fix(start-plugin-core): use duck-type check for RunnableDevEnvironment to avoid dual-package hazard by sleitor · Pull Request #6994 · TanStack/router

sleitor · 2026-03-20T10:33:48Z

Summary

When is aliased to another package via pnpm overrides (e.g. vite: npm:@voidzero-dev/vite-plus-core@latest), two different RunnableDevEnvironment class references exist in memory. The isRunnableDevEnvironment() helper uses instanceof which returns false, causing SSR middleware to never be registered and all routes returning 404.

Changes

Replace isRunnableDevEnvironment(serverEnv) (instanceof-based) with a duck-type check 'runner' in serverEnv in packages/start-plugin-core/src/dev-server-plugin/plugin.ts.

The runner property (a public getter) is unique to RunnableDevEnvironment — FetchableDevEnvironment and DevEnvironment don't have it. The existing 'dispatchFetch' in serverEnv guard is preserved to correctly handle Nitro's FetchableDevEnvironment.

RunnableDevEnvironment is still imported as a type only (for the TypeScript cast on serverEnv.runner.import()), so no runtime instanceof check remains.

Testing

ESLint passes
Type errors in test:types are pre-existing (missing sibling package builds in standalone test run)

Summary by CodeRabbit

Bug Fixes

Fixed a compatibility issue when multiple versions or alternative distributions of the build tool were loaded in the same project, ensuring the plugin works reliably in complex dependency environments.

…t to avoid dual-package hazard Replace isRunnableDevEnvironment (instanceof-based) with duck-type check 'runner' in serverEnv to avoid false negatives when vite is aliased via pnpm overrides (e.g. vite-plus), which creates a dual-package hazard where two different RunnableDevEnvironment class references exist in memory. The 'runner' property (public getter) is unique to RunnableDevEnvironment and not present on FetchableDevEnvironment or DevEnvironment. Fixes TanStack#6982

coderabbitai · 2026-03-20T10:34:09Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7fe9e726-2799-4481-832c-845f4b1a582f

📥 Commits

Reviewing files that changed from the base of the PR and between 91cc628 and 96eb75d.

📒 Files selected for processing (2)

.changeset/fix-6982-duck-type-runnable-dev-env.md
packages/start-plugin-core/src/dev-server-plugin/plugin.ts

📝 Walkthrough

Walkthrough

Added a changeset entry documenting a bug fix in @tanstack/start-plugin-core. Replaced instanceof checks with duck-typing by testing for the 'runner' property in dev server middleware guards to resolve vite alias/override issues.

Changes

Cohort / File(s)	Summary
Changeset Documentation `.changeset/fix-6982-duck-type-runnable-dev-env.md`	Added patch release note documenting the duck-typing fix for dual-package hazard with vite aliases.
Dev Server Plugin `packages/start-plugin-core/src/dev-server-plugin/plugin.ts`	Replaced `isRunnableDevEnvironment(serverEnv)` instanceof check with duck-typing (`'runner' in serverEnv`). Added `RunnableDevEnvironment` type import and applied explicit type assertion on runner property access to maintain type safety.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A rabbit hops through vite's tangled maze,
Where aliases once clouded SSR's gaze—
We typed with ducks instead of instanceof chains,
Now middleware flows through dev's pathways,
And routes deliver where logic reigns! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly summarizes the main change: replacing instanceof checks with duck-typing for RunnableDevEnvironment to avoid dual-package hazard issues.
Linked Issues check	✅ Passed	The PR fully implements the fix suggested in `#6982`: replacing instanceof checks with duck-typing for the 'runner' property, exactly as documented in the linked issue.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the dual-package hazard: the Changeset entry documents the fix and the plugin.ts modifications implement the suggested duck-typing approach without unrelated alterations.

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nx-cloud · 2026-03-20T10:35:57Z

View your CI Pipeline Execution ↗ for commit 96eb75d

Command	Status	Duration	Result
`nx affected --targets=test:eslint,test:unit,tes...`	✅ Succeeded	9m 42s	View ↗
`nx run-many --target=build --exclude=examples/*...`	✅ Succeeded	27s	View ↗

☁️ Nx Cloud last updated this comment at 2026-03-20 10:46:24 UTC

pkg-pr-new · 2026-03-20T10:37:50Z

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commit: 96eb75d

github-actions · 2026-03-20T10:38:50Z

Bundle Size Benchmarks

Commit: 91cc62899b75
Measured at: 2026-03-20T10:38:13.089Z
Baseline source: history:91cc62899b75
Dashboard: bundle-size history

Scenario	Current (gzip)	Delta vs baseline	Raw	Brotli	Trend
`react-router.minimal`	88.56 KiB	0 B (0.00%)	279.34 KiB	76.84 KiB	▁▁▁▁▁▁▁▁███
`react-router.full`	91.73 KiB	0 B (0.00%)	290.07 KiB	79.48 KiB	▁▁▁▁▁▁▁▁███
`solid-router.minimal`	36.13 KiB	0 B (0.00%)	108.98 KiB	32.41 KiB	████████▁▁▁
`solid-router.full`	40.47 KiB	0 B (0.00%)	122.08 KiB	36.26 KiB	████████▁▁▁
`vue-router.minimal`	54.11 KiB	0 B (0.00%)	155.27 KiB	48.48 KiB	▁▁▁▁▁▁▁▁███
`vue-router.full`	58.89 KiB	0 B (0.00%)	170.42 KiB	52.63 KiB	▁▁▁▁▁▁▁▁███
`react-start.minimal`	103.00 KiB	0 B (0.00%)	327.41 KiB	89.02 KiB	▁▁▁▁▁▁▁▁███
`react-start.full`	106.37 KiB	0 B (0.00%)	337.72 KiB	91.83 KiB	▁▁▁▁▁▁▁▁███
`solid-start.minimal`	50.32 KiB	0 B (0.00%)	155.47 KiB	44.32 KiB	████████▁▁▁
`solid-start.full`	55.72 KiB	0 B (0.00%)	171.27 KiB	48.90 KiB	████████▁▁▁

Trend sparkline is historical gzip bytes ending with this PR measurement; lower is better.

codspeed-hq · 2026-03-20T10:53:51Z

Merging this PR will not alter performance

✅ 5 untouched benchmarks
⏩ 1 skipped benchmark¹

_{Comparing sleitor:fix-6982 (96eb75d) with main (91cc628)}

1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

github-actions bot added the package: start-plugin-core label Mar 20, 2026

ci: apply automated fixes

96eb75d

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fix(start-plugin-core): use duck-type check for RunnableDevEnvironment to avoid dual-package hazard#6994

fix(start-plugin-core): use duck-type check for RunnableDevEnvironment to avoid dual-package hazard#6994
sleitor wants to merge 2 commits intoTanStack:mainfrom
sleitor:fix-6982

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