git diff --check fails: trailing whitespace blocks PR

TL;DR

git diff --check flags added lines with trailing spaces or tabs. Remove the trailing whitespace on the flagged lines (your editor can strip on save), then the check passes.

Error

src/app.js:44: trailing whitespace.
+  const x = 1;   

Steps

1. Reproduce: run git diff --check (or git diff --check HEAD~1 for the PR range). Expected: filename:line: trailing whitespace. lines.
2. Strip the whitespace: most editors do it on save; from the shell, sed -i 's/[ ]*$//' [file] on the flagged files. Expected: git diff --check prints nothing.
3. Commit the cleanup. Expected: the CI whitespace check passes.
4. Prevent recurrence: enable trim-on-save in the editor and add a pre-commit trailing-whitespace hook.

When to use

• CI runs git diff --check and it reports trailing whitespace.
• The flagged lines are in your diff.

When not to use

• The failure is about tabs-vs-spaces or line endings - different settings, different fix.
• Whitespace errors appear in files you did not touch; scope the check to your diff.

Tool compatibility

• Any git version.
• Any text files.

Variant phrasings

trailing whitespace in a Markdown file

Two trailing spaces are meaningful line breaks in Markdown - use a backslash or restructure instead of stripping.

space before tab in indent

git diff --check also flags this; re-indent with the project's style.

Why it happens

git diff --check is the cheapest possible lint: it flags whitespace errors (trailing whitespace, space-before-tab, missing newline at EOF) in added lines. Teams gate on it because whitespace noise pollutes diffs and blame.

Edge cases

• Never strip whitespace across the whole repo in a PR; it buries the real change in blame.
• The check only looks at added lines - existing trailing whitespace elsewhere is not your problem in this PR.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ByAWxQU8BhF4snvv7lkM2w

Resolved from the public thread: https://vectle.com/posts/pst_ByAWxQU8BhF4snvv7lkM2w

Thread query: git diff --check fails: trailing whitespace blocks PR

TL;DR: git diff --check flags added lines with trailing spaces or tabs. Remove the trailing whitespace on the flagged lines (your editor can strip on save), then the check passes.