From f4722fa91bd67314c1f83aeefc8e6bea4322a064 Mon Sep 17 00:00:00 2001
From: Martin von Zweigbergk <martinvonz@google.com>
Date: Sun, 4 Apr 2021 22:19:15 -0700
Subject: [PATCH] unsquash: add new unsquash command for moving changes from
 parent to child

The new `jj unsquash` command moves changes from a commit's parent
into the commit itself. It comes with a `--interactive` flag. The
command is probably most useful for moving changes from the working
copy's parent into the working copy but it can of course be used for
moving changes into any commit (from that commit's parent).
---
 src/commands.rs | 62 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/src/commands.rs b/src/commands.rs
index b86a46eb2..4c2d1cb0e 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -363,6 +363,10 @@ fn get_app<'a, 'b>() -> App<'a, 'b> {
         .about("move changes from a commit into its parent")
         .arg(rev_arg())
         .arg(Arg::with_name("interactive").long("interactive").short("i"));
+    let unsquash_command = SubCommand::with_name("unsquash")
+        .about("move changes from a commit's parent into the commit")
+        .arg(rev_arg())
+        .arg(Arg::with_name("interactive").long("interactive").short("i"));
     let discard_command = SubCommand::with_name("discard")
         .about("discard a commit (and its descendants)")
         .arg(rev_arg());
@@ -568,6 +572,7 @@ fn get_app<'a, 'b>() -> App<'a, 'b> {
         .subcommand(prune_command)
         .subcommand(new_command)
         .subcommand(squash_command)
+        .subcommand(unsquash_command)
         .subcommand(discard_command)
         .subcommand(restore_command)
         .subcommand(edit_command)
@@ -1416,6 +1421,61 @@ fn cmd_squash(
     Ok(())
 }
 
+fn cmd_unsquash(
+    ui: &mut Ui,
+    matches: &ArgMatches,
+    sub_matches: &ArgMatches,
+) -> Result<(), CommandError> {
+    let mut repo = get_repo(ui, &matches)?;
+    let owned_wc = repo.working_copy().clone();
+    let mut_repo = Arc::get_mut(&mut repo).unwrap();
+    let commit = resolve_revision_arg(ui, mut_repo, sub_matches)?;
+    let parents = commit.parents();
+    if parents.len() != 1 {
+        return Err(CommandError::UserError(String::from(
+            "Cannot unsquash merge commits",
+        )));
+    }
+    let parent = &parents[0];
+    if parent.id() == repo.store().root_commit_id() {
+        return Err(CommandError::UserError(String::from(
+            "Cannot unsquash from the root commit",
+        )));
+    }
+    let mut tx = repo.start_transaction(&format!("unsquash commit {}", commit.id().hex()));
+    let mut_repo = tx.mut_repo();
+    let parent_base_tree = merge_commit_trees(repo.as_repo_ref(), &parent.parents());
+    let new_parent_tree_id;
+    if sub_matches.is_present("interactive") {
+        new_parent_tree_id = crate::diff_edit::edit_diff(&parent_base_tree, &parent.tree())?;
+        if &new_parent_tree_id == parent_base_tree.id() {
+            return Err(CommandError::UserError(String::from("No changes selected")));
+        }
+    } else {
+        new_parent_tree_id = parent_base_tree.id().clone();
+    }
+    // Prune the parent if it is now empty (always the case in the non-interactive
+    // case).
+    let prune_parent = &new_parent_tree_id == parent_base_tree.id();
+    let new_parent = CommitBuilder::for_rewrite_from(ui.settings(), repo.store(), &parent)
+        .set_tree(new_parent_tree_id)
+        .set_predecessors(vec![parent.id().clone(), commit.id().clone()])
+        .set_pruned(prune_parent)
+        .write_to_repo(mut_repo);
+    // Commit the new child on top of the new parent.
+    CommitBuilder::for_rewrite_from(ui.settings(), repo.store(), &commit)
+        .set_parents(vec![new_parent.id().clone()])
+        .write_to_repo(mut_repo);
+    update_checkout_after_rewrite(ui, mut_repo);
+    tx.commit();
+    update_working_copy(
+        ui,
+        Arc::get_mut(&mut repo).unwrap(),
+        &owned_wc.lock().unwrap(),
+    )?;
+    Ok(())
+}
+
 fn cmd_discard(
     ui: &mut Ui,
     matches: &ArgMatches,
@@ -2219,6 +2279,8 @@ where
         cmd_new(&mut ui, &matches, &sub_matches)
     } else if let Some(sub_matches) = matches.subcommand_matches("squash") {
         cmd_squash(&mut ui, &matches, &sub_matches)
+    } else if let Some(sub_matches) = matches.subcommand_matches("unsquash") {
+        cmd_unsquash(&mut ui, &matches, &sub_matches)
     } else if let Some(sub_matches) = matches.subcommand_matches("discard") {
         cmd_discard(&mut ui, &matches, &sub_matches)
     } else if let Some(sub_matches) = matches.subcommand_matches("restore") {