Building a Better Codebase with Lint - Droidcon APAC

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KeepTruckin Subhrajyoti Sen Droidcon APAC 2020 Building a Better Codebase with Lint

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What is Lint? < / >

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What is Lint? • Static analysis tool

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What is Lint? • Static analysis tool • Open Source

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What is Lint? • Static analysis tool • Open Source • Works on .java, .kt, .gradle and a lot more

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What is Lint? • Static analysis tool • Open Source • Works on .java, .kt, .gradle and a lot more • Can be used outside Android as well

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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

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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

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What does Lint look like? < / >

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Internationalization

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Security

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Performance

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Accessibility

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Why consider Lint? < / >

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Why consider Lint? • Opinionated codebase

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Why consider Lint? • Opinionated codebase • Simpler code reviews

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Why consider Lint? • Opinionated codebase • Simpler code reviews • Adherence to style guide

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Setup < / >

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Create a new module

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Dependencies dependencies { compileOnly "org.jetbrains.kotlin:kotlin stdlib:$kotlin_version" compileOnly 'com.android.tools.lint:lint api:27.1.1' compileOnly 'com.android.tools.lint:lint checks:27.1.1' testImplementation "com.android.tools.lint:lint tests:27.1.1" } lint/build.gradle

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Issue Registry class Registry : IssueRegistry() { override val api: Int = CURRENT_API @get:NotNull override val issues: List get() = listOf() }

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Register Issue Registry jar { manifest { attributes 'Lint-Registry-V2': 'me.subhrajyoti.lint.Registry' } } lint/build.gradle

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Add dependency on lint module dependencies { lintChecks project(':lint') } app/build.gradle

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The Basic Elements Scope The kind of files the lint rule applies to • JAVA_FILE_SCOPE • GRADLE_SCOPE • MANIFEST_SCOPE • PROGUARD_SCOPE • RESOURCE_FILE_SCOPE

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The Basic Elements Severity How severe is the issue • INFORMATIONAL • WARNING • ERROR • FATAL

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The Basic Elements Category The category the issue falls in, from a pre-defined list of categories • SECURITY • PERFORMANCE • L10N • A11Y

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Use case - Style Migration V1.TextView.Header1 V2.TextView.Header1 →

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Custom Rule Structure val ISSUE: Issue = Issue.create( "V1StyleUsageDetector", "Replace V1 styles with V2", "V1 styles have been deprecated and " + "you should use V2 styles for all TextView going forward", Category.CORRECTNESS, 5, Severity.ERROR, Implementation( V1StyleUsageDetector::class.java, Scope.RESOURCE_FILE_SCOPE ) )

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Custom Rule Structure class V1StyleUsageDetector : ResourceXmlDetector() { }

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Custom Rule Structure class V1StyleUsageDetector : ResourceXmlDetector() { override fun getApplicableElements(): Collection { return listOf("TextView") } }

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Custom Rule Structure class V1StyleUsageDetector : ResourceXmlDetector() { override fun getApplicableElements(): Collection { return listOf(SdkConstants.TEXT_VIEW) } }

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Custom Rule Structure class V1StyleUsageDetector : ResourceXmlDetector() { //.. override fun appliesTo(folderType: ResourceFolderType): Boolean { return folderType == ResourceFolderType.LAYOUT } }

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Custom Rule Structure class V1StyleUsageDetector : ResourceXmlDetector() { //.. override fun visitElement(context: XmlContext, element: Element) { if (element.hasAttribute(SdkConstants.ATTR_STYLE)) { val attributeValue = element.getAttribute(SdkConstants.ATTR_STYLE) if (attributeValue.startsWith("@style/V1")) { context.report( ISSUE, element, context.getLocation(element), "Replace V1 style with V2") } } }

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Issue Registry class Registry : IssueRegistry() { override val api: Int = CURRENT_API @get:NotNull override val issues: List get() = listOf(V1StyleUsageDetector.ISSUE) }

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Lint x val newValue = element.getAttribute(SdkConstants.ATTR_STYLE).replace("V1", "V2") val compositeFix = LintFix.create() .name("Replace V1 with V2") .composite( LintFix.create() .unset(null, SdkConstants.ATTR_STYLE) .build(), LintFix.create() .set(null, SdkConstants.ATTR_STYLE, newValue) .build(), )

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Lint x context.report( ISSUE, element, context.getLocation(element), "Replace V1 style with V2", compositeFix )

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Auto x val newValue = element.getAttribute(SdkConstants.ATTR_STYLE).replace("V1", "V2") val compositeFix = LintFix.create() .name("Replace V1 with V2") .composite( LintFix.create() .unset(null, SdkConstants.ATTR_STYLE) .build(), LintFix.create() .set(null, SdkConstants.ATTR_STYLE, newValue) .build(), ) .autofix()

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Lint x ./gradlew app:lintFix

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Testing

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Testing @RunWith(JUnit4 class) class V1StyleUsageDetectorTest : LintDetectorTest() { override fun getIssues(): MutableList = mutableListOf(V1StyleUsageDetector.ISSUE) override fun getDetector(): Detector = V1StyleUsageDetector() }

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@RunWith(JUnit4 class) class V1StyleUsageDetectorTest : LintDetectorTest() { @Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """

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@Test fun `check exactly 1 lint error`() { lint() .files( xml( "res/layout/layout.xml", """

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@Test fun `check exactly 1 lint error`() { lint() .files( xml( ).indented() ) .run() .expectErrorCount(1) .expect( """ res/layout/layout.xml:1 Error: Replace V1 style with V2 [V1StyleUsageDetector]

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Integration

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Integration • Incremental fixes

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Integration • Incremental fixes • Using a baseline

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Baseline android { lintOptions { baseline file("lint baseline.xml") } }

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Baseline - Pass 1

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Baseline - Pass 2

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lint-baseline.xml

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Performance

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Performance • Single pass • Missing attribute • Fast • Enable in IDE

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Performance • Single pass • Missing attribute • Fast • Enable in IDE • Multiple pass • Unused resources • Slow • Disable in IDE

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Kotlin Considerations?

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Kotlin Considerations? • No explicit return statements

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Kotlin Considerations? • No explicit return statements • No explicit type declarations

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Kotlin Considerations? • No explicit return statements • No explicit type declarations • Write one test case for Kotlin usage

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References • https://groups.google.com/g/lint-dev • https://github.com/SubhrajyotiSen/LintTalk • https://github.com/vanniktech/lint-rules • https://www.youtube.com/watch?v=p8yX5-lPS6o • https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio- master-dev:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/

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@iamsubhrajyoti