Compiler: scan deferred class frame captures once

[chrisbbreuer]

Parents: #465, #493, #496
Related: #615, #616, #618

Problem

classDeferredBodiesCaptureFrame walks every deferred class member body once for every frame binding in the current and enclosing plain-function scopes. A function with many locals plus a large method/field/static-block surface therefore multiplies frame-binding count by deferred-class AST size during bytecode admission, even when the class references only globals.

The fallback is semantically necessary today: eval_class may capture Environment-backed bindings but cannot recover an arbitrary VM frame slot. The classifier must remain conservative and exact; broad class rejection is not an optimization.

Scope

• Freeze production parse + plain-function admission/compile rows at 1K/2K/4K frame widths with method/field/static-block and early/late/global-only controls.
• Collect frame-slot names across the exact FnScope ancestry once, excluding bindings already backed by Environment Records.
• Traverse deferred class bodies once against exact frame-name membership while leaving eager superclass and computed-key evaluation unchanged.
• Preserve conservative shadowing, TDZ policy, class template/chunk structure, unsupported-reason identity, and allocation accounting.
• Keep the zero/one-frame-name common path allocation-free.

No-workaround rules

• No class syntax refusal, heuristic cutoff, skipped deferred member kind, eager-key conflation, tree-walker fallback presented as optimization, source rewriting, or process-global cache.
• A new class member/AST node kind must not silently create a frame-capture false negative.

Acceptance

• Benchmark-first rows preserve exact admission/rejection reason, structural checksum, and allocation replay across every control.
• Parent → candidate exact evidence demonstrates bounded classifier scaling and names the complete scored boundary.
• Real frame captures remain rejected; global-only and Environment-backed captures remain admitted with tree-walker/required-bytecode identity.
• Focused compiler/class tests, full units, relevant Test262 class/function/lexical subtrees, and applicable TSan gates pass with exact before → after accounting.
• Evidence and parent issues are cross-linked without promoting diagnostic host noise.

[chrisbbreuer]

Benchmark contract pushed in be27ecd4 (bench(frontend): add deferred class frame witness (#619)).

The production frontend runner now freezes ten parse + plain-function admission/compile rows: global-only deferred members at 1,024/2,048/4,096 frame widths, first/last method captures, instance-field capture, static-block capture, eager computed-key and superclass controls, and an Environment-backed repeated-body capture. Every row validates compiled-versus-unsupported admission, exact rejection reason, complete chunk structure, checksum, and an untimed identical-work allocation replay.

All 10/10 contracts pass. The existing #618 1K control remains exact and dependency audit stays at 15 classified edges / 0 migrations / 60 tools. A discarded occupied-host probe shows the global-only instruction sequence growing about 150M → 579M → 2.24B as width doubles, confirming the static multiplication, but this benchmark-only commit makes no timing or publication claim. The single-scan implementation starts from this exact first parent.

[chrisbbreuer]

Single-scan implementation pushed in 8bbbf402 (perf(compiler): scan deferred class frames once (#619)).

The compiler now collects ordinary and non-Environment-backed lexical frame-slot names across the exact FnScope ancestry once, then scans each deferred method, field initializer, and static block once against exact membership. Eager computed keys remain outside the deferred scan, Environment-backed captures remain eligible, and zero/one-name cases allocate no table. The existing exhaustive AST walker remains conservative about shadowing and prevents new node kinds from silently becoming false negatives.

Validation at the implementation commit:

• 10/10 frozen benchmark controls preserve exact admission/rejection identity, checksum, and allocation replay;
• expanded class admission matrix covers global-only methods, eager computed keys, Environment-backed method captures, and frame captures from methods, fields, and static blocks;
• compiler-filtered units: 70 passed, 0 failed, 0 leaked;
• focused frontend: 12/12;
• dependency audit: 15 classified edges, 0 migration targets, 60 classified tools.

A non-evidence occupied-host diagnostic changed the 1K/2K/4K global-only retired-instruction sequence from roughly 150M/579M/2.24B to 14M/29M/58M, consistent with removing the multiplicative scan. Exact isolated parent→candidate evidence, full units, and relevant Test262 accounting remain pending; no timing or conformance claim is made from that diagnostic.

[chrisbbreuer]

Full integration unit gate at candidate main 8bbbf402: 1,733 passed, 1 platform skip, 0 failed, 0 leaked across 10 shards in 238.1 seconds. Exact parent/candidate Test262 class/function/lexical accounting remains pending and will run from the frozen be27ecd4 and 8bbbf402 binaries without overlapping other corpus or host jobs.

[chrisbbreuer]

Incremental exact correctness evidence for #619:

Frozen identities:

• parent be27ecd46dbb20b1bca090a256ad5927ae84b981 Test262 SHA-256 024cc0cc6e7410700fb08d2c5b83c735abd3ca7f9c12745b4ecb842ea67381a2
• candidate 8bbbf402d723815b19ad3de5da4d698ac1a74cd5 Test262 SHA-256 241d768312530153e433178150fffe9f9c8e1cea91af5820ebb00513964889cb

Each retained pair had clear process snapshots before, between, and after, and byte-identical transcripts:

• expressions/function: 0 fail / 264 pass → 0 / 264
• statements/function: 0 / 451 → 0 / 451
• block-scope: 0 / 145 → 0 / 145
• statements/let: 0 / 145 → 0 / 145
• statements/const: 0 / 136 → 0 / 136

Subtotal: 0 fail / 1,141 pass → 0 / 1,141, zero flips.

Compiler-focused TSan also passes 71/71 with zero failures/leaks, including the exact global-only/frame-capture class admission matrix. The full 1,733-pass / one-skip unit gate remains green.

This is deliberately partial: statements/class (4,367 files before configured exclusions) and expressions/class (4,059) remain pending an uninterrupted serial parent/candidate window. No full class-boundary or performance claim is made yet.