From d7b091e762121ee38ca313ab25006abf4723d203 Mon Sep 17 00:00:00 2001
From: Batuhan Taskaya <isidentical@gmail.com>
Date: Tue, 16 Nov 2021 05:38:40 +0300
Subject: [PATCH] black/parser: optimize deepcopying nodes (#2611)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

The implementation of the new backtracking logic depends heavily on deepcopying the current state of the parser before seeing one of the new keywords, which by default is an very expensive operations. On my system, formatting these 3 files takes 1.3 seconds.

```
 $ touch tests/data/pattern_matching_*; time python -m black -tpy310 tests/data/pattern_matching_*             19ms
All done! ✨ 🍰 ✨
3 files left unchanged.
python -m black -tpy310 tests/data/pattern_matching_*  2,09s user 0,04s system 157% cpu 1,357 total
```

which can be optimized 3X if we integrate the existing copying logic (`clone`) to the deepcopy system;
```
 $ touch tests/data/pattern_matching_*; time python -m black -tpy310 tests/data/pattern_matching_*              1ms
All done! ✨ 🍰 ✨
3 files left unchanged.
python -m black -tpy310 tests/data/pattern_matching_*  0,66s user 0,02s system 147% cpu 0,464 total
```

This still might have some potential, but that would be way trickier than this initial patch.
---
 src/blib2to3/pytree.py                |  5 ++++-
 tests/data/pattern_matching_extras.py | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/blib2to3/pytree.py b/src/blib2to3/pytree.py
index 7843467..001652d 100644
--- a/src/blib2to3/pytree.py
+++ b/src/blib2to3/pytree.py
@@ -52,7 +52,7 @@ def type_repr(type_num: int) -> Union[Text, int]:
     return _type_reprs.setdefault(type_num, type_num)
 
 
-_P = TypeVar("_P")
+_P = TypeVar("_P", bound="Base")
 
 NL = Union["Node", "Leaf"]
 Context = Tuple[Text, Tuple[int, int]]
@@ -109,6 +109,9 @@ class Base(object):
         """
         raise NotImplementedError
 
+    def __deepcopy__(self: _P, memo: Any) -> _P:
+        return self.clone()
+
     def clone(self: _P) -> _P:
         """
         Return a cloned (deep) copy of self.
diff --git a/tests/data/pattern_matching_extras.py b/tests/data/pattern_matching_extras.py
index b17922d..614e66a 100644
--- a/tests/data/pattern_matching_extras.py
+++ b/tests/data/pattern_matching_extras.py
@@ -1,3 +1,5 @@
+import match
+
 match something:
     case [a as b]:
         print(b)
@@ -7,3 +9,21 @@ match something:
         print(b)
     case Point(int() as x, int() as y):
         print(x, y)
+
+
+match = 1
+case: int = re.match(something)
+
+match re.match(case):
+    case type("match", match):
+        pass
+    case match:
+        pass
+
+
+def func(match: case, case: match) -> case:
+    match Something():
+        case another:
+            ...
+        case func(match, case):
+            ...
-- 
2.39.2