refactor(lowering): Made function not return Maybe and possibly hide diags.

[orizi]

Summary

function_with_body_lowering_diagnostics now returns Diagnostics directly instead of Maybe<Diagnostics>. The in_cycle error case is handled inline using matches!(..., Ok(true)) rather than propagating via ?, allowing the function to be infallible. All call sites are updated to remove .unwrap_or_default() and ? unwrapping accordingly.

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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

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Why is this change needed?

function_with_body_lowering_diagnostics was returning Maybe<Diagnostics> despite having no meaningful failure path — the only ? usage was on db.in_cycle(...), which on error would silently swallow all diagnostics collected up to that point. This meant a query failure could cause legitimate diagnostics to be lost rather than reported.

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What was the behavior or documentation before?

If db.in_cycle(function_id, DependencyType::Cost) returned an Err, the function would early-return Err, discarding any diagnostics already accumulated in the builder. Call sites used .unwrap_or_default() to recover, silently dropping those diagnostics.

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What is the behavior or documentation after?

The function is now infallible and always returns a Diagnostics value. The in_cycle result is checked with matches!(..., Ok(true)), so errors are treated as "not in cycle" without aborting diagnostic collection. All diagnostics gathered before the cycle check are preserved and returned regardless of whether in_cycle succeeds.

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Related issue or discussion (if any)

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Additional context

The test helper in block_generator_test.rs is also updated to remove the now-unnecessary .unwrap() call.

[reviewable-StarkWare]

This change is 

[orizi]

• refactor(lowering): Made function not return Maybe and possibly hide diags. #9916 👈 (View in Graphite)
• main

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[cursor]

PR Summary

Medium Risk
Changes the type/signature and error-handling behavior of function_with_body_lowering_diagnostics, which affects compilation/lowering control flow and could subtly change when errors are surfaced or suppressed.

Overview
function_with_body_lowering_diagnostics now returns Diagnostics directly (no Maybe), ensuring diagnostics collected during lowering/borrow-checking aren’t dropped due to an in_cycle query error.

Call sites are updated to stop propagating/unwrap’ing this query (lowered_body no longer uses ?, semantic aggregation no longer uses unwrap_or_default, and the Sierra generator test removes an unwrap()), and the cycle check treats in_cycle failures as “not in cycle” via matches!(..., Ok(true)).

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[TomerStarkware]

@TomerStarkware reviewed 2 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on orizi).