Use debug f-strings for feature detection (#3215)

[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 aca9fe040171d15ad314834d7cf4321af321e363..fab4bca120e634f26ec79ef4de9412c2de6196fa 100644 (file)
--- a/docs/the_black_code_style/future_style.md
+++ b/docs/the_black_code_style/future_style.md
@@ -33,3 +33,88 @@ with \
 
 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.
+
+## Preview style
+
+Experimental, potentially disruptive style changes are gathered under the `--preview`
+CLI flag. At the end of each year, these changes may be adopted into the default style,
+as described in [The Black Code Style](./index.rst). Because the functionality is
+experimental, feedback and issue reports are highly encouraged!
+
+### Improved string processing
+
+_Black_ will split long string literals and merge short ones. Parentheses are used where
+appropriate. When split, parts of f-strings that don't need formatting are converted to
+plain strings. User-made splits are respected when they do not exceed the line length
+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 newlines in the beginning of code blocks
+
+_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`.
+
+### Improved parentheses management
+
+_Black_ will format parentheses around return annotations similarly to other sets of
+parentheses. For example:
+
+```python
+def foo() -> (int):
+    ...
+
+def foo() -> looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong:
+    ...
+```
+
+will be changed to:
+
+```python
+def foo() -> int:
+    ...
+
+
+def foo() -> (
+    looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong
+):
+    ...
+```
+
+And, extra parentheses in `await` expressions and `with` statements are removed. For
+example:
+
+```python
+with ((open("bla.txt")) as f, open("x")):
+    ...
+
+async def main():
+    await (asyncio.sleep(1))
+```
+
+will be changed to:
+
+```python
+with open("bla.txt") as f, open("x"):
+    ...
+
+
+async def main():
+    await asyncio.sleep(1)
+```