Pin CI actions to commit SHAs

.github/workflows/ci.yml

@@ -17,10 +17,10 @@ jobs:
         python-version: ["3.11", "3.12", "3.13"]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: ${{ matrix.python-version }}
 
@@ -36,10 +36,10 @@ jobs:
   dependency-security:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
 
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
 

tests/test_ci_workflow.py

@@ -1,10 +1,12 @@
 from __future__ import annotations
 
+import re
 from pathlib import Path
 
 
 ROOT = Path(__file__).resolve().parents[1]
 CI_WORKFLOW = ROOT / ".github" / "workflows" / "ci.yml"
+TAGGED_ACTION_REF = re.compile(r"uses:\s+[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+@v\d+")
 
 
 def test_ci_workflow_has_dependency_security_gate() -> None:
@@ -16,3 +18,13 @@ def test_ci_workflow_has_dependency_security_gate() -> None:
     assert 'python -m pip install --upgrade "pip>=26.1"' in workflow
     assert "python -m pip install pip-audit" in workflow
     assert "python -m pip_audit --progress-spinner off" in workflow
+
+
+def test_github_actions_are_pinned_to_commit_shas() -> None:
+    offenders = [
+        line.strip()
+        for line in CI_WORKFLOW.read_text().splitlines()
+        if TAGGED_ACTION_REF.search(line)
+    ]
+
+    assert offenders == []