pretty: support truncating in %>, %< and %><

%>(N,trunc) truncates the right part after N columns and replace the
last two letters with "..". ltrunc does the same on the left. mtrunc
cuts the middle out.

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

Documentation/pretty-formats.txt

@@ -164,8 +164,11 @@ The placeholders are:
 - '%x00': print a byte from a hex code
 - '%w([<w>[,<i1>[,<i2>]]])': switch line wrapping, like the -w option of
   linkgit:git-shortlog[1].
-- '%<(<N>)': make the next placeholder take at least N columns,
-  padding spaces on the right if necessary
+- '%<(<N>[,trunc|ltrunc|mtrunc])': make the next placeholder take at
+  least N columns, padding spaces on the right if necessary.
+  Optionally truncate at the beginning (ltrunc), the middle (mtrunc)
+  or the end (trunc) if the output is longer than N columns.
+  Note that truncating only works correctly with N >= 2.
 - '%<|(<N>)': make the next placeholder take at least until Nth
   columns, padding spaces on the right if necessary
 - '%>(<N>)', '%>|(<N>)': similar to '%<(<N>)', '%<|(<N>)'

pretty.c

@@ -776,6 +776,13 @@ enum flush_type {
 	flush_both
 };
 
+enum trunc_type {
+	trunc_none,
+	trunc_left,
+	trunc_middle,
+	trunc_right
+};
+
 struct format_commit_context {
 	const struct commit *commit;
 	const struct pretty_print_context *pretty_ctx;
@@ -783,6 +790,7 @@ struct format_commit_context {
 	unsigned commit_message_parsed:1;
 	struct signature_check signature_check;
 	enum flush_type flush_type;
+	enum trunc_type truncate;
 	char *message;
 	char *commit_encoding;
 	size_t width, indent1, indent2;
@@ -1033,7 +1041,7 @@ static size_t parse_padding_placeholder(struct strbuf *sb,
 
 	if (*ch == '(') {
 		const char *start = ch + 1;
-		const char *end = strchr(start, ')');
+		const char *end = start + strcspn(start, ",)");
 		char *next;
 		int width;
 		if (!end || end == start)
@@ -1043,6 +1051,23 @@ static size_t parse_padding_placeholder(struct strbuf *sb,
 			return 0;
 		c->padding = to_column ? -width : width;
 		c->flush_type = flush_type;
+
+		if (*end == ',') {
+			start = end + 1;
+			end = strchr(start, ')');
+			if (!end || end == start)
+				return 0;
+			if (!prefixcmp(start, "trunc)"))
+				c->truncate = trunc_right;
+			else if (!prefixcmp(start, "ltrunc)"))
+				c->truncate = trunc_left;
+			else if (!prefixcmp(start, "mtrunc)"))
+				c->truncate = trunc_middle;
+			else
+				return 0;
+		} else
+			c->truncate = trunc_none;
+
 		return end - placeholder + 1;
 	}
 	return 0;
@@ -1309,9 +1334,29 @@ static size_t format_and_pad_commit(struct strbuf *sb, /* in UTF-8 */
 		total_consumed++;
 	}
 	len = utf8_strnwidth(local_sb.buf, -1, 1);
-	if (len > padding)
+	if (len > padding) {
+		switch (c->truncate) {
+		case trunc_left:
+			strbuf_utf8_replace(&local_sb,
+					    0, len - (padding - 2),
+					    "..");
+			break;
+		case trunc_middle:
+			strbuf_utf8_replace(&local_sb,
+					    padding / 2 - 1,
+					    len - (padding - 2),
+					    "..");
+			break;
+		case trunc_right:
+			strbuf_utf8_replace(&local_sb,
+					    padding - 2, len - (padding - 2),
+					    "..");
+			break;
+		case trunc_none:
+			break;
+		}
 		strbuf_addstr(sb, local_sb.buf);
-	else {
+	} else {
 		int sb_len = sb->len, offset = 0;
 		if (c->flush_type == flush_left)
 			offset = padding - len;

t/t4205-log-pretty-formats.sh

@@ -143,6 +143,45 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success 'left alignment formatting with trunc' '
+	git log --pretty="format:%<(10,trunc)%s" >actual &&
+	# complete the incomplete line at the end
+	echo >>actual &&
+	qz_to_tab_space <<\EOF >expected &&
+message ..
+message ..
+add bar  Z
+initial  Z
+EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'left alignment formatting with ltrunc' '
+	git log --pretty="format:%<(10,ltrunc)%s" >actual &&
+	# complete the incomplete line at the end
+	echo >>actual &&
+	qz_to_tab_space <<\EOF >expected &&
+..sage two
+..sage one
+add bar  Z
+initial  Z
+EOF
+	test_cmp expected actual
+'
+
+test_expect_success 'left alignment formatting with mtrunc' '
+	git log --pretty="format:%<(10,mtrunc)%s" >actual &&
+	# complete the incomplete line at the end
+	echo >>actual &&
+	qz_to_tab_space <<\EOF >expected &&
+mess.. two
+mess.. one
+add bar  Z
+initial  Z
+EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'right alignment formatting' '
 	git log --pretty="format:%>(40)%s" >actual &&
 	# complete the incomplete line at the end

utf8.c

@@ -421,6 +421,52 @@ void strbuf_add_wrapped_bytes(struct strbuf *buf, const char *data, int len,
 	free(tmp);
 }
 
+void strbuf_utf8_replace(struct strbuf *sb_src, int pos, int width,
+			 const char *subst)
+{
+	struct strbuf sb_dst = STRBUF_INIT;
+	char *src = sb_src->buf;
+	char *end = src + sb_src->len;
+	char *dst;
+	int w = 0, subst_len = 0;
+
+	if (subst)
+		subst_len = strlen(subst);
+	strbuf_grow(&sb_dst, sb_src->len + subst_len);
+	dst = sb_dst.buf;
+
+	while (src < end) {
+		char *old;
+		size_t n;
+
+		while ((n = display_mode_esc_sequence_len(src))) {
+			memcpy(dst, src, n);
+			src += n;
+			dst += n;
+		}
+
+		old = src;
+		n = utf8_width((const char**)&src, NULL);
+		if (!src) 	/* broken utf-8, do nothing */
+			return;
+		if (n && w >= pos && w < pos + width) {
+			if (subst) {
+				memcpy(dst, subst, subst_len);
+				dst += subst_len;
+				subst = NULL;
+			}
+			w += n;
+			continue;
+		}
+		memcpy(dst, old, src - old);
+		dst += src - old;
+		w += n;
+	}
+	strbuf_setlen(&sb_dst, dst - sb_dst.buf);
+	strbuf_attach(sb_src, strbuf_detach(&sb_dst, NULL),
+		      sb_dst.len, sb_dst.alloc);
+}
+
 int is_encoding_utf8(const char *name)
 {
 	if (!name)

utf8.h

@@ -15,6 +15,8 @@ void strbuf_add_wrapped_text(struct strbuf *buf,
 		const char *text, int indent, int indent2, int width);
 void strbuf_add_wrapped_bytes(struct strbuf *buf, const char *data, int len,
 			     int indent, int indent2, int width);
+void strbuf_utf8_replace(struct strbuf *sb, int pos, int width,
+			 const char *subst);
 
 #ifndef NO_ICONV
 char *reencode_string_iconv(const char *in, size_t insz,