Building a Better Codebase with Lint - Kotlin Mumbai

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Building a Better Codebase with Lint Subhrajyoti Sen @iamsubhrajyoti

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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 it 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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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' }

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

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Setup jar { manifest { attributes 'Lint-Registry-V2': 'me.subhrajyoti.lint.Registry' } }

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Setup dependencies { lintChecks project(':lint') }

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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

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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 ● I18N ● A11Y

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A Use case - TextView

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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 ) )

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A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { }

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A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { @Nullable override fun getApplicableElements(): Collection? { return listOf(“TextView”) } }

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A Custom Rule Structure class MissingStyleAttributeDetector : ResourceXmlDetector() { @Nullable override fun getApplicableElements(): Collection? { return listOf(SdkConstants.TEXT_VIEW) } }

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

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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" ) } } }

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A Custom Rule Structure class Registry : IssueRegistry() { @get:NotNull override val issues: List get() = listOf(MissingStyleAttributeDetector.ISSUE) }

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Remember! class MissingStyleAttributeDetector : ResourceXmlDetector() { @Nullable override fun getApplicableElements(): Collection? { return listOf(SdkConstants.TEXT_VIEW) } }

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A small Bug

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A Use case - Snackbar

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A Custom Rule Structure val ISSUE = Issue.create( "CustomSnackbarIssue", DESCRIPTION, EXPLANATION, Category.CORRECTNESS, 5, Severity.ERROR, Implementation( MaterialSnackbarUsageDetector::class.java, Scope.JAVA_FILE_SCOPE ) )

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A Custom Rule Structure class MaterialSnackbarUsageDetector : Detector(), SourceCodeScanner { }

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A Custom Rule Structure class MaterialSnackbarUsageDetector : Detector(), SourceCodeScanner { override fun getApplicableMethodNames() = listOf("make") }

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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 } } }

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Testing a rule

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Testing a rule ● JUnit tests

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Testing a rule ● JUnit tests ● lint-tests library

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Testing a rule ● JUnit tests ● lint-tests library ● IDE syntax checker and code highlight

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IDE syntax check

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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" }

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A successful case

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@Test fun `check no lint error`() { lint() }

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@Test fun `check no lint error`() { lint() .files() }

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@Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ """ ) ) }

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@Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ """ ) ) .run() }

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@Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ """ ) ) .run() .expectClean() }

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@Test fun `check no lint error`() { lint() .files( xml( "res/layout/layout.xml", """ """ ) ) .run() .expectClean() }

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An error case

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

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

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@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]

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Integration

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Integration ● Incremental fixes

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Integration ● Incremental fixes ● Use a baseline

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

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Baseline

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Baseline

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Baseline

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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 ● 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

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References ● https://groups.google.com/g/lint-dev ● https://github.com/SubhrajyotiSen/LintTalk/ ● https://www.youtube.com/watch?v=p8yX5-lPS6o

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Thank You @iamsubhrajyoti