Remove flake8 W503 from docs as it is ignored by default (#1661)

Fixes #1660

.flake8

@@ -1,7 +1,7 @@
 [flake8]
-ignore = E203, E266, E501, W503
+extend-ignore = E203, E266, E501
 # line length is intentionally set to 80 here because black uses Bugbear
-# See https://github.com/psf/black/blob/master/README.md#line-length for more details
+# See https://github.com/psf/black/blob/master/docs/the_black_code_style.md#line-length for more details
 max-line-length = 80
 max-complexity = 18
 select = B,C,E,F,W,T4,B9

docs/compatible_configs.md

@@ -32,7 +32,7 @@ line_length = 88
 _Black_ wraps imports that surpass `line-length` by moving identifiers into their own
 indented line. If that still doesn't fit the bill, it will put all of them in separate
 lines and put a trailing comma. A more detailed explanation of this behaviour can be
-[found here](https://github.com/psf/black#how-black-wraps-lines).
+[found here](https://github.com/psf/black/blob/master/docs/the_black_code_style.md#how-black-wraps-lines).
 
 isort's default mode of wrapping imports that extend past the `line_length` limit is
 "Grid".
@@ -146,21 +146,15 @@ There are a few deviations that cause incompatibilities with _Black_.
 
 ```
 max-line-length = 88
-extend-ignore = E203, W503
+extend-ignore = E203
 ```
 
 ### Why those options above?
 
-When breaking a line, _Black_ will break it before a binary operator. This is compliant
-with PEP 8, but this behaviour will cause flake8 to raise
-`W503 line break before binary operator` warnings.
-
 In some cases, as determined by PEP 8, _Black_ will enforce an equal amount of
 whitespace around slice operators. Due to this, Flake8 will raise
-`E203 whitespace before ':'` warnings.
-
-Since both of these warnings are not PEP 8 compliant, Flake8 should be configured to
-ignore these warnings via `extend-ignore = E203, W503`.
+`E203 whitespace before ':'` warnings. Since this warning is not PEP 8 compliant, Flake8
+should be configured to ignore it via `extend-ignore = E203`.
 
 Also, as like with isort, flake8 should be configured to allow lines up to the length
 limit of `88`, _Black_'s default. This explains `max-line-length = 88`.
@@ -173,7 +167,7 @@ limit of `88`, _Black_'s default. This explains `max-line-length = 88`.
 ```ini
 [flake8]
 max-line-length = 88
-extend-ignore = E203, W503
+extend-ignore = E203
 ```
 
 </details>
@@ -184,7 +178,7 @@ extend-ignore = E203, W503
 ```cfg
 [flake8]
 max-line-length = 88
-extend-ignore = E203, W503
+extend-ignore = E203
 ```
 
 </details>
@@ -195,7 +189,7 @@ extend-ignore = E203, W503
 ```ini
 [flake8]
 max-line-length = 88
-extend-ignore = E203, W503
+extend-ignore = E203
 ```
 
 </details>

docs/the_black_code_style.md

@@ -199,12 +199,12 @@ You'd do it like this:
 max-line-length = 80
 ...
 select = C,E,F,W,B,B950
-ignore = E203, E501, W503
+extend-ignore = E203, E501
 ```
 
 You'll find _Black_'s own .flake8 config file is configured like this. Explanation of
-why W503 and E203 are disabled can be found further in this documentation. And if you're
-curious about the reasoning behind B950,
+why E203 is disabled can be found further in this documentation. And if you're curious
+about the reasoning behind B950,
 [Bugbear's documentation](https://github.com/PyCQA/flake8-bugbear#opinionated-warnings)
 explains it. The tl;dr is "it's like highway speed limits, we won't bother you if you
 overdo it by a few km/h".
@@ -309,10 +309,6 @@ multiple lines. This is so that _Black_ is compliant with the recent changes in
 [PEP 8](https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator)
 style guide, which emphasizes that this approach improves readability.
 
-This behaviour may raise `W503 line break before binary operator` warnings in style
-guide enforcement tools like Flake8. Since `W503` is not PEP 8 compliant, you should
-tell Flake8 to ignore these warnings.
-
 ### Slices
 
 PEP 8