feat(constant): Added support for const calculation for inner variants and lets.

[orizi]

Summary

Extends constant evaluation to support a broader set of pattern matching constructs. The destructure_pattern function now returns Option<()> to indicate whether a pattern matched, enabling proper handling of non-matching arms. Match expressions now iterate arms using destructure_pattern for all pattern types (including wildcards, literals, tuples, fixed-size arrays, and structs) rather than only enum variants. let-else statements in constant blocks are now evaluated: if the pattern fails to match, the else clause is executed. if let chains and if let conditions similarly use the generalized destructure_pattern path. Boolean condition evaluation in if expressions now compares against cached true/false const values directly instead of extracting the enum variant.

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Type of change

Please check one:

• Bug fix (fixes incorrect behavior)

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Why is this change needed?

Constant evaluation previously only handled enum variant patterns in match expressions and if let conditions. Wildcard patterns, literal patterns, tuple patterns, array patterns, and struct patterns in match arms were not correctly evaluated, causing incorrect or missing constant folding. Additionally, let-else statements inside constant blocks were not evaluated at all — the else clause was never considered, so refutable patterns with a let-else would silently produce wrong results instead of executing the panic branch.

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What was the behavior or documentation before?

• match on non-enum types (e.g., u8, felt252, tuples, structs) with wildcard or literal patterns would fail to evaluate correctly.
• let-else in a constant block would ignore the else clause even when the pattern did not match.
• if let chains were restricted to enum variant patterns only.

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What is the behavior or documentation after?

• match expressions in constants correctly evaluate wildcard, literal, tuple, fixed-size array, struct, and enum variant patterns.
• let-else in constant blocks executes the else clause (typically a panic) when the pattern does not match, producing the appropriate Failed to calculate constant diagnostic.
• if let and if let chains work with the full set of supported patterns.

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Related issue or discussion (if any)

Fixes #9887.

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Additional context

A regression test (tests/bug_samples/issue9887.cairo) covers wildcard, literal, tuple, struct, and unit patterns in constant match expressions. New constant test cases in the semantic test data cover match with wildcards and literals, let-else, if let, and if let chains with multiple conditions.

[reviewable-StarkWare]

This change is 

[orizi]

• bugfix(semantic): fix ICE on nested const fn in const fn. #9901
• feat(constant): Added support for const calculation for inner variants and lets. #9899 👈 (View in Graphite)
• main

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[cursor]

PR Summary

Medium Risk
Extends compile-time constant evaluation semantics for pattern matching and let-else, which can change which constants successfully fold or now error; risk is moderated by added regression tests but impacts core compiler behavior.

Overview
Constant folding now understands more pattern constructs. Const evaluation no longer assumes match/if let patterns are enum-only; it uses a generalized destructure_pattern that returns match success, enabling wildcard/literal/tuple/array/struct/unit patterns and correct arm selection.

let bindings in const blocks now handle else clauses. During evaluation and validation, let-else is evaluated so non-matching refutable patterns execute the else branch (typically producing a Failed to calculate constant diagnostic).

Adds semantic test cases and a new bug sample (issue9887) to lock in behavior for const match, destructuring, and if let chains.

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[TomerStarkware]

@TomerStarkware reviewed 4 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on orizi).

[TomerStarkware]

@TomerStarkware reviewed 2 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on orizi).

[orizi]

@orizi resolved 1 discussion.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on orizi).