step sixty two: don't allow force push

src/base.rs

@@ -459,6 +459,17 @@ pub fn get_working_tree() -> HashMap<String, String> {
     return result;
 }
 
+pub fn is_ancestor_of(commit: String, maybe_ancestor: String) -> bool {
+    let mut commits = VecDeque::new();
+    commits.push_front(commit);
+    for oid in iter_commits_and_parents(commits) {
+        if maybe_ancestor == oid {
+            return true;
+        }
+    }
+    return false;
+}
+
 fn empty_current_directory(dir: &str) -> io::Result<()> {
     // Delete current directory, except the ignored directories and files
     for entry in fs::read_dir(dir)? {

src/remote.rs

@@ -31,9 +31,17 @@ pub fn fetch(path: String) {
 }
 
 pub fn push(remote_path: String, reference: String) {
+    let refs = get_remote_refs(remote_path.clone(), REMOTE_REFS_BASE);
+    let empty = "".to_owned();
+    let remote_ref = refs.get(&reference).unwrap_or(&empty);
     let local_ref = data::get_ref(reference.clone(), true).value;
     assert!(local_ref != "".to_string());
 
+    // Don't allow force push
+    assert!(
+        *remote_ref == "".to_owned() || base::is_ancestor_of(local_ref.clone(), remote_ref.clone())
+    );
+
     let commit_oids = vec![&local_ref];
     base::copy_objects_in_commits_and_parents(commit_oids, remote_path.clone(), true);