check-case-conflict reports false positives for case-only renames in ref-scoped checks

[Guria]

Description

hk check reports a false case conflict for case-only renames during ref-scoped checks, even though the resulting Git tree contains only one path.

For example:

src/pages/login/ui/authSwitcherTrigger.tsx
→ src/pages/login/ui/AuthSwitcherTrigger.tsx

The ref diff contains the old path as deleted and the new path as added, but the case-conflict step receives both path names and reports them as simultaneous files.

Environment

• hk 1.54.1
• macOS with a case-insensitive filesystem

Reproduction

With a branch containing a case-only rename, run:

hk check --check --from-ref origin/rewrite --to-ref HEAD --step check-case-conflict

The check reports:

Case conflict:
  src/pages/login/ui/authSwitcherTrigger.tsx
  src/pages/login/ui/AuthSwitcherTrigger.tsx

An equivalent full-tree check passes:

hk check --all

Expected behavior

Case-only renames should be treated as a single rename, or deleted paths should be excluded before running the case-conflict check. Alternatively, the check could inspect the resulting tracked tree rather than the raw ref-diff path list.

[Guria]

Follow-up observation

After changing the case-conflict step to inspect the current tracked tree, the case check passes during the ref-scoped pre-push run. However, the same stale deleted paths are still passed to the lint step.

First, vp lint reports:

Unmatched files found: .../src/pages/login/ui/authSwitcherTrigger.tsx
Unmatched files found: .../src/widgets/app-shell/ui/shellSwitcherTrigger.tsx

On a subsequent pre-push attempt, the ref-scoped lint invocation caused tsgolint to panic:

panic: Expected file '.../src/widgets/app-shell/ui/shellSwitcherTrigger.tsx, .../src/pages/login/ui/authSwitcherTrigger.tsx' to be in program '.../tsconfig.app.json'
Error running tsgolint: "exit status: exit status: 2"

The full-tree checks pass independently:

npx tsc -b                         # passes
mr lint                            # 0 warnings, 0 errors
hk check --all                     # passes

This suggests the issue is broader than check-case-conflict: ref-scoped file selection should preserve Git status and exclude deleted paths before passing files to formatter/linter/type-aware tooling. The panic also suggests that the selected paths may be combined into a single comma-separated argument in some invocation.

[jdx]

Confirmed: this is a shared libgit2 ref-scoped file-selection bug, not an issue specific to check-case-conflict.

The libgit2 backend was using Path::exists() to filter deleted deltas. On a case-insensitive filesystem, the deleted spelling in a case-only rename still resolves to the new path, so both spellings were passed to every matching step.

I opened #1177 to skip git2::Delta::Deleted explicitly while retaining the existing existence check for live paths. It also adds a portable regression test that exercises both HK_LIBGIT2=1 and 0 and verifies that only the target spelling is passed.

Until a release containing the fix is available, HK_LIBGIT2=false remains the workaround for the complete pre-push invocation.

I did not find hk joining file arguments with commas: shell templates quote and space-separate {{files}}, while structured argv commands expand the file list into distinct arguments. The comma-shaped tsgolint panic therefore remains a separate observation unless trace output shows a single comma-containing argv entry after the stale deleted paths are removed.

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