gh-141276: Return before reading source in _get_module_code

Move the compile_source=False early return above the archive read, so
get_filename() no longer decompresses source it immediately discards.
Also update the NEWS entry with itamaro's suggested wording and add
tests covering the deferred-SyntaxError behavior: find_spec()/
get_filename() succeed and get_filename() emits no warnings for a
module with a syntax error, a valid .pyc still wins over a bad
sibling .py, and a package's __init__.py error doesn't fall through
to a same-named sibling module.

Author: harjothkhara

Lib/test/test_zipimport.py

@@ -247,6 +247,64 @@ def test_syntax_warning(self):
         self.assertEqual(len(caught), 1)
         self.assertIsInstance(caught[0].message, SyntaxWarning)
 
+    def test_syntax_error_defers_to_exec(self):
+        files = {TESTMOD + ".py": "x =\n"}
+        self.makeZip(files)
+        zi = zipimport.zipimporter(TEMP_ZIP)
+        expected_path = os.path.join(TEMP_ZIP, TESTMOD + ".py")
+
+        spec = zi.find_spec(TESTMOD)
+        self.assertIsNotNone(spec)
+        self.assertEqual(spec.origin, expected_path)
+        self.assertEqual(zi.get_filename(TESTMOD), expected_path)
+
+        mod = importlib.util.module_from_spec(spec)
+        with self.assertRaises(SyntaxError):
+            spec.loader.exec_module(mod)
+
+    def test_get_filename_no_warnings(self):
+        files = {TESTMOD + ".py": "x = 1 is 1\n"}
+        self.makeZip(files)
+        zi = zipimport.zipimporter(TEMP_ZIP)
+
+        with warnings.catch_warnings(record=True) as caught:
+            warnings.simplefilter("always", SyntaxWarning)
+            zi.get_filename(TESTMOD)
+
+        self.assertEqual(caught, [])
+
+    def test_syntax_error_in_source_with_valid_pyc(self):
+        bad_src = "x =\n"
+        files = {TESTMOD + ".py": bad_src,
+                 TESTMOD + pyc_ext: make_pyc(test_co, NOW, len(bad_src))}
+        self.makeZip(files)
+        zi = zipimport.zipimporter(TEMP_ZIP)
+        expected_path = os.path.join(TEMP_ZIP, TESTMOD + pyc_ext)
+
+        spec = zi.find_spec(TESTMOD)
+        self.assertIsNotNone(spec)
+        self.assertEqual(spec.origin, expected_path)
+
+        mod = importlib.util.module_from_spec(spec)
+        spec.loader.exec_module(mod)
+        self.assertEqual(mod.get_file(), expected_path)
+
+    def test_syntax_error_in_package_init_no_fallthrough(self):
+        packdir = TESTPACK + os.sep
+        files = {packdir + "__init__.py": "x =\n",
+                 TESTPACK + ".py": test_src}
+        self.makeZip(files)
+        zi = zipimport.zipimporter(TEMP_ZIP)
+        expected_path = os.path.join(TEMP_ZIP, TESTPACK, "__init__.py")
+
+        spec = zi.find_spec(TESTPACK)
+        self.assertIsNotNone(spec)
+        self.assertEqual(spec.origin, expected_path)
+
+        mod = importlib.util.module_from_spec(spec)
+        with self.assertRaises(SyntaxError):
+            spec.loader.exec_module(mod)
+
     def testPyc(self):
         files = {TESTMOD + pyc_ext: test_pyc}
         self.doTest(pyc_ext, files, TESTMOD)

Lib/zipimport.py

@@ -808,6 +808,8 @@ def _get_module_code(self, fullname, *, compile_source=True):
             pass
         else:
             modpath = toc_entry[0]
+            if not isbytecode and not compile_source:
+                return None, ispackage, modpath
             data = _get_data(self.archive, toc_entry)
             code = None
             if isbytecode:
@@ -816,8 +818,6 @@ def _get_module_code(self, fullname, *, compile_source=True):
                 except ImportError as exc:
                     import_error = exc
             else:
-                if not compile_source:
-                    return None, ispackage, modpath
                 code = _compile_source(modpath, data, fullname)
             if code is None:
                 # bad magic number or non-matching mtime

Misc/NEWS.d/next/Library/2026-07-15-21-45-33.gh-issue-141276.xH7qP2.rst

@@ -1,2 +1,3 @@
-Fix duplicate :exc:`SyntaxWarning` messages when importing source modules
-from ZIP archives.
+``zipimporter.get_filename()`` and ``find_spec()`` no longer compile source
+modules; a :exc:`SyntaxError` in a zipped source module is now raised when the
+module is executed, matching the behavior of filesystem-based loaders.