[PATCH 3/8] merge-tree: add option parsing and initial shell for real merge function

["Elijah Newren via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Elijah Newren <newren@xxxxxxxxx>

Let merge-tree accept a `--real` parameter for choosing real merges
instead of trivial merges.  Note that real merges differ from trivial
merges in that they handle:
  - three way content merges
  - recursive ancestor consolidation
  - renames
  - proper directory/file conflict handling
  - etc.
Basically all the stuff you'd expect from `git merge`, just without
updating the index and working tree.  The initial shell added here does
nothing more than die with "real merges are not yet implemented", but
that will be fixed in subsequent commits.

Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
---
 builtin/merge-tree.c | 56 +++++++++++++++++++++++++++++++++++++-------
 git.c                |  2 +-
 2 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index 9fe5b99f623..f04b1eaad0a 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -3,13 +3,12 @@
 #include "tree-walk.h"
 #include "xdiff-interface.h"
 #include "object-store.h"
+#include "parse-options.h"
 #include "repository.h"
 #include "blob.h"
 #include "exec-cmd.h"
 #include "merge-blobs.h"
 
-static const char merge_tree_usage[] = "git merge-tree <base-tree> <branch1> <branch2>";
-
 struct merge_list {
 	struct merge_list *next;
 	struct merge_list *link;	/* other stages for this object */
@@ -366,14 +365,16 @@ static void *get_tree_descriptor(struct repository *r,
 	return buf;
 }
 
-static int trivial_merge(int argc, const char **argv) {
+static int trivial_merge(const char *base,
+			 const char *branch1,
+			 const char *branch2) {
 	struct repository *r = the_repository;
 	struct tree_desc t[3];
 	void *buf1, *buf2, *buf3;
 
-	buf1 = get_tree_descriptor(r, t+0, argv[1]);
-	buf2 = get_tree_descriptor(r, t+1, argv[2]);
-	buf3 = get_tree_descriptor(r, t+2, argv[3]);
+	buf1 = get_tree_descriptor(r, t+0, base);
+	buf2 = get_tree_descriptor(r, t+1, branch1);
+	buf3 = get_tree_descriptor(r, t+2, branch2);
 	trivial_merge_trees(t, "");
 	free(buf1);
 	free(buf2);
@@ -383,9 +384,46 @@ static int trivial_merge(int argc, const char **argv) {
 	return 0;
 }
 
+struct merge_tree_options {
+	int real;
+};
+
+static int real_merge(struct merge_tree_options *o,
+		      const char *branch1, const char *branch2)
+{
+	die(_("real merges are not yet implemented"));
+}
+
 int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 {
-	if (argc != 4)
-		usage(merge_tree_usage);
-	return trivial_merge(argc, argv);
+	struct merge_tree_options o = { 0 };
+	int expected_remaining_argc;
+
+	const char * const merge_tree_usage[] = {
+		N_("git merge-tree --real <branch1> <branch2>"),
+		N_("git merge-tree <base-tree> <branch1> <branch2>"),
+		NULL
+	};
+	struct option mt_options[] = {
+		OPT_BOOL(0, "real", &o.real,
+			 N_("do a real merge instead of a trivial merge")),
+		OPT_END()
+	};
+
+	/* Check for a request for basic help */
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage_with_options(merge_tree_usage, mt_options);
+
+	/* Parse arguments */
+	argc = parse_options(argc, argv, prefix, mt_options,
+			     merge_tree_usage, 0);
+	expected_remaining_argc = (o.real ? 2 : 3);
+	if (argc != expected_remaining_argc)
+		usage_with_options(merge_tree_usage, mt_options);
+
+	/* Do the relevant type of merge */
+	if (o.real)
+		return real_merge(&o, argv[0], argv[1]);
+	else
+		return trivial_merge(argv[0], argv[1], argv[2]);
 }
diff --git a/git.c b/git.c
index 7edafd8ecff..0124c053878 100644
--- a/git.c
+++ b/git.c
@@ -561,7 +561,7 @@ static struct cmd_struct commands[] = {
 	{ "merge-recursive-ours", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
 	{ "merge-recursive-theirs", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
 	{ "merge-subtree", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
-	{ "merge-tree", cmd_merge_tree, RUN_SETUP | NO_PARSEOPT },
+	{ "merge-tree", cmd_merge_tree, RUN_SETUP },
 	{ "mktag", cmd_mktag, RUN_SETUP | NO_PARSEOPT },
 	{ "mktree", cmd_mktree, RUN_SETUP },
 	{ "multi-pack-index", cmd_multi_pack_index, RUN_SETUP },
-- 
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