Teach revision walking machinery to walk multiple times sequencially

Previously it was not possible to iterate revisions twice using the
revision walking api. We add a reset_revision_walk() which clears the
used flags. This allows us to do multiple sequencial revision walks.

We add the appropriate calls to the existing submodule machinery doing
revision walks. This is done to avoid surprises if future code wants to
call these functions more than once during the processes lifetime.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -183,6 +183,7 @@
 /test-mktemp
 /test-parse-options
 /test-path-utils
+/test-revision-walking
 /test-run-command
 /test-sha1
 /test-sigchain

Documentation/technical/api-revision-walking.txt

@@ -56,6 +56,11 @@ function.
 	returning a `struct commit *` each time you call it. The end of the
 	revision list is indicated by returning a NULL pointer.
 
+`reset_revision_walk`::
+
+	Reset the flags used by the revision walking api. You can use
+	this to do multiple sequencial revision walks.
+
 Data structures
 ---------------
 

Makefile

@@ -479,6 +479,7 @@ TEST_PROGRAMS_NEED_X += test-match-trees
 TEST_PROGRAMS_NEED_X += test-mktemp
 TEST_PROGRAMS_NEED_X += test-parse-options
 TEST_PROGRAMS_NEED_X += test-path-utils
+TEST_PROGRAMS_NEED_X += test-revision-walking
 TEST_PROGRAMS_NEED_X += test-run-command
 TEST_PROGRAMS_NEED_X += test-sha1
 TEST_PROGRAMS_NEED_X += test-sigchain

object.c

@@ -275,3 +275,14 @@ void object_array_remove_duplicates(struct object_array *array)
 		array->nr = dst;
 	}
 }
+
+void clear_object_flags(unsigned flags)
+{
+	int i;
+
+	for (i=0; i < obj_hash_size; i++) {
+		struct object *obj = obj_hash[i];
+		if (obj)
+			obj->flags &= ~flags;
+	}
+}

object.h

@@ -76,4 +76,6 @@ void add_object_array(struct object *obj, const char *name, struct object_array
 void add_object_array_with_mode(struct object *obj, const char *name, struct object_array *array, unsigned mode);
 void object_array_remove_duplicates(struct object_array *);
 
+void clear_object_flags(unsigned flags);
+
 #endif /* OBJECT_H */

revision.c

@@ -2061,6 +2061,11 @@ static void set_children(struct rev_info *revs)
 	}
 }
 
+void reset_revision_walk(void)
+{
+	clear_object_flags(SEEN | ADDED | SHOWN);
+}
+
 int prepare_revision_walk(struct rev_info *revs)
 {
 	int nr = revs->pending.nr;

revision.h

@@ -192,6 +192,7 @@ extern void parse_revision_opt(struct rev_info *revs, struct parse_opt_ctx_t *ct
 				 const char * const usagestr[]);
 extern int handle_revision_arg(const char *arg, struct rev_info *revs,int flags,int cant_be_filename);
 
+extern void reset_revision_walk(void);
 extern int prepare_revision_walk(struct rev_info *revs);
 extern struct commit *get_revision(struct rev_info *revs);
 extern char *get_revision_mark(const struct rev_info *revs, const struct commit *commit);

submodule.c

@@ -404,6 +404,7 @@ int check_submodule_needs_pushing(unsigned char new_sha1[20], const char *remote
 	while ((commit = get_revision(&rev)) && !needs_pushing)
 		commit_need_pushing(commit, &needs_pushing);
 
+	reset_revision_walk();
 	free(sha1_copy);
 	strbuf_release(&remotes_arg);
 
@@ -741,6 +742,7 @@ static int find_first_merges(struct object_array *result, const char *path,
 		if (in_merge_bases(b, &commit, 1))
 			add_object_array(o, NULL, &merges);
 	}
+	reset_revision_walk();
 
 	/* Now we've got all merges that contain a and b. Prune all
 	 * merges that contain another found merge and save them in

t/t0062-revision-walking.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+#
+# Copyright (c) 2012 Heiko Voigt
+#
+
+test_description='Test revision walking api'
+
+. ./test-lib.sh
+
+cat >run_twice_expected <<-EOF
+1st
+ > add b
+ > add a
+2nd
+ > add b
+ > add a
+EOF
+
+test_expect_success 'setup' '
+	echo a > a &&
+	git add a &&
+	git commit -m "add a" &&
+	echo b > b &&
+	git add b &&
+	git commit -m "add b"
+'
+
+test_expect_success 'revision walking can be done twice' '
+	test-revision-walking run-twice > run_twice_actual
+	test_cmp run_twice_expected run_twice_actual
+'
+
+test_done

test-revision-walking.c

@@ -0,0 +1,66 @@
+/*
+ * test-revision-walking.c: test revision walking API.
+ *
+ * (C) 2012 Heiko Voigt <hvoigt@hvoigt.net>
+ *
+ * This code is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include "cache.h"
+#include "commit.h"
+#include "diff.h"
+#include "revision.h"
+
+static void print_commit(struct commit *commit)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct pretty_print_context ctx = {0};
+	ctx.date_mode = DATE_NORMAL;
+	format_commit_message(commit, " %m %s", &sb, &ctx);
+	printf("%s\n", sb.buf);
+	strbuf_release(&sb);
+}
+
+static int run_revision_walk(void)
+{
+	struct rev_info rev;
+	struct commit *commit;
+	const char *argv[] = {NULL, "--all", NULL};
+	int argc = ARRAY_SIZE(argv) - 1;
+	int got_revision = 0;
+
+	init_revisions(&rev, NULL);
+	setup_revisions(argc, argv, &rev, NULL);
+	if (prepare_revision_walk(&rev))
+		die("revision walk setup failed");
+
+	while ((commit = get_revision(&rev)) != NULL) {
+		print_commit(commit);
+		got_revision = 1;
+	}
+
+	reset_revision_walk();
+	return got_revision;
+}
+
+int main(int argc, char **argv)
+{
+	if (argc < 2)
+		return 1;
+
+	if (!strcmp(argv[1], "run-twice")) {
+		printf("1st\n");
+		if (!run_revision_walk())
+			return 1;
+		printf("2nd\n");
+		if (!run_revision_walk())
+			return 1;
+
+		return 0;
+	}
+
+	fprintf(stderr, "check usage\n");
+	return 1;
+}