Add missing null annotation detector

WordPressLint/src/main/java/org/wordpress/android/lint/MissingNullAnnotationDetector.kt

@@ -0,0 +1,179 @@
+package org.wordpress.android.lint
+
+import com.android.tools.lint.client.api.UElementHandler
+import com.android.tools.lint.detector.api.Category.Companion.CORRECTNESS
+import com.android.tools.lint.detector.api.Detector
+import com.android.tools.lint.detector.api.Implementation
+import com.android.tools.lint.detector.api.Issue
+import com.android.tools.lint.detector.api.JavaContext
+import com.android.tools.lint.detector.api.LintFix
+import com.android.tools.lint.detector.api.Scope.Companion.JAVA_FILE_SCOPE
+import com.android.tools.lint.detector.api.Severity
+import com.android.tools.lint.detector.api.SourceCodeScanner
+import com.android.tools.lint.detector.api.isJava
+import com.intellij.psi.PsiPrimitiveType
+import org.jetbrains.uast.UAnnotated
+import org.jetbrains.uast.UAnnotationMethod
+import org.jetbrains.uast.UElement
+import org.jetbrains.uast.UEnumConstant
+import org.jetbrains.uast.UField
+import org.jetbrains.uast.UMethod
+import org.jetbrains.uast.UParameter
+import org.jetbrains.uast.UVariable
+
+class MissingNullAnnotationDetector : Detector(), SourceCodeScanner {
+    override fun getApplicableUastTypes(): List<Class<out UElement>> = listOf(
+            UField::class.java,
+            UMethod::class.java,
+    )
+
+    override fun createUastHandler(context: JavaContext): UElementHandler? = with(context) {
+        if (!isJava(uastFile?.sourcePsi)) {
+            return null
+        }
+        object : UElementHandler() {
+            override fun visitField(node: UField) {
+                if (node.requiresNullAnnotation && !node.isNullAnnotated) {
+                    report(node, MISSING_FIELD_ANNOTATION)
+                }
+            }
+
+            override fun visitMethod(node: UMethod) {
+                node.uastParameters.forEach { visitParameter(node, it) }
+
+                if (node.requiresNullAnnotation && !node.isNullAnnotated) {
+                    report(node, MISSING_METHOD_RETURN_TYPE_ANNOTATION)
+                }
+            }
+
+            private fun visitParameter(node: UMethod, parameter: UParameter) {
+                if (parameter.requiresNullAnnotation && !parameter.isNullAnnotated) {
+                    if (node.isConstructor)
+                        report(parameter, MISSING_CONSTRUCTOR_PARAMETER_ANNOTATION)
+                    else
+                        report(parameter, MISSING_METHOD_PARAMETER_ANNOTATION)
+                }
+            }
+        }
+    }
+
+    companion object {
+        val MISSING_FIELD_ANNOTATION = Issue.create(
+                id = "MissingNullAnnotationOnField",
+                briefDescription = "Nullable/NonNull annotation missing on field",
+                explanation = "Checks for missing `@NonNull/@Nullable` annotations for fields.",
+        )
+        val MISSING_CONSTRUCTOR_PARAMETER_ANNOTATION = Issue.create(
+                id = "MissingNullAnnotationOnConstructorParameter",
+                briefDescription = "Nullable/NonNull annotation missing on constructor parameter",
+                explanation = "Checks for missing `@NonNull/@Nullable` annotations on constructor parameters.",
+        )
+        val MISSING_METHOD_PARAMETER_ANNOTATION = Issue.create(
+                id = "MissingNullAnnotationOnMethodParameter",
+                briefDescription = "Nullable/NonNull annotation missing on method parameter",
+                explanation = "Checks for missing `@NonNull/@Nullable` annotations on method parameters.",
+        )
+        val MISSING_METHOD_RETURN_TYPE_ANNOTATION = Issue.create(
+                id = "MissingNullAnnotationOnMethodReturnType",
+                briefDescription = "Nullable/NonNull annotation missing on method return type",
+                explanation = "Checks for missing `@NonNull/@Nullable` annotations on method return types.",
+        )
+
+        val acceptableNullAnnotations = listOf(
+                "androidx.annotation.NonNull",
+                "androidx.annotation.Nullable",
+        )
+    }
+}
+
+/* UVariable Extensions */
+private val UVariable.isPrimitive get() = this.type is PsiPrimitiveType
+private val UVariable.isEnum get() = this is UEnumConstant
+private val UVariable.isInjected
+    get() = this.annotations.any { annotation ->
+        annotation.qualifiedName?.endsWith("Inject") ?: false
+    }
+private val UVariable.isConstant get() = this.isStatic && this.isFinal
+private val UVariable.isInitializedFinalField
+    get() = this.isFinal
+            && this.uastInitializer != null
+private val UVariable.requiresNullAnnotation
+    get() =
+        !this.isPrimitive
+                && !this.isEnum
+                && !this.isConstant
+                && !this.isInitializedFinalField
+                && !this.isInjected
+
+/* UMethod Extensions */
+private val UMethod.isPrimitive get() = this.returnType is PsiPrimitiveType
+private val UMethod.requiresNullAnnotation
+    get() =
+        this !is UAnnotationMethod
+                && !this.isPrimitive
+                && !this.isConstructor
+
+/* UAnnotated Extensions */
+private val UAnnotated.isNullAnnotated
+    get() = this.uAnnotations.any { annotation ->
+        MissingNullAnnotationDetector.acceptableNullAnnotations.any { nullAnnotation ->
+            annotation.qualifiedName == nullAnnotation
+        }
+    }
+
+/* Issue.Companion Extensions */
+private fun Issue.Companion.create(
+        id: String,
+        briefDescription: String,
+        explanation: String,
+) = create(
+        id = id,
+        briefDescription = briefDescription,
+        explanation = explanation,
+        category = CORRECTNESS,
+        priority = 5,
+        severity = Severity.INFORMATIONAL,
+        implementation = Implementation(
+                MissingNullAnnotationDetector::class.java,
+                JAVA_FILE_SCOPE,
+        )
+)
+
+/* JavaContext Extensions */
+private fun JavaContext.report(node: UElement, issue: Issue) = report(
+        issue,
+        node,
+        getLocation(node),
+        "Missing null annotation",
+        node.fixes,
+)
+
+/* UElement Extensions */
+private val UElement.fixes
+    get() = this.asSourceString().let { sourceString ->
+        val nullableReplacement = "@Nullable $sourceString"
+        val nonNullReplacement = "@NonNull $sourceString"
+
+        LintFix.create().group()
+                .add(
+                        LintFix.create()
+                                .name("Annotate as @Nullable")
+                                .replace()
+                                .text(sourceString)
+                                .shortenNames()
+                                .reformat(true)
+                                .with(nullableReplacement)
+                                .build()
+                )
+                .add(
+                        LintFix.create()
+                                .name("Annotate as @NonNull")
+                                .replace()
+                                .text(sourceString)
+                                .shortenNames()
+                                .reformat(true)
+                                .with(nonNullReplacement)
+                                .build()
+                )
+                .build()
+    }

WordPressLint/src/main/java/org/wordpress/android/lint/WordPressIssueRegistry.kt

@@ -3,22 +3,24 @@ package org.wordpress.android.lint
 import com.android.tools.lint.client.api.IssueRegistry
 import com.android.tools.lint.client.api.Vendor
 import com.android.tools.lint.detector.api.CURRENT_API
-import org.wordpress.android.lint.WordPressAndroidImportInViewModelDetector.Companion.ISSUE_ANDROID_IMPORT_IN_VIEWMODEL
 
 class WordPressIssueRegistry : IssueRegistry() {
     override val api = CURRENT_API
     override val minApi = MIN_API
-    override val issues get() = listOf(
-            WordPressRtlCodeDetector.SET_PADDING,
-            WordPressRtlCodeDetector.SET_MARGIN,
-            WordPressRtlCodeDetector.GET_PADDING,
-            ISSUE_ANDROID_IMPORT_IN_VIEWMODEL,
-    )
+    override val issues
+        get() = listOf(
+                MissingNullAnnotationDetector.MISSING_FIELD_ANNOTATION,
+                MissingNullAnnotationDetector.MISSING_CONSTRUCTOR_PARAMETER_ANNOTATION,
+                MissingNullAnnotationDetector.MISSING_METHOD_PARAMETER_ANNOTATION,
+                MissingNullAnnotationDetector.MISSING_METHOD_RETURN_TYPE_ANNOTATION,
+        )
+
     override val vendor = Vendor(
             vendorName = "WordPress Android",
             feedbackUrl = "https://github.com/wordpress-mobile/WordPress-Lint-Android/issues",
             identifier = "org.wordpress.android.lint",
     )
+
     companion object {
         const val MIN_API = 10
     }