinOp::Eq,
-            left: base_op,
+            left: Operand::Copy(Place::Local(base_local)),
             right: Operand::Constant(Constant::Null),
         };
@@
             self.builder.set_current_block(bb_access);
-            self.lower_optional_index_access(base, index, dest, bb_null);
+            self.lower_optional_index_access(
+                Operand::Copy(Place::Local(base_local)),
+                base_ty,
+                index,
+                dest,
+                bb_null,
+            );
         } else {
@@
             self.builder.set_current_block(bb_access);
-            self.lower_optional_index_access(base, index, dest.clone(), bb_null);
+            self.lower_optional_index_access(
+                Operand::Copy(Place::Local(base_local)),
+                base_ty,
+                index,
+                dest.clone(),
+                bb_null,
+            );
@@
     fn lower_optional_index_access(
         &mut self,
-        base: AstExprId,
+        base_op: Operand,
+        base_ty: RuntimeTy,
         index: AstExprId,
         dest: Place,
         bb_null: BlockId,
     ) {
-        let base_ty = self.expr_ty(base);
-        let base_op = self.lower_to_operand(base);
         let index_ty = self.expr_ty(index);

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler2_mir/src/lower.rs` around lines 6327 -
6383, The `lower_optional_index` function lowers the base expression once to
check for null (line 6328), but then passes the original AstExprId to
`lower_optional_index_access` which lowers it again (line 6383). This causes
side-effectful bases to be evaluated twice, potentially yielding different
values. Fix this by modifying the `lower_optional_index_access` method signature
to accept the already-lowered Operand instead of the AstExprId, then pass the
base_op operand from `lower_optional_index` and remove the duplicate lowering
inside `lower_optional_index_access`.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@baml_language/crates/baml_compiler2_tir/src/builder.rs`:
- Around line 4703-4755: The check_index_key_type method conditionally strips
null from index types when allow_null is true (lines 4722-4726), assuming
indices in optional chains are non-null in the narrowed context, but no
narrowing analysis is actually performed on index expressions. This allows null
indices to pass compile-time checks and fail at runtime. Either remove the
allow_null conditional logic entirely and always validate the index_ty directly
against the expected_key type without stripping null, or implement actual
narrowing analysis for indices in optional indexing chains (in
infer_optional_index_expr or similar) to guarantee non-null indices before
passing allow_null as true to check_index_key_type.

---

Outside diff comments:
In `@baml_language/crates/baml_compiler2_mir/src/lower.rs`:
- Around line 6327-6383: The `lower_optional_index` function lowers the base
expression once to check for null (line 6328), but then passes the original
AstExprId to `lower_optional_index_access` which lowers it again (line 6383).
This causes side-effectful bases to be evaluated twice, potentially yielding
different values. Fix this by modifying the `lower_optional_index_access` method
signature to accept the already-lowered Operand instead of the AstExprId, then
pass the base_op operand from `lower_optional_index` and remove the duplicate
lowering inside `lower_optional_index_access`.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: a9e79bcf-2a9a-4e37-b1a8-4d0eb50ce794

📥 Commits

Reviewing files that changed from the base of the PR and between 4796a2b and b49b605.

⛔ Files ignored due to path filters (9)

• baml_language/Cargo.lock is excluded by !**/*.lock
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_builtin_package_listing.snap is excluded by !**/*.snap
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_describe_alias_string.snap is excluded by !**/*.snap
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_describe_builtin_item_by_definition.snap is excluded by !**/*.snap
• baml_language/crates/baml_cli/src/snapshots/baml_cli__describe_command_tests__render_describe_builtin_string.snap is excluded by !**/*.snap
• baml_language/crates/baml_lsp2_actions/src/snapshots/baml_lsp2_actions__describe_tests__describe_builtin_string_with_compiler2_visible_files.snap is excluded by !**/*.snap
• baml_language/crates/baml_tests/snapshots/compiles/__baml_std__/baml_tests__compiles____baml_std____03_hir.snap is excluded by !**/*.snap
• baml_language/crates/baml_tests/snapshots/compiles/__baml_std__/baml_tests__compiles____baml_std____04_5_mir.snap is excluded by !**/*.snap
• baml_language/crates/baml_tests/snapshots/compiles/__baml_std__/baml_tests__compiles____baml_std____06_codegen.snap is excluded by !**/*.snap

📒 Files selected for processing (4)

• baml_language/crates/baml_builtins2/baml_std/baml/string.baml
• baml_language/crates/baml_compiler2_mir/src/lower.rs
• baml_language/crates/baml_compiler2_tir/src/builder.rs
• baml_language/crates/baml_compiler2_tir/src/inference.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• baml_language/crates/baml_builtins2/baml_std/baml/string.baml
• baml_language/crates/baml_compiler2_tir/src/inference.rs

🛑 Comments failed to post (1)

baml_language/crates/baml_compiler2_tir/src/builder.rs (1)

4703-4755: ⚠️ Potential issue | 🟠 Major

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Remove the null-stripping logic in optional indexing or enforce narrowing to guarantee non-null indices.

The code strips null from index types in optional indexing contexts (line 4723, when allow_null=true) with the comment claiming this avoids "false positives" because indices are "typically nullable-by-type yet non-null in the narrowed chain context" (e.g., node?.children?.[node?.value]).

However, no narrowing analysis is applied to index expressions. The narrowing module handles control flow (if/else conditions, truthiness, instanceof), not subscript indices. In infer_optional_index_expr, the index type is inferred directly without any type narrowing, then passed to check_index_key_type with allow_null=true, which unconditionally strips null.

Since the runtime aborts when indexing with a null subscript (as noted in the comment), this allows code that will fail at runtime to pass compile-time type checking. The comment's assumption that the index is "typically" non-null in chained contexts is not enforced by the compiler.

Either remove the allow_null logic to catch these errors at compile time, or implement narrowing analysis for indices in optional chains to guarantee non-null at the point of indexing.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler2_tir/src/builder.rs` around lines 4703 -
4755, The check_index_key_type method conditionally strips null from index types
when allow_null is true (lines 4722-4726), assuming indices in optional chains
are non-null in the narrowed context, but no narrowing analysis is actually
performed on index expressions. This allows null indices to pass compile-time
checks and fail at runtime. Either remove the allow_null conditional logic
entirely and always validate the index_ty directly against the expected_key type
without stripping null, or implement actual narrowing analysis for indices in
optional indexing chains (in infer_optional_index_expr or similar) to guarantee
non-null indices before passing allow_null as true to check_index_key_type.

[coderabbitai]

🧹 Nitpick comments (1)

baml_language/crates/baml_base/src/dedent.rs (1)

38-55: 💤 Low value

consumed and split_at are redundant.

Both variables are incremented by exactly the same amount (c.len_utf8()) in every iteration and will always be equal. A single variable would suffice.

♻️ Suggested simplification

 fn strip_leading_indent(line: &str, target_bytes: usize) -> &str {
     if target_bytes == 0 {
         return line;
     }
-    let mut consumed = 0usize;
-    let mut split_at = 0usize;
+    let mut stripped = 0usize;
     for c in line.chars() {
         if !c.is_whitespace() {
             break;
         }
-        consumed += c.len_utf8();
-        split_at += c.len_utf8();
-        if consumed >= target_bytes {
+        stripped += c.len_utf8();
+        if stripped >= target_bytes {
             break;
         }
     }
-    &line[split_at..]
+    &line[stripped..]
 }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_base/src/dedent.rs` around lines 38 - 55, In the
strip_leading_indent function, the variables consumed and split_at are redundant
as they are incremented identically in each loop iteration and maintain equal
values throughout. Consolidate these into a single variable that tracks the byte
offset. Remove one of the variable declarations and use only one variable for
both the comparison against target_bytes and for slicing the return value in the
expression &line[...].

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@baml_language/crates/baml_base/src/dedent.rs`:
- Around line 38-55: In the strip_leading_indent function, the variables
consumed and split_at are redundant as they are incremented identically in each
loop iteration and maintain equal values throughout. Consolidate these into a
single variable that tracks the byte offset. Remove one of the variable
declarations and use only one variable for both the comparison against
target_bytes and for slicing the return value in the expression &line[...].

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 545943a1-f0d4-483b-8df3-8fd18c223498

📥 Commits

Reviewing files that changed from the base of the PR and between b49b605 and ecc3784.

📒 Files selected for processing (5)

• baml_language/crates/baml_base/src/dedent.rs
• baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs
• baml_language/crates/baml_compiler2_mir/src/lower.rs
• baml_language/crates/baml_compiler2_tir/src/builder.rs
• baml_language/crates/baml_compiler2_tir/src/infer_context.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• baml_language/crates/baml_compiler2_ast/src/lower_expr_body.rs
• baml_language/crates/baml_compiler2_tir/src/builder.rs

👮 Files not reviewed due to content moderation or server errors (1)

• baml_language/crates/baml_compiler2_mir/src/lower.rs

[coderabbitai]

🧹 Nitpick comments (2)

baml_language/crates/baml_compiler2_ast/src/companions.rs (1)

168-177: ⚡ Quick win

Avoid silently downgrading new-mode companions to legacy synthesis.

On Line 168, a missing stashed body falls back to the legacy 3-arg call. For backtick/new-mode parents, that can hide an upstream lowering mismatch and change prompt-render behavior. Consider guarding this with an invariant check (or diagnostic) when companion_bodies is non-empty but target is missing.

Suggested hardening

-    let (body, source_map) = llm_companion_body(parent, target).unwrap_or_else(|| {
-        synthesize_llm_builtin_call(
-            target,
-            parent.name.as_str(),
-            &param_names,
-            client_arg_name,
-            Vec::new(),
-            parent.span,
-        )
-    });
+    let (body, source_map) = if let Some(pair) = llm_companion_body(parent, target) {
+        pair
+    } else {
+        if let Some(DeclarativeMeta::Llm(llm)) = &parent.declarative_meta {
+            debug_assert!(
+                llm.companion_bodies.is_empty(),
+                "missing stashed companion body for target `{target}` on `{}`",
+                parent.name
+            );
+        }
+        synthesize_llm_builtin_call(
+            target,
+            parent.name.as_str(),
+            &param_names,
+            client_arg_name,
+            Vec::new(),
+            parent.span,
+        )
+    };

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_compiler2_ast/src/companions.rs` around lines 168 -
177, The unwrap_or_else call on llm_companion_body at line 168 silently falls
back to synthesize_llm_builtin_call when a target is missing, which can hide
upstream lowering mismatches for new-mode companions. Add a guard before this
fallback to check if companion_bodies is non-empty but target is missing
(indicating an unexpected state), and emit an invariant check or diagnostic in
that case to prevent silently downgrading to legacy synthesis behavior rather
than proceeding with the fallback.

baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm.baml (1)

91-94: ⚡ Quick win

Reuse prompt_template_for to avoid branch-logic drift.

The legacy/new-mode jinja_string match is duplicated in two places even though prompt_template_for now centralizes this rule. Reusing it keeps execution-path behavior aligned with preview/build helpers.

Suggested diff

 function call_llm_function<T>(client: Client, function_name: string, args: map<string, unknown>, prompt_closure: ((Context) -> PromptAst)? = null) -> T {
-  // New-mode (backtick) functions have no Jinja template registered; the
-  // closure renders the prompt, so only look one up for the legacy path.
-  let jinja_string = match (prompt_closure) {
-    null => get_jinja_template(function_name),
-    _ => "",
-  };
+  let jinja_string = prompt_template_for(function_name, prompt_closure);

   let context = ExecutionContext {
     jinja_string: jinja_string,
@@
 function stream_llm_function<TStream, TFinal>(client: Client, function_name: string, args: map<string, unknown>, prompt_closure: ((Context) -> PromptAst)? = null) -> Stream<TStream, TFinal> {
-    // New-mode (backtick) functions have no Jinja template registered; the
-    // closure renders the prompt, so only look one up for the legacy path.
-    let jinja_string = match (prompt_closure) {
-        null => get_jinja_template(function_name),
-        _ => "",
-    };
+    let jinja_string = prompt_template_for(function_name, prompt_closure);

     let context = ExecutionContext {
         jinja_string: jinja_string,

Also applies to: 115-118

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm.baml` around
lines 91 - 94, The jinja_string variable initialization uses a match statement
on prompt_closure that is duplicated in two locations. Instead of maintaining
this duplicate match logic in both places, refactor both occurrences (the one at
lines 91-94 and the one at lines 115-118) to use the existing
prompt_template_for function which already centralizes this branch logic. This
will eliminate the duplication and ensure consistent behavior across all
execution paths.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm.baml`:
- Around line 91-94: The jinja_string variable initialization uses a match
statement on prompt_closure that is duplicated in two locations. Instead of
maintaining this duplicate match logic in both places, refactor both occurrences
(the one at lines 91-94 and the one at lines 115-118) to use the existing
prompt_template_for function which already centralizes this branch logic. This
will eliminate the duplication and ensure consistent behavior across all
execution paths.

In `@baml_language/crates/baml_compiler2_ast/src/companions.rs`:
- Around line 168-177: The unwrap_or_else call on llm_companion_body at line 168
silently falls back to synthesize_llm_builtin_call when a target is missing,
which can hide upstream lowering mismatches for new-mode companions. Add a guard
before this fallback to check if companion_bodies is non-empty but target is
missing (indicating an unexpected state), and emit an invariant check or
diagnostic in that case to prevent silently downgrading to legacy synthesis
behavior rather than proceeding with the fallback.

---

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⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 709a6bec-cf01-41a5-ae01-10c37f1d16d2

📥 Commits

Reviewing files that changed from the base of the PR and between 2c45813 and 4bf504b.

⛔ Files ignored due to path filters (26)

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📒 Files selected for processing (6)

• baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm.baml
• baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm_types.baml
• baml_language/crates/baml_compiler2_ast/src/ast.rs
• baml_language/crates/baml_compiler2_ast/src/companions.rs
• baml_language/crates/baml_compiler2_ast/src/lower_cst.rs
• baml_language/crates/bex_engine/tests/build_request.rs

🚧 Files skipped from review as they are similar to previous changes (3)

• baml_language/crates/baml_compiler2_ast/src/lower_cst.rs
• baml_language/crates/baml_compiler2_ast/src/ast.rs
• baml_language/crates/baml_builtins2/baml_std/baml/ns_llm/llm_types.baml