Replace the heuristic lookup of Cairo variables with a semantic walk in FunctionDebugInfo

[integraledelebesgue]

Summary

This PR reworks the Sierra -> Cairo variable reconstruction logic.
Instead of a heuristic lookup, we perform a top-down walk through the function's semantic model and construct the mapping by hand, using a dedicated logic for every type of statement and expression.
This allows to handle all problematic cases of Cairo variables, like re-binds or loops.

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Type of change

Please check one:

• Bug fix (fixes incorrect behavior)
• New feature
• Performance improvement
• Documentation change with concrete technical impact
• Style, wording, formatting, or typo-only change

⚠️ Note:
To keep maintainer workload sustainable, we generally do not accept PRs that
are only minor wording, grammar, formatting, or style changes.
Such PRs may be closed without detailed review.

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Why is this change needed?

It allows the Cairo debugger to properly handle variables in general and support loops.

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What was the behavior or documentation before?

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What is the behavior or documentation after?

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Related issue or discussion (if any)

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Additional context

[integraledelebesgue]

This change is part of the following stack:

• Emit a multi-map of Sierra to Cairo variables in FunctionDebugInfo #9991
  • Replace the heuristic lookup of Cairo variables with a semantic walk in FunctionDebugInfo #9992 ◀

_{Change managed by git-spice.}

[reviewable-StarkWare]

This change is 

[cursor]

PR Summary

Medium Risk
Changes debugger-facing debug metadata generation across compiler, Starknet, and test builds; behavior should improve but regressions in variable display are possible in edge cases (generics, loops, closures).

Overview
Replaces statement-location heuristics with a semantic-model walk when building Sierra→Cairo variable mappings for FunctionDebugInfo (cairo-debugger annotations).

extract_serializable_debug_info no longer takes StatementsLocations or a ProgramRegistry; compiler, Starknet, and test-plugin call sites pass only the Sierra program. Mapping is built by resolving the Sierra function to FunctionWithBodyId, indexing Sierra vars by stable syntax pointers from variables_locations, inferring var types from libfunc signatures, and walking the body with BindingCollector (lets, assignments, if/match/for/while/loop, compound assignment, pattern binds, and rebinds via an alias map).

Large blocks of syntax-tree identifier lookup and lookup-item resolution are removed in favor of this structured traversal.

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[cursor]

Let-else else mutates aliases early

Medium Severity

For Statement::Let with a let-else clause, the walker visits the else expression before it resolves the RHS Sierra variable and binds the pattern. Because resolve_rhs_sierra_var uses the live alias_map, any rebindings performed while visiting the else branch can change how the main let RHS is resolved, producing incorrect Sierra-to-Cairo mappings on the success path.

 

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[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

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[cursor]

Control flow merges alias state

Medium Severity

BindingCollector keeps one global alias_map while visiting every if branch and every match arm in order. Later branches overwrite earlier bindings, so code after control flow (and later arms) resolves Cairo variables using the last visited branch’s Sierra slots, not the branch that would run at runtime.

Additional Locations (1)

• crates/cairo-lang-sierra-generator/src/debug_info/function_debug_info.rs#L383-L386

 

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[cursor]

Loop body walked once

Medium Severity

Expr::Loop and Expr::While call visit_expr on the body a single time, so each reassignment inside the loop produces at most one rebind event. Sierra variables allocated on later iterations at the same source locations are never added to bindings, leaving many loop-live slots without Cairo names.

Additional Locations (1)

• crates/cairo-lang-sierra-generator/src/debug_info/function_debug_info.rs#L420-L421

 

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