Ability to configure skipping build all (#255)

* Add ability to configure skipping buildAll in case no projects changed

* Update Doc

README.md

@@ -95,6 +95,7 @@ affectedModuleDetector {
     ignoredFiles = [
         ".*\\.md", ".*\\.txt", ".*README"
     ]
+    buildAllWhenNoProjectsChanged = true // default is true
     includeUncommitted = true
     top = "HEAD"
     customTasks = [
@@ -113,6 +114,7 @@ affectedModuleDetector {
  - `logFolder`: A folder to output the log file in
  - `specifiedBranch`: A branch to specify changes against. Must be used in combination with configuration `compareFrom = "SpecifiedBranchCommit"` 
  - `ignoredFiles`: A set of files that will be filtered out of the list of changed files retrieved by git. 
+ - `buildAllWhenNoProjectsChanged`: If true, the plugin will build all projects when no projects are considered affected.
  - `compareFrom`: A commit to compare the branch changes against. Can be either:
     - PreviousCommit: compare against the previous commit
     - ForkCommit: compare against the commit the branch was forked from

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

@@ -115,6 +115,11 @@ class AffectedModuleConfiguration {
      */
     var includeUncommitted: Boolean = true
 
+    /**
+     * If we should build all projects when no projects have changed
+     */
+    var buildAllWhenNoProjectsChanged: Boolean = true
+
     /**
      * The top of the git log to use, only used when [includeUncommitted] is false
      */

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

@@ -482,7 +482,7 @@ class AffectedModuleDetectorImpl constructor(
         var buildAll = false
 
         // Should only trigger if there are no changedFiles
-        if (changedProjects.isEmpty() && unknownFiles.isEmpty()) {
+        if (config.buildAllWhenNoProjectsChanged && changedProjects.isEmpty() && unknownFiles.isEmpty()) {
             buildAll = true
         }
         logger?.info(

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

@@ -1,6 +1,8 @@
 package com.dropbox.affectedmoduledetector
 
 import com.google.common.truth.Truth.assertThat
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
 import org.junit.Assert.fail
 import org.junit.Before
 import org.junit.Rule
@@ -324,4 +326,29 @@ class AffectedModuleConfigurationTest {
 
         assert(actual.first().taskDescription == "Description of fake task")
     }
+
+    @Test
+    fun `GIVEN AffectedModuleConfiguration WHEN buildAllWhenNoProjectsChanged THEN then default value is true`() {
+        // GIVEN
+        // config
+
+        // WHEN
+        val buildAllWhenNoProjectsChanged = config.buildAllWhenNoProjectsChanged
+
+        // THEN
+        assertTrue(buildAllWhenNoProjectsChanged)
+    }
+
+    @Test
+    fun `GIVEN AffectedModuleConfiguration WHEN buildAllWhenNoProjectsChanged is set to false THEN then value is false`() {
+        // GIVEN
+        val buildAll = false
+        config.buildAllWhenNoProjectsChanged = buildAll
+
+        // WHEN
+        val actual = config.buildAllWhenNoProjectsChanged
+
+        // THEN
+        assertFalse(actual)
+    }
 }

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

@@ -337,6 +337,29 @@ class AffectedModuleDetectorImplTest {
         )
     }
 
+    @Test
+    fun noChangeSkipAll() {
+        val detector = AffectedModuleDetectorImpl(
+            rootProject = root,
+            logger = logger,
+            ignoreUnknownProjects = false,
+            projectSubset = ProjectSubset.ALL_AFFECTED_PROJECTS,
+            injectedGitClient = MockGitClient(
+                changedFiles = emptyList(),
+                tmpFolder = tmpFolder.root
+            ),
+            config = affectedModuleConfiguration.also {
+                it.buildAllWhenNoProjectsChanged = false
+            }
+        )
+        MatcherAssert.assertThat(
+            detector.affectedProjects,
+            CoreMatchers.`is`(
+                emptySet()
+            )
+        )
+    }
+
     @Test
     fun changeInOneOnlyDependent() {
         val detector = AffectedModuleDetectorImpl(