Remove the use of attrs/dataclasses to help mypyc

mypyc currently falls back to creating non-extension classes for
dataclasses, which prevents most of the useful optimizations from
happening. Rewrite all the classes to not rely on dataclass.

Co-authored-by: Sanjit Kalapatapu <sanjitkal@gmail.com>
Co-authored-by: Michael J. Sullivan <sully@msully.net>

black.py

@@ -40,7 +40,6 @@
 from typing_extensions import Final
 
 from appdirs import user_cache_dir
-from attr import dataclass, evolve, Factory
 import click
 import toml
 from typed_ast import ast3, ast27
@@ -185,12 +184,23 @@ class Feature(Enum):
 }
 
 
-@dataclass
 class FileMode:
-    target_versions: Set[TargetVersion] = Factory(set)
-    line_length: int = DEFAULT_LINE_LENGTH
-    string_normalization: bool = True
-    is_pyi: bool = False
+    target_versions: Set[TargetVersion]
+    line_length: int
+    string_normalization: bool
+    is_pyi: bool
+
+    def __init__(
+        self,
+        target_versions: Optional[Set[TargetVersion]] = None,
+        line_length: int = DEFAULT_LINE_LENGTH,
+        string_normalization: bool = True,
+        is_pyi: bool = False,
+    ) -> None:
+        self.target_versions = target_versions if target_versions is not None else set()
+        self.line_length = line_length
+        self.string_normalization = string_normalization
+        self.is_pyi = is_pyi
 
     def get_cache_key(self) -> str:
         if self.target_versions:
@@ -642,7 +652,9 @@ def format_file_in_place(
     `mode` and `fast` options are passed to :func:`format_file_contents`.
     """
     if src.suffix == ".pyi":
-        mode = evolve(mode, is_pyi=True)
+        mode = FileMode(
+            mode.target_versions, mode.line_length, mode.string_normalization, True
+        )
 
     then = datetime.utcfromtimestamp(src.stat().st_mtime)
     with open(src, "rb") as buf:
@@ -895,9 +907,11 @@ def visit_default(self, node: LN) -> Iterator[T]:
                 yield from self.visit(child)
 
 
-@dataclass
 class DebugVisitor(Visitor[T]):
-    tree_depth: int = 0
+    tree_depth: int
+
+    def __init__(self) -> None:
+        self.tree_depth = 0
 
     def visit_default(self, node: LN) -> Iterator[T]:
         indent = " " * (2 * self.tree_depth)
@@ -1043,16 +1057,22 @@ def show(cls, code: Union[str, Leaf, Node]) -> None:
 DOT_PRIORITY: Final = 1
 
 
-@dataclass
 class BracketTracker:
     """Keeps track of brackets on a line."""
 
     depth: int = 0
-    bracket_match: Dict[Tuple[Depth, NodeType], Leaf] = Factory(dict)
-    delimiters: Dict[LeafID, Priority] = Factory(dict)
-    previous: Optional[Leaf] = None
-    _for_loop_depths: List[int] = Factory(list)
-    _lambda_argument_depths: List[int] = Factory(list)
+    bracket_match: Dict[Tuple[Depth, NodeType], Leaf]
+    delimiters: Dict[LeafID, Priority]
+    previous: Optional[Leaf]
+    _for_loop_depths: List[int]
+    _lambda_argument_depths: List[int]
+
+    def __init__(self) -> None:
+        self.bracket_match = {}
+        self.delimiters = {}
+        self.previous = None
+        self._for_loop_depths = []
+        self._lambda_argument_depths = []
 
     def mark(self, leaf: Leaf) -> None:
         """Mark `leaf` with bracket-related metadata. Keep track of delimiters.
@@ -1175,17 +1195,23 @@ def get_open_lsqb(self) -> Optional[Leaf]:
         return self.bracket_match.get((self.depth - 1, token.RSQB))
 
 
-@dataclass
 class Line:
     """Holds leaves and comments. Can be printed with `str(line)`."""
 
-    depth: int = 0
-    leaves: List[Leaf] = Factory(list)
-    comments: Dict[LeafID, List[Leaf]] = Factory(dict)  # keys ordered like `leaves`
-    bracket_tracker: BracketTracker = Factory(BracketTracker)
-    inside_brackets: bool = False
+    depth: int
+    leaves: List[Leaf]
+    comments: Dict[LeafID, List[Leaf]]  # keys ordered like `leaves`
+    bracket_tracker: BracketTracker
+    inside_brackets: bool
     should_explode: bool = False
 
+    def __init__(self, *, depth: int = 0, inside_brackets: bool = False) -> None:
+        self.depth = depth
+        self.inside_brackets = inside_brackets
+        self.leaves = []
+        self.comments = {}
+        self.bracket_tracker = BracketTracker()
+
     def append(self, leaf: Leaf, preformatted: bool = False) -> None:
         """Add a new `leaf` to the end of the line.
 
@@ -1497,7 +1523,6 @@ def __bool__(self) -> bool:
         return bool(self.leaves or self.comments)
 
 
-@dataclass
 class EmptyLineTracker:
     """Provides a stateful method that returns the number of potential extra
     empty lines needed before and after the currently processed line.
@@ -1507,10 +1532,14 @@ class EmptyLineTracker:
     are consumed by `maybe_empty_lines()` and included in the computation.
     """
 
-    is_pyi: bool = False
+    is_pyi: bool
     previous_line: Optional[Line] = None
     previous_after: int = 0
-    previous_defs: List[int] = Factory(list)
+    previous_defs: List[int]
+
+    def __init__(self, *, is_pyi: bool = False) -> None:
+        self.is_pyi = is_pyi
+        self.previous_defs = []
 
     def maybe_empty_lines(self, current_line: Line) -> Tuple[int, int]:
         """Return the number of extra empty lines before and after the `current_line`.
@@ -1614,18 +1643,25 @@ def _maybe_empty_lines_for_class_or_def(
         return newlines, 0
 
 
-@dataclass
 class LineGenerator(Visitor[Line]):
     """Generates reformatted Line objects.  Empty lines are not emitted.
 
     Note: destroys the tree it's visiting by mutating prefixes of its leaves
     in ways that will no longer stringify to valid Python code on the tree.
     """
 
-    is_pyi: bool = False
-    normalize_strings: bool = True
-    current_line: Line = Factory(Line)
-    remove_u_prefix: bool = False
+    def __init__(
+        self,
+        is_pyi: bool = False,
+        normalize_strings: bool = True,
+        current_line: Optional[Line] = None,
+        remove_u_prefix: bool = False,
+    ) -> None:
+        self.is_pyi = is_pyi
+        self.normalize_strings = normalize_strings
+        self.current_line = current_line if current_line is not None else Line()
+        self.remove_u_prefix = remove_u_prefix
+        self._setup_visit_methods()
 
     def line(self, indent: int = 0) -> Iterator[Line]:
         """Generate a line.
@@ -1805,7 +1841,7 @@ def visit_STANDALONE_COMMENT(self, leaf: Leaf) -> Iterator[Line]:
             yield from self.line()
         yield from self.visit_default(leaf)
 
-    def __attrs_post_init__(self) -> None:
+    def _setup_visit_methods(self) -> None:
         """You are in a twisty little maze of passages."""
         v = self.visit_stmt
         Ø: Set[str] = set()
@@ -2256,8 +2292,7 @@ def generate_comments(leaf: LN) -> Iterator[Leaf]:
         yield Leaf(pc.type, pc.value, prefix="\n" * pc.newlines)
 
 
-@dataclass
-class ProtoComment:
+class ProtoComment:  # noqa  # flake8 wants this to use __slots__ but mypyc will
     """Describes a piece of syntax that is a comment.
 
     It's not a :class:`blib2to3.pytree.Leaf` so that:
@@ -2273,6 +2308,12 @@ class ProtoComment:
     newlines: int  # how many newlines before the comment
     consumed: int  # how many characters of the original leaf's prefix did we consume
 
+    def __init__(self, type: int, value: str, newlines: int, consumed: int) -> None:
+        self.type = type
+        self.value = value
+        self.newlines = newlines
+        self.consumed = consumed
+
 
 @lru_cache(maxsize=4096)
 def list_comments(prefix: str, *, is_endmarker: bool) -> List[ProtoComment]:
@@ -3501,7 +3542,6 @@ def find_project_root(srcs: Iterable[str]) -> Path:
     return directory
 
 
-@dataclass
 class Report:
     """Provides a reformatting counter. Can be rendered with `str(report)`."""
 
@@ -3512,6 +3552,13 @@ class Report:
     same_count: int = 0
     failure_count: int = 0
 
+    def __init__(
+        self, *, check: bool = False, quiet: bool = False, verbose: bool = False
+    ) -> None:
+        self.check = check
+        self.quiet = quiet
+        self.verbose = verbose
+
     def done(self, src: Path, changed: Changed) -> None:
         """Increment the counter for successful reformatting. Write out a message."""
         if changed is Changed.YES: