resolveWorktree only matches a parent named `.git`, so worktrees of a bare repository fail

[delanym]

Describe the bug (required)

Essentially there is no support for worktrees created off a bare git repository (a practice I imagine will become more common with agentic coding).

GitDirLocator.resolveWorktree identifies a linked worktree by matching path names — the
worktree administrative directory must sit under a directory literally named .git. Git itself
places no such constraint: git worktree add from a bare repository produces
<bare>/worktrees/<name>, where <bare> is conventionally something.git or, in the widely used
bare-clone layout, .bare.

For those repositories resolveWorktree returns the gitdir unchanged, NativeGitProvider then runs
git in its parent (<bare>/worktrees), which is not a work tree, and the build fails.

Steps to Reproduce (required)

  #!/usr/bin/env bash
  set -e
  BASE=$(mktemp -d); cd "$BASE"

  cat > pom.xml <<'EOF'
  <project xmlns="http://maven.apache.org/POM/4.0.0">
    <modelVersion>4.0.0</modelVersion>
    <groupId>example</groupId><artifactId>wt-repro</artifactId><version>1</version>
    <build><plugins><plugin>
      <groupId>io.github.git-commit-id</groupId>
      <artifactId>git-commit-id-maven-plugin</artifactId>
      <version>10.0.0</version>
      <configuration>
        <useNativeGit>true</useNativeGit>
        <generateGitPropertiesFile>true</generateGitPropertiesFile>
        <generateGitPropertiesFilename>${project.build.directory}/git.properties</generateGitPropertiesFilename>
      </configuration>
      <executions><execution><id>x</id><goals><goal>revision</goal></goals><phase>initialize</phase></execution></executions>
    </plugin></plugins></build>
  </project>
  EOF

  # ---- layout A: ordinary clone, plus a conventional linked worktree under <main>/.git/worktrees/
  mkdir -p A/main && cd A/main
  git init -q -b main . && git config user.email t@t && git config user.name t
  cp ../../pom.xml . && git add pom.xml && git commit -qm "commit on main"
  git worktree add -q -b feature ../wt
  cd ../wt && git config user.email t@t && git config user.name t
  cp ../../pom.xml . && echo x > f.txt && git add . && git commit -qm "commit on feature worktree"
  cd "$BASE"

  # ---- layout B: bare clone, plus a linked worktree under <bare>/worktrees/
  git clone -q --bare A/main B/.bare
  git -C B/.bare worktree add -q "$BASE/B/master" main
  cp pom.xml B/master/

  for d in A/main A/wt B/master; do
    echo "=========== $d"
    echo "  real HEAD : $(git -C $d rev-parse --abbrev-ref HEAD) @ $(git -C $d rev-parse --short=7 HEAD)"
    ( cd "$d" && mvn -q -B initialize 2>&1 | grep -E "ERROR.*(Failed|fatal)" | head -2
      if [ -f target/git.properties ]; then
        echo "  reported  : $(grep -h -E 'git.branch=|git.commit.id.abbrev=' target/git.properties | tr '\n' ' ')"
      else
        echo "  reported  : (no git.properties written)"
      fi )
  done
  echo; echo "workdir: $BASE"

Actual output

=========== A/main
  real HEAD : main @ 88ae4cd
  reported  : git.branch=main git.commit.id.abbrev=88ae4cd
=========== A/wt
  real HEAD : feature @ 920ca94
  reported  : git.branch=main git.commit.id.abbrev=88ae4cd
=========== B/master
  real HEAD : main @ 88ae4cd
[ERROR] Failed to execute goal io.github.git-commit-id:git-commit-id-maven-plugin:10.0.0:revision (x) on project wt-repro: Git command exited with invalid status [128]: directory: `/tmp/tmp.hxld3BHkek/B/.bare/worktrees`, command: `git describe --always --dirty=-dirty --match=* --abbrev=7`, stdout: ``, stderr: `fatal: this operation must be run in a work tree
  reported  : (no git.properties written)

Expected: every row reports the branch and commit of the checkout the build ran in.

Two separate defects are visible:

1. B/master fails outright — the bare-repository worktree layout is not recognised at all.
2. A/wt silently reports the wrong commit — the worktree is recognised, but resolution lands
   on the main checkout, so the build is stamped with main @ 88ae4cd instead of
   feature @ 920ca94. This is
   worktree processing not complete git-commit-id-maven-plugin#882, and it shares the root cause below.

Is there a (public) project where this issue can be reproduced? (optional)

No response

Your Environment (optional)

No response

Context (optional)

Root cause

static File resolveWorktree(File fileLocation) {
  Path parent = fileLocation.toPath().getParent();
  if (parent == null) {
    return fileLocation;
  } 
  if (parent.endsWith(Path.of(".git", "worktrees"))) {
    return parent.getParent().toFile();
  } 
  return fileLocation;
} 

• parent.endsWith(Path.of(".git", "worktrees")) fails for <bare>/worktrees/<name> whenever the
  repository directory is not named exactly .git — .bare/worktrees/master, froggy.git/worktrees/x
  — which is defect 1. GitDirLocatorTest.testWorktreeResolution currently asserts
  "a.git/worktrees/b" as a noop case, so this is pinned by a test; I believe that assertion is
  itself the bug, since that path is exactly what git worktree add creates from a bare clone.
• parent.getParent() is the main checkout's git directory, not the linked worktree's, which is
  defect 2.

Both come from inferring the layout from path names. Git records it explicitly instead:
<worktree-admin-dir>/gitdir holds the absolute path of that worktree's own .git file — its parent
is the working tree — and <worktree-admin-dir>/commondir points at the shared repository. Reading
those (or asking git rev-parse --path-format=absolute --git-common-dir --show-toplevel) fixes both
defects: native git would then run inside the worktree being built, which both succeeds for a bare
host repository and reports that worktree's own branch/commit.

Note on JGit

With <useNativeGit>false</useNativeGit> the same bare-repo layout fails differently —
Could not get HEAD Ref, are you sure you have some commits in the dotGitDirectory (currently set to <bare>/worktrees/<name>)? — consistent with the long-standing
git-commit-id/git-commit-id-maven-plugin#215. A fix to the native path won't cover JGit.

Workaround

Setting the environment explicitly makes native git resolve the right worktree and produces correct
properties:

GIT_DIR=$(git rev-parse --absolute-git-dir) GIT_WORK_TREE=$(git rev-parse --show-toplevel) mvn verify

Related

• Plugin fails in git worktree even when native git is used git-commit-id-maven-plugin#639 — fixed the <main>/.git/worktrees/ case (PR #642, v7.0.0)
• worktree processing not complete git-commit-id-maven-plugin#882 — wrong worktree's data reported (defect 2 above), open
• Support of git worktree option (for JGIT) git-commit-id-maven-plugin#215 — JGit worktree support, open