pretty: support %>> that steal trailing spaces

This is pretty useful in `%<(100)%s%Cred%>(20)% an' where %s does not
use up all 100 columns and %an needs more than 20 columns. By
replacing %>(20) with %>>(20), %an can steal spaces from %s.

%>> understands escape sequences, so %Cred does not stop it from
stealing spaces in %<(100).

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pretty-formats.txt

@@ -173,7 +173,10 @@ The placeholders are:
   columns, padding spaces on the right if necessary
 - '%>(<N>)', '%>|(<N>)': similar to '%<(<N>)', '%<|(<N>)'
   respectively, but padding spaces on the left
-- '%><(<N>)', '%><|(<N>)': similar to '%<(<N>)', '%<|(<N>)'
+- '%>>(<N>)', '%>>|(<N>)': similar to '%>(<N>)', '%>|(<N>)'
+  respectively, except that if the next placeholder takes more spaces
+  than given and there are spaces on its left, use those spaces
+- '%><(<N>)', '%><|(<N>)': similar to '% <(<N>)', '%<|(<N>)'
   respectively, but padding both sides (i.e. the text is centered)
 
 NOTE: Some placeholders may depend on other options given to the

pretty.c

@@ -773,6 +773,7 @@ enum flush_type {
 	no_flush,
 	flush_right,
 	flush_left,
+	flush_left_and_steal,
 	flush_both
 };
 
@@ -1026,6 +1027,9 @@ static size_t parse_padding_placeholder(struct strbuf *sb,
 		if (*ch == '<') {
 			flush_type = flush_both;
 			ch++;
+		} else if (*ch == '>') {
+			flush_type = flush_left_and_steal;
+			ch++;
 		} else
 			flush_type = flush_left;
 		break;
@@ -1334,6 +1338,36 @@ static size_t format_and_pad_commit(struct strbuf *sb, /* in UTF-8 */
 		total_consumed++;
 	}
 	len = utf8_strnwidth(local_sb.buf, -1, 1);
+
+	if (c->flush_type == flush_left_and_steal) {
+		const char *ch = sb->buf + sb->len - 1;
+		while (len > padding && ch > sb->buf) {
+			const char *p;
+			if (*ch == ' ') {
+				ch--;
+				padding++;
+				continue;
+			}
+			/* check for trailing ansi sequences */
+			if (*ch != 'm')
+				break;
+			p = ch - 1;
+			while (ch - p < 10 && *p != '\033')
+				p--;
+			if (*p != '\033' ||
+			    ch + 1 - p != display_mode_esc_sequence_len(p))
+				break;
+			/*
+			 * got a good ansi sequence, put it back to
+			 * local_sb as we're cutting sb
+			 */
+			strbuf_insert(&local_sb, 0, p, ch + 1 - p);
+			ch = p - 1;
+		}
+		strbuf_setlen(sb, ch + 1 - sb->buf);
+		c->flush_type = flush_left;
+	}
+
 	if (len > padding) {
 		switch (c->truncate) {
 		case trunc_left:

t/t4205-log-pretty-formats.sh

@@ -260,4 +260,18 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'left/right alignment formatting with stealing' '
+	git commit --amend -m short --author "long long long <long@me.com>" &&
+	git log --pretty="format:%<(10,trunc)%s%>>(10,ltrunc)% an" >actual &&
+	# complete the incomplete line at the end
+	echo >>actual &&
+	cat <<\EOF >expected &&
+short long  long long
+message ..   A U Thor
+add bar      A U Thor
+initial      A U Thor
+EOF
+	test_cmp expected actual
+'
+
 test_done

utf8.c

@@ -9,7 +9,7 @@ struct interval {
   int last;
 };
 
-static size_t display_mode_esc_sequence_len(const char *s)
+size_t display_mode_esc_sequence_len(const char *s)
 {
 	const char *p = s;
 	if (*p++ != '\033')

utf8.h

@@ -3,6 +3,7 @@
 
 typedef unsigned int ucs_char_t;  /* assuming 32bit int */
 
+size_t display_mode_esc_sequence_len(const char *s);
 int utf8_width(const char **start, size_t *remainder_p);
 int utf8_strnwidth(const char *string, int len, int skip_ansi);
 int utf8_strwidth(const char *string);