Avoid building all projects when only ignored files are changed in affected module detector

affectedmoduledetector/src/main/kotlin/com/dropbox/affectedmoduledetector/AffectedModuleDetector.kt

@@ -147,7 +147,7 @@ abstract class AffectedModuleDetector {
                     rootProject.extensions.findByType(AffectedModuleConfiguration::class.java)
                 ) {
                     "Root project ${rootProject.path} must have the AffectedModuleConfiguration " +
-                        "extension added."
+                            "extension added."
                 }
 
             val logger =
@@ -415,6 +415,10 @@ class AffectedModuleDetectorImpl constructor(
             top = top,
             includeUncommitted = includeUncommitted
         ).forEach { fileName ->
+            if (isIgnoredFile(fileName)) {
+                // Skip ignored files
+                return@forEach
+            }
             if (affectsAllModules(fileName)) {
                 return allProjects
             }
@@ -429,20 +433,24 @@ class AffectedModuleDetectorImpl constructor(
                 unknownFiles.add(filePath)
                 logger?.info(
                     "Couldn't find containing project for file$filePath. " +
-                        "Adding to unknownFiles."
+                            "Adding to unknownFiles."
                 )
             } else {
                 changedProjects.add(containingProject)
                 logger?.info(
                     "For file $filePath containing project is $containingProject. " +
-                        "Adding to changedProjects."
+                            "Adding to changedProjects."
                 )
             }
         }
 
         return changedProjects
     }
 
+    private fun isIgnoredFile(filePath: String): Boolean {
+        return config.ignoredFiles.any { filePath.matches(it.toRegex()) }
+    }
+
     /**
      * Gets all dependent projects from the set of changedProjects. This doesn't include the
      * original changedProjects. Always build is still here to ensure at least 1 thing is built
@@ -475,13 +483,13 @@ class AffectedModuleDetectorImpl constructor(
 
         var buildAll = false
 
-        // Should only trigger if there are no changedFiles
-        if (changedProjects.isEmpty() && unknownFiles.isEmpty()) {
+        // Should only trigger if there are no changedFiles and no changes in non-ignored files
+        if (changedProjects.isEmpty() && unknownFiles.isEmpty() && changedFiles.isEmpty()) {
             buildAll = true
         }
         logger?.info(
             "unknownFiles: $unknownFiles, changedProjects: $changedProjects, buildAll: " +
-                "$buildAll"
+                    "$buildAll"
         )
 
         // If we're in a buildAll state, we return allProjects unless it's the changed target,

affectedmoduledetector/src/test/kotlin/com/dropbox/affectedmoduledetector/AffectedModuleDetectorImplTest.kt

@@ -223,6 +223,7 @@ class AffectedModuleDetectorImplTest {
         affectedModuleConfiguration = AffectedModuleConfiguration().also {
             it.baseDir = tmpDir.absolutePath
             it.pathsAffectingAllModules = pathsAffectingAllModules
+            it.ignoredFiles = setOf(".*\\.md", ".*\\.txt", ".*README")
         }
     }
 
@@ -1522,6 +1523,69 @@ class AffectedModuleDetectorImplTest {
         )
     }
 
+    @Test
+    fun changeInIgnoredFile() {
+        val detector = AffectedModuleDetectorImpl(
+            rootProject = root,
+            logger = logger,
+            ignoreUnknownProjects = false,
+            projectSubset = ProjectSubset.ALL_AFFECTED_PROJECTS,
+            injectedGitClient = MockGitClient(
+                changedFiles = listOf("README.md"),
+                tmpFolder = tmpFolder.root
+            ),
+            config = affectedModuleConfiguration
+        )
+        MatcherAssert.assertThat(
+            detector.affectedProjects,
+            CoreMatchers.`is`(
+                emptySet()
+            )
+        )
+    }
+
+    @Test
+    fun changeInIgnoredFileWithDependentProjects() {
+        val detector = AffectedModuleDetectorImpl(
+            rootProject = root,
+            logger = logger,
+            ignoreUnknownProjects = false,
+            projectSubset = ProjectSubset.DEPENDENT_PROJECTS,
+            injectedGitClient = MockGitClient(
+                changedFiles = listOf("README.md"),
+                tmpFolder = tmpFolder.root
+            ),
+            config = affectedModuleConfiguration
+        )
+        MatcherAssert.assertThat(
+            detector.affectedProjects,
+            CoreMatchers.`is`(
+                emptySet()
+            )
+        )
+    }
+
+    @Test
+    fun changeInIgnoredFileWithChangedProjects() {
+        val detector = AffectedModuleDetectorImpl(
+            rootProject = root,
+            logger = logger,
+            ignoreUnknownProjects = false,
+            projectSubset = ProjectSubset.CHANGED_PROJECTS,
+            injectedGitClient = MockGitClient(
+                changedFiles = listOf("README.md"),
+                tmpFolder = tmpFolder.root
+            ),
+            config = affectedModuleConfiguration
+        )
+        MatcherAssert.assertThat(
+            detector.affectedProjects,
+            CoreMatchers.`is`(
+                emptySet()
+            )
+        )
+    }
+
     // For both Linux/Windows
     fun convertToFilePath(vararg list: String): String {
         return list.toList().joinToString(File.separator)