Add docs for setting up Android Studio to auto format Kotlin code (flutter#159209)

Docs to make Android Studio auto format kotlin code in a way compatible
with the format check that we make in CI.

Open to suggestions as to a better place to put them, but there wasn't
an existing doc that seemed like an obvious fit to me.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [ ] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [ ] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

---------

Co-authored-by: Gray Mackall <[email protected]>
Co-authored-by: Reid Baker <[email protected]>

Author: 3 people

dev/bots/analyze.dart

@@ -2126,7 +2126,8 @@ Future<void> lintKotlinFiles(String workingDirectory) async {
         'To reproduce this lint locally:\n'
         '1. Identify the CIPD version tag used to resolve this particular version of ktlint (check the dependencies section of this shard in the ci.yaml). \n'
         '2. Download that version from https://chrome-infra-packages.appspot.com/p/flutter/ktlint/linux-amd64/+/<version_tag>\n'
-        '3. From the repository root, run `<path_to_ktlint>/ktlint --editorconfig=$editorConfigRelativePath --baseline=$baselineRelativePath`';
+        '3. From the repository root, run `<path_to_ktlint>/ktlint --editorconfig=$editorConfigRelativePath --baseline=$baselineRelativePath`\n'
+        'Alternatively, if you use Android Studio, follow the docs at docs/platforms/android/Kotlin-android-studio-formatting.md to enable auto formatting.';
     foundError(<String>[errorMessage]);
   }
 }

docs/platforms/android/Kotlin-android-studio-formatting.md

@@ -0,0 +1,27 @@
+# Setting up Kotlin formatting in Android Studio
+
+Kotlin code in this repository is formatted and linted with [`ktlint`](https://github.com/pinterest/ktlint).
+If you
+1. have submitted Kotlin code only to learn this when the analyzer check fails
+2. use Android Studio
+
+
+then there is good news! Android Studio can be configured to use `ktlint` to automatically apply formatting and highlight issues. To do this:
+
+
+1. Install the `ktlint` extension for Android Studio
+
+   a. On Mac, this is `Android Studio > Settings > Plugins > ` Search for `ktlint`.
+
+2. Set the ruleset to be the same as the version used in [`.ci.yaml`](../../../.ci.yaml) (as of writing this is 1.1.1), and the baseline to be `dev/bots/test/analyze-test-input/ktlint-baseline.xml`.
+
+   a. Both of these options should be available under `Android Studio > Settings > Tools > ktlint`.
+
+3. Additionally, Kotlin code in the Flutter repository currently uses some additional rules for compatibility with older versions of Kotlin.
+These rules can only be configured by an `.editorconfig` file in the directory from which Android Studio was opened. To configure these rules, create a new `.editorconfig` file in the root of your flutter repository with the following content
+```
+[*.{kt,kts}]
+# Disable trailing commas to allow compatibility with Kotlin versions less than 1.4.
+ij_kotlin_allow_trailing_comma = false
+ij_kotlin_allow_trailing_comma_on_call_site = false
+```