gpg-interface: address -Wsign-comparison warnings

There are a couple of -Wsign-comparison warnings in "gpg-interface.c".
Most of them are trivial and simply using signed integers to loop
towards an upper unsigned bound.

But in `parse_signed_buffer()` we have one case where the different
signedness of the two values of a ternary expression results in a
warning. Given that:

  - `size` will always be bigger than `len` due to the loop condition.

  - `eol` will always be after `buf + len` because it is found via
    memchr(3p) starting from `buf + len`.

We know that both values will always be natural integers.

Squelch the warning by casting the left-hand side to `size_t`.

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

Author: pks-t

gpg-interface.c

@@ -1,5 +1,4 @@
 #define USE_THE_REPOSITORY_VARIABLE
-#define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "git-compat-util.h"
 #include "commit.h"
@@ -128,19 +127,17 @@ static struct gpg_format *use_format = &gpg_format[0];
 
 static struct gpg_format *get_format_by_name(const char *str)
 {
-	int i;
-
-	for (i = 0; i < ARRAY_SIZE(gpg_format); i++)
+	for (size_t i = 0; i < ARRAY_SIZE(gpg_format); i++)
 		if (!strcmp(gpg_format[i].name, str))
 			return gpg_format + i;
 	return NULL;
 }
 
 static struct gpg_format *get_format_by_sig(const char *sig)
 {
-	int i, j;
+	int j;
 
-	for (i = 0; i < ARRAY_SIZE(gpg_format); i++)
+	for (size_t i = 0; i < ARRAY_SIZE(gpg_format); i++)
 		for (j = 0; gpg_format[i].sigs[j]; j++)
 			if (starts_with(sig, gpg_format[i].sigs[j]))
 				return gpg_format + i;
@@ -228,7 +225,7 @@ static void parse_gpg_output(struct signature_check *sigc)
 {
 	const char *buf = sigc->gpg_status;
 	const char *line, *next;
-	int i, j;
+	int j;
 	int seen_exclusive_status = 0;
 
 	/* Iterate over all lines */
@@ -243,7 +240,7 @@ static void parse_gpg_output(struct signature_check *sigc)
 			continue;
 
 		/* Iterate over all search strings */
-		for (i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
+		for (size_t i = 0; i < ARRAY_SIZE(sigcheck_gpg_status); i++) {
 			if (skip_prefix(line, sigcheck_gpg_status[i].check, &line)) {
 				/*
 				 * GOODSIG, BADSIG etc. can occur only once for
@@ -700,7 +697,7 @@ size_t parse_signed_buffer(const char *buf, size_t size)
 			match = len;
 
 		eol = memchr(buf + len, '\n', size - len);
-		len += eol ? eol - (buf + len) + 1 : size - len;
+		len += eol ? (size_t) (eol - (buf + len) + 1) : size - len;
 	}
 	return match;
 }