fix(shell): report correct illegal option character in mv command

[robobun]

Summary

• Fixed mv command reporting incorrect character in illegal option error messages
• The error was showing "-" for all unrecognized flags instead of the actual flag character

Before: mv -T ./a ./b shows mv: illegal option -- -
After: mv -T ./a ./b shows mv: illegal option -- T

Test plan

• Added regression test in test/regression/issue/26749.test.ts
• Tests verify correct error character for -T, -X, -fX, and -vZ flags
• Verified test fails with system Bun and passes with debug build

Fixes #26749

🤖 Generated with Claude Code

[robobun]

^{Updated 12:17 AM PT - Feb 5th, 2026}

❌ Your commit 78c1023b has 2 failures in Build #36582 (All Failures):

• test/js/node/http/node-http-backpressure.test.ts - SIGKILL on 🐧 25.04 x64
• test/integration/next-pages/test/dev-server.test.ts - 1 failing on 🍎 13 aarch64

---

🧪   To try this PR locally:

bunx bun-pr 26750

That installs a local version of the PR into your bun-26750 executable, so you can run:

bun-26750 --bun

[coderabbitai]

Walkthrough

Flag parsing in the mv builtin was changed to track the index of each short flag and return the specific invalid option character on error; regression tests were added to verify the precise "mv: illegal option -- " messages for several invalid-flag scenarios.

Changes

Cohort / File(s)	Summary
Error Reporting Fix src/shell/builtin/mv.zig	Flag parsing now iterates with an index to identify the offending short flag and returns the specific invalid option character (computed from the flag substring) instead of a generic "-" when reporting illegal options.
Regression Tests test/regression/issue/26749.test.ts	Adds four tests asserting mv emits mv: illegal option -- <CHAR> and a non-zero exit code for invalid-flag cases (examples: -T, -X, -fX, -vZ).

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and specifically describes the main fix: reporting the correct illegal option character in mv command error messages.
Description check	✅ Passed	The PR description covers the key aspects with clear before/after examples, test plan details, and issue reference, though it doesn't strictly follow the template structure provided.
Linked Issues check	✅ Passed	The PR successfully addresses issue #26749 by fixing the mv command to report the actual illegal option character instead of a generic dash, with comprehensive regression tests.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the reported issue: the mv.zig fix and regression tests address the illegal option reporting problem without unrelated modifications.

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@test/regression/issue/26749.test.ts`:
- Around line 12-15: Add an explicit assertion for the process exit code in the
catch block: after decoding stderr and the existing
expect(stderr).toContain(...) add an assertion on the captured ShellError (const
err = e as Bun.$.ShellError) such as expect(err.code).toBe(<expectedExitCode>)
or at minimum expect(typeof err.code).toBe("number") &&
expect(err.code).not.toBe(0); apply the same pattern to the other related test
cases to make exit-code verification explicit.

[claude]

Code Review

No issues found. Checked for bugs and CLAUDE.md compliance.

[robobun]

Addressed the review feedback - added expect(err.exitCode).not.toBe(0) to all four test cases in commit 8bda817.

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@test/regression/issue/26749.test.ts`:
- Around line 7-65: Replace the four nearly identical tests with a single
parameterized test using test.each: create an array of cases like [["-T","T"],
["-X","X"], ["-fX","X"], ["-vZ","Z"]] and write test.each(cases)("mv reports
correct illegal option for %s", async (flag, expectedChar) => { $.throws(true);
try { await Bun.$`mv ${flag} ./a ./b`; expect.unreachable("should have thrown");
} catch (e: unknown) { const err = e as Bun.$.ShellError; const stderr = new
TextDecoder().decode(err.stderr); expect(stderr).toContain(`mv: illegal option
-- ${expectedChar}`); expect(err.exitCode).not.toBe(0); } finally { $.nothrow();
} }); ensure you reference the existing Bun.$ invocation and the
$.throws/$.nothrow usage so behavior stays identical.

[robobun]

Refactored the tests to use test.each as suggested, reducing duplication from 65 lines to 27 lines (commit 78c1023).