black/parser: partial support for pattern matching (#2586)

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

diff --git a/src/blib2to3/pgen2/driver.py b/src/blib2to3/pgen2/driver.py
index af1dc6b8aebe032b701df42e9a9ff11257cf3dc4..5edd75b1333991d692a8f57ac84101b1a609e916 100644 (file)
--- a/src/blib2to3/pgen2/driver.py
+++ b/src/blib2to3/pgen2/driver.py
@@ -28,19 +28,92 @@ from typing import (
     List,
     Optional,
     Text,
+    Iterator,
     Tuple,
+    TypeVar,
+    Generic,
     Union,
 )
+from dataclasses import dataclass, field
 
 # Pgen imports
 from . import grammar, parse, token, tokenize, pgen
 from logging import Logger
 from blib2to3.pytree import _Convert, NL
 from blib2to3.pgen2.grammar import Grammar
+from contextlib import contextmanager
 
 Path = Union[str, "os.PathLike[str]"]
 
 
+@dataclass
+class ReleaseRange:
+    start: int
+    end: Optional[int] = None
+    tokens: List[Any] = field(default_factory=list)
+
+    def lock(self) -> None:
+        total_eaten = len(self.tokens)
+        self.end = self.start + total_eaten
+
+
+class TokenProxy:
+    def __init__(self, generator: Any) -> None:
+        self._tokens = generator
+        self._counter = 0
+        self._release_ranges: List[ReleaseRange] = []
+
+    @contextmanager
+    def release(self) -> Iterator["TokenProxy"]:
+        release_range = ReleaseRange(self._counter)
+        self._release_ranges.append(release_range)
+        try:
+            yield self
+        finally:
+            # Lock the last release range to the final position that
+            # has been eaten.
+            release_range.lock()
+
+    def eat(self, point: int) -> Any:
+        eaten_tokens = self._release_ranges[-1].tokens
+        if point < len(eaten_tokens):
+            return eaten_tokens[point]
+        else:
+            while point >= len(eaten_tokens):
+                token = next(self._tokens)
+                eaten_tokens.append(token)
+            return token
+
+    def __iter__(self) -> "TokenProxy":
+        return self
+
+    def __next__(self) -> Any:
+        # If the current position is already compromised (looked up)
+        # return the eaten token, if not just go further on the given
+        # token producer.
+        for release_range in self._release_ranges:
+            assert release_range.end is not None
+
+            start, end = release_range.start, release_range.end
+            if start <= self._counter < end:
+                token = release_range.tokens[self._counter - start]
+                break
+        else:
+            token = next(self._tokens)
+        self._counter += 1
+        return token
+
+    def can_advance(self, to: int) -> bool:
+        # Try to eat, fail if it can't. The eat operation is cached
+        # so there wont be any additional cost of eating here
+        try:
+            self.eat(to)
+        except StopIteration:
+            return False
+        else:
+            return True
+
+
 class Driver(object):
     def __init__(
         self,
@@ -57,14 +130,18 @@ class Driver(object):
     def parse_tokens(self, tokens: Iterable[Any], debug: bool = False) -> NL:
         """Parse a series of tokens and return the syntax tree."""
         # XXX Move the prefix computation into a wrapper around tokenize.
+        proxy = TokenProxy(tokens)
+
         p = parse.Parser(self.grammar, self.convert)
-        p.setup()
+        p.setup(proxy=proxy)
+
         lineno = 1
         column = 0
         indent_columns = []
         type = value = start = end = line_text = None
         prefix = ""
-        for quintuple in tokens:
+
+        for quintuple in proxy:
             type, value, start, end, line_text = quintuple
             if start != (lineno, column):
                 assert (lineno, column) <= start, ((lineno, column), start)