Add a linter requiring Nullability Annotations

-This linter only check Java source and its public methods.
-Apply to method return type not primitives or void.
-Apply to method parameters not primitives.
-Check the android.annotation.NonNull / android.annotation.Nullable
 to replace with androidx.annotation.NonNull / androidx.annotation.Nullable.

Bug: 307770597
Test: manual test
Change-Id: I32422e23c8387c52e9f0cad3e5833b2cab1fa842

3 files changed, 207 insertions, 0 deletions

diff --git a/packages/SettingsLib/LintChecker/Android.bp b/packages/SettingsLib/LintChecker/Android.bp
new file mode 100644
index 000000000000..eb489b1de380
--- /dev/null
+++ b/packages/SettingsLib/LintChecker/Android.bp
@@ -0,0 +1,33 @@
+// Copyright (C) 2023 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package {
+    // See: http://go/android-license-faq
+    // A large-scale-change added 'default_applicable_licenses' to import
+    // all of the 'license_kinds' from "frameworks_base_license"
+    // to get the below license kinds:
+    //   SPDX-license-identifier-Apache-2.0
+    default_applicable_licenses: ["frameworks_base_license"],
+}
+
+java_library_host {
+    name: "SettingsLibLintChecker",
+    srcs: ["src/**/*.kt"],
+    plugins: ["auto_service_plugin"],
+    libs: [
+        "auto_service_annotations",
+        "lint_api",
+    ],
+    kotlincflags: ["-Xjvm-default=all"],
+}
diff --git a/packages/SettingsLib/LintChecker/src/com/android/settingslib/tools/lint/NullabilityAnnotationsDetector.kt b/packages/SettingsLib/LintChecker/src/com/android/settingslib/tools/lint/NullabilityAnnotationsDetector.kt
new file mode 100644
index 000000000000..1f062619b261
--- /dev/null
+++ b/packages/SettingsLib/LintChecker/src/com/android/settingslib/tools/lint/NullabilityAnnotationsDetector.kt
@@ -0,0 +1,146 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settingslib.tools.lint
+
+import com.android.tools.lint.client.api.UElementHandler
+import com.android.tools.lint.detector.api.Category
+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
+import com.android.tools.lint.detector.api.Severity
+import com.intellij.psi.PsiModifier
+import com.intellij.psi.PsiPrimitiveType
+import com.intellij.psi.PsiType
+import org.jetbrains.uast.UAnnotated
+import org.jetbrains.uast.UElement
+import org.jetbrains.uast.UMethod
+
+class NullabilityAnnotationsDetector : Detector(), Detector.UastScanner {
+    override fun getApplicableUastTypes(): List<Class<out UElement>> = listOf(UMethod::class.java)
+
+    override fun createUastHandler(context: JavaContext): UElementHandler? {
+        if (!context.isJavaFile()) return null
+
+        return object : UElementHandler() {
+            override fun visitMethod(node: UMethod) {
+                if (node.isPublic() && node.name != ANONYMOUS_CONSTRUCTOR) {
+                    node.verifyMethod()
+                    node.verifyMethodParameters()
+                }
+            }
+
+            private fun UMethod.isPublic() = modifierList.hasModifierProperty(PsiModifier.PUBLIC)
+
+            private fun UMethod.verifyMethod() {
+                if (isConstructor) return
+                if (returnType.isPrimitive()) return
+                checkAnnotation(METHOD_MSG)
+            }
+
+            private fun UMethod.verifyMethodParameters() {
+                for (parameter in uastParameters) {
+                    if (parameter.type.isPrimitive()) continue
+                    parameter.checkAnnotation(PARAMETER_MSG)
+                }
+            }
+
+            private fun PsiType?.isPrimitive() = this is PsiPrimitiveType
+
+            private fun UAnnotated.checkAnnotation(message: String) {
+                val oldAnnotation = findOldNullabilityAnnotation()
+                val oldAnnotationName = oldAnnotation?.qualifiedName?.substringAfterLast('.')
+
+                if (oldAnnotationName != null) {
+                    val annotation = "androidx.annotation.$oldAnnotationName"
+                    reportIssue(
+                        REQUIRE_NULLABILITY_ISSUE,
+                        "Prefer $annotation",
+                        LintFix.create()
+                                .replace()
+                                .range(context.getLocation(oldAnnotation))
+                                .with("@$annotation")
+                                .autoFix()
+                                .build()
+                    )
+                } else if (!hasNullabilityAnnotation()) {
+                    reportIssue(REQUIRE_NULLABILITY_ISSUE, message)
+                }
+            }
+
+            private fun UElement.reportIssue(
+                issue: Issue,
+                message: String,
+                quickfixData: LintFix? = null,
+            ) {
+                context.report(
+                    issue = issue,
+                    scope = this,
+                    location = context.getNameLocation(this),
+                    message = message,
+                    quickfixData = quickfixData,
+                )
+            }
+
+            private fun UAnnotated.findOldNullabilityAnnotation() =
+                uAnnotations.find { it.qualifiedName in oldAnnotations }
+
+            private fun UAnnotated.hasNullabilityAnnotation() =
+                uAnnotations.any { it.qualifiedName in validAnnotations }
+        }
+    }
+
+    private fun JavaContext.isJavaFile() = psiFile?.fileElementType.toString().startsWith("java")
+
+    companion object {
+        private val validAnnotations = arrayOf("androidx.annotation.NonNull",
+            "androidx.annotation.Nullable")
+
+        private val oldAnnotations = arrayOf("android.annotation.NonNull",
+            "android.annotation.Nullable",
+        )
+
+        private const val ANONYMOUS_CONSTRUCTOR = "<anon-init>"
+
+        private const val METHOD_MSG =
+                "Java public method return with non-primitive type must add androidx annotation. " +
+                        "Example: @NonNull | @Nullable Object functionName() {}"
+
+        private const val PARAMETER_MSG =
+                "Java public method parameter with non-primitive type must add androidx " +
+                        "annotation. Example: functionName(@NonNull Context context, " +
+                        "@Nullable Object obj) {}"
+
+        internal val REQUIRE_NULLABILITY_ISSUE = Issue
+            .create(
+                id = "RequiresNullabilityAnnotation",
+                briefDescription = "Requires nullability annotation for function",
+                explanation = "All public java APIs should specify nullability annotations for " +
+                        "methods and parameters.",
+                category = Category.CUSTOM_LINT_CHECKS,
+                priority = 3,
+                severity = Severity.WARNING,
+                androidSpecific = true,
+                implementation = Implementation(
+                  NullabilityAnnotationsDetector::class.java,
+                  Scope.JAVA_FILE_SCOPE,
+                ),
+            )
+    }
+}
\ No newline at end of file
diff --git a/packages/SettingsLib/LintChecker/src/com/android/settingslib/tools/lint/SettingsLintIssueRegistry.kt b/packages/SettingsLib/LintChecker/src/com/android/settingslib/tools/lint/SettingsLintIssueRegistry.kt
new file mode 100644
index 000000000000..e0ab24afee5a
--- /dev/null
+++ b/packages/SettingsLib/LintChecker/src/com/android/settingslib/tools/lint/SettingsLintIssueRegistry.kt
@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settingslib.tools.lint
+
+import com.android.tools.lint.client.api.IssueRegistry
+import com.android.tools.lint.detector.api.CURRENT_API
+import com.google.auto.service.AutoService
+
+@AutoService(IssueRegistry::class)
+class SettingsLintIssueRegistry : IssueRegistry() {
+    override val issues = listOf(NullabilityAnnotationsDetector.REQUIRE_NULLABILITY_ISSUE)
+
+    override val api: Int = CURRENT_API
+}
\ No newline at end of file