Merge pull request #161 from JeffreyVdb/evaluate-pip-cache-dir-after-…

…custom-check

_service/pypi.py: Do not execute pip cache command when a custom directory is provided

CHANGELOG.md

@@ -24,6 +24,14 @@ All versions prior to 0.0.9 are untracked.
   `--strict` mode) is produced
   ([#162](https://github.com/trailofbits/pip-audit/pull/162))
 
+* CLI: When providing the `--cache-dir` flag, the command to read the pip cache
+  directory is no longer executed. Previously this was always executed and
+  could result into failure when the command fails. In CI environments, the
+  default `~/.cache` directory is typically not writable by the build user and
+  this meant that the `python -m pip cache dir` would fail before this fix,
+  even if the `--cache-dir` flag was provided.
+  ([#161](https://github.com/trailofbits/pip-audit/pull/161))
+
 ### Removed
 
 ## [1.0.0] - 2021-12-1

pip_audit/_service/pypi.py

@@ -109,12 +109,11 @@ def _get_pip_cache() -> str:
 
 
 def _get_cache_dir(custom_cache_dir: Optional[Path]) -> str:
-    pip_cache_dir: Optional[str] = (
-        _get_pip_cache() if _PIP_VERSION >= _MINIMUM_PIP_VERSION else None
-    )
     if custom_cache_dir is not None:
         return str(custom_cache_dir)
-    elif pip_cache_dir is not None:  # pragma: no cover
+
+    pip_cache_dir = _get_pip_cache() if _PIP_VERSION >= _MINIMUM_PIP_VERSION else None
+    if pip_cache_dir is not None:  # pragma: no cover
         return pip_cache_dir
     else:
         fallback_path = os.path.join(Path.home(), ".pip-audit-cache")