Rust output fails to compile (E0594) when a body assigns to a parameter's field or to self.x in an operator, because mut is not added

[matt-edmondson]

What's wrong

PR #93 declares a Rust parameter mut when the body reassigns it, but two cases were left out.

1. Coder/Languages/RustGenerator.cs:1002: ReassignedParameters only matches AssignmentStatement { Target: VariableReference target } whose name is exactly a parameter's name. Member access is written as a dotted VariableReference("p.x"), the repo's own convention (CompiledExemplar.cs:154). So p.x = … / p.x += … never matches, and p stays immutable.
2. RustGenerator.cs:688-695: operator impls write self / rhs directly and never consult the reassignment set at all.

Failure scenario

A free function shifted(p: Point) -> Point { p.x += 1; return p; } generates:

pub fn shifted(p: Point) -> Point { … }

rustc rejects it: error[E0594]: cannot assign to 'p.x', as 'p' is not declared as mutable.

An operator + (rhs: Point) whose body is self.x += rhs.x; return self; generates:

fn add(self, rhs: Point) -> Point { … }

rustc rejects it: error[E0594]: cannot assign to 'self.x', as 'self' is not declared as mutable.

Expected: mut p: Point and fn add(mut self, rhs: Point).

I reproduced both by running the built ktsu.Coder.dll and compiling the output with rustc.

Suggested fix / acceptance criteria

• In ReassignedParameters, match on the root of a dotted target (the text before the first .).
• In the operator path, run the same scan. Treat self as a candidate for the by-value (self, not &self) operator traits, and write mut on every parameter it finds.
• Add both cases to RustGeneratedSourceCompilesTests.

[matt-edmondson]

Triage

• Category: Bug
• Priority: Medium. The generated Rust fails to compile (E0594) with a clear error. It covers common patterns (mutating a by-value param's field, self.x += in an operator), but nothing miscompiles silently.
• Area / suggested assignee: Rust generator, RustGenerator.cs (ReassignedParameters and the operator impl path). Owner: @matt-edmondson
• Duplicates / in progress: no duplicate. This follows up merged PR Declare a Rust parameter mut when the body assigns to it #93. Open PR Write a Rust type's constant fields as associated constants #94 (Rust associated constants) also edits RustGenerator.cs but not these methods, so a conflict is unlikely.
• Next step: match the root of dotted assignment targets, run the same scan for operator self/rhs, and add both cases to RustGeneratedSourceCompilesTests.

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Generated by Claude Code