lint/docs/internal/guidelines.md.html

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**Lint Development Guidelines**

(This folder should also contain architectural information documents.)

# Setup

To develop lint, use a recent IntelliJ, check out the Android tools
repository and then open up the folder `tools/` as a Gradle project.

# Code

* All new files should be written in Kotlin.

* Code should be formatted using “cd lint && gradle formatLint”, which
  will format both the Java and Kotlin files according to the
  configured style.

* All lint checks must have tests checking both for false positives and
  false negatives.

* Make sure that lint checks have the correct platform applied (e.g.
  androidSpecific=true in the issue registration for any Android
  checks.)

# Debugging lint under Gradle

To be able to attach to and debug lint when invoked from within the
Android Gradle plugin, add this to the `gradle.properties` file in the
target project before invoking gradle with the debug flags:

```
android.experimental.runLintInProcess=true
```

# Debugging lint in the IDE

When debugging lint running in the IDE, machinery the IDE has
to avoid UI freezes involves throwing exceptions if read operations
are taking too long -- and then the editor restarting highlighting
at a later time. This makes debugging tricky. There are probably
better ways to do this (I remember an IntelliJ registry key to set
that I can't find now), but what I do is open `LintIdeClient` and
in the `runReadAction` method, I change

```
if (application.isUnitTestMode()) {
```

to

```
if (true || application.isUnitTestMode()) {
```

# Updating Baselines

If you've added a new lint check which has a number of existing
violations in the Studio tree, you can run the following target
to update the baselines:

```
bazel run --test_env=UPDATE_LINT_BASELINE=1  \
  $(bazel query --output=label 'kind(.*lint_test, //tools/...)')
```

# Registering Inspections

When lint runs in the IDE, all lint checks are wrapped as IntelliJ
inspections, such that they show up in the Inspections options list
etc. Lazily discovered lint checks (3rd party lint checks) will show up
as soon as lint has run to discover them, but for built-in checks we
should register them in advance such that they always show up. To do
this, open the `tools/adt/idea` project and run the
`LintInspectionRegistrationTest` test. To have your sources updated in
place, either set `$ADT_SOURCE_TREE` or edit the test first to point
the `sourceTree` var to point to your checkout.

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