format_trailers(): use strbuf instead of FILE

This is another preparatory refactor to unify the trailer formatters.

Make format_trailers() also write to a strbuf, to align with
format_trailers_from_commit() which also does the same. Doing this makes
format_trailers() behave similar to format_trailer_info() (which will
soon help us replace one with the other).

Signed-off-by: Linus Arver <linusa@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/interpret-trailers.c

@@ -140,6 +140,7 @@ static void interpret_trailers(const struct process_trailer_options *opts,
 {
 	LIST_HEAD(head);
 	struct strbuf sb = STRBUF_INIT;
+	struct strbuf trailer_block = STRBUF_INIT;
 	struct trailer_info info;
 	FILE *outfile = stdout;
 
@@ -169,8 +170,11 @@ static void interpret_trailers(const struct process_trailer_options *opts,
 		process_trailers_lists(&head, &arg_head);
 	}
 
-	format_trailers(opts, &head, outfile);
+	/* Print trailer block. */
+	format_trailers(opts, &head, &trailer_block);
 	free_trailers(&head);
+	fwrite(trailer_block.buf, 1, trailer_block.len, outfile);
+	strbuf_release(&trailer_block);
 
 	/* Print the lines after the trailers as is */
 	if (!opts->only_trailers)

trailer.c

@@ -144,12 +144,12 @@ static char last_non_space_char(const char *s)
 	return '\0';
 }
 
-static void print_tok_val(FILE *outfile, const char *tok, const char *val)
+static void print_tok_val(struct strbuf *out, const char *tok, const char *val)
 {
 	char c;
 
 	if (!tok) {
-		fprintf(outfile, "%s\n", val);
+		strbuf_addf(out, "%s\n", val);
 		return;
 	}
 
@@ -157,13 +157,14 @@ static void print_tok_val(FILE *outfile, const char *tok, const char *val)
 	if (!c)
 		return;
 	if (strchr(separators, c))
-		fprintf(outfile, "%s%s\n", tok, val);
+		strbuf_addf(out, "%s%s\n", tok, val);
 	else
-		fprintf(outfile, "%s%c %s\n", tok, separators[0], val);
+		strbuf_addf(out, "%s%c %s\n", tok, separators[0], val);
 }
 
 void format_trailers(const struct process_trailer_options *opts,
-		     struct list_head *trailers, FILE *outfile)
+		     struct list_head *trailers,
+		     struct strbuf *out)
 {
 	struct list_head *pos;
 	struct trailer_item *item;
@@ -171,7 +172,7 @@ void format_trailers(const struct process_trailer_options *opts,
 		item = list_entry(pos, struct trailer_item, list);
 		if ((!opts->trim_empty || strlen(item->value) > 0) &&
 		    (!opts->only_trailers || item->token))
-			print_tok_val(outfile, item->token, item->value);
+			print_tok_val(out, item->token, item->value);
 	}
 }
 

trailer.h

@@ -102,7 +102,8 @@ void trailer_info_release(struct trailer_info *info);
 
 void trailer_config_init(void);
 void format_trailers(const struct process_trailer_options *,
-		     struct list_head *trailers, FILE *outfile);
+		     struct list_head *trailers,
+		     struct strbuf *out);
 void free_trailers(struct list_head *);
 
 /*