Add fast option to Black

[khatchad]

Black takes arguments. How do we pipe these in? For example, I'd like to send Black the --fast command-line arguments.

https://github.com/diffplug/spotless/blob/224f8f96df3ad42cac81064a0461e6d4ee91dcaf/plugin-maven/src/main/java/com/diffplug/spotless/maven/python/Black.java#L25-L31

We can add a property to run it fast:

--fast / --safe            By default, Black performs an AST safety
                                  check after formatting your code. The --fast
                                  flag turns off this check and the --safe
                                  flag explicitly enables it. [default:
                                  --safe]

[khatchad]

I'm also seeing that args is a private field that is never assigned outside this class:

https://github.com/diffplug/spotless/blob/1ad019da39f8994d5b7ccd86a536678cb38fbdea/lib/src/main/java/com/diffplug/spotless/python/BlackStep.java#L89-L107

[khatchad]

Here's an example of one that takes a command-line argument:

• https://github.com/diffplug/spotless/blob/1ad019da39f8994d5b7ccd86a536678cb38fbdea/lib/src/main/java/com/diffplug/spotless/cpp/ClangFormatStep.java#L44-L46
• https://github.com/diffplug/spotless/blob/1ad019da39f8994d5b7ccd86a536678cb38fbdea/lib/src/main/java/com/diffplug/spotless/cpp/ClangFormatStep.java#L126-L129

[khatchad]

Actually, running black from the command-line was very fast even without the flag.

[khatchad]

When I run mvn spotless:apply on the same code, it's extremely slow.

[khatchad]

OK, I fixed the problem by altering my include/exclude tags. Now it's fast without any modifications to spotless:

diff --git a/pom.xml b/pom.xml
index 3eee11b8..df773850 100644
--- a/pom.xml
+++ b/pom.xml
@@ -201,13 +201,8 @@
             </pom>
             <python>
               <includes>
-                <include>**/*.py</include>
+                <include>.</include>
               </includes>
-              <excludes>
-                <!-- Don't format generated files. -->
-                <exclude>**/bin/</exclude>
-                <exclude>**/target/</exclude>
-              </excludes>
               <black>
                 <version>${black.version}</version>
               </black>

I just told black to process all files and walla. I think it would still be helpful, however, to have a property for --fast.