[PATCH v2 1/3] revision: add a per-email field to rev-info

[Kristoffer Haugsbakk <code@khaugsbakk.name>]

Add `pe_header` to `rev_info` to store per-email headers.

The next commit will add an option to `format-patch` which will allow
the user to store headers per-email; a complement to options like
`--add-header`.

To make this possible we need a new field to store these headers. We
also need to take ownership of `extra_headers_p` in
`log_write_email_headers`; facilitate this by removing constness from
the relevant pointers.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
---

Notes (series):
    v2:
    • Replaces “log-tree: take ownership of pointer”
      • Link: https://lore.kernel.org/git/3b12a8cf393b6d8f0877fd7d87173c565d7d5a90.1709841147.git.code@khaugsbakk.name/
    • More preliminary work
      • Link: https://lore.kernel.org/git/20240313065454.GB125150@coredump.intra.peff.net/

 log-tree.c | 21 +++++++++++----------
 log-tree.h |  2 +-
 pretty.h   |  2 +-
 revision.h |  4 +++-
 4 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/log-tree.c b/log-tree.c
index e5438b029d9..f6cdde6e8f3 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -470,16 +470,21 @@ void fmt_output_email_subject(struct strbuf *sb, struct rev_info *opt)
 }
 
 void log_write_email_headers(struct rev_info *opt, struct commit *commit,
-			     const char **extra_headers_p,
+			     char **extra_headers_p,
 			     int *need_8bit_cte_p,
 			     int maybe_multipart)
 {
-	const char *extra_headers = opt->extra_headers;
+	struct strbuf headers = STRBUF_INIT;
 	const char *name = oid_to_hex(opt->zero_commit ?
 				      null_oid() : &commit->object.oid);
 
 	*need_8bit_cte_p = 0; /* unknown */
 
+	if (opt->extra_headers)
+		strbuf_addstr(&headers, opt->extra_headers);
+	if (opt->pe_headers)
+		strbuf_addstr(&headers, opt->pe_headers);
+
 	fprintf(opt->diffopt.file, "From %s Mon Sep 17 00:00:00 2001\n", name);
 	graph_show_oneline(opt->graph);
 	if (opt->message_id) {
@@ -496,16 +501,13 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
 		graph_show_oneline(opt->graph);
 	}
 	if (opt->mime_boundary && maybe_multipart) {
-		static struct strbuf subject_buffer = STRBUF_INIT;
 		static struct strbuf buffer = STRBUF_INIT;
 		struct strbuf filename =  STRBUF_INIT;
 		*need_8bit_cte_p = -1; /* NEVER */
 
-		strbuf_reset(&subject_buffer);
 		strbuf_reset(&buffer);
 
-		strbuf_addf(&subject_buffer,
-			 "%s"
+		strbuf_addf(&headers,
 			 "MIME-Version: 1.0\n"
 			 "Content-Type: multipart/mixed;"
 			 " boundary=\"%s%s\"\n"
@@ -516,10 +518,8 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
 			 "Content-Type: text/plain; "
 			 "charset=UTF-8; format=fixed\n"
 			 "Content-Transfer-Encoding: 8bit\n\n",
-			 extra_headers ? extra_headers : "",
 			 mime_boundary_leader, opt->mime_boundary,
 			 mime_boundary_leader, opt->mime_boundary);
-		extra_headers = subject_buffer.buf;
 
 		if (opt->numbered_files)
 			strbuf_addf(&filename, "%d", opt->nr);
@@ -539,7 +539,7 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
 		opt->diffopt.stat_sep = buffer.buf;
 		strbuf_release(&filename);
 	}
-	*extra_headers_p = extra_headers;
+	*extra_headers_p = headers.len ? strbuf_detach(&headers, NULL) : NULL;
 }
 
 static void show_sig_lines(struct rev_info *opt, int status, const char *bol)
@@ -678,7 +678,7 @@ void show_log(struct rev_info *opt)
 	struct log_info *log = opt->loginfo;
 	struct commit *commit = log->commit, *parent = log->parent;
 	int abbrev_commit = opt->abbrev_commit ? opt->abbrev : the_hash_algo->hexsz;
-	const char *extra_headers = opt->extra_headers;
+	char *extra_headers = opt->extra_headers;
 	struct pretty_print_context ctx = {0};
 
 	opt->loginfo = NULL;
@@ -857,6 +857,7 @@ void show_log(struct rev_info *opt)
 
 	strbuf_release(&msgbuf);
 	free(ctx.notes_message);
+	free(ctx.after_subject);
 
 	if (cmit_fmt_is_mail(ctx.fmt) && opt->idiff_oid1) {
 		struct diff_queue_struct dq;
diff --git a/log-tree.h b/log-tree.h
index 41c776fea52..94978e2c838 100644
--- a/log-tree.h
+++ b/log-tree.h
@@ -29,7 +29,7 @@ void format_decorations(struct strbuf *sb, const struct commit *commit,
 			int use_color, const struct decoration_options *opts);
 void show_decorations(struct rev_info *opt, struct commit *commit);
 void log_write_email_headers(struct rev_info *opt, struct commit *commit,
-			     const char **extra_headers_p,
+			     char **extra_headers_p,
 			     int *need_8bit_cte_p,
 			     int maybe_multipart);
 void load_ref_decorations(struct decoration_filter *filter, int flags);
diff --git a/pretty.h b/pretty.h
index 421209e9ec2..bdce3191875 100644
--- a/pretty.h
+++ b/pretty.h
@@ -35,7 +35,7 @@ struct pretty_print_context {
 	 */
 	enum cmit_fmt fmt;
 	int abbrev;
-	const char *after_subject;
+	char *after_subject;
 	int preserve_subject;
 	struct date_mode date_mode;
 	unsigned date_mode_explicit:1;
diff --git a/revision.h b/revision.h
index 94c43138bc3..95e92397a7a 100644
--- a/revision.h
+++ b/revision.h
@@ -290,7 +290,9 @@ struct rev_info {
 	struct ident_split from_ident;
 	struct string_list *ref_message_ids;
 	int		add_signoff;
-	const char	*extra_headers;
+	char		*extra_headers;
+	/* per-email headers */
+	char		*pe_headers;
 	const char	*log_reencode;
 	const char	*subject_prefix;
 	int		patch_name_max;
-- 
2.44.0.144.g29ae9861142