fix(wasm-host): auto-provision wasm-host in all compile paths

[jdalton]

Problem

A program referencing WebAssembly.* did NOT reliably get the wasm-host cargo feature enabled on perry-runtime, causing link failures:

Undefined symbols for architecture arm64: "_js_webassembly_module_new"

This blocks sdxgen (whose acorn.wasm path needs it) and is the concrete instance of the --enable-wasm-runtime / wasm-host auto-detect gap.

Root cause — three broken paths

1. --enable-wasm-runtime did not enable the feature. The flag only linked libperry_wasm_host.a (run_pipeline.rs:5288 checked args.enable_wasm_runtime) but never enabled perry-runtime/wasm-host in the auto-optimize cargo invocation (freshness.rs:192 only checked ctx.needs_wasm_runtime, NOT args.enable_wasm_runtime). So the runtime archive lacked js_webassembly_* symbol definitions while the host library was linked — the symbol stayed undefined.

2. PERRY_NO_AUTO_OPTIMIZE=1 never enabled wasm-host. The no-auto path (no_auto.rs) only resolved prebuilt well-known ext archives. The prebuilt libperry_runtime.a is built WITHOUT wasm-host (deliberately kept out of default to avoid wasmi bloat on non-wasm programs). So even though feature_detect.rs set ctx.needs_wasm_runtime = true, the no-auto path never rebuilt the runtime with the feature.

3. Dynamic WebAssembly access was not detected. The static lowering (module_static.rs) sets hir_module.uses_webassembly for direct WebAssembly.Module/instantiate/etc. call sites, but a minified bundle can reach WebAssembly via dynamic property access (const WA = WebAssembly; WA.Module(bytes), globalThis.WebAssembly) that lowers to an ordinary PropertyGet without hitting any set-site. The codegen still emits js_webassembly_* FFI calls for those paths, so the link died.

Fix

1. --enable-wasm-runtime override (run_pipeline.rs): fold args.enable_wasm_runtime into ctx.needs_wasm_runtime before any feature/library provisioning so the flag triggers the same provisioning as auto-detection — the wasm-host cargo feature, the runtime rebuild, the library link, and the symbol-stub scan all see it.

2. No-auto runtime rebuild (no_auto.rs): when ctx.needs_wasm_runtime is set, build perry-runtime-static with default features + perry-runtime/wasm-host into a dedicated target dir (target/perry-wasm-host-runtime) so the prebuilt libperry_runtime.a is not clobbered. This is the same on-demand build pattern build_missing_prebuilt_ext_lib uses for CPU-only ext wrappers. perry-wasm-host has no tokio dep, so there is no perry-ext-net: outbound TCP panics — LTO dead-strips tokio CONTEXT statics #507 shared-tokio concern.

3. Dynamic access fallback (feature_detect.rs): add a fallback grep for "WebAssembly" in the HIR debug string, mirroring the fetch/crypto/EventEmitter fallbacks. Over-matching only over-links the wasm host (a size cost); the rule is zero false negatives.

Verification

• cargo test -p perry --bin perry -- compile::optimized_libs — 34 passed (31 existing + 3 new regression tests).
• cargo test -p perry-hir --lib — 315 passed.
• New regression tests: wasm-usage → wasm-host cross-feature provisioned; non-wasm → not provisioned; wasm usage changes the cache key.

Backward compat

• --enable-wasm-runtime still works (now actually enables the feature, not just the library).
• Non-wasm programs don't link the host — wasm-host stays out of default, the detection only fires on WebAssembly.* usage, and the no-auto rebuild only runs when needs_wasm_runtime is set.

Summary by CodeRabbit

• New Features

  • Improved WebAssembly runtime support during compilation.
  • The compiler now detects WebAssembly usage more reliably and enables the required runtime automatically.
  • Explicit WebAssembly runtime options are consistently applied across compilation and linking.
  • When needed, the runtime is rebuilt with WebAssembly host support for the target platform.

• Bug Fixes

  • Improved fallback behavior when runtime sources, SDKs, or cross-compilation tools are unavailable, preserving the prebuilt runtime when possible.
  • Optimized runtime caching now distinguishes WebAssembly-enabled builds from standard builds.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: 6e11d8ab-dec0-4f50-a49c-524d2e91fa57

📥 Commits

Reviewing files that changed from the base of the PR and between 7441e1f and 34684d8.

📒 Files selected for processing (4)

• crates/perry/src/commands/compile/collect_modules/feature_detect.rs
• crates/perry/src/commands/compile/optimized_libs/no_auto.rs
• crates/perry/src/commands/compile/optimized_libs/tests.rs
• crates/perry/src/commands/compile/run_pipeline.rs

Included review availability: Your plan includes up to 8 reviews per rolling hour; 4 remain after this review.

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📝 Walkthrough

Walkthrough

The compiler now detects WebAssembly references through lowered HIR fallback scanning and explicit flags. It propagates one runtime state to optimized-library selection, rebuilds the wasm-host runtime when needed, and separates wasm and non-wasm cache entries.

Changes

WebAssembly runtime support

Layer / File(s)	Summary
Normalize WebAssembly runtime detection crates/perry/src/commands/compile/collect_modules/feature_detect.rs, crates/perry/src/commands/compile/run_pipeline.rs	Fallback HIR scanning and --enable-wasm-runtime now set the shared ctx.needs_wasm_runtime flag.
Build the wasm-host runtime crates/perry/src/commands/compile/optimized_libs/no_auto.rs	The no-auto path builds perry-runtime-static with wasm-host, applies platform-specific cross-compilation settings, and falls back to the prebuilt runtime on failure.
Validate feature and cache separation crates/perry/src/commands/compile/optimized_libs/tests.rs	Tests verify wasm-host feature selection, omission for non-WebAssembly code, and separate cache keys.

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

Merge Risk: ⚪ Minimal · up to 34684

The change improves wasm-host provisioning across compile paths, and no actionable merge-blocking risk remains at the current head after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant CompilePipeline
  participant CompileContext
  participant ResolveNoAutoOptimizedLibs
  participant BuildWasmHostRuntime
  participant Cargo
  CompilePipeline->>CompileContext: normalize WebAssembly runtime state
  CompileContext->>ResolveNoAutoOptimizedLibs: provide needs_wasm_runtime
  ResolveNoAutoOptimizedLibs->>BuildWasmHostRuntime: request wasm-host runtime
  BuildWasmHostRuntime->>Cargo: build perry-runtime with wasm-host
  Cargo-->>BuildWasmHostRuntime: return platform-specific archive
  BuildWasmHostRuntime-->>ResolveNoAutoOptimizedLibs: return runtime or fallback

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: automatic wasm-host provisioning across all compile paths.
Description check	✅ Passed	The description clearly explains the problem, root causes, fixes, verification results, and backward compatibility impact.
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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• Create PR with unit tests

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[proggeramlug]

Merging — everything passes except cargo fmt --all -- --check, which flags
optimized_libs/no_auto.rs (lines 5, 89, 98, 134, 154) and
optimized_libs/tests.rs:1299. I confirmed it is this branch and not the merge
with #8338: clean main is fmt-clean (exit 0), and this branch alone on current
main still fails, including in no_auto.rs, which #8338 never touched.

Since this is a fork branch I can't push the fix here, so I'm landing the
formatting as an immediate follow-up rather than bouncing the PR for whitespace.

Validated otherwise: optimized_libs bin tests 36/36 (up from 33 — your three
new ones), perry-runtime --lib 2579, perry-stdlib --lib 124, and 49 of 50
gates including the compile tier (cargo check --workspace --all-targets under
-D warnings and cargo clippy --workspace).

One note for later, not a blocker: the new WebAssembly fallback builds a
format!("{:?}") of the whole HIR. That is consistent with the file rather than
new — feature_detect.rs already does this six separate times on main — but
it means a large module now gets its HIR formatted to a string seven times per
compile. On the Next.js fixture (104 modules, multi-MB IR) that is real time and
peak RSS. Computing hir_debug once at the top of detect_optional_feature_usage
and passing &str to each check would collapse all seven.