Make workingDir property internal and only expose the .git directory

src/main/java/org/shipkit/changelog/GenerateChangelogTask.java

@@ -139,11 +139,27 @@ public void setOutputFile(File outputFile) {
         this.outputFile = outputFile;
     }
 
-    @InputDirectory
+    @Internal
     public File getWorkingDir() {
         return workingDir;
     }
 
+    @Optional
+    @InputDirectory
+    @PathSensitive(PathSensitivity.RELATIVE)
+    public File getGitDir() {
+        return provideGitDir(workingDir);
+    }
+
+    static File provideGitDir(File workingDir) {
+        if (workingDir == null) {
+            return null;
+        }
+
+        File gitDir = new File(workingDir, ".git");
+        return gitDir.isDirectory() ? gitDir : null;
+    }
+
     public void setWorkingDir(File workingDir) {
         this.workingDir = workingDir;
     }

src/test/groovy/org/shipkit/changelog/GenerateChangelogTaskTest.groovy

@@ -0,0 +1,22 @@
+package org.shipkit.changelog
+
+import org.junit.Rule
+import org.junit.rules.TemporaryFolder
+import spock.lang.Specification
+
+import static org.shipkit.changelog.GenerateChangelogTask.provideGitDir
+
+class GenerateChangelogTaskTest extends Specification {
+
+    @Rule TemporaryFolder tmp = new TemporaryFolder()
+
+    def "getGitDir is safe"() {
+        expect:
+        provideGitDir(null) == null
+        provideGitDir(new File("missing")) == null
+
+        and:
+        def gitDir = tmp.newFolder(".git")
+        provideGitDir(gitDir.parentFile) == gitDir
+    }
+}