#701: add testcases to demonstrate the issue

src/main/java/pl/project13/maven/git/GitDirLocator.java

@@ -135,22 +135,27 @@ private File processGitDirFile(@Nonnull File file) {
       }
 
       // All seems ok so return the "gitdir" value read from the file.
-      File gitDir = resolveWorktree(new File(parts[1]));
+      String extractFromConfig = parts[1];
+      File gitDir = resolveWorktree(new File(extractFromConfig));
       if (gitDir.isAbsolute()) {
         // gitdir value is an absolute path. Return as-is
         return gitDir;
       } else {
         // gitdir value is relative.
-        return new File(file.getParentFile(), parts[1]);
+        return new File(file.getParentFile(), extractFromConfig);
       }
     } catch (IOException e) {
       return null;
     }
   }
 
   /**
-   * If the file looks like the location of a worktree, return the .git folder of the git repository
-   * of the worktree. If not, return the file as is.
+   * Attempts to resolve the actual location of the .git folder for a given
+   * worktree.
+   * For example for a worktree like {@code a/.git/worktrees/X} structure would return {@code a/.git}.
+   *
+   * If the conditions for a git worktree like file structure are met simply return the provided
+   * argument as is.
    */
   static File resolveWorktree(File fileLocation) {
     Path parent = fileLocation.toPath().getParent();

src/test/java/pl/project13/maven/git/GitDirLocatorTest.java

@@ -25,7 +25,9 @@
 import java.util.Collections;
 import java.util.List;
 import org.apache.maven.project.MavenProject;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
@@ -37,18 +39,20 @@ public class GitDirLocatorTest {
 
   List<MavenProject> reactorProjects = Collections.emptyList();
 
+  @Rule
+  public TemporaryFolder folder = new TemporaryFolder();
+
   @Test
   public void shouldUseTheManuallySpecifiedDirectory() throws Exception {
     // given
-    File dotGitDir = Files.createTempDirectory("temp").toFile();
+    File dotGitDir = folder.newFolder("temp");
     try {
-
       // when
       GitDirLocator locator = new GitDirLocator(project, reactorProjects);
       File foundDirectory = locator.lookupGitDirectory(dotGitDir);
 
       // then
-      assert foundDirectory != null;
+      assertThat(foundDirectory).isNotNull();
       assertThat(foundDirectory.getAbsolutePath()).isEqualTo(dotGitDir.getAbsolutePath());
     } finally {
       if (!dotGitDir.delete()) {
@@ -57,12 +61,66 @@ public void shouldUseTheManuallySpecifiedDirectory() throws Exception {
     }
   }
 
+  @Test
+  public void shouldResolveRelativeSubmodule() throws Exception {
+    // given
+    folder.newFolder("main-project");
+    folder.newFolder("main-project", ".git", "modules", "sub-module");
+    folder.newFolder("main-project", "sub-module");
+
+    // and a .git dir in submodule that points to the main's project .git/modules/submodule
+    File dotGitDir = folder.getRoot().toPath()
+      .resolve("main-project")
+      .resolve("sub-module")
+      .resolve(".git")
+      .toFile();
+    Files.write(
+      dotGitDir.toPath(),
+      "gitdir: ../.git/modules/sub-module".getBytes()
+    );
+
+    try {
+      // when
+      GitDirLocator locator = new GitDirLocator(project, reactorProjects);
+      File foundDirectory = locator.lookupGitDirectory(dotGitDir);
+
+      // then
+      assertThat(foundDirectory).isNotNull();
+      assertThat(
+        foundDirectory.getCanonicalFile()
+      ).isEqualTo(
+        folder.getRoot().toPath()
+          .resolve("main-project")
+          .resolve(".git")
+          .resolve("modules")
+          .resolve("sub-module")
+          .toFile()
+      );
+    } finally {
+      if (!dotGitDir.delete()) {
+        dotGitDir.deleteOnExit();
+      }
+    }
+  }
+
   @Test
   public void testWorktreeResolution() {
-    String[] noopCases = {"", "a", "a/b", ".git/worktrees", ".git/worktrees/", "a.git/worktrees/b"};
+    // tests to ensure we do not try to modify things that should not be modified
+    String[] noopCases = {
+      "",
+      "a",
+      "a/b",
+      ".git/worktrees",
+      ".git/worktrees/",
+      "a.git/worktrees/b",
+      ".git/modules",
+      ".git/modules/",
+      "a.git/modules/b",
+    };
     for (String path : noopCases) {
       assertThat(GitDirLocator.resolveWorktree(new File(path))).isEqualTo(new File(path));
     }
+    // tests that worktree resolution works
     assertThat(GitDirLocator.resolveWorktree(new File("a/.git/worktrees/b")))
         .isEqualTo(new File("a/.git"));
     assertThat(GitDirLocator.resolveWorktree(new File("/a/.git/worktrees/b")))

src/test/java/pl/project13/maven/git/GitSubmodulesTest.java

@@ -21,6 +21,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.io.File;
+import java.nio.file.Files;
 import java.util.Properties;
 import javax.annotation.Nonnull;
 import org.apache.maven.project.MavenProject;
@@ -49,6 +50,34 @@ public void shouldResolvePropertiesOnDefaultSettingsForNonPomProject() throws Ex
     assertGitPropertiesPresentInProject(targetProject.getProperties());
   }
 
+  @Test
+  public void shouldGeneratePropertiesWithSubmodules() throws Exception {
+    // given
+    mavenSandbox
+      .withParentProject("my-pom-project", "pom")
+      .withGitRepoInParent(AvailableGitTestRepo.WITH_REMOTE_SUBMODULES)
+      .withChildProject("remote-module", "jar")
+      .create();
+    MavenProject targetProject = mavenSandbox.getChildProject();
+    setProjectToExecuteMojoIn(targetProject);
+
+    // create a relative pointer to trigger the relative path logic in GitDirLocator#lookupGitDirectory
+    // makes the dotGitDirectory look like "my-pom-project/.git/modules/remote-module"
+    Files.write(
+      mavenSandbox.getChildProject().getBasedir().toPath().resolve(".git"),
+      "gitdir: ../.git/modules/remote-module".getBytes()
+    );
+
+    mojo.useNativeGit = true; // FIXME: make me a parameter
+
+    // when
+    mojo.execute();
+
+    // then
+    assertGitPropertiesPresentInProject(targetProject.getProperties());
+    assertThat(targetProject.getProperties().getProperty("git.commit.id.abbrev")).isEqualTo("945bfe6");
+  }
+
   public void setProjectToExecuteMojoIn(@Nonnull MavenProject project) {
     mojo.project = project;
     mojo.dotGitDirectory = new File(project.getBasedir(), ".git");