fix(workshop-utils): Windows path compatibility in diff pipeline

[AlemTuzlak]

What

Three small Windows path fixes in packages/workshop-utils/src/diff.server.ts.

Why

On Windows, path.join and path.relative return backslash-separated paths. The diff pipeline assumed POSIX-style forward slashes in three places, so the Diff tab in any workshop crashes for Windows users with:

TypeError: Cannot read properties of undefined (reading 'trim')
    at processPatch (.../@pierre/diffs/.../parsePatchFiles.ts:90)
    at parsePatchFiles (.../parsePatchFiles.ts:297)
    at children (.../@epic-web/workshop-app/app/components/diff.tsx:368)

The root cause chain:

1. `git diff --no-index` quotes any path that contains a backslash. That quoted output trips `@pierre/diffs`'s patch parser, which only reads the unquoted capture groups of its filename regex and `.trim()`s an `undefined`.
2. `copyUnignoredFiles` passes the result of `path.relative(...)` directly to the `ignore` package. The `ignore` package only understands POSIX paths, so any gitignore pattern with a slash in it (`/build/`, `/.react-router`, etc.) silently fails to match.
3. `.slice(1)` was used to strip a leading slash from absolute paths. On POSIX (`/tmp/foo` → `tmp/foo`) this works; on Windows (`C:/Users/foo` → `:/Users/foo`) it strips the drive letter, breaking the subsequent `replaceAll` substitutions.

Changes

1. `copyUnignoredFiles` — normalise `path.relative(...)` to POSIX before passing to `ignore`. Without this, gitignore patterns containing slashes silently fail to match on Windows.

2. `prepareForDiff` — normalise `app1CopyPath` / `app2CopyPath` to POSIX after `path.join`. Git now sees forward-slash paths and emits unquoted output, which the patch parser can handle.

3. `getDiffPatchImpl` and `getDiffOutputWithRelativePaths` — replace `.slice(1)` with `.replace(/^//, '')` so Windows paths (no leading slash) keep their drive letter. The `a${absPath}` patterns become `a/${relativePath}` so they line up with the slash that git always inserts, on both platforms.

A small `toPosixPath(p)` helper is defined locally in the file; happy to extract it to a shared module if you'd prefer.

Testing

• POSIX behaviour unchanged. The new `a/${relative}` pattern produces the same search string as the old `a${absPath}` form (since absPath always starts with `/` on POSIX, you'd get `a/` in both cases). The new `replace(/^//, '')` produces the same result as the old `.slice(1)` whenever the input has exactly one leading slash.
• Windows: verified locally against a workshop with exercise paths under `F:\projects...`. Before this PR the Diff tab crashes immediately; after, it renders.
• Workshop-utils typecheck passes.
• Existing test failures (`data-storage.test.ts` + a few others) are pre-existing Windows POSIX-path assumptions in unrelated modules, not introduced by this PR. Happy to file follow-ups for those.

Notes

The downstream `@pierre/diffs` parser also has a latent bug — its `diff --git` line destructure only reads the unquoted capture groups, even though its own regex has a quoted-path branch. Fixing this PR is sufficient to make the diff tab work because git no longer emits quoted paths, but the parser fix is worth pursuing upstream as well.

[nx-cloud]

View your CI Pipeline Execution ↗ for commit f47550d

Command	Status	Duration	Result
nx run-many --target typecheck	✅ Succeeded	19s	View ↗
nx run-many --target build	✅ Succeeded	38s	View ↗
nx lint	✅ Succeeded	31s	View ↗

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☁️ Nx Cloud last updated this comment at 2026-05-17 17:03:07 UTC

[kentcdodds]

Bugbot review