Merge "Update lint README to document global linter"

# Android Framework Lint Checker

# Android Lint Checks for AOSP

Custom lint checks written here are going to be executed for modules that opt in to those (e.g. any

Custom Android Lint checks are written here to be executed against java modules

in AOSP. These checks are broken down into two subdirectories:

1. [Global Checks](#android-global-lint-checker)

2. [Framework Checks](#android-framework-lint-checker)

# [Android Global Lint Checker](/global)

Checks written here are executed for the entire tree. The `AndroidGlobalLintChecker`

build target produces a jar file that is included in the overall build output

(`AndroidGlobalLintChecker.jar`).  This file is then downloaded as a prebuilt under the

`prebuilts/cmdline-tools` subproject, and included by soong with all invocations of lint.

## How to add new global lint checks

1. Write your detector with its issues and put it into

   `global/checks/src/main/java/com/google/android/lint`.

2. Add your detector's issues into `AndroidGlobalIssueRegistry`'s `issues`

   field.

3. Write unit tests for your detector in one file and put it into

   `global/checks/test/java/com/google/android/lint`.

4. Have your change reviewed and merged.  Once your change is merged,

   obtain a build number from a successful build that includes your change.

5. Run `prebuilts/cmdline-tools/update-android-global-lint-checker.sh

   <build_number>`. The script will create a commit that you can upload for

   approval to the `prebuilts/cmdline-tools` subproject.

6. Done! Your lint check should be applied in lint report builds across the

   entire tree!

# [Android Framework Lint Checker](/framework)

Checks written here are going to be executed for modules that opt in to those (e.g. any

`services.XXX` module) and results will be automatically reported on CLs on gerrit.

## How to add new lint checks

## How to add new framework lint checks

1. Write your detector with its issues and put it into

   `checks/src/main/java/com/google/android/lint`.

   `framework/checks/src/main/java/com/google/android/lint`.

2. Add your detector's issues into `AndroidFrameworkIssueRegistry`'s `issues` field.

3. Write unit tests for your detector in one file and put it into

   `checks/test/java/com/google/android/lint`.

   `framework/checks/test/java/com/google/android/lint`.

4. Done! Your lint checks should be applied in lint report builds for modules that include

   `AndroidFrameworkLintChecker`.

  environment variable with the id of the lint. For example:

  `ANDROID_LINT_CHECK=UnusedTokenOfOriginalCallingIdentity m out/[...]/lint-report.html`

## How to apply automatic fixes suggested by lint

# How to apply automatic fixes suggested by lint

See [lint_fix](fix/README.md)

## Create or update a baseline

# Create or update a baseline

Baseline files can be used to silence known errors (and warnings) that are deemed to be safe. When

there is a lint-baseline.xml file in the root folder of the java library, soong will

[lint.go](http://cs/aosp-master/build/soong/java/lint.go;l=451;rcl=2e778d5bc4a8d1d77b4f4a3029a4a254ad57db75)

adding `cmd.Flag("--nowarn")` and running lint again.

## Documentation

# Documentation

- [Android Lint Docs](https://googlesamples.github.io/android-custom-lint-rules/)

- [Lint Check Unit Testing](https://googlesamples.github.io/android-custom-lint-rules/api-guide/unit-testing.md.html)