fix(hydration): stop the /index.js retry burying a reached-module error - #3674
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The Pages Router client loads <route>.js and, on failure, retries <route>/index.js because a route may be authored as either <route>.tsx or <route>/index.tsx. That retry fired unconditionally — so when <route>.js loaded and threw at *evaluation* (e.g. the server→client adapter leak in #3661 dereferencing a browser-absent O_NOFOLLOW), the client still probed the sibling <route>/index.js, which 404s for an extension-style route and put a misleading "module not found" on top of the real error (#3667). A module that ran far enough to throw its own runtime error is the served file, so the sibling probe can only 404. Skip the retry in exactly that case (`isReachedModuleEvaluationError`), while keeping it for the missing-module and proxy-HTML-shell rejections it exists to recover — the cases pinned by the existing retry tests. Regenerated hydration-runtime.generated.ts. Closes #3667.
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📝 WalkthroughWalkthroughThe renderer now distinguishes module evaluation failures from missing-module failures. It skips the ChangesPages Router module fallback handling
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The change prevents unnecessary fallback requests for most module evaluation failures, but two edge cases can still cause an extra /index.js request and obscure the original failure: a punctuated Safari error message and non-Error thrown values. The PR is otherwise mergeable with explicit owner follow-up on these bounded cases. Possibly related issues
Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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…retry # Conflicts: # src/html/hydration-script-builder/hydration-runtime.generated.ts
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In `@src/html/hydration-script-builder/runtime/renderer.ts`:
- Line 42: Update the message check in the relevant error-classification
function to match only the bare Safari message “Load failed” and no trailing
period. Add a regression test covering “Load failed.” that verifies no /index.js
fallback request is made.
- Around line 72-75: Update isReachedModuleEvaluationError so non-Error
rejection values are classified as reached-module failures, while preserving the
existing exclusions for SyntaxError and known module-not-found errors. Add a
focused test covering Promise.reject("evaluation failure") and verify the loader
does not request /index.js after the route module has loaded.
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src/html/hydration-script-builder/hydration-runtime.generated.tsis excluded by!**/*.generated.*
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src/html/hydration-script-builder/runtime/renderer-modules.test.tssrc/html/hydration-script-builder/runtime/renderer.ts
Two findings, both right. The match allowed an optional trailing period. Safari's message has none, so the latitude only widened the match past the engine wording, and an application error is free to end in a full stop. Now exact. A rejection that is not an Error can only come from module code that ran: the loader's own failures reject with TypeError or SyntaxError. Returning false for a thrown string or null sent the loader after <route>/index.js, which can only 404 and bury the throw. Both now refuse the retry, with a test each.
2 participants
Bug
For an extension-style page route (
pages/vector-a.tsx, noindex.tsxfolder), the client requested/_vf_modules/pages/vector-a/index.js→ 404, and the server logged a misleadingModule not found modulePath=pages/vector-a/index.js(#3667).Root cause
The Pages Router client loads
<route>.jsand, on failure, retries<route>/index.js— a route may be authored as either<route>.tsxor<route>/index.tsx(loadPageModuleWithIndexFallback,runtime/renderer.ts). That retry was unconditional. So when<route>.jsloaded but threw at evaluation — e.g. the server→client adapter leak in #3661 dereferencing a browser-absentfs.constants.O_NOFOLLOW— the client still probed the sibling<route>/index.js, which 404s for an extension-style route and stacked a confusing "module not found" on top of the real error.The masking itself is already guarded by
preferReachedModuleError(the #3003 fix), so the real error survives — but the spurious/index.jsprobe still fires and pollutes the console/dev log. Confirmed againstmain: the O_NOFOLLOW eval error is thrown correctly, yet both<route>.jsand<route>/index.jsare requested.Fix
A module that ran far enough to throw its own runtime error is the served file, so the sibling
<route>/index.jsprobe can only 404. Skip the retry in exactly that case —isReachedModuleEvaluationError: anErrorthat is neither aSyntaxError(never linked — a missing export, or a proxy's HTML shell) nor a fetch failure (isModuleNotFoundError).This deliberately keeps the retry for the two cases it exists to recover, both pinned by existing tests:
<route>.jsgenuinely missing → retry finds<route>/index.js;SyntaxError) → retry (the case that made gating-on-wording blank-page routes).Tests (red→green)
Added
does not probe /index.js when <route>.js reached a module and threw at evaluationtorenderer-modules.test.ts: asserts only<route>.jsis requested and the realTypeErrorsurfaces. Fails onmain(2 requests), passes with the fix. All existing retry/error-selection tests stay green (25 steps). Regeneratedhydration-runtime.generated.ts.Closes #3667. The underlying eval crash it surfaced is the leak tracked in #3661.
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