merge: remember conflict labels

When recreating merge conflicts with "git checkout -m <path>" the
original conflict labels are lost. For commands like "git merge" and
"git cherry-pick" we could use the presence of the related root
ref (MERGE_HEAD and CHERRY_PICK_HEAD respectively) to recreate the
labels. However if the conflicts are from "git stash pop" or "git
checkout -m <branch>" then there is no ref to deduce the labels from. To
ensure the labels are always available the merge machinery is updated to
record the labels .git/MERGE_LABELS when it updates the worktree and
there are conflicts. The labels are then read from the file by "git
checkout -m <path>" when recreating the conflicts.

There is a subtlety with "git checkout -m <branch>" in that it resets the
index to remove the conflict entries but they are saved in merge undo so
we want to preserve the MERGE_LABELS file when switching branches if
there were conflicts.

Signed-off-by: Phillip Wood <[email protected]>

Author: phillipwood

branch.c

@@ -826,9 +826,11 @@ void create_branches_recursively(struct repository *r, const char *name,
 	free(branch_point);
 }
 
-void remove_merge_branch_state(struct repository *r)
+void remove_merge_branch_state(struct repository *r, unsigned flags)
 {
 	unlink(git_path_merge_head(r));
+	if (!(flags & REMOVE_BRANCH_STATE_PRESERVE_CONFLICT_LABELS))
+		unlink(git_path_merge_labels(r));
 	unlink(git_path_merge_rr(r));
 	unlink(git_path_merge_msg(r));
 	unlink(git_path_merge_mode(r));
@@ -837,11 +839,11 @@ void remove_merge_branch_state(struct repository *r)
 	save_autostash_ref(r, "MERGE_AUTOSTASH");
 }
 
-void remove_branch_state(struct repository *r, int verbose)
+void remove_branch_state(struct repository *r, unsigned flags)
 {
-	sequencer_post_commit_cleanup(r, verbose);
+	sequencer_post_commit_cleanup(r, flags & REMOVE_BRANCH_STATE_VERBOSE);
 	unlink(git_path_squash_msg(r));
-	remove_merge_branch_state(r);
+	remove_merge_branch_state(r, flags);
 }
 
 void die_if_checked_out(const char *branch, int ignore_current_worktree)

branch.h

@@ -123,17 +123,19 @@ int validate_branchname(const char *name, struct strbuf *ref);
  */
 int validate_new_branchname(const char *name, struct strbuf *ref, int force);
 
+#define REMOVE_BRANCH_STATE_VERBOSE (1u << 0)
+#define REMOVE_BRANCH_STATE_PRESERVE_CONFLICT_LABELS (1u << 1)
 /*
  * Remove information about the merge state on the current
  * branch. (E.g., MERGE_HEAD)
  */
-void remove_merge_branch_state(struct repository *r);
+void remove_merge_branch_state(struct repository *r, unsigned flags);
 
 /*
  * Remove information about the state of working on the current
  * branch. (E.g., MERGE_HEAD)
  */
-void remove_branch_state(struct repository *r, int verbose);
+void remove_branch_state(struct repository *r, unsigned flags);
 
 /*
  * Configure local branch "local" as downstream to branch "remote"

builtin/checkout.c

@@ -15,6 +15,7 @@
 #include "hex.h"
 #include "hook.h"
 #include "merge-ll.h"
+#include "merge.h"
 #include "lockfile.h"
 #include "mem-pool.h"
 #include "merge-ort-wrappers.h"
@@ -263,6 +264,7 @@ static int checkout_merged(int pos, const struct checkout *state,
 	struct cache_entry *ce = the_repository->index->cache[pos];
 	const char *path = ce->name;
 	mmfile_t ancestor, ours, theirs;
+	char *base_label, *ours_label, *theirs_label;
 	enum ll_merge_result merge_status;
 	int status;
 	struct object_id oid;
@@ -293,10 +295,19 @@ static int checkout_merged(int pos, const struct checkout *state,
 
 	git_config_get_bool("merge.renormalize", &renormalize);
 	ll_opts.renormalize = renormalize;
+	if (read_merge_labels(the_repository, &base_label, &ours_label,
+				 &theirs_label)) {
+		base_label = xstrdup("base");
+		ours_label = xstrdup("ours");
+		theirs_label = xstrdup("theirs");
+	}
 	ll_opts.conflict_style = conflict_style;
-	merge_status = ll_merge(&result_buf, path, &ancestor, "base",
-				&ours, "ours", &theirs, "theirs",
+	merge_status = ll_merge(&result_buf, path, &ancestor, base_label,
+				&ours, ours_label, &theirs, theirs_label,
 				state->istate, &ll_opts);
+	free(base_label);
+	free(ours_label);
+	free(theirs_label);
 	free(ancestor.ptr);
 	free(ours.ptr);
 	free(theirs.ptr);
@@ -692,6 +703,7 @@ static void describe_detached_head(const char *msg, struct commit *commit)
 }
 
 #define ERROR_FLAG_WRITEOUT (1u << 0)
+#define ERROR_FLAG_CONFLICTS (1u << 1)
 
 static int reset_tree(struct tree *tree, const struct checkout_opts *o,
 		      int worktree, unsigned int *error_flags,
@@ -916,6 +928,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
 						     old_tree);
 			if (ret < 0)
 				exit(128);
+			if (!ret)
+				*error_flags |= ERROR_FLAG_CONFLICTS;
 			ret = reset_tree(new_tree,
 					 opts, 0,
 					 error_flags, new_branch_info);
@@ -951,10 +965,13 @@ static void report_tracking(struct branch_info *new_branch_info)
 
 static void update_refs_for_switch(const struct checkout_opts *opts,
 				   struct branch_info *old_branch_info,
-				   struct branch_info *new_branch_info)
+				   struct branch_info *new_branch_info,
+				   int merge_conflicts)
 {
 	struct strbuf msg = STRBUF_INIT;
 	const char *old_desc, *reflog_msg;
+	unsigned flags = 0;
+
 	if (opts->new_branch) {
 		if (opts->new_orphan_branch) {
 			enum log_refs_config log_all_ref_updates =
@@ -1046,7 +1063,11 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 						   old_branch_info->path);
 		}
 	}
-	remove_branch_state(the_repository, !opts->quiet);
+	if (!opts->quiet)
+		flags |= REMOVE_BRANCH_STATE_VERBOSE;
+	if (merge_conflicts)
+		flags |= REMOVE_BRANCH_STATE_PRESERVE_CONFLICT_LABELS;
+	remove_branch_state(the_repository, flags);
 	strbuf_release(&msg);
 	if (!opts->quiet &&
 	    !opts->force_detach &&
@@ -1218,12 +1239,13 @@ static int switch_branches(const struct checkout_opts *opts,
 	if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
 		orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);
 
-	update_refs_for_switch(opts, &old_branch_info, new_branch_info);
+	update_refs_for_switch(opts, &old_branch_info, new_branch_info,
+			       !!(error_flags & ERROR_FLAG_CONFLICTS));
 
 	ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
 	branch_info_release(&old_branch_info);
 
-	return ret || error_flags;
+	return ret || !!(error_flags & ~ERROR_FLAG_CONFLICTS);
 }
 
 static int git_checkout_config(const char *var, const char *value,

builtin/commit.c

@@ -1920,6 +1920,7 @@ int cmd_commit(int argc,
 
 	sequencer_post_commit_cleanup(the_repository, 0);
 	unlink(git_path_merge_head(the_repository));
+	unlink(git_path_merge_labels(the_repository));
 	unlink(git_path_merge_msg(the_repository));
 	unlink(git_path_merge_mode(the_repository));
 	unlink(git_path_squash_msg(the_repository));

builtin/merge.c

@@ -416,7 +416,7 @@ static void finish_up_to_date(void)
 		else
 			puts(_("Already up to date."));
 	}
-	remove_merge_branch_state(the_repository);
+	remove_merge_branch_state(the_repository, 0);
 }
 
 static void squash_message(struct commit *commit, struct commit_list *remoteheads)
@@ -946,8 +946,7 @@ static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 			&result_commit, NULL, sign_commit))
 		die(_("failed to write commit object"));
 	finish(head, remoteheads, &result_commit, "In-index merge");
-
-	remove_merge_branch_state(the_repository);
+	remove_merge_branch_state(the_repository, 0);
 	free_commit_list(parents);
 	return 0;
 }
@@ -976,7 +975,7 @@ static int finish_automerge(struct commit *head,
 	finish(head, remoteheads, &result_commit, buf.buf);
 
 	strbuf_release(&buf);
-	remove_merge_branch_state(the_repository);
+	remove_merge_branch_state(the_repository, 0);
 	free_commit_list(parents);
 	return 0;
 }
@@ -1386,7 +1385,7 @@ int cmd_merge(int argc,
 				      builtin_merge_usage,
 				      builtin_merge_options);
 
-		remove_merge_branch_state(the_repository);
+		remove_merge_branch_state(the_repository, 0);
 		goto done;
 	}
 
@@ -1621,7 +1620,7 @@ int cmd_merge(int argc,
 		}
 
 		finish(head_commit, remoteheads, &commit->object.oid, msg);
-		remove_merge_branch_state(the_repository);
+		remove_merge_branch_state(the_repository, 0);
 		goto done;
 	} else if (!remoteheads->next && common->next)
 		;

merge-ort.c

@@ -35,6 +35,7 @@
 #include "hex.h"
 #include "entry.h"
 #include "merge-ll.h"
+#include "merge.h"
 #include "match-trees.h"
 #include "mem-pool.h"
 #include "object-file.h"
@@ -405,6 +406,9 @@ struct merge_options_internal {
 
 	/* field that holds submodule conflict information */
 	struct string_list conflicted_submodules;
+
+	/* Copies of the labels used for conflict markers */
+	char *labels[3];
 };
 
 struct conflicted_submodule_item {
@@ -4870,6 +4874,16 @@ void merge_switch_to_result(struct merge_options *opt,
 			return;
 		}
 		trace2_region_leave("merge", "write_auto_merge", opt->repo);
+
+		trace2_region_enter("merge", "write_merge_labels",
+				    opt->repo);
+		opt->priv = result->priv;
+		write_merge_labels(opt->repo, opt->priv->labels[0],
+				      opt->priv->labels[1],
+				      opt->priv->labels[2]);
+		opt->priv = NULL;
+		trace2_region_leave("merge", "write_merge_labels",
+				    opt->repo);
 	}
 	if (display_update_msgs)
 		merge_display_update_messages(opt, /* detailed */ 0, result);
@@ -5134,6 +5148,14 @@ static void move_opt_priv_to_result_priv(struct merge_options *opt,
 	 * to move it.
 	 */
 	assert(opt->priv && !result->priv);
+	if (!result->clean) {
+		opt->priv->labels[0] = mem_pool_strdup(&opt->priv->pool,
+						       opt->ancestor);
+		opt->priv->labels[1] = mem_pool_strdup(&opt->priv->pool,
+						       opt->branch1);
+		opt->priv->labels[2] = mem_pool_strdup(&opt->priv->pool,
+						       opt->branch2);
+	}
 	result->priv = opt->priv;
 	result->_properly_initialized = RESULT_INITIALIZED;
 	opt->priv = NULL;

merge.c

@@ -8,11 +8,14 @@
 #include "merge.h"
 #include "commit.h"
 #include "repository.h"
+#include "path.h"
 #include "run-command.h"
 #include "resolve-undo.h"
 #include "tree.h"
 #include "tree-walk.h"
 #include "unpack-trees.h"
+#include "wrapper.h"
+#include <stdio.h>
 
 static const char *merge_argument(struct commit *commit)
 {
@@ -111,3 +114,61 @@ int checkout_fast_forward(struct repository *r,
 		return error(_("unable to write new index file"));
 	return 0;
 }
+
+int write_merge_labels(struct repository *r, const char *base,
+			  const char *ours, const char *theirs)
+{
+	FILE *f = fopen_or_warn(git_path_merge_labels(r), "w");
+	if (!f)
+		return -1;
+	fprintf(f, "%s\n%s\n%s\n", base, ours, theirs);
+	if (fclose(f))
+		return error_errno("could not write '%s'",
+				   git_path_merge_labels(r));
+
+	return 0;
+}
+
+static int parse_merge_label_line(const char **p, char **line)
+{
+	const char *eol = strchr(*p, '\n');
+	if (!eol)
+		return -1;
+
+	*line = xmemdupz(*p, eol - *p);
+	*p = eol + 1;
+
+	return 0;
+}
+
+int read_merge_labels(struct repository *r,
+		      char **pbase, char** pours, char** ptheirs)
+{
+	struct strbuf buf = STRBUF_INIT;
+	const char *p;
+	char *base = NULL, *ours = NULL, *theirs = NULL;
+	int ret = -1;
+
+	if (strbuf_read_file(&buf, git_path_merge_labels(r), 0) < 0)
+		return -1;
+	p = buf.buf;
+	if (parse_merge_label_line(&p, &base))
+		goto out;
+	if (parse_merge_label_line(&p, &ours))
+		goto out;
+	if (parse_merge_label_line(&p, &theirs))
+		goto out;
+	ret = 0;
+	*pbase = base;
+	*pours = ours;
+	*ptheirs = theirs;
+out:
+	if (ret) {
+		free(base);
+		free(ours);
+		free(theirs);
+	}
+	strbuf_release(&buf);
+
+	return ret;
+}

merge.h

@@ -13,5 +13,9 @@ int checkout_fast_forward(struct repository *r,
 			  const struct object_id *from,
 			  const struct object_id *to,
 			  int overwrite_ignore);
+int write_merge_labels(struct repository *r,
+		       const char *base, const char *ours, const char *theirs);
+int read_merge_labels(struct repository *r,
+		      char **base, char **ours, char **theirs);
 
 #endif /* MERGE_H */

path.c

@@ -1681,3 +1681,4 @@ REPO_GIT_PATH_FUNC(merge_mode, "MERGE_MODE")
 REPO_GIT_PATH_FUNC(merge_head, "MERGE_HEAD")
 REPO_GIT_PATH_FUNC(fetch_head, "FETCH_HEAD")
 REPO_GIT_PATH_FUNC(shallow, "shallow")
+REPO_GIT_PATH_FUNC(merge_labels, "MERGE_LABELS")

path.h

@@ -138,6 +138,7 @@ const char *git_path_merge_mode(struct repository *r);
 const char *git_path_merge_head(struct repository *r);
 const char *git_path_fetch_head(struct repository *r);
 const char *git_path_shallow(struct repository *r);
+const char *git_path_merge_labels(struct repository *r);
 
 int ends_with_path_components(const char *path, const char *components);