Android Lint Checks for AOSP

Custom Android Lint checks are written here to be executed against java modules in AOSP. These checks are broken down into two subdirectories:

Global Checks
Framework Checks

Android Global Lint Checker

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

Write your detector with its issues and put it into global/checks/src/main/java/com/google/android/lint.
Add your detector's issues into AndroidGlobalIssueRegistry's issues field.
Write unit tests for your detector in one file and put it into global/checks/test/java/com/google/android/lint.
Have your change reviewed and merged. Once your change is merged, obtain a build number from a successful build that includes your change.
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.
Done! Your lint check should be applied in lint report builds across the entire tree!

Android Framework Lint Checker

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 framework lint checks

Write your detector with its issues and put it into framework/checks/src/main/java/com/google/android/lint.
Add your detector's issues into AndroidFrameworkIssueRegistry's issues field.
Write unit tests for your detector in one file and put it into framework/checks/test/java/com/google/android/lint.
Done! Your lint checks should be applied in lint report builds for modules that include AndroidFrameworkLintChecker.

How to run lint against your module

Add the following lint attribute to the module definition, e.g. services.autofill:

java_library_static {
    name: "services.autofill",
    ...
    lint: {
        extra_check_modules: ["AndroidFrameworkLintChecker"],
    },
}

Run the following command to verify that the report is being correctly built:

m out/soong/.intermediates/frameworks/base/services/autofill/services.autofill/android_common/lint/lint-report.html

(Lint report can be found in the same path, i.e. out/../lint-report.html)

Now lint issues should appear on gerrit!

Notes:

Lint report will not be produced if you just build the module, i.e. m services.autofill will not build the lint report.
If you want to build lint reports for more than 1 module and they include a common module in their defaults field, e.g. platform_service_defaults, you can add the lint property to that common module instead of adding it in every module.
If you want to run a single lint type, use the ANDROID_LINT_CHECK 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

See lint_fix

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 automatically use it. You can override the file using lint properties too.

java_library {
    lint: {
        baseline_filename: "my-baseline.xml", // default: lint-baseline.xml;
    }
}

When using soong to create a lint report (as described above), it also creates a reference baseline file. This contains all lint errors and warnings that were found. So the next time you run lint, if you use this baseline file, there should be 0 findings.

After the previous invocation, you can find the baseline here:

out/soong/.intermediates/frameworks/base/services/autofill/services.autofill/android_common/lint/lint-baseline.xml

As noted above, this baseline file contains warnings too, which might be undesirable. For example, CI tools might surface these warnings in code reviews. In order to create this file without warnings, we need to pass another flag to lint: --nowarn. One option is to add the flag to your Android.bp file and then run lint again:

  lint: {
    extra_check_modules: ["AndroidFrameworkLintChecker"],
    flags: ["--nowarn"],
  }