Fix parser bug where "type" was misinterpreted as a keyword inside a match (#3950)

[etc/vim.git] / src / blib2to3 / pgen2 / parse.py

diff --git a/src/blib2to3/pgen2/parse.py b/src/blib2to3/pgen2/parse.py
index 17bf118e9fcd8053b655b4efc42e26f840b40465..ad51a3dad08dfbbe1fee7cc9b7845eeb7cb263fd 100644 (file)
--- a/src/blib2to3/pgen2/parse.py
+++ b/src/blib2to3/pgen2/parse.py
@@ -10,24 +10,25 @@ how this parsing engine works.
 
 """
 from contextlib import contextmanager
-
-# Local imports
-from . import grammar, token, tokenize
 from typing import (
-    cast,
+    TYPE_CHECKING,
     Any,
-    Optional,
-    Union,
-    Tuple,
+    Callable,
     Dict,
-    List,
     Iterator,
-    Callable,
+    List,
+    Optional,
     Set,
-    TYPE_CHECKING,
+    Tuple,
+    Union,
+    cast,
 )
+
 from blib2to3.pgen2.grammar import Grammar
-from blib2to3.pytree import convert, NL, Context, RawNode, Leaf, Node
+from blib2to3.pytree import NL, Context, Leaf, Node, RawNode, convert
+
+# Local imports
+from . import grammar, token, tokenize
 
 if TYPE_CHECKING:
     from blib2to3.pgen2.driver import TokenProxy
@@ -112,7 +113,9 @@ class Recorder:
                     args.insert(0, ilabel)
                 func(*args)
 
-    def determine_route(self, value: Optional[str] = None, force: bool = False) -> Optional[int]:
+    def determine_route(
+        self, value: Optional[str] = None, force: bool = False
+    ) -> Optional[int]:
         alive_ilabels = self.ilabels
         if len(alive_ilabels) == 0:
             *_, most_successful_ilabel = self._dead_ilabels
@@ -208,6 +211,7 @@ class Parser:
         # See note in docstring above. TL;DR this is ignored.
         self.convert = convert or lam_sub
         self.is_backtracking = False
+        self.last_token: Optional[int] = None
 
     def setup(self, proxy: "TokenProxy", start: Optional[int] = None) -> None:
         """Prepare for parsing.
@@ -233,6 +237,7 @@ class Parser:
         self.rootnode: Optional[NL] = None
         self.used_names: Set[str] = set()
         self.proxy = proxy
+        self.last_token = None
 
     def addtoken(self, type: int, value: str, context: Context) -> bool:
         """Add a token; return True iff this is the end of the program."""
@@ -314,6 +319,7 @@ class Parser:
                         dfa, state, node = self.stack[-1]
                         states, first = dfa
                     # Done with this token
+                    self.last_token = type
                     return False
 
             else:
@@ -340,9 +346,23 @@ class Parser:
                 return [self.grammar.keywords[value]]
             elif value in self.grammar.soft_keywords:
                 assert type in self.grammar.tokens
+                # Current soft keywords (match, case, type) can only appear at the
+                # beginning of a statement. So as a shortcut, don't try to treat them
+                # like keywords in any other context.
+                # ('_' is also a soft keyword in the real grammar, but for our grammar
+                # it's just an expression, so we don't need to treat it specially.)
+                if self.last_token not in (
+                    None,
+                    token.INDENT,
+                    token.DEDENT,
+                    token.NEWLINE,
+                    token.SEMI,
+                    token.COLON,
+                ):
+                    return [self.grammar.tokens[type]]
                 return [
-                    self.grammar.soft_keywords[value],
                     self.grammar.tokens[type],
+                    self.grammar.soft_keywords[value],
                 ]
 
         ilabel = self.grammar.tokens.get(type)