[PATCH 2/4] sequencer: add "make_patch" function to save a patch

[Christian Couder <chriscool@tuxfamily.org>]

This function generates an informational patch file.

The "make_patch" and the "get_commit" functions are copied from the
GSoC sequencer project:

git://repo.or.cz/git/sbeyer.git

(commit e7b8dab0c2a73ade92017a52bb1405ea1534ef20)

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 builtin-sequencer--helper.c |   75 ++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 74 insertions(+), 1 deletions(-)

diff --git a/builtin-sequencer--helper.c b/builtin-sequencer--helper.c
index 721c0d8..8d32480 100644
--- a/builtin-sequencer--helper.c
+++ b/builtin-sequencer--helper.c
@@ -1,15 +1,83 @@
 #include "builtin.h"
 #include "cache.h"
 #include "parse-options.h"
+#include "run-command.h"
+
+#define SEQ_DIR "rebase-merge"
+
+#define PATCH_FILE	git_path(SEQ_DIR "/patch")
 
 static const char * const git_sequencer_helper_usage[] = {
 	"git sequencer--helper --make-patch <commit>",
 	NULL
 };
 
+/* Generate purely informational patch file */
+static void make_patch(struct commit *commit)
+{
+	struct commit_list *parents = commit->parents;
+	const char **args;
+	struct child_process chld;
+	int fd = open(PATCH_FILE, O_WRONLY | O_CREAT, 0666);
+	if (fd < 0)
+		return;
+
+	memset(&chld, 0, sizeof(chld));
+	if (!parents) {
+		write(fd, "Root commit\n", 12);
+		close(fd);
+		return;
+	} else if (!parents->next) {
+		args = xcalloc(5, sizeof(char *));
+		args[0] = "diff-tree";
+		args[1] = "-p";
+		args[2] = xstrdup(sha1_to_hex(parents->item->object.sha1));
+		args[3] = xstrdup(sha1_to_hex(((struct object *)commit)->sha1));
+	} else {
+		int i = 0;
+		int count = 1;
+
+		for (; parents; parents = parents->next)
+			++count;
+		args = xcalloc(count + 3, sizeof(char *));
+		args[i++] = "diff";
+		args[i++] = "--cc";
+		args[i++] = xstrdup(sha1_to_hex(commit->object.sha1));
+
+		for (parents = commit->parents; parents;
+		     parents = parents->next)
+			args[i++] = xstrdup(sha1_to_hex(
+					    parents->item->object.sha1));
+	}
+
+	chld.argv = args;
+	chld.git_cmd = 1;
+	chld.out = fd;
+
+	/* Run, ignore errors. */
+	if (start_command(&chld))
+		return;
+	finish_command(&chld);
+
+	/* TODO: free dup'ed SHAs in argument list */
+}
+
+/* Return a commit object of "arg" */
+static struct commit *get_commit(const char *arg)
+{
+	unsigned char sha1[20];
+
+	if (get_sha1(arg, sha1)) {
+		error("Could not find '%s'", arg);
+		return NULL;
+	}
+	return lookup_commit_reference(sha1);
+}
+
 int cmd_sequencer__helper(int argc, const char **argv, const char *prefix)
 {
 	char *commit = NULL;
+	struct commit *c;
 	struct option options[] = {
 		OPT_STRING(0, "make-patch", &commit, "commit",
 			   "create a patch from commit"),
@@ -22,6 +90,11 @@ int cmd_sequencer__helper(int argc, const char **argv, const char *prefix)
 	if (!commit)
 		usage_with_options(git_sequencer_helper_usage, options);
 
-	/* Nothing to do yet */
+	c = get_commit(commit);
+	if (!c)
+		return 1;
+
+	make_patch(c);
+
 	return 0;
 }
-- 
1.6.3.GIT