feat(rebase): Update RebaseCommand::Pick to support squashing commits

Author: claytonrcarter

git-branchless-lib/src/core/rewrite/execute.rs

@@ -354,7 +354,8 @@ mod in_memory {
     use crate::core::rewrite::move_branches;
     use crate::core::rewrite::plan::{OidOrLabel, RebaseCommand, RebasePlan};
     use crate::git::{
-        CherryPickFastError, CherryPickFastOptions, GitRunInfo, MaybeZeroOid, NonZeroOid, Repo,
+        AmendFastOptions, CherryPickFastError, CherryPickFastOptions, GitRunInfo, MaybeZeroOid,
+        NonZeroOid, Repo,
     };
     use crate::util::ExitCode;
 
@@ -487,10 +488,15 @@ mod in_memory {
                     let current_commit = repo
                         .find_commit_or_fail(current_oid)
                         .wrap_err("Finding current commit")?;
-                    let commit_to_apply_oid = match commits_to_apply_oids.as_slice() {
-                        [commit_to_apply_oid] => commit_to_apply_oid,
-                        [..] => unimplemented!("Picking multiple commits"),
-                    };
+                    let (commit_to_apply_oid, fixup_commit_oids) =
+                        match commits_to_apply_oids.as_slice() {
+                            [] => eyre::bail!("BUG: No commits to apply!"),
+                            [commit_to_apply_oid] => (commit_to_apply_oid, Vec::new()),
+                            [commit_to_apply_oid, fixup_commits @ ..] => {
+                                (commit_to_apply_oid, Vec::from(fixup_commits))
+                            }
+                        };
+
                     let commit_to_apply = repo
                         .find_commit_or_fail(*commit_to_apply_oid)
                         .wrap_err("Finding commit to apply")?;
@@ -549,7 +555,7 @@ mod in_memory {
                     } else {
                         commit_to_apply.get_committer().update_timestamp(*now)?
                     };
-                    let rebased_commit_oid = repo
+                    let mut rebased_commit_oid = repo
                         .create_commit(
                             None,
                             &commit_to_apply.get_author(),
@@ -560,9 +566,45 @@ mod in_memory {
                         )
                         .wrap_err("Applying rebased commit")?;
 
-                    let rebased_commit = repo
+                    let mut rebased_commit = repo
                         .find_commit_or_fail(rebased_commit_oid)
                         .wrap_err("Looking up just-rebased commit")?;
+
+                    for fixup_commit_oid in fixup_commit_oids.iter() {
+                        let fixup_commit = repo
+                            .find_commit_or_fail(*fixup_commit_oid)
+                            .wrap_err("Finding commit to apply")?;
+                        let fixup_commit_description = printable_styled_string(
+                            effects.get_glyphs(),
+                            fixup_commit.friendly_describe(effects.get_glyphs())?,
+                        )?;
+                        progress.notify_status(format!(
+                            "Applying patch for commit: {}",
+                            fixup_commit_description
+                        ));
+                        let commit_tree = repo.amend_fast(
+                            &rebased_commit,
+                            &AmendFastOptions::FromCommit {
+                                commit: fixup_commit,
+                            },
+                        )?;
+
+                        rebased_commit_oid = repo
+                            .create_commit(
+                                None,
+                                &rebased_commit.get_author(),
+                                &committer_signature,
+                                commit_message,
+                                &commit_tree,
+                                vec![&current_commit],
+                            )
+                            .wrap_err("Applying rebased commit")?;
+
+                        rebased_commit = repo
+                            .find_commit_or_fail(rebased_commit_oid)
+                            .wrap_err("Looking up just-rebased commit")?;
+                    }
+
                     let commit_description = printable_styled_string(
                         effects.get_glyphs(),
                         repo.friendly_describe_commit_from_oid(
@@ -576,16 +618,22 @@ mod in_memory {
 
                         writeln!(
                             effects.get_output_stream(),
-                            "[{}/{}] Skipped now-empty commit: {}",
-                            i,
-                            num_picks,
+                            "{} Skipped now-empty commit: {}",
+                            commit_num,
                             commit_description
                         )?;
                     } else {
                         rewritten_oids.insert(
                             *original_commit_oid,
                             MaybeZeroOid::NonZero(rebased_commit_oid),
                         );
+                        for fixup_commit_oid in fixup_commit_oids {
+                            rewritten_oids.insert(
+                                fixup_commit_oid,
+                                MaybeZeroOid::NonZero(rebased_commit_oid),
+                            );
+                        }
+
                         current_oid = rebased_commit_oid;
 
                         writeln!(