Recognize untagged payloads only by annotations and builtin types by cknitt · Pull Request #8949 · rescript-lang/rescript

cknitt · 2026-10-21T18:13:15Z

Stacked on #8950, which declares and annotates the stdlib's runtime classes.

Now that the stdlib's classes declare themselves, untagged variant payloads are recognized only by @instanceOf/@typeOf or by the builtin type they expand to: string, int, float, bigint, bool, dict, array, tuples, promise and functions. These have no declaration to annotate. Removed:

type_to_instanceof_backed_obj and its list of 21 stdlib type names, which the classifier consulted both before and after expanding a type.
type_is_builtin_object with its "Stdlib.Dict.t"/"Stdlib_Dict.t" name checks. The classifier expands the type to the builtin dict, and in Typeopt it was redundant next to type_cannot_contain_undefined, which already knows dict.

Generated code is unchanged across all test projects.

The next step, as discussed, is moving File and Blob out of the stdlib to WebAPI, which can now declare them the same way.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Fc7LEuyEfynjaKCVEBPmTF

codecov · 2026-10-21T18:19:58Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.22%. Comparing base (63ef81c) to head (7d2fd82).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           instanceof-typeof-annotations    #8949      +/-   ##
=================================================================
+ Coverage                          81.19%   81.22%   +0.02%     
=================================================================
  Files                                457      457              
  Lines                              64027    63987      -40     
=================================================================
- Hits                               51987    51973      -14     
+ Misses                             12040    12014      -26

Files with missing lines	Coverage Δ
compiler/ml/ast_untagged_variants.ml	`83.93% <ø> (+4.18%)`	⬆️
compiler/ml/typeopt.ml	`84.90% <100.00%> (+0.97%)`	⬆️
compiler/ml/variant_layout.ml	`93.33% <100.00%> (+2.59%)`	⬆️

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cknitt · 2026-10-21T18:30:40Z

@codex review

chatgpt-codex-connector · 2026-10-21T18:30:57Z

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-22T19:23:00.554430Z	`526b304`	Manual request

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Reviewed commit: c7381a1e6c

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cknitt · 2026-10-21T18:37:11Z

@codex review

github-actions · 2026-10-21T18:37:20Z

Semantic diff: https://cdn.rescript-lang.org/semantic-diff/pr-8949/index.html?v=7a1118fa2

chatgpt-codex-connector · 2026-10-21T18:39:47Z

Codex Review: Didn't find any major issues. 🚀

Reviewed commit: 7a1118fa21

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pkg-pr-new · 2026-10-21T18:48:22Z

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rescript

npm i https://pkg.pr.new/rescript@8949

@rescript/belt

npm i https://pkg.pr.new/@rescript/belt@8949

@rescript/darwin-arm64

npm i https://pkg.pr.new/@rescript/darwin-arm64@8949

@rescript/linux-arm64

npm i https://pkg.pr.new/@rescript/linux-arm64@8949

@rescript/linux-x64

npm i https://pkg.pr.new/@rescript/linux-x64@8949

@rescript/runtime

npm i https://pkg.pr.new/@rescript/runtime@8949

@rescript/win32-x64

npm i https://pkg.pr.new/@rescript/win32-x64@8949

commit: 7d2fd82

cknitt · 2026-10-22T19:20:57Z

@codex review

chatgpt-codex-connector · 2026-10-22T19:22:59Z

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: 526b3049a5

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Why: With the stdlib annotated, the classifier's list of stdlib type names only matched types that happen to be printed like a stdlib type, and its name-based dict check took any type named `dict` for an object. The list, matched before and after expansion, is gone, and so is the dict check: a payload is recognized by its `@instanceOf` or `@typeOf`, or by the builtin type it expands to. Generated code is unchanged for the stdlib's types. Diagnostic added (a local type named dict): Example: type dict<'a> @unboxed type t = D(dict<int>) | S(string) Before (js): if (typeof v === "object") { return "D"; } else { return "S"; } After (diagnostic): This untagged variant definition is invalid: Case D has a payload that is not of one of the recognized shapes (object, array, etc). Then it must be the only case with payloads. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Fc7LEuyEfynjaKCVEBPmTF Signed-off-by: Christoph Knittel <ck@cca.io>

Why: The classifier used to recognize payloads by the printed path of their type; nothing pinned that it no longer does. An unannotated local `Stdlib_Date.t`, which the removed list would have taken for a date, is an unknown payload, and aliases of builtin types are recognized through their expansion. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Fc7LEuyEfynjaKCVEBPmTF Signed-off-by: Christoph Knittel <ck@cca.io>

Why: Payloads are now recognized only by annotations and builtin types, so the spec's list of stdlib type names and the fallback to it are gone. Rule 4 lists `promise<_>` as the one builtin class and says that a type is never recognized by its name; rule 5 keeps the stdlib's annotations. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Fc7LEuyEfynjaKCVEBPmTF Signed-off-by: Christoph Knittel <ck@cca.io>

github-actions · 2026-10-22T19:29:28Z

Semantic Diff

3 commits · Full page

Recognize untagged payloads only by annotations and builtin types

_{237d5bf · Christoph Knittel with Claude Opus 5.5 · Oct 21, 2026}

Why

With the stdlib annotated, the classifier's list of stdlib type names only matched types that happen to be printed like a stdlib type, and its name-based dict check took any type named dict for an object.

The list, matched before and after expansion, is gone, and so is the dict check: a payload is recognized by its @instanceOf or @typeOf, or by the builtin type it expands to. Generated code is unchanged for the stdlib's types.

Diagnostic added (a local type named dict)

type dict<'a>
@unboxed type t = D(dict<int>) | S(string)

js · Before

if (typeof v === "object") { return "D"; } else { return "S"; }

diagnostic · After

This untagged variant definition is invalid: Case D has a payload that is not of one of the recognized shapes (object, array, etc). Then it must be the only case with payloads.

Test that payloads are not recognized by type name

_{0a2f6d5 · Christoph Knittel with Claude Opus 5.5 · Oct 21, 2026}

Why

The classifier used to recognize payloads by the printed path of their type; nothing pinned that it no longer does.

An unannotated local Stdlib_Date.t, which the removed list would have taken for a date, is an unknown payload, and aliases of builtin types are recognized through their expansion.

Drop the name list from the untagged variants spec

_{7d2fd82 · Christoph Knittel with Claude Opus 5.5 · Oct 22, 2026}

Why

Payloads are now recognized only by annotations and builtin types, so the spec's list of stdlib type names and the fallback to it are gone.

Rule 4 lists promise<_> as the one builtin class and says that a type is never recognized by its name; rule 5 keeps the stdlib's annotations.

cknitt added the changelog:skip No release notes needed label Oct 21, 2026

cknitt added this pull request to stack #8951 October 21, 2026 18:14

cknitt force-pushed the untagged-no-hardcoded-classes branch from 3aafb3f to c7381a1 Compare October 21, 2026 18:22

chatgpt-codex-connector Bot reviewed Oct 21, 2026

View reviewed changes

Comment thread compiler/ml/variant_layout.ml

cknitt marked this pull request as ready for review October 21, 2026 19:24

cknitt requested a review from cristianoc October 21, 2026 19:24

cristianoc mentioned this pull request Oct 22, 2026

Declare the runtime class or typeof of types, and annotate the stdlib #8950

Open

cknitt force-pushed the untagged-no-hardcoded-classes branch from 7a1118f to b786fd3 Compare October 22, 2026 17:01

cknitt mentioned this pull request Oct 22, 2026

Render the semantic diff with the workflow's own scripts #8963

Merged

Base automatically changed from stdlib-instanceof-annotations to instanceof-typeof-annotations October 22, 2026 18:46

cknitt removed this pull request from stack #8951 October 22, 2026 18:46

cknitt mentioned this pull request Oct 22, 2026

Annotate the stdlib's runtime classes #8948

Merged

cknitt force-pushed the untagged-no-hardcoded-classes branch from b786fd3 to 526b304 Compare October 22, 2026 19:14

cknitt mentioned this pull request Oct 22, 2026

Check @notUndefined of an interface against the implementation #8966

Draft

cknitt added this pull request to stack #8968 October 22, 2026 19:15

cknitt and others added 3 commits October 22, 2026 19:28

cknitt force-pushed the untagged-no-hardcoded-classes branch from 526b304 to 7d2fd82 Compare October 22, 2026 19:29

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Recognize untagged payloads only by annotations and builtin types - #8949

Recognize untagged payloads only by annotations and builtin types#8949
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