cli: branch: on create/set/rename, assume deleted tracking branch sti…

…ll exists

While explaining branch tracking behavior, I find it's bad UX that a deleted
branch can be re-"create"d with tracking state preserved. It's rather a "set"
operation. Since deleted tracking branch is still listed, I think it's better
to assume that the local branch name is reserved.

#3871

is_fast_forward() is restored from 8706fad "cli: inline check for
non-fast-forwardable branch move."

cli/src/commands/branch.rs

@@ -251,14 +251,19 @@ fn cmd_branch_create(
         workspace_command.resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
     let view = workspace_command.repo().view();
     let branch_names = &args.names;
-    if let Some(branch_name) = branch_names
-        .iter()
-        .find(|&name| view.get_local_branch(name).is_present())
-    {
-        return Err(user_error_with_hint(
-            format!("Branch already exists: {branch_name}"),
-            "Use `jj branch set` to update it.",
-        ));
+    for name in branch_names {
+        if view.get_local_branch(name).is_present() {
+            return Err(user_error_with_hint(
+                format!("Branch already exists: {name}"),
+                "Use `jj branch set` to update it.",
+            ));
+        }
+        if has_tracked_remote_branches(view, name) {
+            return Err(user_error_with_hint(
+                format!("Tracked remote branches exist for deleted branch: {name}"),
+                "Use `jj branch set` to restore local branch.",
+            ));
+        }
     }
 
     if branch_names.len() > 1 {
@@ -302,6 +307,11 @@ fn cmd_branch_rename(
     if view.get_local_branch(new_branch).is_present() {
         return Err(user_error(format!("Branch already exists: {new_branch}")));
     }
+    if has_tracked_remote_branches(view, new_branch) {
+        return Err(user_error(format!(
+            "Tracked remote branches exist for deleted branch: {new_branch}"
+        )));
+    }
 
     let mut tx = workspace_command.start_transaction();
     tx.mut_repo()
@@ -346,16 +356,20 @@ fn cmd_branch_set(
         workspace_command.resolve_single_rev(args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
     let repo = workspace_command.repo().as_ref();
     let is_fast_forward = |old_target: &RefTarget| {
-        // Strictly speaking, "all" old targets should be ancestors, but we allow
-        // conflict resolution by setting branch to "any" of the old target descendants.
-        old_target
-            .added_ids()
-            .any(|old| repo.index().is_ancestor(old, target_commit.id()))
+        if old_target.is_present() {
+            // Strictly speaking, "all" old targets should be ancestors, but we allow
+            // conflict resolution by setting branch to "any" of the old target descendants.
+            old_target
+                .added_ids()
+                .any(|old| repo.index().is_ancestor(old, target_commit.id()))
+        } else {
+            true
+        }
     };
     let branch_names = &args.names;
     for name in branch_names {
         let old_target = repo.view().get_local_branch(name);
-        if old_target.is_absent() {
+        if old_target.is_absent() && !has_tracked_remote_branches(repo.view(), name) {
             return Err(user_error_with_hint(
                 format!("No such branch: {name}"),
                 "Use `jj branch create` to create it.",

cli/tests/test_branch_command.rs

@@ -96,6 +96,14 @@ fn test_branch_move() {
     test_env.jj_cmd_ok(test_env.env_root(), &["git", "init", "repo"]);
     let repo_path = test_env.env_root().join("repo");
 
+    // Set up remote
+    let git_repo_path = test_env.env_root().join("git-repo");
+    git2::Repository::init_bare(git_repo_path).unwrap();
+    test_env.jj_cmd_ok(
+        &repo_path,
+        &["git", "remote", "add", "origin", "../git-repo"],
+    );
+
     let stderr = test_env.jj_cmd_failure(&repo_path, &["branch", "set", "foo"]);
     insta::assert_snapshot!(stderr, @r###"
     Error: No such branch: foo
@@ -126,6 +134,45 @@ fn test_branch_move() {
         &["branch", "set", "-r@-", "--allow-backwards", "foo"],
     );
     insta::assert_snapshot!(stderr, @"");
+
+    // Delete branch locally, but is still tracking remote
+    test_env.jj_cmd_ok(&repo_path, &["describe", "@-", "-mcommit"]);
+    test_env.jj_cmd_ok(&repo_path, &["git", "push", "-r@-"]);
+    test_env.jj_cmd_ok(&repo_path, &["branch", "delete", "foo"]);
+    insta::assert_snapshot!(get_branch_output(&test_env, &repo_path), @r###"
+    foo (deleted)
+      @origin: qpvuntsm 74205c97 (empty) commit
+    "###);
+
+    // Deleted tracking branch name should still be allocated
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["branch", "create", "foo"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Error: Tracked remote branches exist for deleted branch: foo
+    Hint: Use `jj branch set` to restore local branch.
+    "###);
+
+    // Restoring local target shouldn't invalidate tracking state
+    let (_stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["branch", "set", "foo"]);
+    insta::assert_snapshot!(stderr, @"");
+    insta::assert_snapshot!(get_branch_output(&test_env, &repo_path), @r###"
+    foo: mzvwutvl c3cc8247 (empty) (no description set)
+      @origin (behind by 1 commits): qpvuntsm 74205c97 (empty) commit
+    "###);
+
+    // Untracked remote branch shouldn't block creation of local branch
+    test_env.jj_cmd_ok(&repo_path, &["branch", "untrack", "foo@origin"]);
+    test_env.jj_cmd_ok(&repo_path, &["branch", "delete", "foo"]);
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["branch", "set", "foo"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Error: No such branch: foo
+    Hint: Use `jj branch create` to create it.
+    "###);
+    let (_stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["branch", "create", "foo"]);
+    insta::assert_snapshot!(stderr, @"");
+    insta::assert_snapshot!(get_branch_output(&test_env, &repo_path), @r###"
+    foo: mzvwutvl c3cc8247 (empty) (no description set)
+    foo@origin: qpvuntsm 74205c97 (empty) commit
+    "###);
 }
 
 #[test]
@@ -230,6 +277,32 @@ fn test_branch_rename() {
     Warning: Branch bremote has tracking remote branches which were not renamed.
     Hint: to rename the branch on the remote, you can `jj git push --branch bremote` first (to delete it on the remote), and then `jj git push --branch bremote2`. `jj git push --all` would also be sufficient.
     "###);
+
+    insta::assert_snapshot!(get_branch_output(&test_env, &repo_path), @r###"
+    bexist: yqosqzyt 372e2731 (empty) commit-1
+    blocal1: qpvuntsm c177823f (empty) commit-0
+    bremote (deleted)
+      @origin: kpqxywon 1a9dae5e (empty) commit-2
+    bremote2: kpqxywon 1a9dae5e (empty) commit-2
+    "###);
+
+    // Deleted tracking branch name should still be allocated
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["branch", "rename", "blocal1", "bremote"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Error: Tracked remote branches exist for deleted branch: bremote
+    "###);
+
+    // Untracked remote branch shouldn't block rename
+    test_env.jj_cmd_ok(&repo_path, &["branch", "untrack", "bremote@origin"]);
+    let (_stdout, stderr) =
+        test_env.jj_cmd_ok(&repo_path, &["branch", "rename", "blocal1", "bremote"]);
+    insta::assert_snapshot!(stderr, @"");
+    insta::assert_snapshot!(get_branch_output(&test_env, &repo_path), @r###"
+    bexist: yqosqzyt 372e2731 (empty) commit-1
+    bremote: qpvuntsm c177823f (empty) commit-0
+    bremote@origin: kpqxywon 1a9dae5e (empty) commit-2
+    bremote2: kpqxywon 1a9dae5e (empty) commit-2
+    "###);
 }
 
 #[test]