gh-96052: codeop: fix handling compiler warnings in incomplete input (GH-96132)

Previously codeop.compile_command() emitted compiler warnings (SyntaxWarning or
DeprecationWarning) and raised a SyntaxError for incomplete input containing
a potentially incorrect code. Now it always returns None for incomplete input
without emitting any warnings.

Author: serhiy-storchaka

Lib/codeop.py

@@ -56,22 +56,22 @@ def _maybe_compile(compiler, source, filename, symbol):
         if symbol != "eval":
             source = "pass"     # Replace it with a 'pass' statement
 
-    try:
-        return compiler(source, filename, symbol)
-    except SyntaxError:  # Let other compile() errors propagate.
-        pass
-
-    # Catch syntax warnings after the first compile
-    # to emit warnings (SyntaxWarning, DeprecationWarning) at most once.
+    # Disable compiler warnings when checking for incomplete input.
     with warnings.catch_warnings():
-        warnings.simplefilter("error")
-
+        warnings.simplefilter("ignore", (SyntaxWarning, DeprecationWarning))
         try:
-            compiler(source + "\n", filename, symbol)
-        except SyntaxError as e:
-            if "incomplete input" in str(e):
+            compiler(source, filename, symbol)
+        except SyntaxError:  # Let other compile() errors propagate.
+            try:
+                compiler(source + "\n", filename, symbol)
                 return None
-            raise
+            except SyntaxError as e:
+                if "incomplete input" in str(e):
+                    return None
+                # fallthrough
+
+    return compiler(source, filename, symbol)
+
 
 def _is_syntax_error(err1, err2):
     rep1 = repr(err1)

Lib/test/test_codeop.py

@@ -321,6 +321,26 @@ def test_warning(self):
             warnings.simplefilter('error', SyntaxWarning)
             compile_command('1 is 1', symbol='exec')
 
+        # Check DeprecationWarning treated as an SyntaxError
+        with warnings.catch_warnings(), self.assertRaises(SyntaxError):
+            warnings.simplefilter('error', DeprecationWarning)
+            compile_command(r"'\e'", symbol='exec')
+
+    def test_incomplete_warning(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter('always')
+            self.assertIncomplete("'\\e' + (")
+        self.assertEqual(w, [])
+
+    def test_invalid_warning(self):
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter('always')
+            self.assertInvalid("'\\e' 1")
+        self.assertEqual(len(w), 1)
+        self.assertEqual(w[0].category, DeprecationWarning)
+        self.assertRegex(str(w[0].message), 'invalid escape sequence')
+        self.assertEqual(w[0].filename, '<input>')
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2022-08-20-10-31-01.gh-issue-96052.a6FhaD.rst

@@ -0,0 +1,4 @@
+Fix handling compiler warnings (SyntaxWarning and DeprecationWarning) in
+:func:`codeop.compile_command` when checking for incomplete input.
+Previously it emitted warnings and raised a SyntaxError. Now it always
+returns ``None`` for incomplete input without emitting any warnings.