Warn user about the working copy when configuring the author

CHANGELOG.md

@@ -99,6 +99,8 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   This simplifies the use case of configuring code formatters for specific file
   types. See `jj help fix` for details.
 
+* When reconfiguring the author, warn that the working copy won't be updated
+
 ### Fixed bugs
 
 * `jj diff --git` no longer shows the contents of binary files.

cli/src/commands/config.rs

@@ -14,9 +14,13 @@
 
 use std::io::Write;
 
+use jj_lib::commit::Commit;
+use jj_lib::repo::Repo;
 use tracing::instrument;
 
-use crate::cli_util::{get_new_config_file_path, run_ui_editor, CommandHelper};
+use crate::cli_util::{
+    get_new_config_file_path, run_ui_editor, CommandHelper, WorkspaceCommandHelper,
+};
 use crate::command_error::{config_error, user_error, CommandError};
 use crate::config::{
     to_toml_value, write_config_value_to_file, AnnotatedValue, ConfigNamePathBuf, ConfigSource,
@@ -285,7 +289,7 @@ pub(crate) fn cmd_config_get(
 
 #[instrument(skip_all)]
 pub(crate) fn cmd_config_set(
-    _ui: &mut Ui,
+    ui: &mut Ui,
     command: &CommandHelper,
     args: &ConfigSetArgs,
 ) -> Result<(), CommandError> {
@@ -296,9 +300,73 @@ pub(crate) fn cmd_config_set(
             path = config_path.display()
         )));
     }
+
+    // If the user is trying to change the author config, we should warn them that
+    // it won't affect the working copy author
+    if args.name == ConfigNamePathBuf::from_iter(vec!["user", "name"]) {
+        check_wc_user_name(command, ui, &args.value)?;
+    } else if args.name == ConfigNamePathBuf::from_iter(vec!["user", "email"]) {
+        check_wc_user_email(command, ui, &args.value)?;
+    };
+
     write_config_value_to_file(&args.name, &args.value, &config_path)
 }
 
+/// Returns the commit of the working copy if it exists.
+fn maybe_wc_commit(helper: &WorkspaceCommandHelper) -> Option<Commit> {
+    let repo = helper.repo();
+    let maybe_wc_commit = helper
+        .get_wc_commit_id()
+        .map(|id| repo.store().get_commit(id))
+        .transpose()
+        .unwrap();
+    maybe_wc_commit
+}
+
+/// Check if the working copy author name matches the user's config value
+/// If it doesn't, print a warning message
+fn check_wc_user_name(
+    command: &CommandHelper,
+    ui: &mut Ui,
+    user_name: &str,
+) -> Result<(), CommandError> {
+    let helper = command.workspace_helper(ui)?;
+    if let Some(wc_commit) = maybe_wc_commit(&helper) {
+        let author = wc_commit.author();
+        if author.name != user_name {
+            warn_wc_author(&author.name, &author.email, ui)?
+        }
+    };
+    Ok(())
+}
+
+/// Check if the working copy author email matches the user's config value
+/// If it doesn't, print a warning message
+fn check_wc_user_email(
+    command: &CommandHelper,
+    ui: &mut Ui,
+    user_email: &str,
+) -> Result<(), CommandError> {
+    let helper = command.workspace_helper(ui)?;
+    if let Some(wc_commit) = maybe_wc_commit(&helper) {
+        let author = wc_commit.author();
+        if author.email != user_email {
+            warn_wc_author(&author.name, &author.email, ui)?
+        }
+    };
+    Ok(())
+}
+
+/// Prints a warning message about the working copy to the user
+fn warn_wc_author(user_name: &str, user_email: &str, ui: &mut Ui) -> Result<(), CommandError> {
+    Ok(writeln!(
+        ui.warning_default(),
+        "This setting will only impact future commits.\nThe author of the working copy will stay \
+         \"{user_name} <{user_email}>\". \nTo change it, use \"jj describe --reset-author \
+         --no-edit\""
+    )?)
+}
+
 #[instrument(skip_all)]
 pub(crate) fn cmd_config_edit(
     _ui: &mut Ui,