commit 179f9db092046395efaa1dc9e767a1ec109e1174
from: James Cook <falsifian@falsifian.org>
date: Tue Jun 20 13:49:35 2023 UTC

Implement fast-forward merges.

Split part of got_worktree_merge_prepare into a new function,
got_worktree_merge_write_refs, since that part doesn't make sense in the
fast-forward case.

ok stsp@

commit - 58e5e037d6e3e5d94bdf674e074fcdf411e80bfc
commit + 179f9db092046395efaa1dc9e767a1ec109e1174
blob - 51fec6b6e692d45a3c6ed44d2cd5a4a5649253e6
blob + 1f7297bf2a0f12c2fbcce5fbb38a533d88f94d4e
--- TODO
+++ TODO
@@ -8,15 +8,9 @@ got:
   instead of the root directory checked out at /usr/src.
   The next LLVM release 12.1 would later be committed onto the llvm-12
   branch and then merged into main at /usr/src/gnu/llvm in the same way.
-- Teach 'got merge' to forward a branch reference if possible, instead of
-  creating a merge commit. Forwarding should only be done if linear
-  history exists from the tip of the branch being merged to the tip of
-  the work tree's branch, and if the tip of the work tree's branch is
-  itself not a merge commit (this makes "stacked" merges possible
-  by default, and prevents a 'main' branch reference from being forwarded
-  to a vendor branch in case no new commits were added to 'main' since
-  the previous vendor merge). Provide an option (-M) which forces creation
-  of a merge commit, for cases where users deem forwarding undesirable.
+- Provide an option (-M) to 'got merge' which forces creation of a merge commit
+  even when forwarding is possible, for cases where users deem forwarding
+  undesirable.
 - When a clone fails the HEAD symref will always point to "refs/heads/main"
   (ie. the internal default HEAD symref of Got). Resuming a failed clone with
   'got fetch' is supposed to work. To make this easier, if the HEAD symref
blob - cf38fa07face9d2a811a09f32c2b6e6bc5cff414
blob + ee5ecec15b1c9954ab672ace7b9165717723b7d2
--- got/got.1
+++ got/got.1
@@ -2796,9 +2796,18 @@ or reverted with
 .Op Ar branch
 .Xc
 .Dl Pq alias: Cm mg
-Create a merge commit based on the current branch of the work tree and
-the specified
-.Ar branch .
+Merge the specified
+.Ar branch
+into the current branch of the work tree.
+If the branches have diverged, creates a merge commit.
+Otherwise, if
+.Ar branch
+already includes all commits from the work tree's branch, updates the work
+tree's branch to be the same as
+.Ar branch
+without creating a commit, and updates the work tree to the most recent commit
+on the branch.
+.Pp
 If a linear project history is desired, then use of
 .Cm got rebase
 should be preferred over
@@ -2854,14 +2863,6 @@ the work tree's current branch unmodified.
 .Pp
 .Cm got merge
 will refuse to run if certain preconditions are not met.
-If history of the
-.Ar branch
-is based on the work tree's current branch, then no merge commit can
-be created and
-.Cm got integrate
-may be used to integrate the
-.Ar branch
-instead.
 If the work tree is not yet fully updated to the tip commit of its
 branch, then the work tree must first be updated with
 .Cm got update .
blob - a14b71c8099e53f924c43a9d3f6a90a70ffe1449
blob + ea8a08baed68affba73cafa577c3125e9756466a
--- got/got.c
+++ got/got.c
@@ -13311,21 +13311,54 @@ cmd_merge(int argc, char *argv[])
 		error = check_path_prefix(wt_branch_tip, branch_tip,
 		    got_worktree_get_path_prefix(worktree),
 		    GOT_ERR_MERGE_PATH, repo);
+		if (error)
+			goto done;
+		error = got_worktree_merge_prepare(&fileindex, worktree, repo);
 		if (error)
 			goto done;
 		if (yca_id && got_object_id_cmp(wt_branch_tip, yca_id) == 0) {
-			static char msg[512];
-			snprintf(msg, sizeof(msg),
-			    "cannot create a merge commit because %s is based "
-			    "on %s; %s can be integrated with 'got integrate' "
-			    "instead", branch_name,
-			    got_worktree_get_head_ref_name(worktree),
-			    branch_name);
-			error = got_error_msg(GOT_ERR_SAME_BRANCH, msg);
+			struct got_pathlist_head paths;
+			if (interrupt_merge) {
+				error = got_error_msg(GOT_ERR_SAME_BRANCH,
+				    "merge is a fast-forward; this is "
+				    "incompatible with got merge -n");
+				goto done;
+			}
+			printf("Forwarding %s to %s\n",
+				got_ref_get_name(wt_branch), branch_name);
+			error = got_ref_change_ref(wt_branch, branch_tip);
+			if (error)
+				goto done;
+			error = got_ref_write(wt_branch, repo);
+			if (error)
+				goto done;
+			error = got_worktree_set_base_commit_id(worktree, repo,
+			    branch_tip);
+			if (error)
+				goto done;
+			TAILQ_INIT(&paths);
+			error = got_pathlist_append(&paths, "", NULL);
+			if (error)
+				goto done;
+			error = got_worktree_checkout_files(worktree,
+			    &paths, repo, update_progress, &upa,
+			    check_cancelled, NULL);
+			got_pathlist_free(&paths, GOT_PATHLIST_FREE_NONE);
+			if (error)
+				goto done;
+			if (upa.did_something) {
+				char *id_str;
+				error = got_object_id_str(&id_str, branch_tip);
+				if (error)
+					goto done;
+				printf("Updated to commit %s\n", id_str);
+				free(id_str);
+			} else
+				printf("Already up-to-date\n");
+			print_update_progress_stats(&upa);
 			goto done;
 		}
-		error = got_worktree_merge_prepare(&fileindex, worktree,
-		    branch, repo);
+		error = got_worktree_merge_write_refs(worktree, branch, repo);
 		if (error)
 			goto done;
 
blob - f7de090bfb2bd10312bdd0c389b5eabe41a33fdd
blob + 5b0b7259e6ff5fc0edf8711ac6780dd49315fe54
--- include/got_worktree.h
+++ include/got_worktree.h
@@ -485,16 +485,22 @@ const struct got_error *got_worktree_merge_in_progress
     struct got_worktree *, struct got_repository *);
 
 /*
- * Prepare for merging a branch into the work tree's current branch.
+ * Prepare for merging a branch into the work tree's current branch: lock the
+ * worktree and check that preconditions are satisfied. The function also
+ * returns a pointer to a fileindex which must be passed back to other
+ * merge-related functions.
+ */
+const struct got_error *got_worktree_merge_prepare(struct got_fileindex **,
+    struct got_worktree *, struct got_repository *);
+
+/*
  * This function creates a reference to the branch being merged, and to
  * this branch's current tip commit, in the "got/worktree/merge/" namespace.
  * These references are used to keep track of merge operation state and are
  * used as input and/or output arguments with other merge-related functions.
- * The function also returns a pointer to a fileindex which must be
- * passed back to other merge-related functions.
  */
-const struct got_error *got_worktree_merge_prepare(struct got_fileindex **,
-    struct got_worktree *, struct got_reference *, struct got_repository *);
+const struct got_error *got_worktree_merge_write_refs(struct got_worktree *,
+    struct got_reference *, struct got_repository *);
 
 /*
  * Continue an interrupted merge operation.
blob - e97f10e73cd0df0521ce4e36b40897121837e8d5
blob + 95e2e6bfa46ac12fd077b083c122ade77e54106f
--- lib/worktree.c
+++ lib/worktree.c
@@ -8486,14 +8486,12 @@ got_worktree_merge_in_progress(int *in_progress, struc
 
 const struct got_error *got_worktree_merge_prepare(
     struct got_fileindex **fileindex, struct got_worktree *worktree,
-    struct got_reference *branch, struct got_repository *repo)
+    struct got_repository *repo)
 {
 	const struct got_error *err = NULL;
 	char *fileindex_path = NULL;
-	char *branch_refname = NULL, *commit_refname = NULL;
-	struct got_reference *wt_branch = NULL, *branch_ref = NULL;
-	struct got_reference *commit_ref = NULL;
-	struct got_object_id *branch_tip = NULL, *wt_branch_tip = NULL;
+	struct got_reference *wt_branch = NULL;
+	struct got_object_id *wt_branch_tip = NULL;
 	struct check_rebase_ok_arg ok_arg;
 
 	*fileindex = NULL;
@@ -8513,14 +8511,6 @@ const struct got_error *got_worktree_merge_prepare(
 	    &ok_arg);
 	if (err)
 		goto done;
-
-	err = get_merge_branch_ref_name(&branch_refname, worktree);
-	if (err)
-		return err;
-
-	err = get_merge_commit_ref_name(&commit_refname, worktree);
-	if (err)
-		return err;
 
 	err = got_ref_open(&wt_branch, repo, worktree->head_ref_name,
 	    0);
@@ -8535,7 +8525,39 @@ const struct got_error *got_worktree_merge_prepare(
 		err = got_error(GOT_ERR_MERGE_OUT_OF_DATE);
 		goto done;
 	}
+
+done:
+	free(fileindex_path);
+	if (wt_branch)
+		got_ref_close(wt_branch);
+	free(wt_branch_tip);
+	if (err) {
+		if (*fileindex) {
+			got_fileindex_free(*fileindex);
+			*fileindex = NULL;
+		}
+		lock_worktree(worktree, LOCK_SH);
+	}
+	return err;
+}
 
+const struct got_error *got_worktree_merge_write_refs(
+    struct got_worktree *worktree, struct got_reference *branch,
+    struct got_repository *repo)
+{
+	const struct got_error *err = NULL;
+	char *branch_refname = NULL, *commit_refname = NULL;
+	struct got_reference *branch_ref = NULL, *commit_ref = NULL;
+	struct got_object_id *branch_tip = NULL;
+
+	err = get_merge_branch_ref_name(&branch_refname, worktree);
+	if (err)
+		return err;
+
+	err = get_merge_commit_ref_name(&commit_refname, worktree);
+	if (err)
+		return err;
+
 	err = got_ref_resolve(&branch_tip, repo, branch);
 	if (err)
 		goto done;
@@ -8557,21 +8579,11 @@ const struct got_error *got_worktree_merge_prepare(
 done:
 	free(branch_refname);
 	free(commit_refname);
-	free(fileindex_path);
 	if (branch_ref)
 		got_ref_close(branch_ref);
 	if (commit_ref)
 		got_ref_close(commit_ref);
-	if (wt_branch)
-		got_ref_close(wt_branch);
-	free(wt_branch_tip);
-	if (err) {
-		if (*fileindex) {
-			got_fileindex_free(*fileindex);
-			*fileindex = NULL;
-		}
-		lock_worktree(worktree, LOCK_SH);
-	}
+	free(branch_tip);
 	return err;
 }
 
blob - 71e5e49a5b7f5ebee4e83f1e29b7b2352977c697
blob + 92b590aa2ef2958738fb2d4e8419cb879fc9bf5c
--- regress/cmdline/merge.sh
+++ regress/cmdline/merge.sh
@@ -52,31 +52,7 @@ test_merge_basic() {
 		return 1
 	fi
 
-	# need a divergant commit on the main branch for 'got merge'
-	(cd $testroot/wt && got merge newbranch \
-		> $testroot/stdout 2> $testroot/stderr)
-	ret=$?
-	if [ $ret -eq 0 ]; then
-		echo "got merge succeeded unexpectedly" >&2
-		test_done "$testroot" "1"
-		return 1
-	fi
-	echo -n "got: cannot create a merge commit because " \
-		> $testroot/stderr.expected
-	echo -n "refs/heads/newbranch is based on refs/heads/master; " \
-		>> $testroot/stderr.expected
-	echo -n "refs/heads/newbranch can be integrated with " \
-		>> $testroot/stderr.expected
-	echo "'got integrate' instead" >> $testroot/stderr.expected
-	cmp -s $testroot/stderr.expected $testroot/stderr
-	ret=$?
-	if [ $ret -ne 0 ]; then
-		diff -u $testroot/stderr.expected $testroot/stderr
-		test_done "$testroot" "$ret"
-		return 1
-	fi
-
-	# create the required dirvergant commit
+	# create a divergent commit
 	(cd $testroot/repo && git checkout -q master)
 	echo "modified zeta on master" > $testroot/repo/epsilon/zeta
 	git_commit $testroot/repo -m "committing to zeta on master"
@@ -363,11 +339,163 @@ gamma/
 gamma/delta
 symlink@ -> alpha
 EOF
+	cmp -s $testroot/stdout.expected $testroot/stdout
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+	fi
+	test_done "$testroot" "$ret"
+}
+
+test_merge_forward() {
+	local testroot=`test_init merge_forward`
+	local commit0=`git_show_head $testroot/repo`
+
+	# Create a commit before branching, which will be used to help test
+	# preconditions for "got merge".
+	echo "modified alpha" > $testroot/repo/alpha
+	git_commit $testroot/repo -m "common commit"
+	local commit1=`git_show_head $testroot/repo`
+
+	(cd $testroot/repo && git checkout -q -b newbranch)
+	echo "modified beta on branch" > $testroot/repo/beta
+	git_commit $testroot/repo -m "committing to beta on newbranch"
+	local commit2=`git_show_head $testroot/repo`
+
+	got checkout -b master $testroot/repo $testroot/wt > /dev/null
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got checkout failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	# must not use a mixed-commit work tree with 'got merge'
+	(cd $testroot/wt && got update -c $commit0 alpha > /dev/null)
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got update failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+	(cd $testroot/wt && got merge newbranch \
+		> $testroot/stdout 2> $testroot/stderr)
+	ret=$?
+	if [ $ret -eq 0 ]; then
+		echo "got merge succeeded unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+	echo -n "got: work tree contains files from multiple base commits; " \
+		> $testroot/stderr.expected
+	echo "the entire work tree must be updated first" \
+		>> $testroot/stderr.expected
+	cmp -s $testroot/stderr.expected $testroot/stderr
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stderr.expected $testroot/stderr
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	(cd $testroot/wt && got update > /dev/null)
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got update failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	# 'got merge -n' refuses to fast-forward
+	(cd $testroot/wt && got merge -n newbranch \
+		> $testroot/stdout 2> $testroot/stderr)
+	ret=$?
+	if [ $ret -eq 0 ]; then
+		echo "got merge succeeded unexpectedly" >&2
+		test_done "$testroot" "1"
+		return 1
+	fi
+	echo -n "got: merge is a fast-forward; " > $testroot/stderr.expected 
+	echo "this is incompatible with got merge -n" \
+		>> $testroot/stderr.expected
+	cmp -s $testroot/stderr.expected $testroot/stderr
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stderr.expected $testroot/stderr
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	(cd $testroot/wt && got merge newbranch \
+		> $testroot/stdout 2> $testroot/stderr)
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got merge failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	echo "Forwarding refs/heads/master to refs/heads/newbranch" \
+		> $testroot/stdout.expected
+	echo "U  beta" >> $testroot/stdout.expected
+	echo "Updated to commit $commit2" \
+		>> $testroot/stdout.expected
 	cmp -s $testroot/stdout.expected $testroot/stdout
 	ret=$?
 	if [ $ret -ne 0 ]; then
 		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
 	fi
+
+	(cd $testroot/wt && got log | grep ^commit > $testroot/stdout)
+	echo -n "commit $commit2 " > $testroot/stdout.expected
+	echo "(master, newbranch)" >> $testroot/stdout.expected
+	echo "commit $commit1" >> $testroot/stdout.expected
+	echo "commit $commit0" >> $testroot/stdout.expected
+	cmp -s $testroot/stdout.expected $testroot/stdout
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+	test_done "$testroot" "$ret"
+}
+
+test_merge_backward() {
+	local testroot=`test_init merge_backward`
+	local commit0=`git_show_head $testroot/repo`
+
+	(cd $testroot/repo && git checkout -q -b newbranch)
+	(cd $testroot/repo && git checkout -q master)
+	echo "modified alpha on master" > $testroot/repo/alpha
+	git_commit $testroot/repo -m "committing to alpha on master"
+
+	got checkout -b master $testroot/repo $testroot/wt > /dev/null
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got checkout failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+
+	(cd $testroot/wt && got merge newbranch \
+		> $testroot/stdout 2> $testroot/stderr)
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		echo "got merge failed unexpectedly" >&2
+		test_done "$testroot" "$ret"
+		return 1
+	fi
+	echo "Already up-to-date" > $testroot/stdout.expected
+	cmp -s $testroot/stdout.expected $testroot/stdout
+	ret=$?
+	if [ $ret -ne 0 ]; then
+		diff -u $testroot/stdout.expected $testroot/stdout
+		test_done "$testroot" "$ret"
+		return 1
+	fi
 	test_done "$testroot" "$ret"
 }
 
@@ -1566,6 +1694,8 @@ test_merge_gitconfig_author() {
 
 test_parseargs "$@"
 run_test test_merge_basic
+run_test test_merge_forward
+run_test test_merge_backward
 run_test test_merge_continue
 run_test test_merge_continue_new_commit
 run_test test_merge_abort