feat(split): add --discard flag

Author: claytonrcarter

git-branchless-lib/src/git/index.rs

@@ -5,7 +5,7 @@ use tracing::instrument;
 
 use crate::core::eventlog::EventTransactionId;
 
-use super::{FileMode, GitRunInfo, GitRunOpts, GitRunResult, MaybeZeroOid, NonZeroOid, Repo};
+use super::{FileMode, GitRunInfo, GitRunOpts, GitRunResult, MaybeZeroOid, NonZeroOid, Repo, Tree};
 
 /// The possible stages for items in the index.
 #[derive(Copy, Clone, Debug)]
@@ -88,6 +88,12 @@ impl Index {
                 },
             })
     }
+
+    /// Update the index from the given tree and write it to disk.
+    pub fn update_from_tree(&mut self, tree: &Tree) -> eyre::Result<()> {
+        self.inner.read_tree(&tree.inner)?;
+        self.inner.write().wrap_err("writing index")
+    }
 }
 
 /// The command to update the index, as defined by `git update-index`.

git-branchless-opts/src/lib.rs

@@ -663,9 +663,13 @@ pub enum Command {
         files: Vec<String>,
 
         /// Restack any descendents onto the split commit, not the extracted commit.
-        #[clap(action, short = 'd', long = "detach")]
+        #[clap(action, short = 'd', long)]
         detach: bool,
 
+        /// After extracting the changes, don't recommit them.
+        #[clap(action, short = 'D', long = "discard", conflicts_with("detach"))]
+        discard: bool,
+
         /// Options for resolving revset expressions.
         #[clap(flatten)]
         resolve_revset_options: ResolveRevsetOptions,

git-branchless/src/commands/mod.rs

@@ -182,14 +182,19 @@ fn command_main(ctx: CommandContext, opts: Opts) -> EyreExitOr<()> {
 
         Command::Split {
             detach,
+            discard,
             files,
             resolve_revset_options,
             revset,
             move_options,
         } => {
-            let split_mode = match detach {
-                true => split::SplitMode::DetachAfter,
-                false => split::SplitMode::InsertAfter,
+            let split_mode = match (detach, discard) {
+                (true, false) => split::SplitMode::DetachAfter,
+                (false, true) => split::SplitMode::Discard,
+                (false, false) => split::SplitMode::InsertAfter,
+                (true, true) => {
+                    unreachable!("clap should prevent this")
+                }
             };
 
             split::split(

git-branchless/src/commands/split.rs

@@ -38,6 +38,7 @@ use tracing::instrument;
 /// What should `split` do with the extracted changes?
 pub enum SplitMode {
     DetachAfter,
+    Discard,
     InsertAfter,
 }
 
@@ -128,12 +129,14 @@ pub fn split(
     let (parent_tree, mut remainder_tree) = match (&split_mode, parent_commits.as_slice()) {
         // split the commit by removing the changes from the target, and then
         // cherry picking the orignal target as the "extracted" commit
-        (SplitMode::InsertAfter, [only_parent]) | (SplitMode::DetachAfter, [only_parent]) => {
+        (SplitMode::InsertAfter, [only_parent])
+        | (SplitMode::Discard, [only_parent])
+        | (SplitMode::DetachAfter, [only_parent]) => {
             (only_parent.get_tree()?, target_commit.get_tree()?)
         }
 
         // no parent: use an empty tree for comparison
-        (SplitMode::InsertAfter, []) | (SplitMode::DetachAfter, []) => {
+        (SplitMode::InsertAfter, []) | (SplitMode::Discard, []) | (SplitMode::DetachAfter, []) => {
             (make_empty_tree(&repo)?, target_commit.get_tree()?)
         }
 
@@ -218,9 +221,9 @@ pub fn split(
         let target_entry = target_tree.get_path(path)?;
         let temp_tree_oid = match (parent_entry, target_entry, &split_mode) {
             // added => remove from remainder commit
-            (None, Some(_), SplitMode::InsertAfter) | (None, Some(_), SplitMode::DetachAfter) => {
-                remainder_tree.remove(&repo, path)?
-            }
+            (None, Some(_), SplitMode::InsertAfter)
+            | (None, Some(_), SplitMode::DetachAfter)
+            | (None, Some(_), SplitMode::Discard) => remainder_tree.remove(&repo, path)?,
 
             // deleted or modified => replace w/ parent content in split commit
             (Some(parent_entry), _, _) => {
@@ -280,6 +283,7 @@ pub fn split(
     }])?;
 
     let extracted_commit_oid = match split_mode {
+        SplitMode::Discard => None,
         SplitMode::InsertAfter | SplitMode::DetachAfter => {
             let extracted_tree = repo.cherry_pick_fast(
                 &target_commit,
@@ -354,6 +358,7 @@ pub fn split(
     struct CleanUp {
         checkout_target: Option<CheckoutTarget>,
         rewritten_oids: Vec<(NonZeroOid, MaybeZeroOid)>,
+        reset_index: bool,
     }
 
     let cleanup = match (target_state, &split_mode, extracted_commit_oid) {
@@ -363,26 +368,36 @@ pub fn split(
             CleanUp {
                 checkout_target: None,
                 rewritten_oids: vec![(target_oid, MaybeZeroOid::NonZero(extracted_commit_oid))],
+                reset_index: false,
             }
         }
 
+        (TargetState::CurrentBranch, SplitMode::Discard, None) => CleanUp {
+            checkout_target: None,
+            rewritten_oids: vec![(target_oid, MaybeZeroOid::NonZero(remainder_commit_oid))],
+            reset_index: true,
+        },
+
         // commit to split checked out as detached HEAD, don't extend any
         // branches, but explicitly check out the newly split commit
         (TargetState::DetachedHead, _, _) => CleanUp {
             checkout_target: Some(CheckoutTarget::Oid(remainder_commit_oid)),
             rewritten_oids: vec![(target_oid, MaybeZeroOid::NonZero(remainder_commit_oid))],
+            reset_index: false,
         },
 
         // some other commit or branch was checked out, default behavior is fine
-        (TargetState::CurrentBranch, _, _) | (TargetState::Other, _, _) => CleanUp {
+        (TargetState::CurrentBranch | TargetState::Other, _, _) => CleanUp {
             checkout_target: None,
             rewritten_oids: vec![(target_oid, MaybeZeroOid::NonZero(remainder_commit_oid))],
+            reset_index: false,
         },
     };
 
     let CleanUp {
         checkout_target,
         rewritten_oids,
+        reset_index,
     } = cleanup;
 
     move_branches(
@@ -410,6 +425,11 @@ pub fn split(
         )?);
     }
 
+    if reset_index {
+        let mut index = repo.get_index()?;
+        index.update_from_tree(&remainder_tree)?;
+    }
+
     let mut builder = RebasePlanBuilder::new(&dag, permissions);
     let children = dag.query_children(CommitSet::from(target_oid))?;
     for child in dag.commit_set_to_vec(&children)? {