X-Git-Url: http://git.scottworley.com/git-cache/blobdiff_plain/50685beba299ab4b601b6aabb013bb8398c8bfb0..HEAD:/git_cache.py

diff --git a/git_cache.py b/git_cache.py
index a34c329..76c0ed4 100644
--- a/git_cache.py
+++ b/git_cache.py
@@ -24,6 +24,11 @@ from typing import Iterator, NamedTuple, Optional, TypeVar, Tuple, Union
 
 import backoff
 
+
+class GitCacheError(Exception):
+    pass
+
+
 Path = str   # eg: "/home/user/.cache/git-cache/v1"
 Repo = str   # eg: "https://github.com/NixOS/nixpkgs.git"
 Ref = str    # eg: "master" or "v1.0.0"
@@ -74,7 +79,7 @@ def is_ancestor(repo: Repo, descendant: RefOrRev, ancestor: RefOrRev) -> bool:
                               'merge-base',
                               '--is-ancestor',
                               ancestor,
-                              descendant],
+                              descendant.removeprefix('tag ')],
                              check=False)
     return process.returncode == 0
 
@@ -85,7 +90,7 @@ def verify_ancestry(
         ancestor: RefOrRev,
         force: bool = False) -> None:
     if not force and not is_ancestor(repo, descendant, ancestor):
-        raise Exception(f'{ancestor} is not an ancestor of {descendant}')
+        raise GitCacheError(f'{ancestor} is not an ancestor of {descendant}')
 
 
 def _read_fetch_log(repo: Repo) -> Iterator[_LogEntry]:
@@ -173,9 +178,12 @@ def _git_fetch(
         repo: Repo,
         ref: Ref,
         force: bool = False) -> None:
+    refargs = (['tag', ref.removeprefix('tag ')]
+               if ref.startswith('tag ')
+               else [f'{ref}:{ref}'])
     subprocess.run(['git', '-C', cachedir, 'fetch'] +
                    (['--force'] if force else []) +
-                   [repo, f'{ref}:{ref}'], check=True)
+                   [repo] + refargs, check=True)
 
 
 def fetch(repo: Repo, ref: Ref, force: bool = False) -> Tuple[Path, Rev]:
@@ -196,7 +204,10 @@ def fetch(repo: Repo, ref: Ref, force: bool = False) -> Tuple[Path, Rev]:
     logging.debug('Fetching ref "%s" from %s', ref, repo)
     _git_fetch(cachedir, repo, ref, force=force)
 
-    with open(os.path.join(cachedir, 'refs', 'heads', ref), encoding='utf-8') as rev_file:
+    rev_path = (['tags', ref.removeprefix('tag ')]
+                if ref.startswith('tag ')
+                else ['heads', ref])
+    with open(os.path.join(cachedir, 'refs', *rev_path), encoding='utf-8') as rev_file:
         rev = Rev(rev_file.read(999).strip())
     verify_ancestry(repo, ref, rev, force=force)
     _log_fetch(repo, ref, rev, force=force)