pretty.c: support <direction>|(<negative number>) forms

%>|(num), %><|(num) and %<|(num), where num is a positive number, sets a
fixed column from the screen's left border. There is no way for us to
specifiy a column relative to the right border, which is useful when you
want to make use of all terminal space (on big screens). Use negative
num for that. Inspired by Go's array syntax (*).

(*) I know Python has this first (or before Go, at least) but the idea
didn't occur to me until I learned Go.

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

pretty.c

@@ -1022,9 +1022,15 @@ static size_t parse_padding_placeholder(struct strbuf *sb,
 		int width;
 		if (!end || end == start)
 			return 0;
-		width = strtoul(start, &next, 10);
+		width = strtol(start, &next, 10);
 		if (next == start || width == 0)
 			return 0;
+		if (width < 0) {
+			if (to_column)
+				width += term_columns();
+			if (width < 0)
+				return 0;
+		}
 		c->padding = to_column ? -width : width;
 		c->flush_type = flush_type;
 

t/t4205-log-pretty-formats.sh

@@ -176,6 +176,17 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'left alignment formatting at the nth column' '
+	COLUMNS=50 git log --pretty="tformat:%h %<|(-10)%s" >actual &&
+	qz_to_tab_space <<EOF >expected &&
+$head1 message two                    Z
+$head2 message one                    Z
+$head3 add bar                        Z
+$head4 $(commit_msg)            Z
+EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'left alignment formatting at the nth column. i18n.logOutputEncoding' '
 	git -c i18n.logOutputEncoding=$test_encoding log --pretty="tformat:%h %<|(40)%s" >actual &&
 	qz_to_tab_space <<EOF | iconv -f utf-8 -t $test_encoding >expected &&
@@ -308,6 +319,17 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'right alignment formatting at the nth column' '
+	COLUMNS=50 git log --pretty="tformat:%h %>|(-10)%s" >actual &&
+	qz_to_tab_space <<EOF >expected &&
+$head1                      message two
+$head2                      message one
+$head3                          add bar
+$head4              $(commit_msg)
+EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'right alignment formatting at the nth column. i18n.logOutputEncoding' '
 	git -c i18n.logOutputEncoding=$test_encoding log --pretty="tformat:%h %>|(40)%s" >actual &&
 	qz_to_tab_space <<EOF | iconv -f utf-8 -t $test_encoding >expected &&
@@ -397,6 +419,17 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'center alignment formatting at the nth column' '
+	COLUMNS=70 git log --pretty="tformat:%h %><|(-30)%s" >actual &&
+	qz_to_tab_space <<EOF >expected &&
+$head1           message two          Z
+$head2           message one          Z
+$head3             add bar            Z
+$head4       $(commit_msg)      Z
+EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'center alignment formatting at the nth column. i18n.logOutputEncoding' '
 	git -c i18n.logOutputEncoding=$test_encoding log --pretty="tformat:%h %><|(40)%s" >actual &&
 	qz_to_tab_space <<EOF | iconv -f utf-8 -t $test_encoding >expected &&