Cache nix store paths of generated tarballs

This eliminates the slow "Generating tarball for git revision" step for
tarballs that have already been generated and are already in the nix store.

diff --git a/pinch.py b/pinch.py
index 10481e472dfb638a5a6a546a41c27cbcfd46df1d..732a91f645c036a4692e6ea55083cad4427373d0 100644 (file)
--- a/pinch.py
+++ b/pinch.py
@@ -222,8 +222,17 @@ def git_cachedir(git_repo: str) -> str:
     return os.path.join(
         xdg.XDG_CACHE_HOME,
         'pinch/git',
-        digest_string(
-            git_repo.encode()))
+        digest_string(git_repo.encode()))
+
+
+def tarball_cache_file(channel: Channel) -> str:
+    return os.path.join(
+        xdg.XDG_CACHE_HOME,
+        'pinch/git-tarball',
+        '%s-%s-%s' %
+        (digest_string(channel.git_repo.encode()),
+         channel.git_revision,
+         channel.release_name))
 
 
 def verify_git_ancestry(v: Verification, channel: Channel) -> None:
@@ -371,6 +380,12 @@ def git_checkout(v: Verification, channel: Channel, dest: str) -> None:
 
 
 def git_get_tarball(v: Verification, channel: Channel) -> str:
+    cache_file = tarball_cache_file(channel)
+    if os.path.exists(cache_file):
+        cached_tarball = open(cache_file).read(9999)
+        if os.path.exists(cached_tarball):
+            return cached_tarball
+
     with tempfile.TemporaryDirectory() as output_dir:
         output_filename = os.path.join(
             output_dir, channel.release_name + '.tar.xz')
@@ -394,7 +409,11 @@ def git_get_tarball(v: Verification, channel: Channel) -> str:
         process = subprocess.run(
             ['nix-store', '--add', output_filename], capture_output=True)
         v.result(process.returncode == 0)
-        return process.stdout.decode().strip()
+        store_tarball = process.stdout.decode().strip()
+
+        os.makedirs(os.path.dirname(cache_file), exist_ok=True)
+        open(cache_file, 'w').write(store_tarball)
+        return store_tarball
 
 
 def check_channel_metadata(