Expose diff format options to describe-like commands

This implements some more powerful version of `git commit --verbose`,
which lets the user get more context in the editor buffer they use to
write a commit message.

We default to `DiffFormat::Summary`, which was the previously hardcoded
value.

cli/src/commands/commit.rs

@@ -22,6 +22,7 @@ use crate::command_error::{user_error, CommandError};
 use crate::description_util::{
     description_template_for_commit, edit_description, join_message_paragraphs,
 };
+use crate::diff_util::DiffFormatArgs;
 use crate::ui::Ui;
 
 /// Update the description and create a new change on top.
@@ -40,6 +41,8 @@ pub(crate) struct CommitArgs {
     /// Put these paths in the first commit
     #[arg(value_hint = clap::ValueHint::AnyPath)]
     paths: Vec<String>,
+    #[command(flatten)]
+    diff_format: DiffFormatArgs,
 }
 
 #[instrument(skip_all)]
@@ -94,6 +97,7 @@ new working-copy commit.
         commit.description(),
         &base_tree,
         &middle_tree,
+        &args.diff_format,
     )?;
 
     let description = if !args.message_paragraphs.is_empty() {

cli/src/commands/describe.rs

@@ -22,6 +22,7 @@ use crate::command_error::CommandError;
 use crate::description_util::{
     description_template_for_describe, edit_description, join_message_paragraphs,
 };
+use crate::diff_util::DiffFormatArgs;
 use crate::ui::Ui;
 
 /// Update the change description or other metadata
@@ -58,6 +59,8 @@ pub(crate) struct DescribeArgs {
     /// $ JJ_USER='Foo Bar' [email protected] jj describe --reset-author
     #[arg(long)]
     reset_author: bool,
+    #[command(flatten)]
+    diff_format: DiffFormatArgs,
 }
 
 #[instrument(skip_all)]
@@ -78,8 +81,13 @@ pub(crate) fn cmd_describe(
     } else if args.no_edit {
         commit.description().to_owned()
     } else {
-        let template =
-            description_template_for_describe(ui, command.settings(), &workspace_command, &commit)?;
+        let template = description_template_for_describe(
+            ui,
+            command.settings(),
+            &workspace_command,
+            &commit,
+            &args.diff_format,
+        )?;
         edit_description(workspace_command.repo(), &template, command.settings())?
     };
     if description == *commit.description() && !args.reset_author {

cli/src/commands/split.rs

@@ -25,6 +25,7 @@ use crate::cli_util::{CommandHelper, RevisionArg};
 use crate::command_error::CommandError;
 use crate::commands::rebase::rebase_descendants;
 use crate::description_util::{description_template_for_commit, edit_description};
+use crate::diff_util::DiffFormatArgs;
 use crate::ui::Ui;
 
 /// Split a revision in two
@@ -57,6 +58,8 @@ pub(crate) struct SplitArgs {
     /// Put these paths in the first commit
     #[arg(value_hint = clap::ValueHint::AnyPath)]
     paths: Vec<String>,
+    #[command(flatten)]
+    diff_format: DiffFormatArgs,
 }
 
 #[instrument(skip_all)]
@@ -119,6 +122,7 @@ the operation will be aborted.
         commit.description(),
         &base_tree,
         &selected_tree,
+        &args.diff_format,
     )?;
     let first_description = edit_description(tx.base_repo(), &first_template, command.settings())?;
     let first_commit = tx
@@ -155,6 +159,7 @@ the operation will be aborted.
             commit.description(),
             second_base_tree,
             &second_tree,
+            &args.diff_format,
         )?;
         edit_description(tx.base_repo(), &second_template, command.settings())?
     };

cli/src/description_util.rs

@@ -7,7 +7,7 @@ use jj_lib::settings::UserSettings;
 
 use crate::cli_util::{edit_temp_file, WorkspaceCommandHelper};
 use crate::command_error::CommandError;
-use crate::diff_util::{self, DiffFormat};
+use crate::diff_util::{self, diff_formats_for_describe, DiffFormatArgs};
 use crate::formatter::PlainTextFormatter;
 use crate::text_util;
 use crate::ui::Ui;
@@ -95,6 +95,7 @@ pub fn description_template_for_describe(
     settings: &UserSettings,
     workspace_command: &WorkspaceCommandHelper,
     commit: &Commit,
+    diff_format: &DiffFormatArgs,
 ) -> Result<String, CommandError> {
     let mut diff_summary_bytes = Vec::new();
     diff_util::show_patch(
@@ -103,7 +104,7 @@ pub fn description_template_for_describe(
         workspace_command,
         commit,
         &EverythingMatcher,
-        &[DiffFormat::Summary],
+        &diff_formats_for_describe(settings, diff_format)?,
     )?;
     let description = if commit.description().is_empty() {
         settings.default_description()
@@ -117,6 +118,7 @@ pub fn description_template_for_describe(
     }
 }
 
+#[allow(clippy::too_many_arguments)]
 pub fn description_template_for_commit(
     ui: &Ui,
     settings: &UserSettings,
@@ -125,6 +127,7 @@ pub fn description_template_for_commit(
     overall_commit_description: &str,
     from_tree: &MergedTree,
     to_tree: &MergedTree,
+    diff_format: &DiffFormatArgs,
 ) -> Result<String, CommandError> {
     let mut diff_summary_bytes = Vec::new();
     diff_util::show_diff(
@@ -134,7 +137,7 @@ pub fn description_template_for_commit(
         from_tree,
         to_tree,
         &EverythingMatcher,
-        &[DiffFormat::Summary],
+        &diff_formats_for_describe(settings, diff_format)?,
     )?;
     let mut template_chunks = Vec::new();
     if !intro.is_empty() {

cli/src/diff_util.rs

@@ -120,6 +120,19 @@ pub fn diff_formats_for_log(
     Ok(formats)
 }
 
+/// Returns a list of requested diff formats for describe-like commands, which
+/// will never be empty.
+pub fn diff_formats_for_describe(
+    settings: &UserSettings,
+    args: &DiffFormatArgs,
+) -> Result<Vec<DiffFormat>, config::ConfigError> {
+    let mut formats = diff_formats_from_args(settings, args)?;
+    if formats.is_empty() {
+        formats.push(DiffFormat::Summary);
+    }
+    Ok(formats)
+}
+
 fn diff_formats_from_args(
     settings: &UserSettings,
     args: &DiffFormatArgs,