solve commit bug (QuantStack#162)

Author: SandrineP

src/wrapper/index_wrapper.cpp

@@ -79,6 +79,11 @@ git_oid index_wrapper::write_tree()
     return tree_id;
 }
 
+size_t index_wrapper::entry_count() const
+{
+    return git_index_entrycount(*this);
+}
+
 bool index_wrapper::has_conflict() const
 {
     return git_index_has_conflicts(*this);

src/wrapper/index_wrapper.hpp

@@ -23,6 +23,8 @@ class index_wrapper : public wrapper_base<git_index>
     void write();
     git_oid write_tree();
 
+    size_t entry_count() const;
+
     void add_entry(const std::string& path);
     void add_entries(std::vector<std::string> patterns);
     void add_all();

src/wrapper/repository_wrapper.cpp

@@ -293,7 +293,6 @@ void repository_wrapper::create_commit(
     {
         if (parents_list)
         {
-            // TODO: write a "as_const" function to replace the following
             auto pl_size = parents_list.value().size();
             git_commit** pl_value = parents_list.value();
             auto pl_value_const = const_cast<const git_commit**>(pl_value);
@@ -313,9 +312,29 @@ void repository_wrapper::create_commit(
     }();
 
     index_wrapper index = this->make_index();
+
+    // Check: initial commit (no parents) with nothing staged
+    if (parents_count == 0 && index.entry_count() == 0)
+    {
+        throw std::runtime_error(
+            "On branch main\n\nInitial commit\n\nnothing to commit "
+            "(create/copy files and use \"git add\" to track)"
+        );
+    }
+
     git_oid tree_id = index.write_tree();
     index.write();
 
+    // Check: tree is identical to parent tree (nothing changed since last commit)
+    if (parents_count > 0 && placeholder[0] != nullptr)
+    {
+        const git_oid* parent_tree_id = git_commit_tree_id(placeholder[0]);
+        if (git_oid_equal(&tree_id, parent_tree_id))
+        {
+            throw std::runtime_error("nothing to commit, working tree clean");
+        }
+    }
+
     auto tree = this->tree_lookup(&tree_id);
 
     throw_if_error(git_commit_create(

test/test_commit.py

@@ -81,3 +81,45 @@ def test_commit_message_via_stdin(
         assert "Author:" in lines[1]
         assert "Date" in lines[2]
         assert commit_msg_out in lines[4]
+
+
+def test_commit_no_changes_initial(commit_env_config, git2cpp_path, tmp_path):
+    """Commit on fresh repo with no staged files should fail"""
+    cmd_init = [git2cpp_path, "init", "."]
+    p_init = subprocess.run(cmd_init, capture_output=True, cwd=tmp_path)
+    assert p_init.returncode == 0
+
+    # Do NOT add any files — attempt to commit immediately
+    cmd_commit = [git2cpp_path, "commit", "-m", "empty commit"]
+    p_commit = subprocess.run(cmd_commit, capture_output=True, cwd=tmp_path, text=True)
+
+    # Should fail: nothing to commit
+    assert p_commit.returncode != 0
+    assert "nothing to commit" in p_commit.stderr or "nothing to commit" in p_commit.stdout
+
+
+def test_commit_no_changes_after_first_commit(commit_env_config, git2cpp_path, tmp_path):
+    """Commit twice without changes between commits should fail"""
+    cmd_init = [git2cpp_path, "init", "."]
+    p_init = subprocess.run(cmd_init, capture_output=True, cwd=tmp_path)
+    assert p_init.returncode == 0
+
+    # Create and commit a file
+    (tmp_path / "file.txt").write_text("hello")
+    subprocess.run([git2cpp_path, "add", "file.txt"], cwd=tmp_path, check=True)
+    p_first = subprocess.run(
+        [git2cpp_path, "commit", "-m", "first commit"], cwd=tmp_path, capture_output=True, text=True
+    )
+    assert p_first.returncode == 0
+
+    # Try to commit again without any new changes
+    p_second = subprocess.run(
+        [git2cpp_path, "commit", "-m", "second commit (no changes)"],
+        cwd=tmp_path,
+        capture_output=True,
+        text=True,
+    )
+
+    # Should fail: nothing to commit
+    assert p_second.returncode != 0
+    assert "nothing to commit" in p_second.stderr or "nothing to commit" in p_second.stdout