[PATCH v4 1/2] blame: prevent error if range ends past end of file

[istephens@atlassian.com]

From: Isabella Stephens <istephens@atlassian.com>

If the -L option is used to specify a line range in git blame, and the
end of the range is past the end of the file, git will fail with a fatal
error. This commit prevents such behavior - instead we display the blame
for existing lines within the specified range. Tests and documentation
are ammended accordingly.

This commit also fixes two corner cases. Blaming -L n,-(n+1) now blames
the first n lines of a file rather than from n to the end of the file.
Blaming -L ,-n will complain of an empty range, rather than blaming the
whole file.

Signed-off-by: Isabella Stephens <istephens@atlassian.com>
---
 Documentation/git-blame.txt   | 10 ++++++++++
 builtin/blame.c               |  6 ++++--
 line-range.c                  |  2 +-
 t/t8003-blame-corner-cases.sh | 17 +++++++++++++----
 4 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-blame.txt b/Documentation/git-blame.txt
index 16323eb80..8cb81f57a 100644
--- a/Documentation/git-blame.txt
+++ b/Documentation/git-blame.txt
@@ -152,6 +152,16 @@ Also you can use a regular expression to specify the line range:
 
 which limits the annotation to the body of the `hello` subroutine.
 
+A range that begins or ends outside the bounds of the file will
+blame the relevant lines. For example:
+
+	git blame -L 10,-20 foo
+	git blame -L 10,+20 foo
+
+will respectively blame the first 10 and last 11 lines of a
+20 line file. However, blaming a line range that is entirely
+outside the bounds of the file will fail.
+
 When you are not interested in changes older than version
 v2.6.18, or changes older than 3 weeks, you can use revision
 range specifiers  similar to 'git rev-list':
diff --git a/builtin/blame.c b/builtin/blame.c
index 9dcb367b9..1204ab142 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -886,13 +886,15 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 				    nth_line_cb, &sb, lno, anchor,
 				    &bottom, &top, sb.path))
 			usage(blame_usage);
-		if (lno < top || ((lno || bottom) && lno < bottom))
+		if (!bottom && top < 0)
+			die("-L invalid empty range");
+		if ((!lno && (top || bottom)) || lno < bottom)
 			die(Q_("file %s has only %lu line",
 			       "file %s has only %lu lines",
 			       lno), path, lno);
 		if (bottom < 1)
 			bottom = 1;
-		if (top < 1)
+		if (top < 1 || lno < top)
 			top = lno;
 		bottom--;
 		range_set_append_unsafe(&ranges, bottom, top);
diff --git a/line-range.c b/line-range.c
index 323399d16..023aee1f5 100644
--- a/line-range.c
+++ b/line-range.c
@@ -47,7 +47,7 @@ static const char *parse_loc(const char *spec, nth_line_fn_t nth_line,
 			else if (!num)
 				*ret = begin;
 			else
-				*ret = begin + num;
+				*ret = begin + num ? begin + num : -1;
 			return term;
 		}
 		return spec;
diff --git a/t/t8003-blame-corner-cases.sh b/t/t8003-blame-corner-cases.sh
index 661f9d430..4a0c51658 100755
--- a/t/t8003-blame-corner-cases.sh
+++ b/t/t8003-blame-corner-cases.sh
@@ -216,14 +216,23 @@ test_expect_success 'blame -L with invalid start' '
 '
 
 test_expect_success 'blame -L with invalid end' '
-	test_must_fail git blame -L1,5 tres 2>errors &&
-	test_i18ngrep "has only 2 lines" errors
+	git blame -L1,5 tres >out &&
+	test_line_count = 2 out
 '
 
 test_expect_success 'blame parses <end> part of -L' '
 	git blame -L1,1 tres >out &&
-	cat out &&
-	test $(wc -l < out) -eq 1
+	test_line_count = 1 out
+'
+
+test_expect_success 'blame -Ln,-(n+1)' '
+	git blame -L3,-4 nine_lines >out &&
+	test_line_count = 3 out
+'
+
+test_expect_success 'blame -L,-n' '
+	test_must_fail git blame -L,-1 tres 2>errors &&
+	test_i18ngrep "-L invalid empty range"
 '
 
 test_expect_success 'indent of line numbers, nine lines' '
-- 
2.14.3 (Apple Git-98)