Allow fastworwards that break the lease

cli/tests/test_git_push.rs

@@ -202,13 +202,15 @@ fn test_git_push_other_remote_has_branch() {
     "###);
     // The branch was moved on the "other" remote as well (since it's actually the
     // same remote), but `jj` is not aware of that since it thinks this is a
-    // different remote. So, the push fails.
-    let stderr = test_env.jj_cmd_failure(&workspace_root, &["git", "push", "--remote=other"]);
+    // different remote. So, the push should fail.
+    //
+    // But it succeeds! That's because the branch is created at the same location as
+    // it is on the remote. This would also work for a descendant.
+    let (stdout, stderr) = test_env.jj_cmd_ok(&workspace_root, &["git", "push", "--remote=other"]);
+    insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     Branch changes to push to other:
       Add branch branch1 to d73041288714
-    Error: Refusing to push a branch that unexpectedly moved on the remote. Affected refs: ["refs/heads/branch1"]
-    Hint: Try fetching from the remote, then make the branch point to where you want it to be, and push again.
     "###);
 }
 
@@ -498,17 +500,14 @@ fn test_git_push_fastforward_but_unexpectedly_moved_sideways_on_remote() {
     insta::assert_snapshot!(get_stderr_string(&assert), @"");
     test_env.jj_cmd_ok(&origin_path, &["git", "export"]);
 
-    // BUG?
     let assert = test_env
-        .jj_cmd(&workspace_root, &["git", "push"])
+        .jj_cmd(&workspace_root, &["git", "push", "-bbranch1"])
         .assert()
-        .failure();
+        .success();
     insta::assert_snapshot!(get_stdout_string(&assert), @"");
     insta::assert_snapshot!(get_stderr_string(&assert), @r###"
     Branch changes to push to origin:
       Force branch branch1 from a0c93395c0a3 to 7a722cf0a4d8
-    Error: Refusing to push a branch that unexpectedly moved on the remote. Affected refs: ["refs/heads/branch1"]
-    Hint: Try fetching from the remote, then make the branch point to where you want it to be, and push again.
     "###);
 }
 
@@ -626,17 +625,14 @@ fn test_git_push_fastforward_but_unexpectedly_moved_up_on_remote() {
     insta::assert_snapshot!(get_stderr_string(&assert), @"");
     test_env.jj_cmd_ok(&origin_path, &["git", "export"]);
 
-    // BUG?
     let assert = test_env
-        .jj_cmd(&workspace_root, &["git", "push"])
+        .jj_cmd(&workspace_root, &["git", "push", "-bbranch1"])
         .assert()
-        .failure();
+        .success();
     insta::assert_snapshot!(get_stdout_string(&assert), @"");
     insta::assert_snapshot!(get_stderr_string(&assert), @r###"
     Branch changes to push to origin:
       Move branch branch1 from 8144f454db0f to 9a0388ceac79
-    Error: Refusing to push a branch that unexpectedly moved on the remote. Affected refs: ["refs/heads/branch1"]
-    Hint: Try fetching from the remote, then make the branch point to where you want it to be, and push again.
     "###);
 }
 

lib/src/git.rs

@@ -1356,7 +1356,7 @@ fn push_refs(
                     update.src_refname(), // Position to update the branch to (!)
                     update.dst_refname(), // Branch to update
                     update.dst(),         // Commit id of `src_refname` (!)
-                    update.src(),         // Expected current position
+                    update.src(),         // Current position
                     &expected_location
                 ); */
                 // See also https://github.com/git/git/blob/master/templates/hooks--pre-push.sample
@@ -1371,6 +1371,16 @@ fn push_refs(
                 /* TODO: Check if src and src_refname point to different things, if not this is a
                  * no-op */
                 {
+                    if update.src() == update.dst()
+                        || git_repo
+                            .graph_descendant_of(update.dst(), update.src())
+                            .unwrap_or(false)
+                    {
+                        // The Git remote would consider this a fast-forward regardless of where our
+                        // remote-tracking branch points. See tests with names that start with
+                        // `test_git_push_fastforward_but_unexpectedly_moved`
+                        continue;
+                    }
                     failed_push_negotiations_ref.push(update.dst_refname().map(|s| s.to_string()));
                 }
             }