Subject: [PATCH v8 03/14] merge-index: libify merge_one_path() and merge_all()

From: Alban Gruin <[email-masked]>
Date: Tue, 9 Aug 2022 20:54:18 +0200

The "resolve" and "octopus" merge strategies do not call directly `git
merge-one-file', they delegate the work to another git command, `git
merge-index', that will loop over files in the index and call the
specified command.  Unfortunately, these functions are not part of
libgit.a, which means that once rewritten, the strategies would still
have to invoke `merge-one-file' by spawning a new process first.

To avoid this, this moves and renames merge_one_path(), merge_all(), and
their helpers to merge-strategies.c.  They also take a callback to
dictate what they should do for each file.  For now, to preserve the
behaviour of `merge-index', only one callback, launching a new process,
is defined.

Signed-off-by: Alban Gruin <[email-masked]>
---
 Makefile               |  1 +
 builtin/merge-index.c  | 92 ++++++++++++++----------------------------
 merge-strategies.c     | 82 +++++++++++++++++++++++++++++++++++++
 merge-strategies.h     | 18 +++++++++
 t/t7607-merge-state.sh |  2 +-
 5 files changed, 133 insertions(+), 62 deletions(-)
 create mode 100644 merge-strategies.c
 create mode 100644 merge-strategies.h

diff --git a/Makefile b/Makefile
index 2ec9b2dc6b..40d1be4e5e 100644
--- a/Makefile
+++ b/Makefile
@@ -991,6 +991,7 @@ LIB_OBJS += merge-blobs.o
 LIB_OBJS += merge-ort.o
 LIB_OBJS += merge-ort-wrappers.o
 LIB_OBJS += merge-recursive.o
+LIB_OBJS += merge-strategies.o
 LIB_OBJS += merge.o
 LIB_OBJS += midx.o
 LIB_OBJS += name-hash.o
diff --git a/builtin/merge-index.c b/builtin/merge-index.c
index c0383fe9df..f66cc515d8 100644
--- a/builtin/merge-index.c
+++ b/builtin/merge-index.c
@@ -1,76 +1,43 @@
 #define USE_THE_INDEX_COMPATIBILITY_MACROS
 #include "builtin.h"
+#include "merge-strategies.h"
 #include "run-command.h"
 
 static const char *pgm;
-static int one_shot, quiet;
-static int err;
 
-static int merge_entry(int pos, const char *path)
+static int merge_one_file_spawn(struct index_state *istate,
+				const struct object_id *orig_blob,
+				const struct object_id *our_blob,
+				const struct object_id *their_blob, const char *path,
+				unsigned int orig_mode, unsigned int our_mode, unsigned int their_mode,
+				void *data)
 {
-	int found;
-	const char *arguments[] = { pgm, "", "", "", path, "", "", "", NULL };
-	char hexbuf[4][GIT_MAX_HEXSZ + 1];
-	char ownbuf[4][60];
+	char oids[3][GIT_MAX_HEXSZ + 1] = {{0}};
+	char modes[3][10] = {{0}};
+	const char *arguments[] = { pgm, oids[0], oids[1], oids[2],
+				    path, modes[0], modes[1], modes[2], NULL };
 
-	if (pos >= active_nr)
-		die("git merge-index: %s not in the cache", path);
-	found = 0;
-	do {
-		const struct cache_entry *ce = active_cache[pos];
-		int stage = ce_stage(ce);
-
-		if (strcmp(ce->name, path))
-			break;
-		found++;
-		oid_to_hex_r(hexbuf[stage], &ce->oid);
-		xsnprintf(ownbuf[stage], sizeof(ownbuf[stage]), "%o", ce->ce_mode);
-		arguments[stage] = hexbuf[stage];
-		arguments[stage + 4] = ownbuf[stage];
-	} while (++pos < active_nr);
-	if (!found)
-		die("git merge-index: %s not in the cache", path);
-
-	if (run_command_v_opt(arguments, 0)) {
-		if (one_shot)
-			err++;
-		else {
-			if (!quiet)
-				die("merge program failed");
-			exit(1);
-		}
+	if (orig_blob) {
+		oid_to_hex_r(oids[0], orig_blob);
+		xsnprintf(modes[0], sizeof(modes[0]), "%06o", orig_mode);
 	}
-	return found;
-}
-
-static void merge_one_path(const char *path)
-{
-	int pos = cache_name_pos(path, strlen(path));
 
-	/*
-	 * If it already exists in the cache as stage0, it's
-	 * already merged and there is nothing to do.
-	 */
-	if (pos < 0)
-		merge_entry(-pos-1, path);
-}
+	if (our_blob) {
+		oid_to_hex_r(oids[1], our_blob);
+		xsnprintf(modes[1], sizeof(modes[1]), "%06o", our_mode);
+	}
 
-static void merge_all(void)
-{
-	int i;
-	/* TODO: audit for interaction with sparse-index. */
-	ensure_full_index(&the_index);
-	for (i = 0; i < active_nr; i++) {
-		const struct cache_entry *ce = active_cache[i];
-		if (!ce_stage(ce))
-			continue;
-		i += merge_entry(i, ce->name)-1;
+	if (their_blob) {
+		oid_to_hex_r(oids[2], their_blob);
+		xsnprintf(modes[2], sizeof(modes[2]), "%06o", their_mode);
 	}
+
+	return run_command_v_opt(arguments, 0);
 }
 
 int cmd_merge_index(int argc, const char **argv, const char *prefix)
 {
-	int i, force_file = 0;
+	int i, force_file = 0, err = 0, one_shot = 0, quiet = 0;
 
 	/* Without this we cannot rely on waitpid() to tell
 	 * what happened to our children.
@@ -94,7 +61,9 @@ int cmd_merge_index(int argc, const char **argv, const char *prefix)
 		quiet = 1;
 		i++;
 	}
+
 	pgm = argv[i++];
+
 	for (; i < argc; i++) {
 		const char *arg = argv[i];
 		if (!force_file && *arg == '-') {
@@ -103,14 +72,15 @@ int cmd_merge_index(int argc, const char **argv, const char *prefix)
 				continue;
 			}
 			if (!strcmp(arg, "-a")) {
-				merge_all();
+				err |= merge_all_index(&the_index, one_shot, quiet,
+						       merge_one_file_spawn, NULL);
 				continue;
 			}
 			die("git merge-index: unknown option %s", arg);
 		}
-		merge_one_path(arg);
+		err |= merge_index_path(&the_index, one_shot, quiet, arg,
+					merge_one_file_spawn, NULL);
 	}
-	if (err && !quiet)
-		die("merge program failed");
+
 	return err;
 }
diff --git a/merge-strategies.c b/merge-strategies.c
new file mode 100644
index 0000000000..418c9dd710
--- /dev/null
+++ b/merge-strategies.c
@@ -0,0 +1,82 @@
+#include "cache.h"
+#include "merge-strategies.h"
+
+static int merge_entry(struct index_state *istate, unsigned int pos,
+		       const char *path, int *err, merge_fn fn, void *data)
+{
+	int found = 0;
+	const struct object_id *oids[3] = {NULL};
+	unsigned int modes[3] = {0};
+
+	do {
+		const struct cache_entry *ce = istate->cache[pos];
+		int stage = ce_stage(ce);
+
+		if (strcmp(ce->name, path))
+			break;
+		found++;
+		oids[stage - 1] = &ce->oid;
+		modes[stage - 1] = ce->ce_mode;
+	} while (++pos < istate->cache_nr);
+	if (!found)
+		return error(_("%s is not in the cache"), path);
+
+	if (fn(istate, oids[0], oids[1], oids[2], path,
+	       modes[0], modes[1], modes[2], data))
+		(*err)++;
+
+	return found;
+}
+
+int merge_index_path(struct index_state *istate, int oneshot, int quiet,
+		     const char *path, merge_fn fn, void *data)
+{
+	int pos = index_name_pos(istate, path, strlen(path)), ret, err = 0;
+
+	/*
+	 * If it already exists in the cache as stage0, it's
+	 * already merged and there is nothing to do.
+	 */
+	if (pos < 0) {
+		ret = merge_entry(istate, -pos - 1, path, &err, fn, data);
+		if (ret == -1)
+			return -1;
+		else if (err) {
+			if (!quiet && !oneshot)
+				error(_("merge program failed"));
+			return 1;
+		}
+	}
+	return 0;
+}
+
+int merge_all_index(struct index_state *istate, int oneshot, int quiet,
+		    merge_fn fn, void *data)
+{
+	int err = 0, ret;
+	unsigned int i;
+
+	/* TODO: audit for interaction with sparse-index. */
+	ensure_full_index(istate);
+	for (i = 0; i < istate->cache_nr; i++) {
+		const struct cache_entry *ce = istate->cache[i];
+		if (!ce_stage(ce))
+			continue;
+
+		ret = merge_entry(istate, i, ce->name, &err, fn, data);
+		if (ret > 0)
+			i += ret - 1;
+		else if (ret == -1)
+			return -1;
+
+		if (err && !oneshot) {
+			if (!quiet)
+				error(_("merge program failed"));
+			return 1;
+		}
+	}
+
+	if (err && !quiet)
+		error(_("merge program failed"));
+	return err;
+}
diff --git a/merge-strategies.h b/merge-strategies.h
new file mode 100644
index 0000000000..88f476f170
--- /dev/null
+++ b/merge-strategies.h
@@ -0,0 +1,18 @@
+#ifndef MERGE_STRATEGIES_H
+#define MERGE_STRATEGIES_H
+
+#include "object.h"
+
+typedef int (*merge_fn)(struct index_state *istate,
+			const struct object_id *orig_blob,
+			const struct object_id *our_blob,
+			const struct object_id *their_blob, const char *path,
+			unsigned int orig_mode, unsigned int our_mode, unsigned int their_mode,
+			void *data);
+
+int merge_index_path(struct index_state *istate, int oneshot, int quiet,
+		     const char *path, merge_fn fn, void *data);
+int merge_all_index(struct index_state *istate, int oneshot, int quiet,
+		    merge_fn fn, void *data);
+
+#endif /* MERGE_STRATEGIES_H */
diff --git a/t/t7607-merge-state.sh b/t/t7607-merge-state.sh
index 89a62ac53b..96befa5b80 100755
--- a/t/t7607-merge-state.sh
+++ b/t/t7607-merge-state.sh
@@ -20,7 +20,7 @@ test_expect_success 'Ensure we restore original state if no merge strategy handl
 	# just hit conflicts, it completely fails and says that it cannot
 	# handle this type of merge.
 	test_expect_code 2 git merge branch2 branch3 >output 2>&1 &&
-	grep "fatal: merge program failed" output &&
+	grep "error: merge program failed" output &&
 	grep "Should not be doing an octopus" output &&
 
 	# Make sure we did not leave stray changes around when no appropriate
-- 
2.37.1.412.gcfdce49ffd