merge: Add --into <ref>

Adds the ability to merge into a branch that isn't pointed at by HEAD

kart/merge.py

@@ -53,7 +53,15 @@ def get_commit_message(
 
 
 def do_merge(
-    repo, ff, ff_only, dry_run, commit, message, launch_editor=True, quiet=False
+    repo,
+    ff,
+    ff_only,
+    dry_run,
+    commit,
+    message,
+    into="HEAD",
+    launch_editor=True,
+    quiet=False,
 ):
     """Does a merge, but doesn't update the working copy."""
     if ff_only and not ff:
@@ -69,9 +77,12 @@ def do_merge(
 
     # accept ref-ish things (refspec, branch, commit)
     theirs = CommitWithReference.resolve(repo, commit)
-    ours = CommitWithReference.resolve(repo, "HEAD")
+    ours = CommitWithReference.resolve(repo, into)
     ancestor_id = repo.merge_base(theirs.id, ours.id)
 
+    if not ours.reference:
+        raise click.BadParameter(f"--into: Ref {into!r} doesn't exist")
+
     if not ancestor_id:
         raise InvalidOperation(f"Commits {theirs.id} and {ours.id} aren't related.")
 
@@ -110,7 +121,7 @@ def do_merge(
         merge_jdict["commit"] = theirs.id.hex
         merge_jdict["fastForward"] = True
         if not dry_run:
-            repo.head.set_target(
+            ours.reference.set_target(
                 theirs.id, f"{merge_context.get_message()}: Fast-forward"
             )
         return merge_jdict
@@ -155,7 +166,7 @@ def do_merge(
                 quiet=quiet,
             )
         merge_commit_id = repo.create_commit(
-            repo.head.name,
+            ours.reference.name,
             user,
             user,
             message,
@@ -329,6 +340,12 @@ def complete_merging_state(ctx):
     help="Use the given message as the commit message.",
     is_eager=True,  # -m is eager and --continue is non-eager so we can access -m from complete_merging_state callback.
 )
+@click.option(
+    "--into",
+    help="Merge into the given ref instead of the currently active branch.",
+    hidden=True,
+    default="HEAD",
+)
 @click.option(
     " /--no-editor",
     "launch_editor",
@@ -351,7 +368,9 @@ def complete_merging_state(ctx):
 )
 @click.argument("commit", required=True, metavar="COMMIT")
 @click.pass_context
-def merge(ctx, ff, ff_only, dry_run, message, launch_editor, output_format, commit):
+def merge(
+    ctx, ff, ff_only, dry_run, message, into, launch_editor, output_format, commit
+):
     """Incorporates changes from the named commits (usually other branch heads) into the current branch."""
 
     repo = ctx.obj.get_repo(
@@ -369,6 +388,7 @@ def merge(ctx, ff, ff_only, dry_run, message, launch_editor, output_format, comm
         dry_run,
         commit,
         message,
+        into=into,
         launch_editor=launch_editor,
         quiet=do_json,
     )

tests/test_merge.py

@@ -1,6 +1,8 @@
 import json
 import pytest
 
+import pygit2
+
 from kart.exceptions import SUCCESS, INVALID_OPERATION, NO_CONFLICT
 from kart.merge_util import (
     MergedIndex,
@@ -360,3 +362,64 @@ def test_merge_state_lock(data_archive, cli_runner):
         assert r.exit_code == SUCCESS
         r = cli_runner.invoke(["resolve", "dummy_conflict", "--with=delete"])
         assert r.exit_code == NO_CONFLICT  # "dummy_conflict" is not a real conflict
+
+
+def test_merge_into_branch(data_archive, tmp_path, cli_runner):
+    with data_archive("points") as repo_path:
+        # create two branches and put a commit on each
+        r = cli_runner.invoke(["branch", "b1", "main"])
+        assert r.exit_code == 0, r.stderr
+        r = cli_runner.invoke(
+            ["commit-files", f"--ref=refs/heads/b1", "-m", "B1", "a=1"]
+        )
+        assert r.exit_code == 0, r.stderr
+        r = cli_runner.invoke(["branch", "b2", "main"])
+        assert r.exit_code == 0, r.stderr
+        r = cli_runner.invoke(
+            ["commit-files", f"--ref=refs/heads/b2", "-m", "B2", "b=1"]
+        )
+        assert r.exit_code == 0, r.stderr
+
+        # Merge b1 into b2, even though main is still checked out
+        r = cli_runner.invoke(["merge", "--into=b2", "b1", "-m", "merged"])
+        assert r.exit_code == 0, r.stderr
+
+        repo = KartRepo(repo_path)
+        # HEAD is unchanged
+        assert repo.head.name == "refs/heads/main"
+        head_commit = repo.head_commit
+        assert head_commit.message == "Improve naming on Coromandel East coast"
+
+        # b2 ref has a merge commit on it
+        b2_commit = repo.references["refs/heads/b2"].peel(pygit2.Commit)
+        assert len(b2_commit.parents) == 2
+        assert b2_commit.message == "merged"
+
+
+def test_merge_into_branch_fastforward(data_archive, tmp_path, cli_runner):
+    with data_archive("points") as repo_path:
+        # create two branches and put a commit on one of them
+        r = cli_runner.invoke(["branch", "b1", "main"])
+        assert r.exit_code == 0, r.stderr
+        r = cli_runner.invoke(
+            ["commit-files", f"--ref=refs/heads/b1", "-m", "B1", "a=1"]
+        )
+        assert r.exit_code == 0, r.stderr
+        r = cli_runner.invoke(["branch", "b2", "main"])
+        assert r.exit_code == 0, r.stderr
+
+        # Merge b1 into b2, even though main is still checked out
+        r = cli_runner.invoke(["merge", "--into=b2", "b1"])
+        assert r.exit_code == 0, r.stderr
+
+        repo = KartRepo(repo_path)
+        b1_commit = repo.references["refs/heads/b1"].peel(pygit2.Commit)
+
+        # HEAD is unchanged
+        assert repo.head.name == "refs/heads/main"
+        head_commit = repo.head_commit
+        assert head_commit.message == "Improve naming on Coromandel East coast"
+
+        # b2 ref is now the same as b1 (because it was fastforwarded)
+        b2_commit = repo.references["refs/heads/b2"].peel(pygit2.Commit)
+        assert b2_commit.hex == b1_commit.hex