cli: add --author argument for commit and describe

CHANGELOG.md

@@ -56,6 +56,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   allows to set a name for the remote instead of using the default
   `origin`.
 
+* `jj commit` and `jj describe` now accept `--author` option allowing to quickly change
+  author of given commit.
+
 ### Fixed bugs
 
  * Fixed panic when parsing invalid conflict markers of a particular form.

cli/src/commands/commit.rs

@@ -22,6 +22,7 @@ use crate::command_error::CommandError;
 use crate::description_util::description_template;
 use crate::description_util::edit_description;
 use crate::description_util::join_message_paragraphs;
+use crate::description_util::parse_user_name_email;
 use crate::ui::Ui;
 
 /// Update the description and create a new change on top.
@@ -50,6 +51,11 @@ pub(crate) struct CommitArgs {
     /// $ JJ_USER='Foo Bar' [email protected] jj commit --reset-author
     #[arg(long)]
     reset_author: bool,
+    /// Set author to the provided string
+    ///
+    /// This changes author name and email while retaining timestamp.
+    #[arg(long, conflicts_with = "reset_author")]
+    author: Option<String>,
 }
 
 #[instrument(skip_all)]
@@ -106,6 +112,15 @@ new working-copy commit.
     if args.reset_author {
         commit_builder.set_author(commit_builder.committer().clone());
     }
+    if let Some(author) = &args.author {
+        let (name, email) = parse_user_name_email(author)?;
+        let new_author = jj_lib::backend::Signature {
+            name,
+            email,
+            timestamp: commit_builder.author().timestamp.clone(),
+        };
+        commit_builder.set_author(new_author);
+    }
 
     let description = if !args.message_paragraphs.is_empty() {
         join_message_paragraphs(&args.message_paragraphs)

cli/src/commands/describe.rs

@@ -29,6 +29,7 @@ use crate::description_util::description_template;
 use crate::description_util::edit_description;
 use crate::description_util::edit_multiple_descriptions;
 use crate::description_util::join_message_paragraphs;
+use crate::description_util::parse_user_name_email;
 use crate::description_util::ParsedBulkEditMessage;
 use crate::ui::Ui;
 
@@ -72,6 +73,11 @@ pub(crate) struct DescribeArgs {
     /// $ JJ_USER='Foo Bar' [email protected] jj describe --reset-author
     #[arg(long)]
     reset_author: bool,
+    /// Set author to the provided string
+    ///
+    /// This changes author name and email while retaining timestamp.
+    #[arg(long, conflicts_with = "reset_author")]
+    author: Option<String>,
 }
 
 #[instrument(skip_all)]
@@ -139,6 +145,15 @@ pub(crate) fn cmd_describe(
                     let new_author = commit_builder.committer().clone();
                     commit_builder.set_author(new_author);
                 }
+                if let Some(author) = &args.author {
+                    let (name, email) = parse_user_name_email(author)?;
+                    let new_author = jj_lib::backend::Signature {
+                        name,
+                        email,
+                        timestamp: commit_builder.author().timestamp.clone(),
+                    };
+                    commit_builder.set_author(new_author);
+                }
                 let temp_commit = commit_builder.write_hidden()?;
                 Ok((commit.id(), temp_commit))
             })

cli/src/description_util.rs

@@ -14,6 +14,7 @@ use crate::cli_util::edit_temp_file;
 use crate::cli_util::short_commit_hash;
 use crate::cli_util::WorkspaceCommandHelper;
 use crate::cli_util::WorkspaceCommandTransaction;
+use crate::command_error::cli_error;
 use crate::command_error::CommandError;
 use crate::formatter::PlainTextFormatter;
 use crate::text_util;
@@ -251,13 +252,22 @@ pub fn description_template(
     Ok(output.into_string_lossy())
 }
 
+pub fn parse_user_name_email(author: &str) -> Result<(String, String), CommandError> {
+    let re = regex::Regex::new(r"(?<name>.*?)\s*<(?<email>.+)>").unwrap();
+    let captures = re
+        .captures(author)
+        .ok_or_else(|| cli_error("Invalid author string"))?;
+    Ok((captures["name"].to_string(), captures["email"].to_string()))
+}
+
 #[cfg(test)]
 mod tests {
     use indexmap::indexmap;
     use indoc::indoc;
     use maplit::hashmap;
 
     use super::parse_bulk_edit_message;
+    use super::parse_user_name_email;
     use crate::description_util::ParseBulkEditMessageError;
 
     #[test]
@@ -410,4 +420,33 @@ mod tests {
         assert!(result.duplicates.is_empty());
         assert!(result.unexpected.is_empty());
     }
+
+    #[test]
+    fn test_parse_author() {
+        let expected_name = "Example";
+        let expected_email = "[email protected]";
+        let parsed = parse_user_name_email(&format!("{expected_name} <{expected_email}>")).unwrap();
+        assert_eq!(
+            (expected_name.to_string(), expected_email.to_string()),
+            parsed
+        );
+    }
+
+    #[test]
+    fn test_parse_author_with_utf8() {
+        let expected_name = "Ąćęłńóśżź";
+        let expected_email = "[email protected]";
+        let parsed = parse_user_name_email(&format!("{expected_name} <{expected_email}>")).unwrap();
+        assert_eq!(
+            (expected_name.to_string(), expected_email.to_string()),
+            parsed
+        );
+    }
+
+    #[test]
+    fn test_parse_author_without_name() {
+        let expected_email = "[email protected]";
+        let parsed = parse_user_name_email(&format!("<{expected_email}>")).unwrap();
+        assert_eq!(("".to_string(), expected_email.to_string()), parsed);
+    }
 }

cli/tests/cli-reference@.md.snap

@@ -446,6 +446,9 @@ Update the description and create a new change on top
    You can use it in combination with the JJ_USER and JJ_EMAIL environment variables to set a different author:
 
    $ JJ_USER='Foo Bar' [email protected] jj commit --reset-author
+* `--author <AUTHOR>` — Set author to the provided string
+
+   This changes author name and email while retaining timestamp.
 
 
 
@@ -599,6 +602,9 @@ Starts an editor to let you edit the description of changes. The editor will be
    You can use it in combination with the JJ_USER and JJ_EMAIL environment variables to set a different author:
 
    $ JJ_USER='Foo Bar' [email protected] jj describe --reset-author
+* `--author <AUTHOR>` — Set author to the provided string
+
+   This changes author name and email while retaining timestamp.