[PATCH v3] blame: prevent error if range ends past end of file

[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, at present git will fail
with a fatal error. This commit prevents such behavior - instead the
blame is displayed for existing lines within the specified range.
Blaming a range that is entirely outside the bounds of the file will
still fail.

This commit also ammends the relevant test and adds clarification to
the documentation.

Signed-off-by: Isabella Stephens <istephens@atlassian.com>
---
 Documentation/git-blame.txt   | 10 ++++++++++
 builtin/blame.c               |  4 ++--
 t/t8003-blame-corner-cases.sh |  7 +++----
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-blame.txt b/Documentation/git-blame.txt
index fdc3aea30..8a28b4114 100644
--- a/Documentation/git-blame.txt
+++ b/Documentation/git-blame.txt
@@ -154,6 +154,16 @@ 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 67adaef4d..b5b9db147 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -878,13 +878,13 @@ 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 ((lno || 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/t/t8003-blame-corner-cases.sh b/t/t8003-blame-corner-cases.sh
index 661f9d430..728209fa3 100755
--- a/t/t8003-blame-corner-cases.sh
+++ b/t/t8003-blame-corner-cases.sh
@@ -216,14 +216,13 @@ 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 'indent of line numbers, nine lines' '
-- 
2.14.1