fix(compile): robust fetch detection for minified bundles + drop runtime fetch stubs when web-fetch is linked

[proggeramlug]

Problem

A minified bundle that uses fetch / Headers / Request segfaults at startup: the real fetch implementation isn't linked, only the no-op runtime stub, which returns garbage the caller dereferences → EXC_BAD_ACCESS in js_object_get_class_id.

Two root causes:

1. uses_fetch detection is shape-fragile. perry-stdlib's real fetch (web-fetch) is linked only when uses_fetch is set, which happens at ~30 shape-specific sites scattered through HIR lowering (expr_new.rs, destructuring/*, …). A minified bundle's new Headers() / new Request() / fetch(...) can reach codegen as Expr::New { class_name: "Headers" } / a Fetch* HIR variant — codegen correctly dispatches those to js_headers_new / js_request_new / js_fetch_with_options — without having hit any uses_fetch set-site. So uses_fetch stays false, web-fetch is stripped, and only the stub remains.

2. The runtime fetch stubs are never compiled out. The js_fetch_* / js_headers_new / js_request_new stubs in perry-runtime are gated #[cfg(not(feature = "external-fetch-symbols"))], but external-fetch-symbols was enabled nowhere in the build. So whenever web-fetch is linked, both the stub (perry-runtime) and the real (perry-stdlib) symbols exist, and on the fresh build path the stub has won the link.

Fix

1. Robust fetch detection (feature_detect.rs): a post-lowering token scan of the final HIR for the fetch web-platform constructors (class_name: "Headers"|"Request"|"Response"|"FormData"|"Blob"|"File") and the dedicated fetch call variants (FetchWithOptions / FetchGetWithAuth / FetchPostWithAuth) → set uses_fetch. This mirrors the existing EventEmitter / URL token-scan fallbacks in the same file. Over-matching only over-links web-fetch (a size cost); the rule is zero false negatives.

2. Drop the stub when the real is linked (freshness.rs, auto_optimized_cross_features): if ctx.uses_fetch { push("perry-runtime/external-fetch-symbols") }, mirroring the existing per-feature lines (regex-engine, url-engine, …). This compiles the stubs out of libperry_runtime.a, leaving only perry-stdlib's real symbols — no dup-symbol gamble.

Both are required together: fix 1 links web-fetch but leaves the dup; fix 2 never fires without fix 1.

Verification

A large minified CLI bundle that uses fetch/Headers/Request (7× new Headers(), 9× fetch() previously linked only the stub and printed [perry] warning: js_headers_new is a no-op stub … (runtime-only build). With both fixes, uses_fetch is detected, the stub warnings are gone, and the real web-fetch symbols are linked.

Summary by CodeRabbit

• Bug Fixes
  • Improved detection of fetch-related code so the correct web-fetch runtime support is kept enabled in more cases.
  • Prevented fresh builds from incorrectly selecting placeholder fetch symbols, reducing missing-runtime issues and link problems.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: ab701108-71ca-4c25-a5e4-f9979f537dba

📥 Commits

Reviewing files that changed from the base of the PR and between 15c91e1 and 22b9edb.

📒 Files selected for processing (2)

• crates/perry/src/commands/compile/collect_modules/feature_detect.rs
• crates/perry/src/commands/compile/optimized_libs/freshness.rs

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📝 Walkthrough

Walkthrough

Fallback fetch detection now scans lowered HIR when uses_fetch was not set during lowering, and the fresh-build cross-feature list now includes perry-runtime/external-fetch-symbols when fetch usage is detected.

Changes

Fetch feature flow

Layer / File(s)	Summary
Fallback fetch detection crates/perry/src/commands/compile/collect_modules/feature_detect.rs	detect_optional_feature_usage serializes the module HIR and scans for fetch-related constructors and Fetch* variants when ctx.uses_fetch is still false, then sets ctx.needs_stdlib and ctx.uses_fetch on a match.
Fresh-build fetch gating crates/perry/src/commands/compile/optimized_libs/freshness.rs	auto_optimized_cross_features appends perry-runtime/external-fetch-symbols to cross_features when ctx.uses_fetch is true.

Sequence Diagram(s)

sequenceDiagram
  participant detect_optional_feature_usage
  participant ctx
  participant auto_optimized_cross_features
  participant cross_features

  detect_optional_feature_usage->>ctx: set uses_fetch and needs_stdlib after HIR scan
  ctx->>auto_optimized_cross_features: uses_fetch = true
  auto_optimized_cross_features->>cross_features: append perry-runtime/external-fetch-symbols

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• PerryTS/perry#5172: Extends the same optional-feature detection path in collect_modules/feature_detect.rs.
• PerryTS/perry#5189: Also adjusts fetch-related feature selection so web-fetch stays available when fetch usage is detected.
• PerryTS/perry#5606: Touches fetch-runtime registrations that depend on the same uses_fetch/feature-gating path.

Poem

A bunny sniffed the HIR so fine,
and found fetch clues in every line.
Now symbols hop where they belong,
and runtime stays swift, bright, and strong.
🐇✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the PR’s main fix: improved fetch detection and excluding runtime fetch stubs when web-fetch is linked.
Description check	✅ Passed	The description covers the problem, fix, and verification, but it does not follow the template headings and omits an explicit related issue and test-plan checklist.
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.

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