First pass at removing implicit Template/str concat

Author: davepeck

Lib/test/test_ast/test_ast.py

@@ -999,13 +999,6 @@ def test_tstring(self):
         self.assertIsInstance(tree.body[0].value.values[0], ast.Constant)
         self.assertIsInstance(tree.body[0].value.values[1], ast.Interpolation)
 
-        # Test AST for implicit concat of t-string with f-string
-        tree = ast.parse('t"Hello {name}" f"{name}"')
-        self.assertIsInstance(tree.body[0].value, ast.TemplateStr)
-        self.assertIsInstance(tree.body[0].value.values[0], ast.Constant)
-        self.assertIsInstance(tree.body[0].value.values[1], ast.Interpolation)
-        self.assertIsInstance(tree.body[0].value.values[2], ast.FormattedValue)
-
 
 class CopyTests(unittest.TestCase):
     """Test copying and pickling AST nodes."""

Lib/test/test_tstring.py

@@ -239,45 +239,20 @@ def test_literal_concatenation(self):
         self.assertTStringEqual(t, ("Hello, ", ""), [(name, "name")])
         self.assertEqual(fstring(t), "Hello, Python")
 
-        # Test concatenation with string literal
-        name = "Python"
-        t = t"Hello, {name}" "and welcome!"
-        self.assertTStringEqual(
-            t, ("Hello, ", "and welcome!"), [(name, "name")]
-        )
-        self.assertEqual(fstring(t), "Hello, Pythonand welcome!")
-
-        # Test concatenation with Unicode literal
-        name = "Python"
-        t = t"Hello, {name}" u"and welcome!"
-        self.assertTStringEqual(
-            t, ("Hello, ", "and welcome!"), [(name, "name")]
-        )
-        self.assertEqual(fstring(t), "Hello, Pythonand welcome!")
-
-        # Test concatenation with f-string literal
-        tab = '\t'
-        t = t"Tab: {tab}. " f"f-tab: {tab}."
-        self.assertTStringEqual(t, ("Tab: ", ". f-tab: \t."), [(tab, "tab")])
-        self.assertEqual(fstring(t), "Tab: \t. f-tab: \t.")
-
-        # Test concatenation with raw string literal
-        tab = '\t'
-        t = t"Tab: {tab}. " r"Raw tab: \t."
-        self.assertTStringEqual(
-            t, ("Tab: ", r". Raw tab: \t."), [(tab, "tab")]
-        )
-        self.assertEqual(fstring(t), "Tab: \t. Raw tab: \\t.")
-
-        # Test concatenation with raw f-string literal
-        tab = '\t'
-        t = t"Tab: {tab}. " rf"f-tab: {tab}. Raw tab: \t."
-        self.assertTStringEqual(
-            t, ("Tab: ", ". f-tab: \t. Raw tab: \\t."), [(tab, "tab")]
-        )
-        self.assertEqual(fstring(t), "Tab: \t. f-tab: \t. Raw tab: \\t.")
-
+        # Test disallowed mix of t-string and string
         what = 't'
+        expected_msg = 'cannot mix str and Template literals'
+        for case in (
+            "t'{what}-string literal' 'str literal'",
+            "t'{what}-string literal' u'unicode literal'",
+            "t'{what}-string literal' f'f-string literal'",
+            "t'{what}-string literal' r'raw string literal'",
+            "t'{what}-string literal' rf'raw f-string literal'",
+        ):
+            with self.assertRaisesRegex(SyntaxError, expected_msg):
+                eval(case)
+
+        # Test disallowed mix of t-string and bytes
         expected_msg = 'cannot mix bytes and nonbytes literals'
         for case in (
             "t'{what}-string literal' b'bytes literal'",

Lib/test/test_unparse.py

@@ -206,10 +206,6 @@ def test_tstrings(self):
         self.check_ast_roundtrip("t'foo'")
         self.check_ast_roundtrip("t'foo {bar}'")
         self.check_ast_roundtrip("t'foo {bar!s:.2f}'")
-        self.check_ast_roundtrip("t'foo {bar}' f'{bar}'")
-        self.check_ast_roundtrip("f'{bar}' t'foo {bar}'")
-        self.check_ast_roundtrip("t'foo {bar}' fr'\\hello {bar}'")
-        self.check_ast_roundtrip("t'foo {bar}' u'bar'")
 
     def test_strings(self):
         self.check_ast_roundtrip("u'foo'")

Parser/action_helpers.c

@@ -1887,6 +1887,11 @@ _PyPegen_concatenate_strings(Parser *p, asdl_expr_seq *strings,
         return NULL;
     }
 
+    if ((unicode_string_found || f_string_found) && t_string_found) {
+        RAISE_SYNTAX_ERROR("cannot mix str and Template literals");
+        return NULL;
+    }
+
     // If it's only bytes or only unicode string, do a simple concat
     if (!f_string_found && !t_string_found) {
         if (len == 1) {
@@ -1902,6 +1907,7 @@ _PyPegen_concatenate_strings(Parser *p, asdl_expr_seq *strings,
         }
     }
 
+
     if (t_string_found) {
         return _build_concatenated_template_str(p, strings, lineno,
             col_offset, end_lineno, end_col_offset, arena);