commit-reach: use size_t to track indices when computing merge bases

The functions `repo_get_merge_bases_many()` and friends accepts an array
of commits as well as a parameter that indicates how large that array
is. This parameter is using a signed integer, which leads to a couple of
warnings with -Wsign-compare.

Refactor the code to use `size_t` to track indices instead and adapt
callers accordingly. While most callers are trivial, there are two
callers that require a bit more scrutiny:

  - builtin/merge-base.c:show_merge_base() subtracts `1` from the
    `rev_nr` before calling `repo_get_merge_bases_many_dirty()`, so if
    the variable was `0` it would wrap. This code is fine though because
    its only caller will execute that code only when `argc >= 2`, and it
    follows that `rev_nr >= 2`, as well.

  - bisect.ccheck_merge_bases() similarly subtracts `1` from `rev_nr`.
    Again, there is only a single caller that populates `rev_nr` with
    `good_revs.nr`. And because a bisection always requires at least one
    good revision it follws that `rev_nr >= 1`.

Mark the file as -Wsign-compare-clean.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bisect.c

@@ -855,7 +855,7 @@ static void handle_skipped_merge_base(const struct object_id *mb)
  * for early success, this will be converted back to 0 in
  * check_good_are_ancestors_of_bad().
  */
-static enum bisect_error check_merge_bases(int rev_nr, struct commit **rev, int no_checkout)
+static enum bisect_error check_merge_bases(size_t rev_nr, struct commit **rev, int no_checkout)
 {
 	enum bisect_error res = BISECT_OK;
 	struct commit_list *result = NULL;

builtin/merge-base.c

@@ -8,7 +8,7 @@
 #include "parse-options.h"
 #include "commit-reach.h"
 
-static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
+static int show_merge_base(struct commit **rev, size_t rev_nr, int show_all)
 {
 	struct commit_list *result = NULL, *r;
 
@@ -149,7 +149,7 @@ int cmd_merge_base(int argc,
 		   struct repository *repo UNUSED)
 {
 	struct commit **rev;
-	int rev_nr = 0;
+	size_t rev_nr = 0;
 	int show_all = 0;
 	int cmdmode = 0;
 	int ret;

commit-reach.c

@@ -1,5 +1,4 @@
 #define USE_THE_REPOSITORY_VARIABLE
-#define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "git-compat-util.h"
 #include "commit.h"
@@ -421,7 +420,7 @@ static int remove_redundant(struct repository *r, struct commit **array,
 
 static int get_merge_bases_many_0(struct repository *r,
 				  struct commit *one,
-				  int n,
+				  size_t n,
 				  struct commit **twos,
 				  int cleanup,
 				  struct commit_list **result)
@@ -469,7 +468,7 @@ static int get_merge_bases_many_0(struct repository *r,
 
 int repo_get_merge_bases_many(struct repository *r,
 			      struct commit *one,
-			      int n,
+			      size_t n,
 			      struct commit **twos,
 			      struct commit_list **result)
 {
@@ -478,7 +477,7 @@ int repo_get_merge_bases_many(struct repository *r,
 
 int repo_get_merge_bases_many_dirty(struct repository *r,
 				    struct commit *one,
-				    int n,
+				    size_t n,
 				    struct commit **twos,
 				    struct commit_list **result)
 {

commit-reach.h

@@ -14,12 +14,12 @@ int repo_get_merge_bases(struct repository *r,
 			 struct commit *rev2,
 			 struct commit_list **result);
 int repo_get_merge_bases_many(struct repository *r,
-			      struct commit *one, int n,
+			      struct commit *one, size_t n,
 			      struct commit **twos,
 			      struct commit_list **result);
 /* To be used only when object flags after this call no longer matter */
 int repo_get_merge_bases_many_dirty(struct repository *r,
-				    struct commit *one, int n,
+				    struct commit *one, size_t n,
 				    struct commit **twos,
 				    struct commit_list **result);
 

t/helper/test-reach.c

@@ -35,7 +35,7 @@ int cmd__reach(int ac, const char **av)
 	struct commit_list *X, *Y;
 	struct object_array X_obj = OBJECT_ARRAY_INIT;
 	struct commit **X_array, **Y_array;
-	int X_nr, X_alloc, Y_nr, Y_alloc;
+	size_t X_nr, X_alloc, Y_nr, Y_alloc;
 	struct strbuf buf = STRBUF_INIT;
 	struct repository *r = the_repository;
 
@@ -157,7 +157,7 @@ int cmd__reach(int ac, const char **av)
 		clear_contains_cache(&cache);
 	} else if (!strcmp(av[1], "get_reachable_subset")) {
 		const int reachable_flag = 1;
-		int i, count = 0;
+		int count = 0;
 		struct commit_list *current;
 		struct commit_list *list = get_reachable_subset(X_array, X_nr,
 								Y_array, Y_nr,
@@ -169,7 +169,7 @@ int cmd__reach(int ac, const char **av)
 				    oid_to_hex(&list->item->object.oid));
 			count++;
 		}
-		for (i = 0; i < Y_nr; i++) {
+		for (size_t i = 0; i < Y_nr; i++) {
 			if (Y_array[i]->object.flags & reachable_flag)
 				count--;
 		}