line-range: teach -L^/RE/ to search from start of file

The -L/RE/ option of blame/log searches from the end of the previous -L
range, if any. Add new notation -L^/RE/ to override this behavior and
search from start of file.

The new ^/RE/ syntax is valid only as the <start> argument of
-L<start>,<end>. The <end> argument, as usual, is relative to <start>.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/line-range-format.txt

@@ -11,6 +11,7 @@ absolute line number (lines count from 1).
 This form will use the first line matching the given
 POSIX regex. If <start> is a regex, it will search from the end of
 the previous `-L` range, if any, otherwise from the start of file.
+If <start> is ``^/regex/'', it will search from the start of file.
 If <end> is a regex, it will search
 starting at the line given by <start>.
 +

line-range.c

@@ -59,8 +59,14 @@ static const char *parse_loc(const char *spec, nth_line_fn_t nth_line,
 		return term;
 	}
 
-	if (begin < 0)
-		begin = -begin;
+	if (begin < 0) {
+		if (spec[0] != '^')
+			begin = -begin;
+		else {
+			begin = 1;
+			spec++;
+		}
+	}
 
 	if (spec[0] != '/')
 		return spec;

t/annotate-tests.sh

@@ -323,6 +323,23 @@ test_expect_success 'blame -L /RE/ (relative: end-of-file)' '
 	test_must_fail $PROG -L, -L/$/ file
 '
 
+test_expect_success 'blame -L ^/RE/ (absolute)' '
+	check_count -L3,3 -L^/dog/,+2 A 1 B2 1
+'
+
+test_expect_success 'blame -L ^/RE/ (absolute: no preceding range)' '
+	check_count -L^/dog/,+2 A 1 B2 1
+'
+
+test_expect_success 'blame -L ^/RE/ (absolute: not found)' '
+	test_must_fail $PROG -L4,4 -L^/tambourine/ file
+'
+
+test_expect_success 'blame -L ^/RE/ (absolute: end-of-file)' '
+	n=$(expr $(wc -l <file) + 1) &&
+	check_count -L$n -L^/$/,+2 A 1 C 1 E 1
+'
+
 test_expect_success 'setup -L :regex' '
 	tr Q "\\t" >hello.c <<-\EOF &&
 	int main(int argc, const char *argv[])
@@ -464,3 +481,7 @@ test_expect_success 'blame -L X,+N (non-numeric N)' '
 test_expect_success 'blame -L X,-N (non-numeric N)' '
 	test_must_fail $PROG -L1,-N file
 '
+
+test_expect_success 'blame -L ,^/RE/' '
+	test_must_fail $PROG -L1,^/99/ file
+'