pretty: drop print_email_subject flag

With one exception, the print_email_subject flag is set if and only if
the commit format is email based:

  - in make_cover_letter() we set it along with CMIT_FMT_EMAIL
    explicitly

  - in show_log(), we set it if cmit_fmt_is_mail() is true. That covers
    format-patch as well as "git log --format=email" (or mboxrd).

The one exception is "rev-list --format=email", which somewhat
nonsensically prints the author and date as email headers, but no
subject, like:

  $ git rev-list --format=email HEAD
  commit 64fc4c2cdd4db2645eaabb47aa4bac820b03cdba
  From: Jeff King <peff@peff.net>
  Date: Tue, 19 Mar 2024 19:39:26 -0400

  this is the subject

  this is the body

It's doubtful that this is a useful format at all (the "commit" lines
replace the "From" lines that would make it work as an actual mbox).
But I think that printing the subject as a header (like this patch does)
is the least surprising thing to do.

So let's drop this field, making the code a little simpler and easier to
reason about. Note that we do need to set the "rev" field of the
pretty_print_context in rev-list, since that is used to check for
subject_prefix, etc. It's not possible to set those fields via rev-list,
so we'll always just print "Subject: ". But unless we pass in our
rev_info, fmt_output_email_subject() would segfault trying to figure it
out.

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

builtin/log.c

@@ -1364,7 +1364,6 @@ static void make_cover_letter(struct rev_info *rev, int use_separate_file,
 	pp.fmt = CMIT_FMT_EMAIL;
 	pp.date_mode.type = DATE_RFC2822;
 	pp.rev = rev;
-	pp.print_email_subject = 1;
 	pp.encode_email_headers = rev->encode_email_headers;
 	pp_user_info(&pp, NULL, &sb, committer, encoding);
 	prepare_cover_text(&pp, description_file, branch_name, &sb,

builtin/rev-list.c

@@ -219,6 +219,7 @@ static void show_commit(struct commit *commit, void *data)
 		ctx.fmt = revs->commit_format;
 		ctx.output_encoding = get_log_output_encoding();
 		ctx.color = revs->diffopt.use_color;
+		ctx.rev = revs;
 		pretty_print_commit(&ctx, commit, &buf);
 		if (buf.len) {
 			if (revs->commit_format != CMIT_FMT_ONELINE)

log-tree.c

@@ -742,7 +742,6 @@ void show_log(struct rev_info *opt)
 		log_write_email_headers(opt, commit, &extra_headers,
 					&ctx.need_8bit_cte, 1);
 		ctx.rev = opt;
-		ctx.print_email_subject = 1;
 	} else if (opt->commit_format != CMIT_FMT_USERFORMAT) {
 		fputs(diff_get_color_opt(&opt->diffopt, DIFF_COMMIT), opt->diffopt.file);
 		if (opt->commit_format != CMIT_FMT_ONELINE)

pretty.c

@@ -2091,19 +2091,14 @@ void pp_email_subject(struct pretty_print_context *pp,
 				pp->preserve_subject ? "\n" : " ");
 
 	strbuf_grow(sb, title.len + 1024);
-	if (pp->print_email_subject) {
-		if (pp->rev)
-			fmt_output_email_subject(sb, pp->rev);
-		if (pp->encode_email_headers &&
-		    needs_rfc2047_encoding(title.buf, title.len))
-			add_rfc2047(sb, title.buf, title.len,
-						encoding, RFC2047_SUBJECT);
-		else
-			strbuf_add_wrapped_bytes(sb, title.buf, title.len,
+	fmt_output_email_subject(sb, pp->rev);
+	if (pp->encode_email_headers &&
+	    needs_rfc2047_encoding(title.buf, title.len))
+		add_rfc2047(sb, title.buf, title.len,
+			    encoding, RFC2047_SUBJECT);
+	else
+		strbuf_add_wrapped_bytes(sb, title.buf, title.len,
 					 -last_line_length(sb), 1, max_length);
-	} else {
-		strbuf_addbuf(sb, &title);
-	}
 	strbuf_addch(sb, '\n');
 
 	if (need_8bit_cte == 0) {
@@ -2319,7 +2314,7 @@ void pretty_print_commit(struct pretty_print_context *pp,
 	}
 
 	pp_header(pp, encoding, commit, &msg, sb);
-	if (pp->fmt != CMIT_FMT_ONELINE && !pp->print_email_subject) {
+	if (pp->fmt != CMIT_FMT_ONELINE && !cmit_fmt_is_mail(pp->fmt)) {
 		strbuf_addch(sb, '\n');
 	}
 

pretty.h

@@ -39,7 +39,6 @@ struct pretty_print_context {
 	int preserve_subject;
 	struct date_mode date_mode;
 	unsigned date_mode_explicit:1;
-	int print_email_subject;
 	int expand_tabs_in_log;
 	int need_8bit_cte;
 	char *notes_message;