cli: colorize commits summary embedded in single revset resolution hint

I think a colorized commit summary is easier to follow.

cli/src/cli_util.rs

@@ -795,27 +795,27 @@ 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 commits_summary = {
+                let write_commits_summary = |formatter: &mut dyn Formatter| {
                     let template = self.commit_summary_template();
-                    let mut output = Vec::new();
-                    let mut formatter = PlainTextFormatter::new(&mut output);
                     for commit in &commits {
                         write!(formatter, "  ")?;
-                        template.format(commit, &mut formatter).unwrap();
+                        template.format(commit, formatter)?;
-                        writeln!(formatter).unwrap();
+                        writeln!(formatter)?;
                     }
                     if elided {
-                        writeln!(formatter, "  ...").unwrap();
+                        writeln!(formatter, "  ...")?;
                     }
-                    output.pop(); // drop last newline
+                    Ok(())
-                    String::from_utf8(output).expect("template output should be utf-8 bytes")
                 };
                 if commits[0].change_id() == commits[1].change_id() {
                     // Separate hint if there's commits with same change id
-                    cmd_err.add_hint(format!(
+                    cmd_err.add_formatted_hint_with(|formatter| {
-                        r#"The revset "{revision_str}" resolved to these revisions:
+                        writeln!(
-{commits_summary}"#
+                            formatter,
-                    ));
+                            r#"The revset "{revision_str}" resolved to these revisions:"#
+                        )?;
+                        write_commits_summary(formatter)
+                    });
                     cmd_err.add_hint(
                         "Some of these commits have the same change id. Abandon one of them with \
                          `jj abandon -r <REVISION>`.",
@@ -824,19 +824,27 @@ impl WorkspaceCommandHelper {
                     revset_expression.as_ref()
                 {
                     // Separate hint if there's a conflicted branch
-                    cmd_err.add_hint(format!(
+                    cmd_err.add_formatted_hint_with(|formatter| {
-                        r#"Branch {branch_name} resolved to multiple revisions because it's conflicted.
+                        writeln!(
-It resolved to these revisions:
+                            formatter,
-{commits_summary}"#));
+                            "Branch {branch_name} resolved to multiple revisions because it's \
+                             conflicted."
+                        )?;
+                        writeln!(formatter, "It resolved to these revisions:")?;
+                        write_commits_summary(formatter)
+                    });
                     cmd_err.add_hint(format!(
                         "Set which revision the branch points to with `jj branch set \
                          {branch_name} -r <REVISION>`.",
                     ));
                 } else {
-                    cmd_err.add_hint(format!(
+                    cmd_err.add_formatted_hint_with(|formatter| {
-                        r#"The revset "{revision_str}" resolved to these revisions:
+                        writeln!(
-{commits_summary}"#,
+                            formatter,
-                    ));
+                            r#"The revset "{revision_str}" resolved to these revisions:"#
+                        )?;
+                        write_commits_summary(formatter)
+                    });
                     if should_hint_about_all_prefix {
                         cmd_err.add_hint(format!(
                             "Prefix the expression with 'all:' to allow any number of revisions \

cli/tests/test_global_opts.rs

@@ -429,6 +429,16 @@ fn test_color_ui_messages() {
     <Error: No commit available>  (elided revisions)
     0000000000000000000000000000000000000000
     "###);
+
+    // formatted hint
+    let stderr = test_env.jj_cmd_failure(&repo_path, &["new", ".."]);
+    insta::assert_snapshot!(stderr, @r###"
+    Error: Revset ".." resolved to more than one revision
+    Hint: The revset ".." resolved to these revisions:
+      mzvwutvl 167f90e7 (empty) (no description set)
+      qpvuntsm 230dd059 (empty) (no description set)
+    Hint: Prefix the expression with 'all:' to allow any number of revisions (i.e. 'all:..').
+    "###);
 }
 
 #[test]