bisect--helper: implement "git bisect--helper"

This patch implements a new "git bisect--helper" builtin plumbing
command that will be used to migrate "git-bisect.sh" to C.

We start by implementing only the "--next-vars" option that will
read bisect refs from "refs/bisect/", and then compute the next
bisect step, and output shell variables ready to be eval'ed by
the shell.

At this step, "git bisect--helper" ignores the paths that may
have been put in "$GIT_DIR/BISECT_NAMES". This will be fixed in a
later patch.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

6 files changed, 105 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 42cabe8162..a2bfad43bc 100644
--- a/Makefile
+++ b/Makefile
@@ -533,6 +533,7 @@ BUILTIN_OBJS += builtin-add.o
 BUILTIN_OBJS += builtin-annotate.o
 BUILTIN_OBJS += builtin-apply.o
 BUILTIN_OBJS += builtin-archive.o
+BUILTIN_OBJS += builtin-bisect--helper.o
 BUILTIN_OBJS += builtin-blame.o
 BUILTIN_OBJS += builtin-branch.o
 BUILTIN_OBJS += builtin-bundle.o
diff --git a/bisect.c b/bisect.c
index 47120c1cd8..94ec011786 100644
--- a/bisect.c
+++ b/bisect.c
@@ -2,11 +2,18 @@
 #include "commit.h"
 #include "diff.h"
 #include "revision.h"
+#include "refs.h"
+#include "list-objects.h"
 #include "sha1-lookup.h"
 #include "bisect.h"
 
 static unsigned char (*skipped_sha1)[20];
 static int skipped_sha1_nr;
+static int skipped_sha1_alloc;
+
+static const char **rev_argv;
+static int rev_argv_nr;
+static int rev_argv_alloc;
 
 /* bits #0-15 in revision.h */
 
@@ -390,6 +397,33 @@ struct commit_list *find_bisection(struct commit_list *list,
 	return best;
 }
 
+static int register_ref(const char *refname, const unsigned char *sha1,
+			int flags, void *cb_data)
+{
+	if (!strcmp(refname, "bad")) {
+		ALLOC_GROW(rev_argv, rev_argv_nr + 1, rev_argv_alloc);
+		rev_argv[rev_argv_nr++] = xstrdup(sha1_to_hex(sha1));
+	} else if (!prefixcmp(refname, "good-")) {
+		const char *hex = sha1_to_hex(sha1);
+		char *good = xmalloc(strlen(hex) + 2);
+		*good = '^';
+		memcpy(good + 1, hex, strlen(hex) + 1);
+		ALLOC_GROW(rev_argv, rev_argv_nr + 1, rev_argv_alloc);
+		rev_argv[rev_argv_nr++] = good;
+	} else if (!prefixcmp(refname, "skip-")) {
+		ALLOC_GROW(skipped_sha1, skipped_sha1_nr + 1,
+			   skipped_sha1_alloc);
+		hashcpy(skipped_sha1[skipped_sha1_nr++], sha1);
+	}
+
+	return 0;
+}
+
+static int read_bisect_refs(void)
+{
+	return for_each_ref_in("refs/bisect/", register_ref, NULL);
+}
+
 static int skipcmp(const void *a, const void *b)
 {
 	return hashcmp(a, b);
@@ -444,3 +478,37 @@ struct commit_list *filter_skipped(struct commit_list *list,
 
 	return filtered;
 }
+
+int bisect_next_vars(const char *prefix)
+{
+	struct rev_info revs;
+	int reaches = 0, all = 0;
+
+	init_revisions(&revs, prefix);
+	revs.abbrev = 0;
+	revs.commit_format = CMIT_FMT_UNSPECIFIED;
+
+	/* argv[0] will be ignored by setup_revisions */
+	ALLOC_GROW(rev_argv, rev_argv_nr + 1, rev_argv_alloc);
+	rev_argv[rev_argv_nr++] = xstrdup("bisect_rev_setup");
+
+	if (read_bisect_refs())
+		die("reading bisect refs failed");
+
+	ALLOC_GROW(rev_argv, rev_argv_nr + 1, rev_argv_alloc);
+	rev_argv[rev_argv_nr++] = xstrdup("--");
+
+	setup_revisions(rev_argv_nr, rev_argv, &revs, NULL);
+
+	revs.limited = 1;
+
+	if (prepare_revision_walk(&revs))
+		die("revision walk setup failed");
+	if (revs.tree_objects)
+		mark_edges_uninteresting(revs.commits, &revs, NULL);
+
+	revs.commits = find_bisection(revs.commits, &reaches, &all,
+				      !!skipped_sha1_nr);
+
+	return show_bisect_vars(&revs, reaches, all, 0, 1);
+}
diff --git a/bisect.h b/bisect.h
index 2489630da0..05eea175f7 100644
--- a/bisect.h
+++ b/bisect.h
@@ -9,7 +9,14 @@ extern struct commit_list *filter_skipped(struct commit_list *list,
 					  struct commit_list **tried,
 					  int show_all);
 
+/*
+ * The "show_all" parameter should be 0 if this function is called
+ * from outside "builtin-rev-list.c" as otherwise it would use
+ * static "revs" from this file.
+ */
 extern int show_bisect_vars(struct rev_info *revs, int reaches, int all,
 			    int show_all, int show_tried);
 
+extern int bisect_next_vars(const char *prefix);
+
 #endif
diff --git a/builtin-bisect--helper.c b/builtin-bisect--helper.c
new file mode 100644
index 0000000000..8fe778766a
--- /dev/null
+++ b/builtin-bisect--helper.c
@@ -0,0 +1,27 @@
+#include "builtin.h"
+#include "cache.h"
+#include "parse-options.h"
+#include "bisect.h"
+
+static const char * const git_bisect_helper_usage[] = {
+	"git bisect--helper --next-vars",
+	NULL
+};
+
+int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
+{
+	int next_vars = 0;
+	struct option options[] = {
+		OPT_BOOLEAN(0, "next-vars", &next_vars,
+			    "output next bisect step variables"),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, options, git_bisect_helper_usage, 0);
+
+	if (!next_vars)
+		usage_with_options(git_bisect_helper_usage, options);
+
+	/* next-vars */
+	return bisect_next_vars(prefix);
+}
diff --git a/builtin.h b/builtin.h
index 1495cf6a20..425ff8e89b 100644
--- a/builtin.h
+++ b/builtin.h
@@ -25,6 +25,7 @@ extern int cmd_add(int argc, const char **argv, const char *prefix);
 extern int cmd_annotate(int argc, const char **argv, const char *prefix);
 extern int cmd_apply(int argc, const char **argv, const char *prefix);
 extern int cmd_archive(int argc, const char **argv, const char *prefix);
+extern int cmd_bisect__helper(int argc, const char **argv, const char *prefix);
 extern int cmd_blame(int argc, const char **argv, const char *prefix);
 extern int cmd_branch(int argc, const char **argv, const char *prefix);
 extern int cmd_bundle(int argc, const char **argv, const char *prefix);
diff --git a/git.c b/git.c
index c2b181ed78..a553926b68 100644
--- a/git.c
+++ b/git.c
@@ -271,6 +271,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "annotate", cmd_annotate, RUN_SETUP },
 		{ "apply", cmd_apply },
 		{ "archive", cmd_archive },
+		{ "bisect--helper", cmd_bisect__helper, RUN_SETUP | NEED_WORK_TREE },
 		{ "blame", cmd_blame, RUN_SETUP },
 		{ "branch", cmd_branch, RUN_SETUP },
 		{ "bundle", cmd_bundle },