oid functions: return an int

Stop returning a void for functions, future-proofing them to allow them
to fail.

include/git2/oid.h

@@ -73,8 +73,9 @@ GIT_EXTERN(int) git_oid_fromstrn(git_oid *out, const char *str, size_t length);
  *
  * @param out oid structure the result is written into.
  * @param raw the raw input bytes to be copied.
+ * @return 0 on success or error code
  */
-GIT_EXTERN(void) git_oid_fromraw(git_oid *out, const unsigned char *raw);
+GIT_EXTERN(int) git_oid_fromraw(git_oid *out, const unsigned char *raw);
 
 /**
  * Format a git_oid into a hex string.
@@ -85,8 +86,9 @@ GIT_EXTERN(void) git_oid_fromraw(git_oid *out, const unsigned char *raw);
  *		oid digits are written; a '\\0' terminator must be added
  *		by the caller if it is required.
  * @param id oid structure to format.
+ * @return 0 on success or error code
  */
-GIT_EXTERN(void) git_oid_fmt(char *out, const git_oid *id);
+GIT_EXTERN(int) git_oid_fmt(char *out, const git_oid *id);
 
 /**
  * Format a git_oid into a partial hex string.
@@ -96,8 +98,9 @@ GIT_EXTERN(void) git_oid_fmt(char *out, const git_oid *id);
  *		will be zeroed; if not, a '\0' terminator is NOT added.
  * @param n number of characters to write into out string
  * @param id oid structure to format.
+ * @return 0 on success or error code
  */
-GIT_EXTERN(void) git_oid_nfmt(char *out, size_t n, const git_oid *id);
+GIT_EXTERN(int) git_oid_nfmt(char *out, size_t n, const git_oid *id);
 
 /**
  * Format a git_oid into a loose-object path string.
@@ -111,8 +114,9 @@ GIT_EXTERN(void) git_oid_nfmt(char *out, size_t n, const git_oid *id);
  *		oid digits are written; a '\\0' terminator must be added
  *		by the caller if it is required.
  * @param id oid structure to format.
+ * @return 0 on success, non-zero callback return value, or error code
  */
-GIT_EXTERN(void) git_oid_pathfmt(char *out, const git_oid *id);
+GIT_EXTERN(int) git_oid_pathfmt(char *out, const git_oid *id);
 
 /**
  * Format a git_oid into a statically allocated c-string.
@@ -151,8 +155,9 @@ GIT_EXTERN(char *) git_oid_tostr(char *out, size_t n, const git_oid *id);
  *
  * @param out oid structure the result is written into.
  * @param src oid structure to copy from.
+ * @return 0 on success or error code
  */
-GIT_EXTERN(void) git_oid_cpy(git_oid *out, const git_oid *src);
+GIT_EXTERN(int) git_oid_cpy(git_oid *out, const git_oid *src);
 
 /**
  * Compare two oid structures.

src/oid.c

@@ -64,13 +64,13 @@ GIT_INLINE(char) *fmt_one(char *str, unsigned int val)
 	return str;
 }
 
-void git_oid_nfmt(char *str, size_t n, const git_oid *oid)
+int git_oid_nfmt(char *str, size_t n, const git_oid *oid)
 {
 	size_t i, max_i;
 
 	if (!oid) {
 		memset(str, 0, n);
-		return;
+		return 0;
 	}
 	if (n > GIT_OID_HEXSZ) {
 		memset(&str[GIT_OID_HEXSZ], 0, n - GIT_OID_HEXSZ);
@@ -84,14 +84,16 @@ void git_oid_nfmt(char *str, size_t n, const git_oid *oid)
 
 	if (n & 1)
 		*str++ = to_hex[oid->id[i] >> 4];
+
+	return 0;
 }
 
-void git_oid_fmt(char *str, const git_oid *oid)
+int git_oid_fmt(char *str, const git_oid *oid)
 {
-	git_oid_nfmt(str, GIT_OID_HEXSZ, oid);
+	return git_oid_nfmt(str, GIT_OID_HEXSZ, oid);
 }
 
-void git_oid_pathfmt(char *str, const git_oid *oid)
+int git_oid_pathfmt(char *str, const git_oid *oid)
 {
 	size_t i;
 
@@ -99,6 +101,8 @@ void git_oid_pathfmt(char *str, const git_oid *oid)
 	*str++ = '/';
 	for (i = 1; i < sizeof(oid->id); i++)
 		str = fmt_one(str, oid->id[i]);
+
+	return 0;
 }
 
 char *git_oid_tostr_s(const git_oid *oid)
@@ -167,14 +171,16 @@ void git_oid__writebuf(git_buf *buf, const char *header, const git_oid *oid)
 	git_buf_putc(buf, '\n');
 }
 
-void git_oid_fromraw(git_oid *out, const unsigned char *raw)
+int git_oid_fromraw(git_oid *out, const unsigned char *raw)
 {
 	memcpy(out->id, raw, sizeof(out->id));
+	return 0;
 }
 
-void git_oid_cpy(git_oid *out, const git_oid *src)
+int git_oid_cpy(git_oid *out, const git_oid *src)
 {
 	memcpy(out->id, src->id, sizeof(out->id));
+	return 0;
 }
 
 int git_oid_cmp(const git_oid *a, const git_oid *b)