format-patch: teach --cover-from-description option

Before, when format-patch generated a cover letter, only the body would
be populated with a branch's description while the subject would be
populated with placeholder text. However, users may want to have the
subject of their cover letter automatically populated in the same way.

Teach format-patch to accept the `--cover-from-description` option and
corresponding `format.coverFromDescription` config, allowing users to
populate different parts of the cover letter (including the subject
now).

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/format.txt

@@ -36,6 +36,12 @@ format.subjectPrefix::
 	The default for format-patch is to output files with the '[PATCH]'
 	subject prefix. Use this variable to change that prefix.
 
+format.coverFromDescription::
+	The default mode for format-patch to determine which parts of
+	the cover letter will be populated using the branch's
+	description. See the `--cover-from-description` option in
+	linkgit:git-format-patch[1].
+
 format.signature::
 	The default for format-patch is to output a signature containing
 	the Git version number. Use this variable to change that default.

Documentation/git-format-patch.txt

@@ -19,6 +19,7 @@ SYNOPSIS
 		   [--start-number <n>] [--numbered-files]
 		   [--in-reply-to=<message id>] [--suffix=.<sfx>]
 		   [--ignore-if-in-upstream]
+		   [--cover-from-description=<mode>]
 		   [--rfc] [--subject-prefix=<subject prefix>]
 		   [(--reroll-count|-v) <n>]
 		   [--to=<email>] [--cc=<email>]
@@ -171,6 +172,26 @@ will want to ensure that threading is disabled for `git send-email`.
 	patches being generated, and any patch that matches is
 	ignored.
 
+--cover-from-description=<mode>::
+	Controls which parts of the cover letter will be automatically
+	populated using the branch's description.
++
+If `<mode>` is `message` or `default`, the cover letter subject will be
+populated with placeholder text. The body of the cover letter will be
+populated with the branch's description. This is the default mode when
+no configuration nor command line option is specified.
++
+If `<mode>` is `subject`, the first paragraph of the branch description will
+populate the cover letter subject. The remainder of the description will
+populate the body of the cover letter.
++
+If `<mode>` is `auto`, if the first paragraph of the branch description
+is greater than 100 bytes, then the mode will be `message`, otherwise
+`subject` will be used.
++
+If `<mode>` is `none`, both the cover letter subject and body will be
+populated with placeholder text.
+
 --subject-prefix=<subject prefix>::
 	Instead of the standard '[PATCH]' prefix in the subject
 	line, instead use '[<subject prefix>]'. This
@@ -347,6 +368,7 @@ with configuration variables.
 	signOff = true
 	outputDirectory = <directory>
 	coverLetter = auto
+	coverFromDescription = auto
 ------------
 
 

builtin/log.c

@@ -37,6 +37,7 @@
 #include "range-diff.h"
 
 #define MAIL_DEFAULT_WRAP 72
+#define COVER_FROM_AUTO_MAX_SUBJECT_LEN 100
 
 /* Set a default date-time format for git log ("log.date" config variable) */
 static const char *default_date_mode = NULL;
@@ -777,6 +778,13 @@ enum thread_level {
 	THREAD_DEEP
 };
 
+enum cover_from_description {
+	COVER_FROM_NONE,
+	COVER_FROM_MESSAGE,
+	COVER_FROM_SUBJECT,
+	COVER_FROM_AUTO
+};
+
 static enum thread_level thread;
 static int do_signoff;
 static int base_auto;
@@ -785,6 +793,23 @@ static const char *signature = git_version_string;
 static const char *signature_file;
 static enum cover_setting config_cover_letter;
 static const char *config_output_directory;
+static enum cover_from_description cover_from_description_mode = COVER_FROM_MESSAGE;
+
+static enum cover_from_description parse_cover_from_description(const char *arg)
+{
+	if (!arg || !strcmp(arg, "default"))
+		return COVER_FROM_MESSAGE;
+	else if (!strcmp(arg, "none"))
+		return COVER_FROM_NONE;
+	else if (!strcmp(arg, "message"))
+		return COVER_FROM_MESSAGE;
+	else if (!strcmp(arg, "subject"))
+		return COVER_FROM_SUBJECT;
+	else if (!strcmp(arg, "auto"))
+		return COVER_FROM_AUTO;
+	else
+		die(_("%s: invalid cover from description mode"), arg);
+}
 
 static int git_format_config(const char *var, const char *value, void *cb)
 {
@@ -891,6 +916,10 @@ static int git_format_config(const char *var, const char *value, void *cb)
 		}
 		return 0;
 	}
+	if (!strcmp(var, "format.coverfromdescription")) {
+		cover_from_description_mode = parse_cover_from_description(value);
+		return 0;
+	}
 
 	return git_log_config(var, value, cb);
 }
@@ -997,20 +1026,6 @@ static void print_signature(FILE *file)
 	putc('\n', file);
 }
 
-static void add_branch_description(struct strbuf *buf, const char *branch_name)
-{
-	struct strbuf desc = STRBUF_INIT;
-	if (!branch_name || !*branch_name)
-		return;
-	read_branch_desc(&desc, branch_name);
-	if (desc.len) {
-		strbuf_addch(buf, '\n');
-		strbuf_addbuf(buf, &desc);
-		strbuf_addch(buf, '\n');
-	}
-	strbuf_release(&desc);
-}
-
 static char *find_branch_name(struct rev_info *rev)
 {
 	int i, positive = -1;
@@ -1057,15 +1072,51 @@ static void show_diffstat(struct rev_info *rev,
 	fprintf(rev->diffopt.file, "\n");
 }
 
+static void prepare_cover_text(struct pretty_print_context *pp,
+			       const char *branch_name,
+			       struct strbuf *sb,
+			       const char *encoding,
+			       int need_8bit_cte)
+{
+	const char *subject = "*** SUBJECT HERE ***";
+	const char *body = "*** BLURB HERE ***";
+	struct strbuf description_sb = STRBUF_INIT;
+	struct strbuf subject_sb = STRBUF_INIT;
+
+	if (cover_from_description_mode == COVER_FROM_NONE)
+		goto do_pp;
+
+	if (branch_name && *branch_name)
+		read_branch_desc(&description_sb, branch_name);
+	if (!description_sb.len)
+		goto do_pp;
+
+	if (cover_from_description_mode == COVER_FROM_SUBJECT ||
+			cover_from_description_mode == COVER_FROM_AUTO)
+		body = format_subject(&subject_sb, description_sb.buf, " ");
+
+	if (cover_from_description_mode == COVER_FROM_MESSAGE ||
+			(cover_from_description_mode == COVER_FROM_AUTO &&
+			 subject_sb.len > COVER_FROM_AUTO_MAX_SUBJECT_LEN))
+		body = description_sb.buf;
+	else
+		subject = subject_sb.buf;
+
+do_pp:
+	pp_title_line(pp, &subject, sb, encoding, need_8bit_cte);
+	pp_remainder(pp, &body, sb, 0);
+
+	strbuf_release(&description_sb);
+	strbuf_release(&subject_sb);
+}
+
 static void make_cover_letter(struct rev_info *rev, int use_stdout,
 			      struct commit *origin,
 			      int nr, struct commit **list,
 			      const char *branch_name,
 			      int quiet)
 {
 	const char *committer;
-	const char *body = "*** SUBJECT HERE ***\n\n*** BLURB HERE ***\n";
-	const char *msg;
 	struct shortlog log;
 	struct strbuf sb = STRBUF_INIT;
 	int i;
@@ -1095,15 +1146,12 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 	if (!branch_name)
 		branch_name = find_branch_name(rev);
 
-	msg = body;
 	pp.fmt = CMIT_FMT_EMAIL;
 	pp.date_mode.type = DATE_RFC2822;
 	pp.rev = rev;
 	pp.print_email_subject = 1;
 	pp_user_info(&pp, NULL, &sb, committer, encoding);
-	pp_title_line(&pp, &msg, &sb, encoding, need_8bit_cte);
-	pp_remainder(&pp, &msg, &sb, 0);
-	add_branch_description(&sb, branch_name);
+	prepare_cover_text(&pp, branch_name, &sb, encoding, need_8bit_cte);
 	fprintf(rev->diffopt.file, "%s\n", sb.buf);
 
 	strbuf_release(&sb);
@@ -1545,6 +1593,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	int use_patch_format = 0;
 	int quiet = 0;
 	int reroll_count = -1;
+	char *cover_from_description_arg = NULL;
 	char *branch_name = NULL;
 	char *base_commit = NULL;
 	struct base_tree_info bases;
@@ -1581,6 +1630,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 		{ OPTION_CALLBACK, 0, "rfc", &rev, NULL,
 			    N_("Use [RFC PATCH] instead of [PATCH]"),
 			    PARSE_OPT_NOARG | PARSE_OPT_NONEG, rfc_callback },
+		OPT_STRING(0, "cover-from-description", &cover_from_description_arg,
+			    N_("cover-from-description-mode"),
+			    N_("generate parts of a cover letter based on a branch's description")),
 		{ OPTION_CALLBACK, 0, "subject-prefix", &rev, N_("prefix"),
 			    N_("Use [<prefix>] instead of [PATCH]"),
 			    PARSE_OPT_NONEG, subject_prefix_callback },
@@ -1672,6 +1724,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			     PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN |
 			     PARSE_OPT_KEEP_DASHDASH);
 
+	if (cover_from_description_arg)
+		cover_from_description_mode = parse_cover_from_description(cover_from_description_arg);
+
 	if (0 < reroll_count) {
 		struct strbuf sprefix = STRBUF_INIT;
 		strbuf_addf(&sprefix, "%s v%d",