Merge pull request #65 from lysnikolaou/more-fstring-errors

Author: pablogsal

Grammar/python.gram

@@ -1363,9 +1363,9 @@ invalid_replacement_field:
     | '{' a='!' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "f-string: expression required before '!'") }
     | '{' a='}' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "f-string: empty expression not allowed") }
     | '{' (yield_expr | star_expressions) "="? invalid_conversion_character
-    | '{' (yield_expr | star_expressions) "="? [ "!" NAME ] [ ':' fstring_format_spec* ] !'}' {
-         RAISE_SYNTAX_ERROR("f-string: expecting '}'")
-    }
+    # We explicitly require either a conversion character or a format spec (or both) in order for this to not get too general
+    | '{' (yield_expr | star_expressions) "="? "!" NAME [':' fstring_format_spec*] !'}' { RAISE_SYNTAX_ERROR("f-string: expecting '}'") }
+    | '{' (yield_expr | star_expressions) "="? ':' fstring_format_spec* !'}' { RAISE_SYNTAX_ERROR("f-string: expecting '}'") }
 invalid_conversion_character:
     | a="!" &(':'|'}') { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "f-string: missed conversion character") }
     | a="!" !NAME { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "f-string: invalid conversion character") }

Lib/test/test_exceptions.py

@@ -294,7 +294,7 @@ def baz():
 
             {
             6
-            0="""''', 6, 15)
+            0="""''', 5, 13)
 
         # Errors thrown by symtable.c
         check('x = [(yield i) for i in range(3)]', 1, 7)

Lib/test/test_fstring.py

@@ -931,7 +931,7 @@ def test_lambda(self):
 
         # lambda doesn't work without parens, because the colon
         #  makes the parser think it's a format_spec
-        self.assertAllRaise(SyntaxError, 'f-string: invalid syntax',
+        self.assertAllRaise(SyntaxError, 'invalid syntax',
                             ["f'{lambda x:x}'",
                              ])
 
@@ -1258,8 +1258,6 @@ def test_mismatched_braces(self):
                              "f'{{{'",
                              "f'{{}}{'",
                              "f'{'",
-                             "f'x{<'",  # See bpo-46762.
-                             "f'x{>'",
                              "f'{i='",  # See gh-93418.
                              ])
 
@@ -1483,7 +1481,7 @@ def test_walrus(self):
         self.assertEqual(x, 10)
 
     def test_invalid_syntax_error_message(self):
-        with self.assertRaisesRegex(SyntaxError, "f-string: invalid syntax"):
+        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
             compile("f'{a $ b}'", "?", "exec")
 
     def test_with_two_commas_in_format_specifier(self):
@@ -1507,11 +1505,11 @@ def test_with_an_underscore_and_a_comma_in_format_specifier(self):
             f'{1:_,}'
 
     def test_syntax_error_for_starred_expressions(self):
-        error_msg = re.escape("cannot use starred expression here")
+        error_msg = re.escape("can't use starred expression here")
         with self.assertRaisesRegex(SyntaxError, error_msg):
             compile("f'{*a}'", "?", "exec")
 
-        error_msg = re.escape("cannot use double starred expression here")
+        error_msg = re.escape("invalid syntax")
         with self.assertRaisesRegex(SyntaxError, error_msg):
             compile("f'{**a}'", "?", "exec")