trailer: libify a couple of functions

Move create_in_place_tempfile() and process_trailers() from
builtin/interpret-trailers.c into trailer.c and expose it via trailer.h.

This reverts most of ae0ec2e (trailer: move interpret_trailers()
to interpret-trailers.c, 2024-03-01) and lets other call sites reuse
the same trailer rewriting logic.

Signed-off-by: Li Chen <me@linux.beauty>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: FirstLoveLife

builtin/interpret-trailers.c

@@ -93,39 +93,6 @@ static int parse_opt_parse(const struct option *opt, const char *arg,
 	return 0;
 }
 
-
-static struct tempfile *create_in_place_tempfile(const char *file)
-{
-	struct tempfile *tempfile = NULL;
-	struct stat st;
-	struct strbuf filename_template = STRBUF_INIT;
-	const char *tail;
-
-	if (stat(file, &st)) {
-		error_errno(_("could not stat %s"), file);
-		return NULL;
-	}
-	if (!S_ISREG(st.st_mode)) {
-		error(_("file %s is not a regular file"), file);
-		return NULL;
-	}
-	if (!(st.st_mode & S_IWUSR)) {
-		error(_("file %s is not writable by user"), file);
-		return NULL;
-	}
-	/* Create temporary file in the same directory as the original */
-	tail = find_last_dir_sep(file);
-	if (tail)
-		strbuf_add(&filename_template, file, tail - file + 1);
-	strbuf_addstr(&filename_template, "git-interpret-trailers-XXXXXX");
-
-	tempfile = mks_tempfile_m(filename_template.buf, st.st_mode);
-
-	strbuf_release(&filename_template);
-
-	return tempfile;
-}
-
 static void read_input_file(struct strbuf *sb, const char *file)
 {
 	if (file) {
@@ -138,42 +105,6 @@ static void read_input_file(struct strbuf *sb, const char *file)
 	strbuf_complete_line(sb);
 }
 
-static void process_trailers(const struct process_trailer_options *opts,
-			     struct list_head *new_trailer_head,
-			     struct strbuf *input, struct strbuf *out)
-{
-	LIST_HEAD(head);
-	struct trailer_block *trailer_block;
-
-	trailer_block = parse_trailers(opts, input->buf, &head);
-
-	/* Print the lines before the trailer block */
-	if (!opts->only_trailers)
-		strbuf_add(out, input->buf, trailer_block_start(trailer_block));
-
-	if (!opts->only_trailers && !blank_line_before_trailer_block(trailer_block))
-		strbuf_addch(out, '\n');
-
-	if (!opts->only_input) {
-		LIST_HEAD(config_head);
-		LIST_HEAD(arg_head);
-		parse_trailers_from_config(&config_head);
-		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
-		list_splice(&config_head, &arg_head);
-		process_trailers_lists(&head, &arg_head);
-	}
-
-	/* Print trailer block. */
-	format_trailers(opts, &head, out);
-	free_trailers(&head);
-
-	/* Print the lines after the trailer block as is. */
-	if (!opts->only_trailers)
-		strbuf_add(out, input->buf + trailer_block_end(trailer_block),
-			   input->len - trailer_block_end(trailer_block));
-	trailer_block_release(trailer_block);
-}
-
 static void interpret_trailers(const struct process_trailer_options *opts,
 			       struct list_head *new_trailer_head,
 			       const char *file)
@@ -188,7 +119,7 @@ static void interpret_trailers(const struct process_trailer_options *opts,
 	read_input_file(&input, file);
 
 	if (opts->in_place) {
-		tempfile = create_in_place_tempfile(file);
+		tempfile = trailer_create_in_place_tempfile(file);
 		if (!tempfile)
 			die(NULL);
 		fd = tempfile->fd;

trailer.c

@@ -9,6 +9,8 @@
 #include "commit.h"
 #include "trailer.h"
 #include "list.h"
+#include "tempfile.h"
+
 /*
  * Copyright (c) 2013, 2014 Christian Couder <chriscool@tuxfamily.org>
  */
@@ -1224,6 +1226,38 @@ void trailer_iterator_release(struct trailer_iterator *iter)
 	strbuf_release(&iter->key);
 }
 
+struct tempfile *trailer_create_in_place_tempfile(const char *file)
+{
+	struct tempfile *tempfile = NULL;
+	struct stat st;
+	struct strbuf filename_template = STRBUF_INIT;
+	const char *tail;
+
+	if (stat(file, &st)) {
+		error_errno(_("could not stat %s"), file);
+		return NULL;
+	}
+	if (!S_ISREG(st.st_mode)) {
+		error(_("file %s is not a regular file"), file);
+		return NULL;
+	}
+	if (!(st.st_mode & S_IWUSR)) {
+		error(_("file %s is not writable by user"), file);
+		return NULL;
+	}
+	/* Create temporary file in the same directory as the original */
+	tail = find_last_dir_sep(file);
+	if (tail)
+		strbuf_add(&filename_template, file, tail - file + 1);
+	strbuf_addstr(&filename_template, "git-interpret-trailers-XXXXXX");
+
+	tempfile = mks_tempfile_m(filename_template.buf, st.st_mode);
+
+	strbuf_release(&filename_template);
+
+	return tempfile;
+}
+
 int amend_file_with_trailers(const char *path, const struct strvec *trailer_args)
 {
 	struct child_process run_trailer = CHILD_PROCESS_INIT;
@@ -1235,3 +1269,39 @@ int amend_file_with_trailers(const char *path, const struct strvec *trailer_args
 	strvec_pushv(&run_trailer.args, trailer_args->v);
 	return run_command(&run_trailer);
 }
+
+void process_trailers(const struct process_trailer_options *opts,
+		      struct list_head *new_trailer_head,
+		      struct strbuf *input, struct strbuf *out)
+{
+	LIST_HEAD(head);
+	struct trailer_block *trailer_block;
+
+	trailer_block = parse_trailers(opts, input->buf, &head);
+
+	/* Print the lines before the trailer block */
+	if (!opts->only_trailers)
+		strbuf_add(out, input->buf, trailer_block_start(trailer_block));
+
+	if (!opts->only_trailers && !blank_line_before_trailer_block(trailer_block))
+		strbuf_addch(out, '\n');
+
+	if (!opts->only_input) {
+		LIST_HEAD(config_head);
+		LIST_HEAD(arg_head);
+		parse_trailers_from_config(&config_head);
+		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
+		list_splice(&config_head, &arg_head);
+		process_trailers_lists(&head, &arg_head);
+	}
+
+	/* Print trailer block. */
+	format_trailers(opts, &head, out);
+	free_trailers(&head);
+
+	/* Print the lines after the trailer block as is. */
+	if (!opts->only_trailers)
+		strbuf_add(out, input->buf + trailer_block_end(trailer_block),
+			   input->len - trailer_block_end(trailer_block));
+	trailer_block_release(trailer_block);
+}

trailer.h

@@ -202,4 +202,20 @@ void trailer_iterator_release(struct trailer_iterator *iter);
  */
 int amend_file_with_trailers(const char *path, const struct strvec *trailer_args);
 
+/*
+ * Create a tempfile ""git-interpret-trailers-XXXXXX" in the same
+ * directory as file.
+ */
+struct tempfile *trailer_create_in_place_tempfile(const char *file);
+
+/*
+ * Rewrite the contents of input by processing its trailer block according to
+ * opts and (optionally) appending trailers from new_trailer_head.
+ *
+ * The rewritten message is appended to out (callers should strbuf_reset()
+ * first if needed).
+ */
+void process_trailers(const struct process_trailer_options *opts,
+		      struct list_head *new_trailer_head,
+		      struct strbuf *input, struct strbuf *out);
 #endif /* TRAILER_H */