Documentation: clarify the state of multiple context managers (#3488)

[etc/vim.git] / docs / the_black_code_style / future_style.md

diff --git a/docs/the_black_code_style/future_style.md b/docs/the_black_code_style/future_style.md
index 8d159e9b0a21cf0890934b56f48e8f1931901ca6..9ca260fc0add91c82ed4b1640a6114f890a851f6 100644 (file)
--- a/docs/the_black_code_style/future_style.md
+++ b/docs/the_black_code_style/future_style.md
@@ -19,20 +19,33 @@ with make_context_manager1() as cm1, make_context_manager2() as cm2, make_contex
     ...  # nothing to split on - line too long
 ```
 
-So _Black_ will eventually format it like this:
+So _Black_ will, when we implement this, format it like this:
 
 ```py3
 with \
-     make_context_manager(1) as cm1, \
-     make_context_manager(2) as cm2, \
-     make_context_manager(3) as cm3, \
-     make_context_manager(4) as cm4 \
+     make_context_manager1() as cm1, \
+     make_context_manager2() as cm2, \
+     make_context_manager3() as cm3, \
+     make_context_manager4() as cm4 \
 :
     ...  # backslashes and an ugly stranded colon
 ```
 
-Although when the target version is Python 3.9 or higher, _Black_ will use parentheses
-instead since they're allowed in Python 3.9 and higher.
+Although when the target version is Python 3.9 or higher, _Black_ will, when we
+implement this, use parentheses instead since they're allowed in Python 3.9 and higher.
+
+An alternative to consider if the backslashes in the above formatting are undesirable is
+to use {external:py:obj}`contextlib.ExitStack` to combine context managers in the
+following way:
+
+```python
+with contextlib.ExitStack() as exit_stack:
+    cm1 = exit_stack.enter_context(make_context_manager1())
+    cm2 = exit_stack.enter_context(make_context_manager2())
+    cm3 = exit_stack.enter_context(make_context_manager3())
+    cm4 = exit_stack.enter_context(make_context_manager4())
+    ...
+```
 
 ## Preview style
 
@@ -50,27 +63,92 @@ limit. Line continuation backslashes are converted into parenthesized strings.
 Unnecessary parentheses are stripped. The stability and status of this feature is
 tracked in [this issue](https://github.com/psf/black/issues/2188).
 
-### Removing trailing newlines after code block open
+### Improved empty line management
+
+1.  _Black_ will remove newlines in the beginning of new code blocks, i.e. when the
+    indentation level is increased. For example:
+
+    ```python
+    def my_func():
+
+        print("The line above me will be deleted!")
+    ```
+
+    will be changed to:
+
+    ```python
+    def my_func():
+        print("The line above me will be deleted!")
+    ```
+
+    This new feature will be applied to **all code blocks**: `def`, `class`, `if`,
+    `for`, `while`, `with`, `case` and `match`.
+
+2.  _Black_ will enforce empty lines before classes and functions with leading comments.
+    For example:
+
+    ```python
+    some_var = 1
+    # Leading sticky comment
+    def my_func():
+        ...
+    ```
+
+    will be changed to:
+
+    ```python
+    some_var = 1
 
-_Black_ will remove trailing newlines after code block openings. That means that the
-following code:
+
+    # Leading sticky comment
+    def my_func():
+        ...
+    ```
+
+### Improved parentheses management
+
+_Black_ will format parentheses around return annotations similarly to other sets of
+parentheses. For example:
 
 ```python
-def my_func():
+def foo() -> (int):
+    ...
 
-    print("The line above me will be deleted!")
+def foo() -> looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong:
+    ...
+```
+
+will be changed to:
+
+```python
+def foo() -> int:
+    ...
 
-    print("But the line above me won't!")
+
+def foo() -> (
+    looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong
+):
+    ...
 ```
 
-Will be changed to:
+And, extra parentheses in `await` expressions and `with` statements are removed. For
+example:
 
 ```python
-def my_func():
-    print("The line above me will be deleted!")
+with ((open("bla.txt")) as f, open("x")):
+    ...
 
-    print("But the line above me won't!")
+async def main():
+    await (asyncio.sleep(1))
 ```
 
-This new feature will be applied to **all code blocks**: `def`, `class`, `if`, `for`,
-`while`, `with`, `case` and `match`.
+will be changed to:
+
+```python
+with open("bla.txt") as f, open("x"):
+    ...
+
+
+async def main():
+    await asyncio.sleep(1)
+```