Enforcing code conventions with Lint

Daniel Vila
LINE App Dev Team7 Software Engineer
https://linedevday.linecorp.com/2020/ja/sessions/1687
https://linedevday.linecorp.com/2020/en/sessions/1687

Transcript

2. Big teams
3. Big teams Big teams bring challenges:
4. Big teams Big teams bring challenges: › Onboarding of new members.
5. Big teams Big teams bring challenges: › Onboarding of new members. › Code consistency.
6. Big teams Big teams bring challenges: › Onboarding of new members. › Code consistency. › Code conventions.
7. Big teams Big teams bring challenges: › Onboarding of new members. › Code consistency. › Code conventions. › Internal APIs.
8. Big teams
9. Code conventions fun getInt()k= (0..10).map { it.also { "Some side effect" } }.also { "Some other side effect" }.apply { size }.let { it.last() }.takeIf { it > 10 }
10. Code conventions fun getInt(): Int?k= (0..10).map { it.also { "Some side effect" } }.also { "Some other side effect" }.apply { size }.let { it.last() }.takeIf { it > 10 }
11. What can we do? k
12. What can we do? Static analysis!
13. Why Lint?
14. Why Lint? › Compatible with Java/Kotlin (UAST).
15. Why Lint? › Compatible with Java/Kotlin (UAST). › Lint client is implemented by Android Studio.
16. Why Lint? › Compatible with Java/Kotlin (UAST). › Lint client is implemented by Android Studio. › Quick fixes in Android Studio.
17. Custom Lint checks
18. Custom Lint checks In order to create a custom Lint check we have to roughly follow these steps:
19. Custom Lint checks In order to create a custom Lint check we have to roughly follow these steps: › Create a Lint Issue.
20. Custom Lint checks In order to create a custom Lint check we have to roughly follow these steps: › Create a Lint Issue. › Register the Issue so lint can track it.
21. Custom Lint checks In order to create a custom Lint check we have to roughly follow these steps: › Create a Lint Issue. › Register the Issue so lint can track it. › Create a detector for the Issue.
22. Custom Lint checks In order to create a custom Lint check we have to roughly follow these steps: › Create a Lint Issue. › Register the Issue so lint can track it. › Create a detector for the Issue. › Report the Issue.
23. Custom Lint checks In order to create a custom Lint check we have to roughly follow these steps: › Create a Lint Issue. › Register the Issue so lint can track it. › Create a detector for the Issue. › Report the Issue. › [Optional] Provide a fix.
24. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType", “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
25. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
26. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
27. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
28. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
29. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
30. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
31. Create an issue class MyDetector : Detector(), SourceCodeScanner { companion object { @JvmField val ISSUE: Issue = Issue.create( “InferredType”, “MyDetector short description", "My detector **very** *long* `description`.", Category.CORRECTNESS, 6, Severity.WARNING, Implementation(MyDetector::class.java, Scope.JAVA_FILE_SCOPE) )k }k …k }k
32. Register the issue Now we have to add the issue to the lint issue registry: class MyIssueRegistry : IssueRegistry() {k override val issues: List<Issue> = listOf(MyDetector.ISSUE) override val api: Int = CURRENT_API override val minApi: Int = MIN_API companion object {k const val MIN_API = 2 // Corresponds to android gradle plugin 3.2+ }k }k
33. Register the issue Now we have to add the issue to the lint issue registry: @AutoService(IssueRegistry::class) class MyIssueRegistry : IssueRegistry() {k override val issues: List<Issue> = listOf(MyDetector.ISSUE) override val api: Int = CURRENT_API override val minApi: Int = MIN_API companion object {k const val MIN_API = 2 // Corresponds to android gradle plugin 3.2+ }k }k
34. Create a detector A Detector is responsible for detecting occurrences of an Issue in the source code.
35. Custom Lint checks Lint has a number of Detector specializations which makes a lot easier to write checks:
36. Custom Lint checks Lint has a number of Detector specializations which makes a lot easier to write checks: › XmlScanner: lets you visit the XML file with DOM.
37. Custom Lint checks Lint has a number of Detector specializations which makes a lot easier to write checks: › XmlScanner: lets you visit the XML file with DOM. › SourceCodeScanner: useful for Kotlin/Java analysis.
38. Custom Lint checks Lint has a number of Detector specializations which makes a lot easier to write checks: › XmlScanner: lets you visit the XML file with DOM. › SourceCodeScanner: useful for Kotlin/Java analysis. › ClassScanner, BinaryResourceScanner, ResourceFolderScanner…
39. SourceCodeScanner fun applicableSuperClasses(): List<String>? fun getApplicableMethodNames(): List<String>? fun getApplicableUastTypes(): List<Class<out UElement>>?
40. SourceCodeScanner fun applicableSuperClasses(): List<String>? fun getApplicableMethodNames(): List<String>? fun getApplicableUastTypes(): List<Class<out UElement>>?
41. SourceCodeScanner fun applicableSuperClasses(): List<String>? fun getApplicableMethodNames(): List<String>? fun getApplicableUastTypes(): List<Class<out UElement>>?
42. SourceCodeScanner fun applicableSuperClasses(): List<String>? fun getApplicableMethodNames(): List<String>? fun getApplicableUastTypes(): List<Class<out UElement>>?
43. SourceCodeScanner fun getInt()k= (0..10).map { it.also { "test" } }.also { “Test2" }.apply { size }.let { it.last() }.takeIf { it > 10 }
44. SourceCodeScanner fun getInt(): Int?k= (0..10).map { it.also { "test" } }.also { “Test2" }.apply { size }.let { it.last() }.takeIf { it > 10 }
45. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k ... } k
46. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k ... } k
47. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k … } k
48. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k … } k
49. SourceCodeScanner private fun isInferredMethod(node: UMethod): Boolean { val function = node.sourcePsi as? KtNamedFunction ?: return false val isFunction = function.funKeyword != null val hasColon = function.colon != null val isVoid = returnType == PsiType.VOID || returnType.presentableText == “Unit" return isFunction && !hasColon && !isVoid }
50. SourceCodeScanner private fun isInferredMethod(node: UMethod): Boolean { val function = node.sourcePsi as? KtNamedFunction ?: return false val isFunction = function.funKeyword != null val hasColon = function.colon != null val isVoid = returnType == PsiType.VOID || returnType.presentableText == “Unit" return isFunction && !hasColon && !isVoid }
51. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k ... } k
52. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k ... } k
53. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k ... } k
54. SourceCodeScanner class MyDetector : Detector(), SourceCodeScanner { ... override fun getApplicableUastTypes(): MutableList<Class<out UElement>> = mutableListOf(UMethod::class.java) override fun createUastHandler(context: JavaContext): UElementHandler = InferredTypeHandler(context) class InferredTypeHandler(private val context: JavaContext) : UElementHandler() { ... override fun visitMethod(node: UMethod) { if (!isKotlin(node)) return if (isInferredMethod(node)){ report(context) } k } k ... } k
55. Report javaContext.report(ISSUE, uMethod, javaContext.getNameLocation(uMethod), getReportMessage(canonicalText))
56. Report javaContext.report(ISSUE, uMethod, javaContext.getNameLocation(uMethod), getReportMessage(canonicalText))
57. Report
58. Report
59. Report
60. Report
61. Examples of checks Some examples of checks we are currently using: › BaseFragment within a package. › Internal APIs to recommend to use a custom subscriber. › Nesting in lambdas. › Nesting in custom LiveData. › Top level class comments. › Internal deprecations.
62. Gist https://gist.github.com/dtvc87/ c4118d25575d91a0e59603b0cf5724a9
63. References › https://engineering.linecorp.com/en/blog/synchronizing-geographically- distributed-teams-with-lint/ › https://groups.google.com/forum/#!forum/lint-dev › https://docs.google.com/presentation/d/ 1Sr-6E3Tk1lBguUob0GigqSEsfN-04qS56Whj0UEr0AE/ edit#slide=id.g29100eff00_3_126 › https://en.wikipedia.org/wiki/Static_program_analysis