cli_util: Make resolve_base_revs use IndexSet

This will make deduplication easier in the next commit.
The error message becomes slightly less informative, unfortunately.

src/cli_util.rs

@@ -1412,19 +1412,16 @@ pub fn resolve_multiple_nonempty_revsets(
 pub fn resolve_base_revs(
     workspace_command: &WorkspaceCommandHelper,
     revisions: &[RevisionArg],
-) -> Result<Vec<Commit>, CommandError> {
-    let mut commits = vec![];
+) -> Result<IndexSet<Commit>, CommandError> {
+    let mut commits = IndexSet::new();
     for revision_str in revisions {
         let commit = workspace_command.resolve_single_rev(revision_str)?;
-        if let Some(i) = commits.iter().position(|c| c == &commit) {
+        let commit_hash = short_commit_hash(commit.id());
+        if !commits.insert(commit) {
             return Err(user_error(format!(
-                r#"Revset "{}" and "{}" resolved to the same revision {}"#,
-                &revisions[i].0,
-                &revision_str.0,
-                short_commit_hash(commit.id()),
+                r#"More than one revset resolved to revision {commit_hash}"#,
             )));
         }
-        commits.push(commit);
     }
 
     let root_commit_id = workspace_command.repo().store().root_commit_id();

src/commands/mod.rs

@@ -1996,7 +1996,9 @@ fn cmd_new(ui: &mut Ui, command: &CommandHelper, args: &NewArgs) -> Result<(), C
         !args.revisions.is_empty(),
         "expected a non-empty list from clap"
     );
-    let commits = resolve_base_revs(&workspace_command, &args.revisions)?;
+    let commits = resolve_base_revs(&workspace_command, &args.revisions)?
+        .into_iter()
+        .collect_vec();
     let parent_ids = commits.iter().map(|c| c.id().clone()).collect();
     let mut tx = workspace_command.start_transaction("new empty commit");
     let merged_tree = merge_commit_trees(tx.base_repo().as_repo_ref(), &commits);
@@ -2685,7 +2687,9 @@ fn cmd_merge(ui: &mut Ui, command: &CommandHelper, args: &NewArgs) -> Result<(),
 
 fn cmd_rebase(ui: &mut Ui, command: &CommandHelper, args: &RebaseArgs) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
-    let new_parents = resolve_base_revs(&workspace_command, &args.destination)?;
+    let new_parents = resolve_base_revs(&workspace_command, &args.destination)?
+        .into_iter()
+        .collect_vec();
     if let Some(rev_str) = &args.revision {
         rebase_revision(ui, command, &mut workspace_command, &new_parents, rev_str)?;
     } else if let Some(source_str) = &args.source {

tests/test_new_command.rs

@@ -96,7 +96,7 @@ fn test_new_merge() {
     // merge with non-unique revisions
     let stderr = test_env.jj_cmd_failure(&repo_path, &["new", "@", "200e"]);
     insta::assert_snapshot!(stderr, @r###"
-    Error: Revset "@" and "200e" resolved to the same revision 200ed1a14c8a
+    Error: More than one revset resolved to revision 200ed1a14c8a
     "###);
 
     // merge with root

tests/test_rebase_command.rs

@@ -324,7 +324,7 @@ fn test_rebase_multiple_destinations() {
 
     let stderr = test_env.jj_cmd_failure(&repo_path, &["rebase", "-r", "a", "-d", "b", "-d", "b"]);
     insta::assert_snapshot!(stderr, @r###"
-    Error: Revset "b" and "b" resolved to the same revision d370aee184ba
+    Error: More than one revset resolved to revision d370aee184ba
     "###);
 
     let stderr =