cli: hint for conflicted branches

cli/src/cli_util.rs

@@ -51,9 +51,9 @@ use jj_lib::repo::{
 };
 use jj_lib::repo_path::{FsPathParseError, RepoPath};
 use jj_lib::revset::{
-    DefaultSymbolResolver, Revset, RevsetAliasesMap, RevsetEvaluationError, RevsetExpression,
-    RevsetIteratorExt, RevsetParseContext, RevsetParseError, RevsetParseErrorKind,
-    RevsetResolutionError, RevsetWorkspaceContext,
+    DefaultSymbolResolver, Revset, RevsetAliasesMap, RevsetCommitRef, RevsetEvaluationError,
+    RevsetExpression, RevsetIteratorExt, RevsetParseContext, RevsetParseError,
+    RevsetParseErrorKind, RevsetResolutionError, RevsetWorkspaceContext,
 };
 use jj_lib::settings::{ConfigResultExt as _, UserSettings};
 use jj_lib::transaction::Transaction;
@@ -1006,7 +1006,7 @@ impl WorkspaceCommandHelper {
         ui: &mut Ui,
     ) -> Result<Commit, CommandError> {
         let revset_expression = self.parse_revset(revision_str, Some(ui))?;
-        let revset = self.evaluate_revset(revset_expression)?;
+        let revset = self.evaluate_revset(revset_expression.clone())?;
         let mut iter = revset.iter().commits(self.repo().store()).fuse();
         match (iter.next(), iter.next()) {
             (Some(commit), None) => Ok(commit?),
@@ -1017,15 +1017,33 @@ impl WorkspaceCommandHelper {
                 let mut iter = [commit0, commit1].into_iter().chain(iter);
                 let commits: Vec<_> = iter.by_ref().take(5).try_collect()?;
                 let elided = iter.next().is_some();
-                let hint = format!(
-                    r#"The revset "{revision_str}" resolved to these revisions:{eol}{commits}{ellipsis}"#,
-                    eol = "\n",
-                    commits = commits
-                        .iter()
-                        .map(|c| self.format_commit_summary(c))
-                        .join("\n"),
-                    ellipsis = elided.then_some("\n...").unwrap_or_default()
-                );
+                let hint = if let RevsetExpression::CommitRef(RevsetCommitRef::Symbol(
+                    branch_name,
+                )) = revset_expression.as_ref()
+                {
+                    // Separate hint if there's a conflicted branch
+                    format!(
+                        r#"Branch {branch_name} resolved to multiple revisions because it's conflicted.
+It resolved to these revisions:
+{commits}{ellipsis}
+Set which revision the branch points to with "jj branch set {branch_name} -r <REVISION>"."#,
+                        commits = commits
+                            .iter()
+                            .map(|c| self.format_commit_summary(c))
+                            .join("\n"),
+                        ellipsis = elided.then_some("\n...").unwrap_or_default()
+                    )
+                } else {
+                    format!(
+                        r#"The revset "{revision_str}" resolved to these revisions:{eol}{commits}{ellipsis}"#,
+                        eol = "\n",
+                        commits = commits
+                            .iter()
+                            .map(|c| self.format_commit_summary(c))
+                            .join("\n"),
+                        ellipsis = elided.then_some("\n...").unwrap_or_default()
+                    )
+                };
                 Err(user_error_with_hint(
                     format!(r#"Revset "{revision_str}" resolved to more than one revision"#),
                     hint,

cli/tests/test_checkout.rs

@@ -100,7 +100,80 @@ fn test_checkout_not_single_rev() {
     "###);
 }
 
+#[test]
+fn test_checkout_conflicting_branches() {
+    // Much of this test is borrowed from `test_git_fetch_conflicting_branches` in
+    // test_git_fetch.rs
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    add_git_remote(&test_env, &repo_path, "rem1");
+
+    // Create a rem1 branch locally
+    test_env.jj_cmd_success(&repo_path, &["new", "root()"]);
+    test_env.jj_cmd_success(&repo_path, &["branch", "create", "rem1"]);
+
+    test_env.jj_cmd_success(
+        &repo_path,
+        &["git", "fetch", "--remote", "rem1", "--branch", "*"],
+    );
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-r", "rem1"]);
+    insta::assert_snapshot!(stdout, @r###"
+    ◉  qxosxrvv [email protected] 1970-01-01 00:00:00.000 +00:00 rem1?? rem1@rem1 6a211027
+    │  message
+    ~
+
+    @  kkmpptxz [email protected] 2001-02-03 04:05:09.000 +07:00 rem1?? fcdbbd73
+    │  (empty) (no description set)
+    ~
+    "###);
+
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["checkout", "rem1"]);
+    insta::assert_snapshot!(stderr, @r###"
+    Error: Revset "rem1" resolved to more than one revision
+    Hint: Branch rem1 resolved to multiple revisions because it's conflicted.
+    It resolved to these revisions:
+    qxosxrvv 6a211027 rem1?? rem1@rem1 | message
+    kkmpptxz fcdbbd73 rem1?? | (empty) (no description set)
+    Set which revision the branch points to with "jj branch set rem1 -r <REVISION>".
+    "###);
+}
+
 fn get_log_output(test_env: &TestEnvironment, cwd: &Path) -> String {
     let template = r#"commit_id ++ " " ++ description"#;
     test_env.jj_cmd_success(cwd, &["log", "-T", template])
 }
+
+fn init_git_remote(test_env: &TestEnvironment, remote: &str) {
+    let git_repo_path = test_env.env_root().join(remote);
+    let git_repo = git2::Repository::init(git_repo_path).unwrap();
+    let signature =
+        git2::Signature::new("Some One", "[email protected]", &git2::Time::new(0, 0)).unwrap();
+    let mut tree_builder = git_repo.treebuilder(None).unwrap();
+    let file_oid = git_repo.blob(remote.as_bytes()).unwrap();
+    tree_builder
+        .insert("file", file_oid, git2::FileMode::Blob.into())
+        .unwrap();
+    let tree_oid = tree_builder.write().unwrap();
+    let tree = git_repo.find_tree(tree_oid).unwrap();
+    git_repo
+        .commit(
+            Some(&format!("refs/heads/{remote}")),
+            &signature,
+            &signature,
+            "message",
+            &tree,
+            &[],
+        )
+        .unwrap();
+}
+
+fn add_git_remote(test_env: &TestEnvironment, repo_path: &Path, remote: &str) {
+    init_git_remote(test_env, remote);
+    test_env.jj_cmd_success(
+        repo_path,
+        &["git", "remote", "add", remote, &format!("../{remote}")],
+    );
+}