Add lint check that detects UI thread continuations.

Author: vkryachko

tools/lint/src/main/kotlin/CheckRegistry.kt

@@ -31,7 +31,8 @@ class CheckRegistry : IssueRegistry() {
         NonAndroidxNullabilityDetector.NON_ANDROIDX_NULLABILITY,
         DeferredApiDetector.INVALID_DEFERRED_API_USE,
         ProviderAssignmentDetector.INVALID_PROVIDER_ASSIGNMENT,
-        ThreadPoolDetector.THREAD_POOL_CREATION
+        ThreadPoolDetector.THREAD_POOL_CREATION,
+        TasksMainThreadDetector.TASK_MAIN_THREAD,
       )
 
   override val api: Int

tools/lint/src/main/kotlin/TasksMainThreadDetector.kt

@@ -0,0 +1,73 @@
+package com.google.firebase.lint.checks
+
+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.Scope
+import com.android.tools.lint.detector.api.Severity
+import com.android.tools.lint.detector.api.SourceCodeScanner
+import com.intellij.psi.PsiClass
+import com.intellij.psi.PsiMethod
+import com.intellij.psi.PsiParameter
+import org.jetbrains.uast.UCallExpression
+
+@Suppress("DetectorIsMissingAnnotations")
+class TasksMainThreadDetector : Detector(), SourceCodeScanner {
+
+  override fun getApplicableMethodNames(): List<String> =
+    listOf(
+      "addOnSuccessListener",
+      "addOnFailureListener",
+      "addOnCompleteListener",
+      "addOnCanceledListener",
+      "continueWith",
+      "continueWithTask",
+      "onSuccessTask"
+    )
+
+  override fun visitMethodCall(context: JavaContext, node: UCallExpression, method: PsiMethod) {
+    if (!isTaskMethod(method)) {
+      return
+    }
+
+    val firstArgument: PsiParameter = method.parameterList.parameters.firstOrNull() ?: return
+    if (!firstArgument.type.equalsToText("java.util.concurrent.Executor")) {
+      context.report(
+        TASK_MAIN_THREAD,
+        context.getCallLocation(node, includeReceiver = false, includeArguments = false),
+        "Use an Executor explicitly to avoid running on the main thread."
+      )
+    }
+  }
+
+  private fun isTaskMethod(method: PsiMethod): Boolean {
+    (method.parent as? PsiClass)?.let {
+      return it.qualifiedName == "com.google.android.gms.tasks.Task"
+    }
+    return false
+  }
+
+  companion object {
+    private val IMPLEMENTATION =
+      Implementation(TasksMainThreadDetector::class.java, Scope.JAVA_FILE_SCOPE)
+
+    /** Calling methods on the wrong thread */
+    @JvmField
+    val TASK_MAIN_THREAD =
+      Issue.create(
+        id = "TaskMainThread",
+        briefDescription = "Use an explicit Executor for Task continuations",
+        explanation =
+          """
+                    Not providing an executor results in continuations to execute on the main thread \
+                    which is not a good default. Please pass in an executor explicitly.
+                """,
+        category = Category.PERFORMANCE,
+        priority = 6,
+        severity = Severity.ERROR,
+        implementation = IMPLEMENTATION
+      )
+  }
+}