pytest_plugin(fix[fixtures]): Import cleanly under pytest 9.1

why: pytest 9.1 rejects marks applied to fixture functions and raises
the error at plugin import, before collection. Because libvcs ships
this plugin as an installed pytest11 entry point, the error aborted the
entire test session for any downstream project (e.g. vcspull) running
pytest 9.1+. The skipif marks stacked on the fixtures were no-ops in
every prior pytest version; the real gating must run inside each fixture
so a missing binary skips instead of erroring.

what:
- Add private _skip_if_git_missing / _skip_if_svn_missing /
  _skip_if_hg_missing helpers that call pytest.skip() when the binary is
  absent; the svn helper requires both svn and svnadmin
- Remove the @skip_if_*_missing decorators from the affected fixtures and
  call the matching helper as the first body statement
- Fold empty_svn_repo's existing inline svn/svnadmin guard into the
  shared helper
- Keep the public skip_if_*_missing marks: they remain valid for
  decorating test functions and importable by downstream suites

Author: tony

src/libvcs/pytest_plugin.py

@@ -43,6 +43,24 @@ def __init__(self, attempts: int, *args: object) -> None:
 )
 
 
+def _skip_if_git_missing() -> None:
+    """Skip the calling fixture when the ``git`` binary is unavailable."""
+    if not shutil.which("git"):
+        pytest.skip(reason="git is not available")
+
+
+def _skip_if_svn_missing() -> None:
+    """Skip the calling fixture when ``svn`` or ``svnadmin`` is unavailable."""
+    if not shutil.which("svn") or not shutil.which("svnadmin"):
+        pytest.skip(reason="svn is not available")
+
+
+def _skip_if_hg_missing() -> None:
+    """Skip the calling fixture when the ``hg`` binary is unavailable."""
+    if not shutil.which("hg"):
+        pytest.skip(reason="hg is not available")
+
+
 DEFAULT_VCS_NAME = "Test user"
 DEFAULT_VCS_EMAIL = "test@example.com"
 
@@ -145,13 +163,13 @@ def set_home(
 
 
 @pytest.fixture(scope="session")
-@skip_if_git_missing
 def vcs_gitconfig(
     user_path: pathlib.Path,
     vcs_email: str,
     vcs_name: str,
 ) -> pathlib.Path:
     """Return git configuration, pytest fixture."""
+    _skip_if_git_missing()
     gitconfig = user_path / ".gitconfig"
 
     gitconfig.write_text(
@@ -173,24 +191,24 @@ def vcs_gitconfig(
 
 
 @pytest.fixture
-@skip_if_git_missing
 def set_vcs_gitconfig(
     monkeypatch: pytest.MonkeyPatch,
     vcs_gitconfig: pathlib.Path,
 ) -> pathlib.Path:
     """Set git configuration."""
+    _skip_if_git_missing()
     monkeypatch.setenv("GIT_CONFIG", str(vcs_gitconfig))
     monkeypatch.setenv("GIT_CONFIG_GLOBAL", str(vcs_gitconfig))  # For child processes
     return vcs_gitconfig
 
 
 @pytest.fixture(scope="session")
-@skip_if_hg_missing
 def vcs_hgconfig(
     user_path: pathlib.Path,
     vcs_user: str,
 ) -> pathlib.Path:
     """Return Mercurial configuration."""
+    _skip_if_hg_missing()
     hgrc = user_path / ".hgrc"
     hgrc.write_text(
         textwrap.dedent(
@@ -209,12 +227,12 @@ def vcs_hgconfig(
 
 
 @pytest.fixture
-@skip_if_hg_missing
 def set_vcs_hgconfig(
     monkeypatch: pytest.MonkeyPatch,
     vcs_hgconfig: pathlib.Path,
 ) -> pathlib.Path:
     """Set Mercurial configuration."""
+    _skip_if_hg_missing()
     monkeypatch.setenv("HGRCPATH", str(vcs_hgconfig))
     return vcs_hgconfig
 
@@ -338,11 +356,11 @@ def empty_git_bare_repo_path(libvcs_test_cache_path: pathlib.Path) -> pathlib.Pa
 
 
 @pytest.fixture(scope="session")
-@skip_if_git_missing
 def empty_git_bare_repo(
     empty_git_bare_repo_path: pathlib.Path,
 ) -> pathlib.Path:
     """Return factory to create git remote repo to for clone / push purposes."""
+    _skip_if_git_missing()
     if (
         empty_git_bare_repo_path.exists()
         and (empty_git_bare_repo_path / ".git").exists()
@@ -357,11 +375,11 @@ def empty_git_bare_repo(
 
 
 @pytest.fixture(scope="session")
-@skip_if_git_missing
 def empty_git_repo(
     empty_git_repo_path: pathlib.Path,
 ) -> pathlib.Path:
     """Return factory to create git remote repo to for clone / push purposes."""
+    _skip_if_git_missing()
     if empty_git_repo_path.exists() and (empty_git_repo_path / ".git").exists():
         return empty_git_repo_path
 
@@ -373,12 +391,12 @@ def empty_git_repo(
 
 
 @pytest.fixture(scope="session")
-@skip_if_git_missing
 def create_git_remote_bare_repo(
     remote_repos_path: pathlib.Path,
     empty_git_bare_repo: pathlib.Path,
 ) -> CreateRepoFn:
     """Return factory to create git remote repo to for clone / push purposes."""
+    _skip_if_git_missing()
 
     def fn(
         remote_repos_path: pathlib.Path = remote_repos_path,
@@ -402,12 +420,12 @@ def fn(
 
 
 @pytest.fixture(scope="session")
-@skip_if_git_missing
 def create_git_remote_repo(
     remote_repos_path: pathlib.Path,
     empty_git_repo: pathlib.Path,
 ) -> CreateRepoFn:
     """Return factory to create git remote repo to for clone / push purposes."""
+    _skip_if_git_missing()
 
     def fn(
         remote_repos_path: pathlib.Path = remote_repos_path,
@@ -455,13 +473,13 @@ def git_remote_repo_single_commit_post_init(
 
 
 @pytest.fixture(scope="session")
-@skip_if_git_missing
 def git_remote_repo(
     create_git_remote_repo: CreateRepoFn,
     vcs_gitconfig: pathlib.Path,
     git_commit_envvars: GitCommitEnvVars,
 ) -> pathlib.Path:
     """Copy the session-scoped Git repository to a temporary directory."""
+    _skip_if_git_missing()
     # TODO: Cache the effect of of this in a session-based repo
     repo_path = create_git_remote_repo()
     git_remote_repo_single_commit_post_init(
@@ -519,15 +537,11 @@ def empty_svn_repo_path(libvcs_test_cache_path: pathlib.Path) -> pathlib.Path:
 
 
 @pytest.fixture(scope="session")
-@skip_if_svn_missing
 def empty_svn_repo(
     empty_svn_repo_path: pathlib.Path,
 ) -> pathlib.Path:
     """Return factory to create svn remote repo to for clone / push purposes."""
-    if not shutil.which("svn") or not shutil.which("svnadmin"):
-        pytest.skip(
-            reason="svn is not available",
-        )
+    _skip_if_svn_missing()
 
     if empty_svn_repo_path.exists() and (empty_svn_repo_path / "conf").exists():
         return empty_svn_repo_path
@@ -540,12 +554,12 @@ def empty_svn_repo(
 
 
 @pytest.fixture(scope="session")
-@skip_if_svn_missing
 def create_svn_remote_repo(
     remote_repos_path: pathlib.Path,
     empty_svn_repo: pathlib.Path,
 ) -> CreateRepoFn:
     """Pre-made svn repo, bare, used as a file:// remote to checkout and commit to."""
+    _skip_if_svn_missing()
 
     def fn(
         remote_repos_path: pathlib.Path = remote_repos_path,
@@ -572,20 +586,20 @@ def fn(
 
 
 @pytest.fixture(scope="session")
-@skip_if_svn_missing
 def svn_remote_repo(
     create_svn_remote_repo: CreateRepoFn,
 ) -> pathlib.Path:
     """Pre-made. Local file:// based SVN server."""
+    _skip_if_svn_missing()
     return create_svn_remote_repo()
 
 
 @pytest.fixture(scope="session")
-@skip_if_svn_missing
 def svn_remote_repo_with_files(
     create_svn_remote_repo: CreateRepoFn,
 ) -> pathlib.Path:
     """Pre-made. Local file:// based SVN server."""
+    _skip_if_svn_missing()
     repo_path = create_svn_remote_repo()
     svn_remote_repo_single_commit_post_init(remote_repo_path=repo_path)
     return repo_path
@@ -629,11 +643,11 @@ def empty_hg_repo_path(libvcs_test_cache_path: pathlib.Path) -> pathlib.Path:
 
 
 @pytest.fixture(scope="session")
-@skip_if_hg_missing
 def empty_hg_repo(
     empty_hg_repo_path: pathlib.Path,
 ) -> pathlib.Path:
     """Return factory to create hg remote repo to for clone / push purposes."""
+    _skip_if_hg_missing()
     if empty_hg_repo_path.exists() and (empty_hg_repo_path / ".hg").exists():
         return empty_hg_repo_path
 
@@ -645,13 +659,13 @@ def empty_hg_repo(
 
 
 @pytest.fixture(scope="session")
-@skip_if_hg_missing
 def create_hg_remote_repo(
     remote_repos_path: pathlib.Path,
     empty_hg_repo: pathlib.Path,
     vcs_hgconfig: pathlib.Path,
 ) -> CreateRepoFn:
     """Pre-made hg repo, bare, used as a file:// remote to checkout and commit to."""
+    _skip_if_hg_missing()
 
     def fn(
         remote_repos_path: pathlib.Path = remote_repos_path,
@@ -681,13 +695,13 @@ def fn(
 
 
 @pytest.fixture(scope="session")
-@skip_if_hg_missing
 def hg_remote_repo(
     remote_repos_path: pathlib.Path,
     create_hg_remote_repo: CreateRepoFn,
     vcs_hgconfig: pathlib.Path,
 ) -> pathlib.Path:
     """Pre-made, file-based repo for push and pull."""
+    _skip_if_hg_missing()
     repo_path = create_hg_remote_repo()
     hg_remote_repo_single_commit_post_init(
         remote_repo_path=repo_path,