action: add a fatal error if no dists were collected (#15)

Author: woodruffw

action.py

@@ -113,8 +113,8 @@ def _collect_dists(patterns: set[str]) -> list[tuple[Path, Distribution]]:
     """
 
     files = _unroll_files(patterns)
-    dists = []
 
+    dists = []
     for file in files:
         try:
             dist = Distribution.from_file(file)
@@ -162,6 +162,13 @@ def _attest(
     and an error will be raised instead.
     """
 
+    if not dists:
+        _fatal(
+            "No distributions to attest",
+            detail="No valid Python distributions were collected from the specified paths.",
+            tip="Ensure that the `paths` input points to valid distribution files.",
+        )
+
     # Before setting up any signing state, precompute the paths we intend
     # to write attestations to (and fail if any already exist and overwrite
     # is disabled).

pyproject.toml

@@ -16,6 +16,7 @@ classifiers = [
 
 [dependency-groups]
 dev = [
+    "inline-snapshot>=0.31.1",
     "pyright>=1.1.407",
     "pytest>=9.0.1",
     "requests>=2.32.5",

test.py

@@ -5,6 +5,7 @@
 
 import pytest
 import requests
+from inline_snapshot import snapshot
 from pypi_attestations import Attestation, GitHubPublisher
 from sigstore import oidc
 
@@ -14,11 +15,16 @@
 
 
 @pytest.fixture(autouse=True)
-def suppress_summary(monkeypatch: pytest.MonkeyPatch) -> None:
+def capture_summary(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> Path:
     """
-    Prevent writing to the GitHub Actions job summary during tests.
+    Capture the GitHub Actions job summary to a temporary file.
     """
-    monkeypatch.delenv("GITHUB_STEP_SUMMARY", raising=False)
+
+    summary_path = tmp_path / "GITHUB_STEP_SUMMARY"
+    summary_path.touch()
+    monkeypatch.setenv("GITHUB_STEP_SUMMARY", str(summary_path))
+
+    return summary_path
 
 
 @pytest.fixture(scope="session")
@@ -213,3 +219,24 @@ def test_attest_verify(
             dist=dist,
             offline=True,
         )
+
+
+def test_attest_no_dists(
+    id_token: oidc.IdentityToken,
+    capture_summary: Path,
+) -> None:
+    with pytest.raises(SystemExit):
+        action._attest(
+            [],
+            id_token,
+            overwrite=False,
+        )
+
+    assert capture_summary.read_text() == snapshot("""\
+### ❌ Fatal: No distributions to attest
+
+No valid Python distributions were collected from the specified paths.
+
+> [!TIP]
+> Ensure that the `paths` input points to valid distribution files.
+""")