fix: stop writing bytecode caches in installs and the test suite

tests/helpers.py

@@ -4,6 +4,9 @@
 from datetime import date, timedelta
 from pathlib import Path
 
+# Tests import the template's own files; never leave bytecode inside it.
+sys.dont_write_bytecode = True
+
 REPO = Path(__file__).resolve().parent.parent
 sys.path.insert(0, str(REPO / "wiki"))
 

tests/test_no_bytecode.py

@@ -0,0 +1,44 @@
+"""Lint runs must leave no bytecode behind. The template ships no
+.gitignore, so a wikilint/__pycache__/ written by a lint run would be
+swept into the wiki's history by the agent's next `git add -A`; and the
+test suite must not litter the template it tests."""
+
+import shutil
+import subprocess
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+from helpers import REPO
+
+
+def pycache_dirs(root):
+    return sorted(p.relative_to(root).as_posix() for p in Path(root).rglob("__pycache__"))
+
+
+class TestNoBytecode(unittest.TestCase):
+    def test_lint_run_writes_no_pycache_in_an_install(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            install = Path(tmp) / "w"
+            shutil.copytree(REPO / "wiki", install,
+                            ignore=shutil.ignore_patterns("__pycache__"))
+            (install / "raw" / "inbox").mkdir(parents=True)
+            result = subprocess.run(
+                [sys.executable, "lint.py", "check"], cwd=install,
+                capture_output=True, text=True,
+                env={"PATH": "/usr/bin:/bin"},  # no inherited PYTHONDONTWRITEBYTECODE
+            )
+            self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+            self.assertEqual(pycache_dirs(install), [])
+
+    def test_suite_does_not_write_bytecode(self):
+        self.assertTrue(sys.dont_write_bytecode)
+
+    def test_compile_check_writes_nothing(self):
+        source = (REPO / "tests" / "test_variants.py").read_text()
+        self.assertNotIn("py_compile", source)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/test_variants.py

@@ -2,7 +2,6 @@
 hook correctness properties, for the shipped template and the feature-named
 extension configs in extension_configs.py."""
 
-import py_compile
 import unittest
 
 from helpers import REPO, VARIANTS, load_variant_config
@@ -13,10 +12,10 @@
 
 class TestEngineIdentity(unittest.TestCase):
     def test_everything_compiles(self):
+        # Builtin compile() checks syntax without writing .pyc files.
         for variant in VARIANTS:
-            py_compile.compile(str(REPO / variant / "lint.py"), doraise=True)
-            for p in (REPO / variant / "wikilint").glob("*.py"):
-                py_compile.compile(str(p), doraise=True)
+            for p in [REPO / variant / "lint.py", *(REPO / variant / "wikilint").glob("*.py")]:
+                compile(p.read_text(encoding="utf-8"), str(p), "exec")
 
 
 class TestConfigSanity(unittest.TestCase):

wiki/lint.py

@@ -102,5 +102,8 @@ def index_entry_extra(fields):
 
 if __name__ == "__main__":
     import sys
+    # No __pycache__: the wiki repo ships no .gitignore, so cached bytecode
+    # would land in history on the next `git add -A`. Recompiling is cheap.
+    sys.dont_write_bytecode = True
     from wikilint import main
     sys.exit(main(CONFIG, index_entry_extra))