gh-133555: Allow regenerating the parser with Python < 3.14 (#133557)

Co-authored-by: Adam Turner <[email protected]>

Author: alexprengere

Grammar/Tokens

@@ -1,3 +1,8 @@
+# When adding new tokens, remember to update the PEG generator in
+# Tools/peg_generator/pegen/parser_generator.py
+# This will ensure that older versions of Python can generate a Python parser
+# using "python -m pegen python <GRAMMAR FILE>".
+
 ENDMARKER
 NAME
 NUMBER

Tools/peg_generator/pegen/parser_generator.py

@@ -81,6 +81,11 @@ def __init__(self, rules: Dict[str, Rule], tokens: Set[str]):
             self.tokens.add("FSTRING_START")
             self.tokens.add("FSTRING_END")
             self.tokens.add("FSTRING_MIDDLE")
+        # If python < 3.14 add the virtual tstring tokens
+        if sys.version_info < (3, 14, 0, 'beta', 1):
+            self.tokens.add("TSTRING_START")
+            self.tokens.add("TSTRING_END")
+            self.tokens.add("TSTRING_MIDDLE")
 
     def visit_NameLeaf(self, node: NameLeaf) -> None:
         if node.value not in self.rules and node.value not in self.tokens: