diff: drop "name" parameter from prepare_temp_file()

The prepare_temp_file() function takes a diff_filespec as well as a
filename. But it is almost certainly an error to pass in a name that
isn't the filespec's "path" parameter, since that is the only thing that
reliably tells us how to find the content (and indeed, this was the
source of a recently-fixed bug).

So let's drop the redundant "name" parameter and just use one->path
throughout the function. This simplifies the interface a little bit, and
makes it impossible for calling code to get it wrong.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -4213,7 +4213,6 @@ static void prep_temp_blob(struct index_state *istate,
 }
 
 static struct diff_tempfile *prepare_temp_file(struct repository *r,
-					       const char *name,
 					       struct diff_filespec *one)
 {
 	struct diff_tempfile *temp = claim_diff_tempfile();
@@ -4231,18 +4230,18 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 
 	if (!S_ISGITLINK(one->mode) &&
 	    (!one->oid_valid ||
-	     reuse_worktree_file(r->index, name, &one->oid, 1))) {
+	     reuse_worktree_file(r->index, one->path, &one->oid, 1))) {
 		struct stat st;
-		if (lstat(name, &st) < 0) {
+		if (lstat(one->path, &st) < 0) {
 			if (errno == ENOENT)
 				goto not_a_valid_file;
-			die_errno("stat(%s)", name);
+			die_errno("stat(%s)", one->path);
 		}
 		if (S_ISLNK(st.st_mode)) {
 			struct strbuf sb = STRBUF_INIT;
-			if (strbuf_readlink(&sb, name, st.st_size) < 0)
-				die_errno("readlink(%s)", name);
-			prep_temp_blob(r->index, name, temp, sb.buf, sb.len,
+			if (strbuf_readlink(&sb, one->path, st.st_size) < 0)
+				die_errno("readlink(%s)", one->path);
+			prep_temp_blob(r->index, one->path, temp, sb.buf, sb.len,
 				       (one->oid_valid ?
 					&one->oid : null_oid()),
 				       (one->oid_valid ?
@@ -4251,7 +4250,7 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 		}
 		else {
 			/* we can borrow from the file in the work tree */
-			temp->name = name;
+			temp->name = one->path;
 			if (!one->oid_valid)
 				oid_to_hex_r(temp->hex, null_oid());
 			else
@@ -4269,7 +4268,7 @@ static struct diff_tempfile *prepare_temp_file(struct repository *r,
 	else {
 		if (diff_populate_filespec(r, one, NULL))
 			die("cannot read data blob for %s", one->path);
-		prep_temp_blob(r->index, name, temp,
+		prep_temp_blob(r->index, one->path, temp,
 			       one->data, one->size,
 			       &one->oid, one->mode);
 	}
@@ -4280,7 +4279,7 @@ static void add_external_diff_name(struct repository *r,
 				   struct strvec *argv,
 				   struct diff_filespec *df)
 {
-	struct diff_tempfile *temp = prepare_temp_file(r, df->path, df);
+	struct diff_tempfile *temp = prepare_temp_file(r, df);
 	strvec_push(argv, temp->name);
 	strvec_push(argv, temp->hex);
 	strvec_push(argv, temp->mode);
@@ -7034,7 +7033,7 @@ static char *run_textconv(struct repository *r,
 	struct strbuf buf = STRBUF_INIT;
 	int err = 0;
 
-	temp = prepare_temp_file(r, spec->path, spec);
+	temp = prepare_temp_file(r, spec);
 	strvec_push(&child.args, pgm);
 	strvec_push(&child.args, temp->name);