cli: extract function that creates "not a single revision" error

This function isn't small, so let's split up into two parts. The extracted
function is the part which depends on the commit summary template.

cli/src/cli_util.rs

@@ -52,7 +52,7 @@ use jj_lib::repo::{
 };
 use jj_lib::repo_path::{FsPathParseError, RepoPath, RepoPathBuf};
 use jj_lib::revset::{
-    RevsetAliasesMap, RevsetCommitRef, RevsetExpression, RevsetFilterPredicate, RevsetIteratorExt,
+    RevsetAliasesMap, RevsetExpression, RevsetFilterPredicate, RevsetIteratorExt,
     RevsetParseContext, RevsetWorkspaceContext,
 };
 use jj_lib::rewrite::restore_tree;
@@ -790,70 +790,17 @@ impl WorkspaceCommandHelper {
                 r#"Revset "{revision_str}" didn't resolve to any revisions"#
             ))),
             (Some(commit0), Some(commit1)) => {
-                let mut cmd_err = user_error(format!(
-                    r#"Revset "{revision_str}" resolved to more than one revision"#
-                ));
                 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 write_commits_summary = |formatter: &mut dyn Formatter| {
-                    let template = self.commit_summary_template();
-                    for commit in &commits {
-                        write!(formatter, "  ")?;
-                        template.format(commit, formatter)?;
-                        writeln!(formatter)?;
-                    }
-                    if elided {
-                        writeln!(formatter, "  ...")?;
-                    }
-                    Ok(())
-                };
-                if commits[0].change_id() == commits[1].change_id() {
-                    // Separate hint if there's commits with same change id
-                    cmd_err.add_formatted_hint_with(|formatter| {
-                        writeln!(
-                            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>`.",
-                    );
-                } else if let RevsetExpression::CommitRef(RevsetCommitRef::Symbol(branch_name)) =
-                    revset_expression.expression().as_ref()
-                {
-                    // Separate hint if there's a conflicted branch
-                    cmd_err.add_formatted_hint_with(|formatter| {
-                        writeln!(
-                            formatter,
-                            "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_formatted_hint_with(|formatter| {
-                        writeln!(
-                            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 \
-                             (i.e. 'all:{revision_str}')."
-                        ));
-                    }
-                };
-                Err(cmd_err)
+                Err(revset_util::format_multiple_revisions_error(
+                    revision_str,
+                    revset_expression.expression(),
+                    &commits,
+                    elided,
+                    &self.commit_summary_template(),
+                    should_hint_about_all_prefix,
+                ))
             }
         }
     }

cli/src/revset_util.rs

@@ -22,14 +22,17 @@ use jj_lib::commit::Commit;
 use jj_lib::id_prefix::IdPrefixContext;
 use jj_lib::repo::Repo;
 use jj_lib::revset::{
-    self, DefaultSymbolResolver, Revset, RevsetAliasesMap, RevsetEvaluationError, RevsetExpression,
-    RevsetIteratorExt as _, RevsetParseContext, RevsetParseError, RevsetResolutionError,
+    self, DefaultSymbolResolver, Revset, RevsetAliasesMap, RevsetCommitRef, RevsetEvaluationError,
+    RevsetExpression, RevsetIteratorExt as _, RevsetParseContext, RevsetParseError,
+    RevsetResolutionError,
 };
 use jj_lib::settings::ConfigResultExt as _;
 use thiserror::Error;
 
 use crate::command_error::{user_error, CommandError};
 use crate::config::LayeredConfigs;
+use crate::formatter::Formatter;
+use crate::templater::TemplateRenderer;
 use crate::ui::Ui;
 
 const BUILTIN_IMMUTABLE_HEADS: &str = "immutable_heads";
@@ -182,3 +185,71 @@ pub fn parse_immutable_expression(
     let heads = revset::parse(immutable_heads_str, context)?;
     Ok(heads.union(&RevsetExpression::root()).ancestors())
 }
+
+pub(super) fn format_multiple_revisions_error(
+    revision_str: &str,
+    expression: &RevsetExpression,
+    commits: &[Commit],
+    elided: bool,
+    template: &TemplateRenderer<'_, Commit>,
+    should_hint_about_all_prefix: bool,
+) -> CommandError {
+    assert!(commits.len() >= 2);
+    let mut cmd_err = user_error(format!(
+        r#"Revset "{revision_str}" resolved to more than one revision"#
+    ));
+    let write_commits_summary = |formatter: &mut dyn Formatter| {
+        for commit in commits {
+            write!(formatter, "  ")?;
+            template.format(commit, formatter)?;
+            writeln!(formatter)?;
+        }
+        if elided {
+            writeln!(formatter, "  ...")?;
+        }
+        Ok(())
+    };
+    if commits[0].change_id() == commits[1].change_id() {
+        // Separate hint if there's commits with same change id
+        cmd_err.add_formatted_hint_with(|formatter| {
+            writeln!(
+                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>`.",
+        );
+    } else if let RevsetExpression::CommitRef(RevsetCommitRef::Symbol(branch_name)) = expression {
+        // Separate hint if there's a conflicted branch
+        cmd_err.add_formatted_hint_with(|formatter| {
+            writeln!(
+                formatter,
+                "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_formatted_hint_with(|formatter| {
+            writeln!(
+                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 (i.e. \
+                 'all:{revision_str}')."
+            ));
+        }
+    };
+    cmd_err
+}