refactor: split gc/layout.rs and codegen/artifacts.rs under the 2000-line cap (unblocks lint on main)

[proggeramlug]

lint is red on main; this unblocks it

./scripts/check_file_size.sh exits 1 against the hard 2000-line cap:

2005  crates/perry-codegen/src/codegen/artifacts.rs
2110  crates/perry-runtime/src/gc/layout.rs

Bisected to #8204 (bf8fd868e, the 56 → 48 B header shrink): gc/layout.rs went 1975 → 2110, and codegen/artifacts.rs was sitting at exactly 2000 — right on the cap, so any addition at all broke it.

check_file_size.sh runs in lint, a required status context, so every open PR is currently blocked behind a failure that has nothing to do with it. That is the "required and red for a pre-existing reason" state — it trains everyone to bypass, and the next genuine failure arrives indistinguishable from the standing one.

The split

file	before	after
codegen/artifacts.rs	2005	1930
codegen/ctor_arity.rs (new)	—	83
gc/layout.rs	2110	1778
gc/layout/typed_shape.rs (new)	—	353

Both land with real headroom rather than scraping under at 1999 — artifacts.rs being at exactly 2000 is what made #8204 break it, and leaving it there would just re-arm the trap.

This is relocation-only, and here is the evidence

A file-size fix is the easiest place for an accidental semantic change to hide behind a large mechanical diff, so the claim is checked rather than asserted. Comparing the multiset of non-blank source lines before against (remainder + extracted) after:

pair	code that vanished	genuinely new
layout.rs → typed_shape.rs	5	23
artifacts.rs → ctor_arity.rs	1	8

All six "vanished" lines reappear in adjusted form, and they are exactly the two categories a relocation produces:

• Path shortening — super::shape_install::{words_contain_slot, words_intersect, hit, record} became shape_install::…, because the extracted module sits inside gc/layout/ and no longer needs the super:: hop.
• One visibility widening — fn synthesized_ctor_param_count( became pub(super) fn, plus use super::ctor_arity::synthesized_ctor_param_count; at the call site.

The 23 + 8 new lines are module headers, use statements and doc comments. No logic edits, no renames visible outside the modules.

Seam choice

Both extractions are cohesive rather than "the last N lines": typed_shape.rs is the typed-shape layout family, ctor_arity.rs is the synthesized-constructor arity helper and its single caller.

Deliberately not touched, both near the cap and owned by in-flight work: gc/cycle.rs (1991) and gc/barrier/mod.rs (1995).

Note for anyone splitting in this area next: adding a matching pub use <new_mod>::*; is an unused-import warning — hence a -D warnings failure — when the extracted items are #[no_mangle] and reached by symbol rather than by path. The module needs mod <new_mod>; only, plus fixing any internal crate::…::<moved_fn> call sites.

No version bump.

Summary by CodeRabbit

• Bug Fixes
  • Improved constructor argument handling for classes without explicit constructors, including inherited and imported classes.
  • Added safer fallback behavior when parent-class information is unavailable.
  • Strengthened typed object layout validation for slot counts and pointer/value masks.
  • Improved typed layout setup for newly allocated objects.
  • Added efficient reuse of previously validated typed layouts.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: a735af77-09e5-4177-b357-28cc34d86ba3

📥 Commits

Reviewing files that changed from the base of the PR and between f8168ec and 42c94a2.

📒 Files selected for processing (2)

• changelog.d/8212-file-size-cap-split.md
• scripts/shape_descriptor_census_baseline.json

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📝 Walkthrough

Walkthrough

The change extracts constructor arity calculation and typed-shape layout installation into dedicated modules. Existing codegen integration and typed-shape C ABI paths remain available through module wiring and re-exports.

Changes

Constructor and typed-shape layout modularization

Layer / File(s)	Summary
Constructor arity extraction crates/perry-codegen/src/codegen/ctor_arity.rs, crates/perry-codegen/src/codegen/artifacts.rs, crates/perry-codegen/src/codegen/mod.rs	Constructor arity calculation now resides in ctor_arity.rs. It handles explicit constructors, native and absent parents, local and imported ancestors, and unresolved parents. Artifact generation imports the helper.
Typed-shape layout module crates/perry-runtime/src/gc/layout/typed_shape.rs, crates/perry-runtime/src/gc/layout.rs, scripts/shape_descriptor_census_baseline.json, changelog.d/8212-file-size-cap-split.md	Typed-shape validation, mask handling, memoized descriptor installation, per-object storage, and both C ABI entry points now reside in typed_shape.rs. layout.rs registers the module and re-exports the APIs. The census baseline and changelog record the relocation.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• PerryTS/perry#6930: Adds related typed-shape initialization in standalone constructor paths.
• PerryTS/perry#6939: Modifies related typed-shape initialization and descriptor installation logic.
• PerryTS/perry#8182: Relocates related typed-shape layout logic from gc/layout.rs.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the motivation and file changes, but it omits the required related issue, test plan, and checklist sections.	Add the template sections and document the verification commands and results, including the related issue or “n/a” and checklist confirmations.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes splitting the two oversized files to satisfy the 2,000-line cap and unblock lint.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/file-size-cap-8204

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