Fix #4689: Add regex check to prohibit post() and postDelayed()

scripts/assets/file_content_validation_checks.textproto

@@ -454,3 +454,14 @@ file_content_checks {
   exempted_file_name: "app/src/main/java/org/oppia/android/app/application/AbstractOppiaApplication.kt"
   exempted_file_patterns: ".+?Test\\.kt"
 }
+file_content_checks {
+  file_path_regex: ".+?.kt"
+  prohibited_content_regex: ".+?\\.(post|postDelayed)[\\s]*(\\(|\\{).*?"
+  failure_message: "Prefer avoiding post() and postDelayed() methods as they can can lead to subtle and difficult-to-debug crashes. Prefer using LifecycleSafeTimerFactory for most cases when an operation needs to run at a future time. For cases when state needs to be synchronized with a view, use doOnPreDraw or doOnLayout instead. For more context on the underlying issue, see: https://betterprogramming.pub/stop-using-post-postdelayed-in-your-android-views-9d1c8eeaadf2."
+  exempted_file_name: "app/src/main/java/org/oppia/android/app/drawer/NavigationDrawerFragmentPresenter.kt"
+  exempted_file_name: "app/src/main/java/org/oppia/android/app/player/state/StateFragmentPresenter.kt"
+  exempted_file_name: "app/src/main/java/org/oppia/android/app/topic/info/TopicInfoFragmentPresenter.kt"
+  exempted_file_name: "app/src/main/java/org/oppia/android/app/utility/ClickableAreasImage.kt"
+  exempted_file_name: "scripts/src/javatests/org/oppia/android/scripts/regex/RegexPatternValidationCheckTest.kt"
+  exempted_file_name: "utility/src/main/java/org/oppia/android/util/parser/image/UrlImageParser.kt"
+}

scripts/src/javatests/org/oppia/android/scripts/regex/RegexPatternValidationCheckTest.kt

@@ -173,6 +173,13 @@ class RegexPatternValidationCheckTest {
     "Use AnalyticsStartupListener to retrieve an instance of WorkManager rather than fetching one" +
       " using getInstance (as the latter may create a WorkManager if one isn't already present, " +
       "and the application may intend to disable it)."
+  private val doesNotUsePostOrPostDelayed =
+    "Prefer avoiding post() and postDelayed() methods as they can can lead to subtle and " +
+      "difficult-to-debug crashes. Prefer using LifecycleSafeTimerFactory for most cases when " +
+      "an operation needs to run at a future time. For cases when state needs to be synchronized " +
+      "with a view, use doOnPreDraw or doOnLayout instead. For more context on the underlying " +
+      "issue, see: https://betterprogramming.pub/stop-using-post-postdelayed-in-your" +
+      "-android-views-9d1c8eeaadf2."
   private val wikiReferenceNote =
     "Refer to https://github.com/oppia/oppia-android/wiki/Static-Analysis-Checks" +
       "#regexpatternvalidation-check for more details on how to fix this."
@@ -2409,6 +2416,81 @@ class RegexPatternValidationCheckTest {
       )
   }
 
+  @Test
+  fun testFileContent_postDelayedUsed_fileContentIsNotCorrect() {
+    val prohibitedContent =
+      """
+        binding.view.postDelayed({ binding.view.visibility = View.GONE }, 1000)
+      """.trimIndent()
+    tempFolder.newFolder("testfiles", "app", "src", "main", "java", "org", "oppia", "android")
+    val stringFilePath = "app/src/main/java/org/oppia/android/TestPresenter.kt"
+    tempFolder.newFile("testfiles/$stringFilePath").writeText(prohibitedContent)
+
+    val exception = assertThrows(Exception::class) {
+      runScript()
+    }
+
+    assertThat(exception).hasMessageThat().contains(REGEX_CHECK_FAILED_OUTPUT_INDICATOR)
+
+    assertThat(outContent.toString().trim())
+      .isEqualTo(
+        """
+        $stringFilePath:1: $doesNotUsePostOrPostDelayed
+        $wikiReferenceNote
+        """.trimIndent()
+      )
+  }
+
+  @Test
+  fun testFileContent_postUsed_withParenthesis_fileContentIsNotCorrect() {
+    val prohibitedContent =
+      """
+        binding.view.post({ binding.view.visibility = View.GONE })
+      """.trimIndent()
+    tempFolder.newFolder("testfiles", "app", "src", "main", "java", "org", "oppia", "android")
+    val stringFilePath = "app/src/main/java/org/oppia/android/TestPresenter.kt"
+    tempFolder.newFile("testfiles/$stringFilePath").writeText(prohibitedContent)
+
+    val exception = assertThrows(Exception::class) {
+      runScript()
+    }
+
+    assertThat(exception).hasMessageThat().contains(REGEX_CHECK_FAILED_OUTPUT_INDICATOR)
+
+    assertThat(outContent.toString().trim())
+      .isEqualTo(
+        """
+        $stringFilePath:1: $doesNotUsePostOrPostDelayed
+        $wikiReferenceNote
+        """.trimIndent()
+      )
+  }
+
+  @Test
+  fun testFileContent_postUsed_withCurlyBraces_fileContentIsNotCorrect() {
+    val prohibitedContent =
+      """
+        binding.view.post { binding.view.visibility = View.GONE }
+      """.trimIndent()
+    tempFolder.newFolder("testfiles", "app", "src", "main", "java", "org", "oppia", "android")
+    val stringFilePath = "app/src/main/java/org/oppia/android/TestPresenter.kt"
+    tempFolder.newFile("testfiles/$stringFilePath").writeText(prohibitedContent)
+
+    val exception = assertThrows(Exception::class) {
+      runScript()
+    }
+
+    assertThat(exception).hasMessageThat().contains(REGEX_CHECK_FAILED_OUTPUT_INDICATOR)
+
+    assertThat(outContent.toString().trim())
+      .isEqualTo(
+        """
+        $stringFilePath:1: $doesNotUsePostOrPostDelayed
+        $wikiReferenceNote
+        """.trimIndent()
+      )
+  }
+
   /** Runs the regex_pattern_validation_check. */
   private fun runScript() {
     main(File(tempFolder.root, "testfiles").absolutePath)