Ensure unique top-level directories for archives when using 'nomerge'

- Align mount-zip behavior with fuse-archive: archives with identical
  base names are uniquely renamed (e.g., 'archive', 'archive (1)')
  rather than merged.
- Implement this by creating and attaching a unique Node for the archive
  directory before scanning its contents.
- Correctly increment the root node's link count for each new archive
  directory.
- Verify that mounting two archives with the same base name using the
  'nomerge' option results in uniquely named top-level directories
  (e.g., 'empty' and 'empty (1)').
- Add a complex test case mounting 'hlink-relative.zip' twice with '-o
  nomerge'.
- Verify that both regular files and hard links are correctly resolved
  within their respective uniquely-named archive directories.

Author: fdegros

lib/tree.cc

@@ -512,9 +512,19 @@ Tree::Tree(std::span<const std::string> paths, Options opts)
   for (const auto& [zip, zip_path] : zips_) {
     path = '/';
     if (!opts_.merge) {
-      path += Path(zip_path).Split().second.WithoutExtension();
+      Node::Ptr archive_node(new Node{
+          .parent = root_,
+          .name = std::string(Path(zip_path).Split().second.WithoutExtension()),
+          .mode = S_IFDIR | 0755,
+          .nlink = 2});
+      Node* const node = RenameIfCollision(std::move(archive_node));
+      root_->AddChild(node);
+      root_->nlink++;
+      path += node->name;
     }
 
+    assert(path.capacity() >= PATH_MAX);
+
     const std::string archive_prefix = path;
     size_t const initial_path_length = path.size();
 

tests/node_test.cc

@@ -22,6 +22,10 @@
 
 namespace {
 
+TEST(NodeTest, StaticSize) {
+  EXPECT_LE(sizeof(Node), 256);
+}
+
 TEST(NodeTest, Basic) {
   Node root{};
   root.name = "/";

tests/test.py

@@ -1580,6 +1580,58 @@ def TestMultiple():
         options=['-o', 'nomerge'],
     )
 
+    want_tree = {
+        '.': {'ino': 1, 'mode': 'drwxr-xr-x', 'nlink': 4},
+        'empty': {'ino': 2, 'mode': 'drwxr-xr-x', 'nlink': 2},
+        'empty (1)': {'ino': 3, 'mode': 'drwxr-xr-x', 'nlink': 2},
+    }
+
+    MountArchiveAndCheckTree(
+        ['empty.zip', 'empty.zip'],
+        want_tree,
+        options=['-o', 'nomerge'],
+    )
+
+    want_tree = {
+        '.': {'ino': 1, 'mode': 'drwxr-xr-x', 'nlink': 4},
+        'hlink-relative': {'ino': 2, 'mode': 'drwxr-xr-x', 'nlink': 2},
+        'hlink-relative/0regular': {
+            'ino': 3,
+            'mode': '-rw-r--r--',
+            'nlink': 2,
+            'size': 10,
+            'md5': 'e09c80c42fda55f9d992e59ca6b3307d',
+        },
+        'hlink-relative/hlink': {
+            'ino': 3,
+            'mode': '-rw-r--r--',
+            'nlink': 2,
+            'size': 10,
+            'md5': 'e09c80c42fda55f9d992e59ca6b3307d',
+        },
+        'hlink-relative (1)': {'ino': 5, 'mode': 'drwxr-xr-x', 'nlink': 2},
+        'hlink-relative (1)/0regular': {
+            'ino': 6,
+            'mode': '-rw-r--r--',
+            'nlink': 2,
+            'size': 10,
+            'md5': 'e09c80c42fda55f9d992e59ca6b3307d',
+        },
+        'hlink-relative (1)/hlink': {
+            'ino': 6,
+            'mode': '-rw-r--r--',
+            'nlink': 2,
+            'size': 10,
+            'md5': 'e09c80c42fda55f9d992e59ca6b3307d',
+        },
+    }
+
+    MountArchiveAndCheckTree(
+        ['hlink-relative.zip', 'hlink-relative.zip'],
+        want_tree,
+        options=['-o', 'nomerge'],
+    )
+
 
 # Tests -o dmask, fmask and default_permissions.
 def TestMasks():