fix: resolve bun.exe when npm shim is in PATH

[zerone0x]

Summary

• avoid returning "bun" on Windows when "where bun" only finds bun.cmd
• resolve bun.exe from the shim location or npm global install dir
• keep bun resolver in sync for the NPX CLI

Testing

• not run (path resolution change only)

[coderabbitai]

Summary by CodeRabbit

• Bug Fixes
  • Enhanced Bun detection on Windows: The tool now more reliably locates Bun installations across additional locations, including user AppData directories, and intelligently handles different executable file formats for improved compatibility with various Windows setup configurations.

Walkthrough

Both files update Windows-specific Bun binary resolution logic. Instead of returning 'bun' when where bun succeeds, they now parse the output to intelligently select the correct executable: preferring .exe, falling back to non-.cmd/.bat files, and checking sibling .exe or node_modules/bun/bin/bun.exe. Windows search paths expanded to include AppData roaming directory. Non-Windows behavior unchanged.

Changes

Cohort / File(s)	Summary
Bun binary resolution on Windows plugin/scripts/bun-runner.js, src/npx-cli/utils/bun-resolver.ts	Updated findBun()/resolveBunBinaryPath() to parse where bun command output into candidate paths instead of returning 'bun' directly. Implements fallback logic: prefer existing .exe, then non-.cmd/.bat executable, then attempt to resolve .cmd/.bat results to sibling .exe or node_modules/bun/bin/bun.exe. Added %APPDATA%/npm/node_modules/bun/bin/bun.exe to Windows-specific search candidate list.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• [Windows] spawn bun ENOENT when bun installed via npm #1595 — Addresses the same Windows bug fix: parsing where bun output to prefer .exe candidates and adding APPDATA npm path to prevent ENOENT errors from .cmd shims.
• Windows: bun-runner.js spawn ENOENT when bun is installed via npm shim #1452 — The implementation directly fulfills the proposed Windows fix by parsing command output, prioritizing .exe, and introducing sibling/node_modules fallback locations plus APPDATA search path.

Poem

🐰 Windows bugs bunny used to fear,
.cmd shims caused bitter tears dear,
But now with parsing and .exe grace,
Bun finds its rightful place!
APPDATA searched, fallbacks abound,
Resolution hopping—solutions found! 🥕

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main fix: resolving bun.exe when npm shim is in PATH on Windows.
Description check	✅ Passed	The description relates to the changeset, detailing the Windows-specific bun.exe resolution improvements and sync efforts across files.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (3)

plugin/scripts/bun-runner.js (2)

100-105: Minor inconsistency with bun-resolver.ts candidate paths.

The TypeScript version (bun-resolver.ts line 24) includes an additional candidate using USERPROFILE:

join(process.env.USERPROFILE || homedir(), '.bun', 'bin', 'bun.exe'),

This file omits that path. While homedir() and USERPROFILE typically resolve identically on Windows, adding it here would maintain exact parity.

📝 Suggested addition for consistency

   const bunPaths = IS_WINDOWS
     ? [
         join(homedir(), '.bun', 'bin', 'bun.exe'),
+        join(process.env.USERPROFILE || homedir(), '.bun', 'bin', 'bun.exe'),
         join(windowsAppData, 'npm', 'node_modules', 'bun', 'bin', 'bun.exe')
       ]

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@plugin/scripts/bun-runner.js` around lines 100 - 105, The bunPaths array for
IS_WINDOWS is missing the USERPROFILE-based candidate present in
bun-resolver.ts; update the bunPaths declaration (used with IS_WINDOWS,
windowsAppData, homedir) to include a candidate that uses
process.env.USERPROFILE || homedir() joining '.bun', 'bin', 'bun.exe' so the JS
runner has identical Windows search paths as bun-resolver.ts.

---

58-94: Logic correctly mirrors bun-resolver.ts.

The Windows resolution logic is identical to the TypeScript version, which aligns with the PR objective to keep them in sync.

Consider future consolidation: Both files now have identical complex resolution logic. If feasible, bun-runner.js could potentially import from a shared module to avoid maintaining duplicate code. However, given that bun-runner.js is a standalone Node.js script (no build step) and needs to work independently, the current duplication is acceptable.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@plugin/scripts/bun-runner.js` around lines 58 - 94, The Windows bun
resolution logic duplicates the implementation in bun-resolver.ts; add a short
comment immediately above the Windows-resolution block in
plugin/scripts/bun-runner.js (the section that checks IS_WINDOWS, parses
pathCheck.stdout, and searches for exeCandidate/plainCandidate/cmdCandidate)
stating that this logic intentionally mirrors bun-resolver.ts and explaining why
it must remain standalone (no build step) to prevent future maintainers from
removing or attempting to centralize it; keep the comment concise and reference
bun-resolver.ts by name.

src/npx-cli/utils/bun-resolver.ts (1)

43-44: Docstring is now inaccurate for Windows behavior.

The comment states it returns 'bun' if found in PATH, but the new Windows logic returns the full path instead. Consider updating to clarify this platform difference.

📝 Suggested docstring update

- * Returns the absolute path to the binary, `'bun'` if it is in PATH,
- * or `null` if Bun cannot be found.
+ * Returns the absolute path to the binary, `'bun'` if it is in PATH (non-Windows),
+ * the resolved `.exe` path on Windows, or `null` if Bun cannot be found.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/npx-cli/utils/bun-resolver.ts` around lines 43 - 44, Update the docstring
for the exported resolver (resolveBunPath) in src/npx-cli/utils/bun-resolver.ts
to reflect the Windows-specific behavior: describe that the function returns a
path string when Bun is found (on Windows this will be the absolute path to the
bun executable; on POSIX it will return 'bun' when using PATH or an absolute
path when resolved), and returns null if Bun cannot be found; replace the
current line "Returns the absolute path to the binary, 'bun' if it is in PATH,
or null if Bun cannot be found." with this clarified platform-aware description.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@plugin/scripts/bun-runner.js`:
- Around line 100-105: The bunPaths array for IS_WINDOWS is missing the
USERPROFILE-based candidate present in bun-resolver.ts; update the bunPaths
declaration (used with IS_WINDOWS, windowsAppData, homedir) to include a
candidate that uses process.env.USERPROFILE || homedir() joining '.bun', 'bin',
'bun.exe' so the JS runner has identical Windows search paths as
bun-resolver.ts.
- Around line 58-94: The Windows bun resolution logic duplicates the
implementation in bun-resolver.ts; add a short comment immediately above the
Windows-resolution block in plugin/scripts/bun-runner.js (the section that
checks IS_WINDOWS, parses pathCheck.stdout, and searches for
exeCandidate/plainCandidate/cmdCandidate) stating that this logic intentionally
mirrors bun-resolver.ts and explaining why it must remain standalone (no build
step) to prevent future maintainers from removing or attempting to centralize
it; keep the comment concise and reference bun-resolver.ts by name.

In `@src/npx-cli/utils/bun-resolver.ts`:
- Around line 43-44: Update the docstring for the exported resolver
(resolveBunPath) in src/npx-cli/utils/bun-resolver.ts to reflect the
Windows-specific behavior: describe that the function returns a path string when
Bun is found (on Windows this will be the absolute path to the bun executable;
on POSIX it will return 'bun' when using PATH or an absolute path when
resolved), and returns null if Bun cannot be found; replace the current line
"Returns the absolute path to the binary, 'bun' if it is in PATH, or null if Bun
cannot be found." with this clarified platform-aware description.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: b6428f19-44a2-4303-b6f6-43fe918a0014

📥 Commits

Reviewing files that changed from the base of the PR and between 76a2729 and 5fca0c9.

📒 Files selected for processing (2)

• plugin/scripts/bun-runner.js
• src/npx-cli/utils/bun-resolver.ts

[thedotmack]

Closed during the April 2026 backlog cleanup. This was verified already-fixed in v12.1.1 HEAD. Please update to the latest build. If you still see the issue on current version, open a fresh ticket with repro.