Resolve worktree .git files to repository .git directory

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

@@ -23,6 +23,7 @@
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.io.*;
+import java.nio.file.Path;
 import java.util.List;
 
 /**
@@ -127,7 +128,7 @@ private File processGitDirFile(@Nonnull File file) {
       }
 
       // All seems ok so return the "gitdir" value read from the file.
-      File gitDir = new File(parts[1]);
+      File gitDir = resolveWorktree(new File(parts[1]));
       if (gitDir.isAbsolute()) {
         // gitdir value is an absolute path. Return as-is
         return gitDir;
@@ -140,6 +141,21 @@ private File processGitDirFile(@Nonnull File file) {
     }
   }
 
+  /**
+   * 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.
+   */
+  static File resolveWorktree(File fileLocation) {
+    Path parent = fileLocation.toPath().getParent();
+    if (parent == null) {
+      return fileLocation;
+    }
+    if (parent.endsWith(Path.of(".git", "worktrees"))) {
+      return parent.getParent().toFile();
+    }
+    return fileLocation;
+  }
+
   /**
    * Helper method to validate that the specified {@code File} is an existing directory.
    * @param fileLocation The  {@code File} that should be checked if it's actually an existing directory.

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

@@ -58,4 +58,13 @@ public void shouldUseTheManuallySpecifiedDirectory() throws Exception {
     }
   }
 
+  @Test
+  public void testWorktreeResolution() {
+    String[] noopCases = {"", "a", "a/b", ".git/worktrees", ".git/worktrees/", "a.git/worktrees/b"};
+    for (String path : noopCases) {
+      assertThat(GitDirLocator.resolveWorktree(new File(path))).isEqualTo(new File(path));
+    }
+    assertThat(GitDirLocator.resolveWorktree(new File("a/.git/worktrees/b"))).isEqualTo(new File("a/.git"));
+    assertThat(GitDirLocator.resolveWorktree(new File("/a/.git/worktrees/b"))).isEqualTo(new File("/a/.git"));
+  }
 }