docs: adds ExitStack alternative to future_style.md (#3247)

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

diff --git a/src/blib2to3/pgen2/parse.py b/src/blib2to3/pgen2/parse.py
index 8c374d35b421c8a49ccd6b9b1309c6cf323111f9..d6deaac6964fa477501a3cd6841ea08ccbb74611 100644 (file)
--- a/src/blib2to3/pgen2/parse.py
+++ b/src/blib2to3/pgen2/parse.py
@@ -9,23 +9,30 @@ See Parser/parser.c in the Python distribution for additional info on
 how this parsing engine works.
 
 """
 how this parsing engine works.
 
 """

+import copy
+from contextlib import contextmanager

 
 # Local imports
 
 # Local imports

-from . import token
+from . import grammar, token, tokenize

 from typing import (
 from typing import (

+    cast,
+    Any,

     Optional,
     Text,
     Optional,
     Text,

-    Sequence,
-    Any,

     Union,
     Tuple,
     Dict,
     List,
     Union,
     Tuple,
     Dict,
     List,

+    Iterator,

     Callable,
     Set,
     Callable,
     Set,

+    TYPE_CHECKING,

 )
 from blib2to3.pgen2.grammar import Grammar
 )
 from blib2to3.pgen2.grammar import Grammar

-from blib2to3.pytree import NL, Context, RawNode, Leaf, Node
+from blib2to3.pytree import convert, NL, Context, RawNode, Leaf, Node
+
+if TYPE_CHECKING:
+    from blib2to3.driver import TokenProxy

 
 
 Results = Dict[Text, NL]
 
 
 Results = Dict[Text, NL]


@@ -39,6 +46,87 @@ def lam_sub(grammar: Grammar, node: RawNode) -> NL:
     return Node(type=node[0], children=node[3], context=node[2])
 
 
     return Node(type=node[0], children=node[3], context=node[2])
 
 

+# A placeholder node, used when parser is backtracking.
+DUMMY_NODE = (-1, None, None, None)
+
+
+def stack_copy(
+    stack: List[Tuple[DFAS, int, RawNode]]
+) -> List[Tuple[DFAS, int, RawNode]]:
+    """Nodeless stack copy."""
+    return [(dfa, label, DUMMY_NODE) for dfa, label, _ in stack]
+
+
+class Recorder:
+    def __init__(self, parser: "Parser", ilabels: List[int], context: Context) -> None:
+        self.parser = parser
+        self._ilabels = ilabels
+        self.context = context  # not really matter
+
+        self._dead_ilabels: Set[int] = set()
+        self._start_point = self.parser.stack
+        self._points = {ilabel: stack_copy(self._start_point) for ilabel in ilabels}
+
+    @property
+    def ilabels(self) -> Set[int]:
+        return self._dead_ilabels.symmetric_difference(self._ilabels)
+
+    @contextmanager
+    def switch_to(self, ilabel: int) -> Iterator[None]:
+        with self.backtrack():
+            self.parser.stack = self._points[ilabel]
+            try:
+                yield
+            except ParseError:
+                self._dead_ilabels.add(ilabel)
+            finally:
+                self.parser.stack = self._start_point
+
+    @contextmanager
+    def backtrack(self) -> Iterator[None]:
+        """
+        Use the node-level invariant ones for basic parsing operations (push/pop/shift).
+        These still will operate on the stack; but they won't create any new nodes, or
+        modify the contents of any other existing nodes.
+
+        This saves us a ton of time when we are backtracking, since we
+        want to restore to the initial state as quick as possible, which
+        can only be done by having as little mutatations as possible.
+        """
+        is_backtracking = self.parser.is_backtracking
+        try:
+            self.parser.is_backtracking = True
+            yield
+        finally:
+            self.parser.is_backtracking = is_backtracking
+
+    def add_token(self, tok_type: int, tok_val: Text, raw: bool = False) -> None:
+        func: Callable[..., Any]
+        if raw:
+            func = self.parser._addtoken
+        else:
+            func = self.parser.addtoken
+
+        for ilabel in self.ilabels:
+            with self.switch_to(ilabel):
+                args = [tok_type, tok_val, self.context]
+                if raw:
+                    args.insert(0, ilabel)
+                func(*args)
+
+    def determine_route(self, value: Optional[Text] = None, force: bool = False) -> Optional[int]:
+        alive_ilabels = self.ilabels
+        if len(alive_ilabels) == 0:
+            *_, most_successful_ilabel = self._dead_ilabels
+            raise ParseError("bad input", most_successful_ilabel, value, self.context)
+
+        ilabel, *rest = alive_ilabels
+        if force or not rest:
+            return ilabel
+        else:
+            return None
+
+

 class ParseError(Exception):
     """Exception to signal the parser is stuck."""
 
 class ParseError(Exception):
     """Exception to signal the parser is stuck."""
 


@@ -102,6 +190,11 @@ class Parser(object):
         to be converted.  The syntax tree is converted from the bottom
         up.
 
         to be converted.  The syntax tree is converted from the bottom
         up.
 

+        **post-note: the convert argument is ignored since for Black's
+        usage, convert will always be blib2to3.pytree.convert. Allowing
+        this to be dynamic hurts mypyc's ability to use early binding.
+        These docs are left for historical and informational value.
+

         A concrete syntax tree node is a (type, value, context, nodes)
         tuple, where type is the node type (a token or symbol number),
         value is None for symbols and a string for tokens, context is
         A concrete syntax tree node is a (type, value, context, nodes)
         tuple, where type is the node type (a token or symbol number),
         value is None for symbols and a string for tokens, context is


@@ -114,9 +207,11 @@ class Parser(object):
 
         """
         self.grammar = grammar
 
         """
         self.grammar = grammar

+        # See note in docstring above. TL;DR this is ignored.

         self.convert = convert or lam_sub
         self.convert = convert or lam_sub

+        self.is_backtracking = False

 
 

-    def setup(self, start: Optional[int] = None) -> None:
+    def setup(self, proxy: "TokenProxy", start: Optional[int] = None) -> None:

         """Prepare for parsing.
 
         This *must* be called before starting to parse.
         """Prepare for parsing.
 
         This *must* be called before starting to parse.


@@ -139,11 +234,57 @@ class Parser(object):
         self.stack: List[Tuple[DFAS, int, RawNode]] = [stackentry]
         self.rootnode: Optional[NL] = None
         self.used_names: Set[str] = set()
         self.stack: List[Tuple[DFAS, int, RawNode]] = [stackentry]
         self.rootnode: Optional[NL] = None
         self.used_names: Set[str] = set()

+        self.proxy = proxy

 
 

-    def addtoken(self, type: int, value: Optional[Text], context: Context) -> bool:
+    def addtoken(self, type: int, value: Text, context: Context) -> bool:

         """Add a token; return True iff this is the end of the program."""
         # Map from token to label
         """Add a token; return True iff this is the end of the program."""
         # Map from token to label

-        ilabel = self.classify(type, value, context)
+        ilabels = self.classify(type, value, context)
+        assert len(ilabels) >= 1
+
+        # If we have only one state to advance, we'll directly
+        # take it as is.
+        if len(ilabels) == 1:
+            [ilabel] = ilabels
+            return self._addtoken(ilabel, type, value, context)
+
+        # If there are multiple states which we can advance (only
+        # happen under soft-keywords), then we will try all of them
+        # in parallel and as soon as one state can reach further than
+        # the rest, we'll choose that one. This is a pretty hacky
+        # and hopefully temporary algorithm.
+        #
+        # For a more detailed explanation, check out this post:
+        # https://tree.science/what-the-backtracking.html
+
+        with self.proxy.release() as proxy:
+            counter, force = 0, False
+            recorder = Recorder(self, ilabels, context)
+            recorder.add_token(type, value, raw=True)
+
+            next_token_value = value
+            while recorder.determine_route(next_token_value) is None:
+                if not proxy.can_advance(counter):
+                    force = True
+                    break
+
+                next_token_type, next_token_value, *_ = proxy.eat(counter)
+                if next_token_type in (tokenize.COMMENT, tokenize.NL):
+                    counter += 1
+                    continue
+
+                if next_token_type == tokenize.OP:
+                    next_token_type = grammar.opmap[next_token_value]
+
+                recorder.add_token(next_token_type, next_token_value)
+                counter += 1
+
+            ilabel = cast(int, recorder.determine_route(next_token_value, force=force))
+            assert ilabel is not None
+
+        return self._addtoken(ilabel, type, value, context)
+
+    def _addtoken(self, ilabel: int, type: int, value: Text, context: Context) -> bool:

         # Loop until the token is shifted; may raise exceptions
         while True:
             dfa, state, node = self.stack[-1]
         # Loop until the token is shifted; may raise exceptions
         while True:
             dfa, state, node = self.stack[-1]


@@ -151,10 +292,18 @@ class Parser(object):
             arcs = states[state]
             # Look for a state with this label
             for i, newstate in arcs:
             arcs = states[state]
             # Look for a state with this label
             for i, newstate in arcs:

-                t, v = self.grammar.labels[i]
-                if ilabel == i:
+                t = self.grammar.labels[i][0]
+                if t >= 256:
+                    # See if it's a symbol and if we're in its first set
+                    itsdfa = self.grammar.dfas[t]
+                    itsstates, itsfirst = itsdfa
+                    if ilabel in itsfirst:
+                        # Push a symbol
+                        self.push(t, itsdfa, newstate, context)
+                        break  # To continue the outer while loop
+
+                elif ilabel == i:

                     # Look it up in the list of labels
                     # Look it up in the list of labels

-                    assert t < 256

                     # Shift a token; we're done with it
                     self.shift(type, value, newstate, context)
                     # Pop while we are in an accept-only state
                     # Shift a token; we're done with it
                     self.shift(type, value, newstate, context)
                     # Pop while we are in an accept-only state


@@ -168,14 +317,7 @@ class Parser(object):
                         states, first = dfa
                     # Done with this token
                     return False
                         states, first = dfa
                     # Done with this token
                     return False

-                elif t >= 256:
-                    # See if it's a symbol and if we're in its first set
-                    itsdfa = self.grammar.dfas[t]
-                    itsstates, itsfirst = itsdfa
-                    if ilabel in itsfirst:
-                        # Push a symbol
-                        self.push(t, self.grammar.dfas[t], newstate, context)
-                        break  # To continue the outer while loop
+

             else:
                 if (0, state) in arcs:
                     # An accepting state, pop it and try something else
             else:
                 if (0, state) in arcs:
                     # An accepting state, pop it and try something else


@@ -187,47 +329,61 @@ class Parser(object):
                     # No success finding a transition
                     raise ParseError("bad input", type, value, context)
 
                     # No success finding a transition
                     raise ParseError("bad input", type, value, context)
 

-    def classify(self, type: int, value: Optional[Text], context: Context) -> int:
-        """Turn a token into a label.  (Internal)"""
+    def classify(self, type: int, value: Text, context: Context) -> List[int]:
+        """Turn a token into a label.  (Internal)
+
+        Depending on whether the value is a soft-keyword or not,
+        this function may return multiple labels to choose from."""

         if type == token.NAME:
             # Keep a listing of all used names
         if type == token.NAME:
             # Keep a listing of all used names

-            assert value is not None

             self.used_names.add(value)
             # Check for reserved words
             self.used_names.add(value)
             # Check for reserved words

-            ilabel = self.grammar.keywords.get(value)
-            if ilabel is not None:
-                return ilabel
+            if value in self.grammar.keywords:
+                return [self.grammar.keywords[value]]
+            elif value in self.grammar.soft_keywords:
+                assert type in self.grammar.tokens
+                return [
+                    self.grammar.soft_keywords[value],
+                    self.grammar.tokens[type],
+                ]
+

         ilabel = self.grammar.tokens.get(type)
         if ilabel is None:
             raise ParseError("bad token", type, value, context)
         ilabel = self.grammar.tokens.get(type)
         if ilabel is None:
             raise ParseError("bad token", type, value, context)

-        return ilabel
+        return [ilabel]

 
 

-    def shift(
-        self, type: int, value: Optional[Text], newstate: int, context: Context
-    ) -> None:
+    def shift(self, type: int, value: Text, newstate: int, context: Context) -> None:

         """Shift a token.  (Internal)"""
         """Shift a token.  (Internal)"""

-        dfa, state, node = self.stack[-1]
-        assert value is not None
-        assert context is not None
-        rawnode: RawNode = (type, value, context, None)
-        newnode = self.convert(self.grammar, rawnode)
-        if newnode is not None:
+        if self.is_backtracking:
+            dfa, state, _ = self.stack[-1]
+            self.stack[-1] = (dfa, newstate, DUMMY_NODE)
+        else:
+            dfa, state, node = self.stack[-1]
+            rawnode: RawNode = (type, value, context, None)
+            newnode = convert(self.grammar, rawnode)

             assert node[-1] is not None
             node[-1].append(newnode)
             assert node[-1] is not None
             node[-1].append(newnode)

-        self.stack[-1] = (dfa, newstate, node)
+            self.stack[-1] = (dfa, newstate, node)

 
     def push(self, type: int, newdfa: DFAS, newstate: int, context: Context) -> None:
         """Push a nonterminal.  (Internal)"""
 
     def push(self, type: int, newdfa: DFAS, newstate: int, context: Context) -> None:
         """Push a nonterminal.  (Internal)"""

-        dfa, state, node = self.stack[-1]
-        newnode: RawNode = (type, None, context, [])
-        self.stack[-1] = (dfa, newstate, node)
-        self.stack.append((newdfa, 0, newnode))
+        if self.is_backtracking:
+            dfa, state, _ = self.stack[-1]
+            self.stack[-1] = (dfa, newstate, DUMMY_NODE)
+            self.stack.append((newdfa, 0, DUMMY_NODE))
+        else:
+            dfa, state, node = self.stack[-1]
+            newnode: RawNode = (type, None, context, [])
+            self.stack[-1] = (dfa, newstate, node)
+            self.stack.append((newdfa, 0, newnode))

 
     def pop(self) -> None:
         """Pop a nonterminal.  (Internal)"""
 
     def pop(self) -> None:
         """Pop a nonterminal.  (Internal)"""

-        popdfa, popstate, popnode = self.stack.pop()
-        newnode = self.convert(self.grammar, popnode)
-        if newnode is not None:
+        if self.is_backtracking:
+            self.stack.pop()
+        else:
+            popdfa, popstate, popnode = self.stack.pop()
+            newnode = convert(self.grammar, popnode)

             if self.stack:
                 dfa, state, node = self.stack[-1]
                 assert node[-1] is not None
             if self.stack:
                 dfa, state, node = self.stack[-1]
                 assert node[-1] is not None