Building a Better Codebase with Lint - Kotlin Mumbai

Lint is a powerful static analysis tool that can be used to enforce coding styles and also find common bugs across a codebase. Google provides a bunch of lint checks by default for Android. On popular demand, the Lint API was extended to support non-Android Kotlin projects too.

In this talk, Subhrajyoti discusses some examples of custom lint checks we use on the Tickertape app to enforce out design guidelines. He will go through the source code of some Android lint checks and then show how to write a custom lint rule. This talk also demonstrates how to write test cases for the rules. By the end of the talk, you will be able to understand how lint works and how you can add custom lint rules to your projects.

Transcript

1. Building a Better Codebase with Lint Subhrajyoti Sen @iamsubhrajyoti
2. What is Lint?
3. What is Lint? • Static analysis tool
4. What is Lint? • Static analysis tool • Open Source
5. What is Lint? • Static analysis tool • Open Source • Works on .java, .kt, .gradle and a lot more
6. What is Lint? • Static analysis tool • Open Source • Works on .java, .kt, .gradle and a lot more • Can be used outside Android as well
7. What is Lint? • Static analysis tool • Open Source • Works on .java, .kt, .gradle and a lot more • Can be used outside Android as well • Can be extended to write custom rules
8. What is Lint? • Static analysis tool • Open Source • Works on .java, .kt, .gradle and a lot more • Can be used outside Android as well • Can be extended to write custom rules • Can be run from both Android Studio and CLI
9. What does it look like?
10. Internationalization
11. Security
12. Performance
13. Accessibility
14. Why Consider Lint
15. Why Consider Lint • Opinionated codebase
16. Why Consider Lint • Opinionated codebase • Simpler code reviews
17. Why Consider Lint • Opinionated codebase • Simpler code reviews • Adherence to style guide
18. Setup
19. Setup dependencies { compileOnly "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" compileOnly 'com.android.tools.lint:lint-api:26.6.3' compileOnly 'com.android.tools.lint:lint-checks:26.6.3' }
20. Setup class Registry : IssueRegistry() { override val api: Int = CURRENT_API @get:NotNull override val issues: List<Issue> get() = listOf() }
21. Setup jar { manifest { attributes 'Lint-Registry-V2': 'me.subhrajyoti.lint.Registry' } }
22. Setup dependencies { lintChecks project(':lint') }
23. The Basic Elements Scope The kind of files the lint rule will apply to • JAVA_FILE_SCOPE (also applied to Kotlin) • GRADLE_SCOPE • MANIFEST_SCOPE • PROGUARD_SCOPE • RESOURCE_FILE_SCOPE
24. The Basic Elements Severity How severe is the issue • INFORMATIONAL • WARNING • ERROR • FATAL
25. The Basic Elements Category The category the issue falls in, from a pre-defined list of categories • SECURITY • PERFORMANCE • I18N • A11Y
26. A Use case - TextView
27. A Custom Rule Structure val ISSUE: Issue = Issue.create( "MissingStyleAttribute", "style attribute is missing", "We should use style to style a TextView " + "in order to provide consistent design", Category.CORRECTNESS, 5, Severity.ERROR, Implementation( MissingStyleAttributeDetector::class.java, Scope.RESOURCE_FILE_SCOPE ) )
28. A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { }
29. A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { @Nullable override fun getApplicableElements(): Collection<String>? { return listOf(“TextView”) } }
30. A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { @Nullable override fun getApplicableElements(): Collection<String>? { return listOf(SdkConstants.TEXT_VIEW) } }
31. A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { override fun appliesTo(folderType: ResourceFolderType): Boolean { return folderType == ResourceFolderType.LAYOUT } }
32. class MissingStyleAttributeDetector : ResourceXmlDetector() { override fun visitElement(context: XmlContext, element: Element) { if (!element.hasAttribute(SdkConstants.ATTR_STYLE)) { context.report( ISSUE, element, context.getLocation(element), "Add style to TextView" ) } } }
33. A Custom Rule Structure class Registry : IssueRegistry() { @get:NotNull override val issues: List<Issue> get() = listOf(MissingStyleAttributeDetector.ISSUE) }
34. Remember! class MissingStyleAttributeDetector : ResourceXmlDetector() { @Nullable override fun getApplicableElements(): Collection<String>? { return listOf(SdkConstants.TEXT_VIEW) } }
35. A small Bug
36. A Use case - Snackbar
37. A Custom Rule Structure val ISSUE = Issue.create( "CustomSnackbarIssue", DESCRIPTION, EXPLANATION, Category.CORRECTNESS, 5, Severity.ERROR, Implementation( MaterialSnackbarUsageDetector::class.java, Scope.JAVA_FILE_SCOPE ) )
38. A Custom Rule Structure class MaterialSnackbarUsageDetector : Detector(), SourceCodeScanner { }
39. A Custom Rule Structure class MaterialSnackbarUsageDetector : Detector(), SourceCodeScanner { override fun getApplicableMethodNames() = listOf("make") }
40. A Custom Rule Structure class MaterialSnackbarUsageDetector : Detector(), SourceCodeScanner { override fun visitMethodCall(context: JavaContext, node: UCallExpression, method: PsiMethod) { if (context.evaluator.isMemberInClass( method, "com.google.android.material.snackbar.Snackbar" )) { // report usage } } }
41. Testing a rule
42. Testing a rule • JUnit tests
43. Testing a rule • JUnit tests • lint-tests library
44. Testing a rule • JUnit tests • lint-tests library • IDE syntax checker and code highlight
45. IDE syntax check
46. lint-test dependency dependencies { compileOnly 'com.android.tools.lint:lint-api:26.6.3' compileOnly 'com.android.tools.lint:lint-checks:26.6.3' testImplementation "com.android.tools.lint:lint-tests:26.6.3" }
47. A successful case
48. @Test fun `check no lint error`() { lint() }
49. @Test fun `check no lint error`() { lint() .files() }
50. @Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/textSpacerNoButtons" style="@style/TextAppearance.AppCompat" xmlns:android="http://schemas.android.com/apk/res/android" /> """ ) ) }
51. @Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/textSpacerNoButtons" style="@style/TextAppearance.AppCompat" xmlns:android="http://schemas.android.com/apk/res/android" /> """ ) ) .run() }
52. @Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/textSpacerNoButtons" style="@style/TextAppearance.AppCompat" xmlns:android="http://schemas.android.com/apk/res/android" /> """ ) ) .run() .expectClean() }
53. @Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/textSpacerNoButtons" style="@style/TextAppearance.AppCompat" xmlns:android="http://schemas.android.com/apk/res/android" /> """ ) ) .run() .expectClean() }
54. An error case
55. @Test fun `check exactly 1 lint error`() { lint() .files( xml( "res/layout/layout.xml", """ <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/textSpacerNoButtons" xmlns:android="http://schemas.android.com/apk/res/android" /> """ ) ) .run() }
56. @Test fun `check exactly 1 lint error`() { lint() .files( xml( "res/layout/layout.xml", """ <TextView android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/textSpacerNoButtons" xmlns:android="http://schemas.android.com/apk/res/android" /> """ ) ) .run() .expectErrorCount(1) }
57. @Test fun `check exactly 1 lint error`() { lint() // .run() .expectErrorCount(1) .expect( """ res/layout/layout.xml:2: Error: Add style to TextView in order to provide consistent design [MissingStyleAttribute] <TextView android:layout_width="match_parent" ^ 1 errors, 0 warnings """ ) }
58. Integration
59. Integration • Incremental fixes
60. Integration • Incremental fixes • Use a baseline
61. Baseline android { lintOptions { baseline file("lint-baseline.xml") } }
62. Baseline
63. Baseline
64. Baseline
65. Performance
66. Performance • Single-pass: ◦ Missing attribute ◦ Fast ◦ Enable in IDE
67. Performance • Single-pass: ◦ Missing attribute ◦ Fast ◦ Enable in IDE • Multiple-pass : ◦ Unused resources ◦ Slow ◦ Disable in IDE
68. Kotlin Considerations • No explicit return statements
69. Kotlin Considerations • No explicit return statements • No explicit type declarations
70. Kotlin Considerations • No explicit return statements • No explicit type declarations • Write one test case for Kotlin
71. References • https://groups.google.com/g/lint-dev • https://github.com/SubhrajyotiSen/LintTalk/ • https://www.youtube.com/watch?v=p8yX5-lPS6o
72. Thank You @iamsubhrajyoti