describe: allow updating the description of multiple commits

If multiple commits are provided, the description of each commit
will be combined into a single file for editing.

CHANGELOG.md

@@ -85,6 +85,8 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 * [The default commit description template](docs/config.md#default-description)
   can now be configured by `templates.draft_commit_description`.
 
+* `jj describe` can now update the description of multiple commits.
+
 ### Fixed bugs
 
 * `jj diff --git` no longer shows the contents of binary files.

cli/src/commands/describe.rs

@@ -12,33 +12,44 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::collections::HashMap;
 use std::io::{self, Read};
 
+use itertools::Itertools;
+use jj_lib::commit::CommitIteratorExt;
 use jj_lib::object_id::ObjectId;
 use tracing::instrument;
 
 use crate::cli_util::{CommandHelper, RevisionArg};
-use crate::command_error::CommandError;
-use crate::description_util::{description_template, edit_description, join_message_paragraphs};
+use crate::command_error::{user_error, CommandError};
+use crate::description_util::{
+    edit_multiple_descriptions, join_message_paragraphs, EditMultipleDescriptionsResult,
+};
 use crate::ui::Ui;
 
 /// Update the change description or other metadata
 ///
-/// Starts an editor to let you edit the description of a change. The editor
+/// Starts an editor to let you edit the description of changes. The editor
 /// will be $EDITOR, or `pico` if that's not defined (`Notepad` on Windows).
 #[derive(clap::Args, Clone, Debug)]
 #[command(visible_aliases = &["desc"])]
 pub(crate) struct DescribeArgs {
-    /// The revision whose description to edit
+    /// The revision(s) whose description to edit
     #[arg(default_value = "@")]
-    revision: RevisionArg,
+    revisions: Vec<RevisionArg>,
     /// Ignored (but lets you pass `-r` for consistency with other commands)
-    #[arg(short = 'r', hide = true)]
-    unused_revision: bool,
+    #[arg(short = 'r', hide = true, action = clap::ArgAction::Count)]
+    unused_revision: u8,
     /// The change description to use (don't open editor)
+    ///
+    /// If multiple revisions are specified, the same description will be used
+    /// for all of them.
     #[arg(long = "message", short, value_name = "MESSAGE")]
     message_paragraphs: Vec<String>,
     /// Read the change description from stdin
+    ///
+    /// If multiple revisions are specified, the same description will be used
+    /// for all of them.
     #[arg(long)]
     stdin: bool,
     /// Don't open an editor
@@ -65,39 +76,136 @@ pub(crate) fn cmd_describe(
     args: &DescribeArgs,
 ) -> Result<(), CommandError> {
     let mut workspace_command = command.workspace_helper(ui)?;
-    let commit = workspace_command.resolve_single_rev(&args.revision)?;
-    workspace_command.check_rewritable([commit.id()])?;
+    let commits: Vec<_> = workspace_command
+        .parse_union_revsets(&args.revisions)?
+        .evaluate_to_commits()?
+        .try_collect()?; // in reverse topological order
+    if commits.is_empty() {
+        writeln!(ui.status(), "No revisions to describe.")?;
+        return Ok(());
+    }
+    workspace_command.check_rewritable(commits.iter().ids())?;
 
     let mut tx = workspace_command.start_transaction();
-    let mut commit_builder = tx
-        .mut_repo()
-        .rewrite_commit(command.settings(), &commit)
-        .detach();
-    if args.reset_author {
-        commit_builder.set_author(commit_builder.committer().clone());
-    }
+    let tx_description = if commits.len() == 1 {
+        format!("describe commit {}", commits[0].id().hex())
+    } else {
+        format!(
+            "describe commit {} and {} more",
+            commits[0].id().hex(),
+            commits.len() - 1
+        )
+    };
 
-    let description = if args.stdin {
+    let shared_description = if args.stdin {
         let mut buffer = String::new();
         io::stdin().read_to_string(&mut buffer)?;
-        buffer
+        Some(buffer)
     } else if !args.message_paragraphs.is_empty() {
-        join_message_paragraphs(&args.message_paragraphs)
-    } else if args.no_edit {
-        commit.description().to_owned()
+        Some(join_message_paragraphs(&args.message_paragraphs))
     } else {
-        if commit_builder.description().is_empty() {
-            commit_builder.set_description(command.settings().default_description());
+        None
+    };
+
+    let commit_descriptions: Vec<(_, _)> = if args.no_edit || shared_description.is_some() {
+        commits
+            .iter()
+            .map(|commit| {
+                let new_description = shared_description
+                    .as_deref()
+                    .unwrap_or_else(|| commit.description());
+                (commit, new_description.to_owned())
+            })
+            .collect()
+    } else {
+        let repo = tx.base_repo().clone();
+        let EditMultipleDescriptionsResult {
+            descriptions,
+            missing,
+            duplicates,
+            unexpected,
+        } = edit_multiple_descriptions(
+            &mut tx,
+            &repo,
+            // Edit descriptions in topological order
+            &commits.iter().rev().collect_vec(),
+            command.settings(),
+        )?;
+        if !missing.is_empty() {
+            return Err(user_error(format!(
+                "The description for the following commits were not found in the edited message: \
+                 {}",
+                missing.join(", ")
+            )));
+        }
+        if !duplicates.is_empty() {
+            return Err(user_error(format!(
+                "The following commits were found in the edited message multiple times: {}",
+                duplicates.join(", ")
+            )));
         }
-        let temp_commit = commit_builder.write_hidden()?;
-        let template = description_template(&tx, "", &temp_commit)?;
-        edit_description(tx.base_repo(), &template, command.settings())?
+        if !unexpected.is_empty() {
+            return Err(user_error(format!(
+                "The following commits were not being edited, but were found in the edited \
+                 message: {}",
+                unexpected.join(", ")
+            )));
+        }
+
+        let commit_descriptions = commits
+            .iter()
+            .filter_map(|commit| {
+                descriptions
+                    .get(commit.id())
+                    .map(|description| (commit, description.to_owned()))
+            })
+            .collect();
+
+        commit_descriptions
     };
-    commit_builder.set_description(description);
 
-    if commit_builder.description() != commit.description() || args.reset_author {
-        commit_builder.write(tx.mut_repo())?;
+    let commit_descriptions: HashMap<_, _> = commit_descriptions
+        .into_iter()
+        .filter_map(|(commit, new_description)| {
+            if *new_description == *commit.description() && !args.reset_author {
+                None
+            } else {
+                Some((commit.id(), new_description))
+            }
+        })
+        .collect();
+
+    let mut num_described = 0;
+    let mut num_rebased = 0;
+    tx.mut_repo().transform_descendants(
+        command.settings(),
+        commit_descriptions
+            .keys()
+            .map(|&id| id.clone())
+            .collect_vec(),
+        |rewriter| {
+            let old_commit_id = rewriter.old_commit().id().clone();
+            let mut commit_builder = rewriter.rebase(command.settings())?;
+            if let Some(description) = commit_descriptions.get(&old_commit_id) {
+                commit_builder = commit_builder.set_description(description);
+                if args.reset_author {
+                    let new_author = commit_builder.committer().clone();
+                    commit_builder = commit_builder.set_author(new_author);
+                }
+                num_described += 1;
+            } else {
+                num_rebased += 1;
+            }
+            commit_builder.write()?;
+            Ok(())
+        },
+    )?;
+    if num_described > 1 {
+        writeln!(ui.status(), "Updated {} commits", num_described)?;
+    }
+    if num_rebased > 0 {
+        writeln!(ui.status(), "Rebased {} descendant commits", num_rebased)?;
     }
-    tx.finish(ui, format!("describe commit {}", commit.id().hex()))?;
+    tx.finish(ui, tx_description)?;
     Ok(())
 }

cli/src/description_util.rs

@@ -1,16 +1,28 @@
+use std::collections::HashMap;
 use std::io::Write as _;
 
 use bstr::ByteVec as _;
 use itertools::Itertools;
+use jj_lib::backend::CommitId;
 use jj_lib::commit::Commit;
 use jj_lib::repo::ReadonlyRepo;
 use jj_lib::settings::UserSettings;
 
-use crate::cli_util::{edit_temp_file, WorkspaceCommandTransaction};
+use crate::cli_util::{edit_temp_file, short_commit_hash, WorkspaceCommandTransaction};
 use crate::command_error::CommandError;
 use crate::formatter::PlainTextFormatter;
 use crate::text_util;
 
+/// Cleanup a description by normalizing line endings, and removing leading and
+/// trailing blank lines.
+fn cleanup_description(description: &str) -> String {
+    let description = description
+        .lines()
+        .filter(|line| !line.starts_with("JJ: "))
+        .join("\n");
+    text_util::complete_newline(description.trim_matches('\n'))
+}
+
 pub fn edit_description(
     repo: &ReadonlyRepo,
     description: &str,
@@ -31,12 +43,138 @@ JJ: Lines starting with "JJ: " (like this one) will be removed.
         settings,
     )?;
 
-    // Normalize line ending, remove leading and trailing blank lines.
-    let description = description
-        .lines()
-        .filter(|line| !line.starts_with("JJ: "))
-        .join("\n");
-    Ok(text_util::complete_newline(description.trim_matches('\n')))
+    Ok(cleanup_description(&description))
+}
+
+#[derive(Debug)]
+pub struct EditMultipleDescriptionsResult {
+    /// The parsed, formatted descriptions.
+    pub descriptions: HashMap<CommitId, String>,
+    /// Commit IDs that were expected while parsing the edited messages, but
+    /// which were not found.
+    pub missing: Vec<String>,
+    /// Commit IDs that were found multiple times while parsing the edited
+    /// messages.
+    pub duplicates: Vec<String>,
+    /// Commit IDs that were found while parsing the edited messages, but which
+    /// were not originally being edited.
+    pub unexpected: Vec<String>,
+}
+
+/// Edits the descriptions of the given commits in a single editor session.
+pub fn edit_multiple_descriptions(
+    tx: &mut WorkspaceCommandTransaction,
+    repo: &ReadonlyRepo,
+    commits: &[&Commit],
+    settings: &UserSettings,
+) -> Result<EditMultipleDescriptionsResult, CommandError> {
+    let mut commits_map = HashMap::new();
+    let mut output_chunks = Vec::new();
+
+    for &commit in commits.iter() {
+        let commit_hash = short_commit_hash(commit.id());
+        if commits.len() > 1 {
+            output_chunks.push(format!("JJ: describe {} -------\n", commit_hash.clone()));
+        }
+        commits_map.insert(commit_hash, commit.id());
+        let mut commit_builder = tx.mut_repo().rewrite_commit(settings, commit).detach();
+        if commit_builder.description().is_empty() {
+            commit_builder.set_description(settings.default_description());
+        }
+        let temp_commit = commit_builder.write_hidden()?;
+        let template = description_template(tx, "", &temp_commit)?;
+        output_chunks.push(template);
+        output_chunks.push("\n".to_owned());
+    }
+    output_chunks
+        .push("JJ: Lines starting with \"JJ: \" (like this one) will be removed.\n".to_owned());
+    let bulk_message = output_chunks.join("");
+
+    let bulk_message = edit_temp_file(
+        "description",
+        ".jjdescription",
+        repo.repo_path(),
+        &bulk_message,
+        settings,
+    )?;
+
+    if commits.len() == 1 {
+        return Ok(EditMultipleDescriptionsResult {
+            descriptions: HashMap::from([(
+                commits[0].id().clone(),
+                cleanup_description(&bulk_message),
+            )]),
+            missing: vec![],
+            duplicates: vec![],
+            unexpected: vec![],
+        });
+    }
+
+    Ok(parse_bulk_edit_message(&bulk_message, &commits_map))
+}
+
+/// Parse the bulk message of edited commit descriptions.
+fn parse_bulk_edit_message(
+    message: &str,
+    commit_ids_map: &HashMap<String, &CommitId>,
+) -> EditMultipleDescriptionsResult {
+    let mut descriptions = HashMap::new();
+    let mut duplicates = Vec::new();
+    let mut unexpected = Vec::new();
+
+    let messages = message.lines().fold(vec![], |mut accum, line| {
+        if let Some(commit_id_prefix) = line.strip_prefix("JJ: describe ") {
+            let commit_id_prefix = commit_id_prefix
+                .strip_suffix(" -------")
+                .unwrap_or(commit_id_prefix);
+            accum.push((commit_id_prefix, vec![]));
+        } else if let Some((_, lines)) = accum.last_mut() {
+            lines.push(line);
+        };
+        accum
+    });
+
+    for (commit_id_prefix, description_lines) in messages {
+        let commit_id = match commit_ids_map.get(commit_id_prefix) {
+            Some(&commit_id) => commit_id,
+            None => {
+                unexpected.push(commit_id_prefix.to_string());
+                continue;
+            }
+        };
+        if descriptions.contains_key(commit_id) {
+            duplicates.push(commit_id_prefix.to_string());
+            continue;
+        }
+        descriptions.insert(
+            commit_id.clone(),
+            cleanup_description(&description_lines.join("\n")),
+        );
+    }
+
+    let missing: Vec<_> = commit_ids_map
+        .keys()
+        .filter_map(|commit_id_prefix| {
+            let commit_id = match commit_ids_map.get(commit_id_prefix) {
+                Some(&commit_id) => commit_id,
+                None => {
+                    return None;
+                }
+            };
+            if !descriptions.contains_key(commit_id) {
+                Some(commit_id_prefix.to_string())
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    EditMultipleDescriptionsResult {
+        descriptions,
+        missing,
+        duplicates,
+        unexpected,
+    }
 }
 
 /// Combines the descriptions from the input commits. If only one is non-empty,