[PATCH] blame: add --fuzzy-lines command line option

[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. It may instead be desirable to perform a git blame for the line
numbers in the intersection of the file and the specified line range.
This patch adds a --fuzzy-lines command line option to allow this.

Signed-off-by: Isabella Stephens <istephens@atlassian.com>
---
 Documentation/blame-options.txt | 5 +++++
 builtin/blame.c                 | 4 ++++
 t/t8003-blame-corner-cases.sh   | 6 ++++++
 3 files changed, 15 insertions(+)

diff --git a/Documentation/blame-options.txt b/Documentation/blame-options.txt
index dc41957af..664cd8f8b 100644
--- a/Documentation/blame-options.txt
+++ b/Documentation/blame-options.txt
@@ -19,6 +19,11 @@
 +
 include::line-range-format.txt[]
 
+--fuzzy-lines::
+	Use fuzzy line ranges. If a range specified with -L starts on a line
+	within the file but ends past the end of the file, display the blame
+	for the existing lines rather than failing.
+
 -l::
 	Show long rev (Default: off).
 
diff --git a/builtin/blame.c b/builtin/blame.c
index 67adaef4d..d25b39d40 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -661,6 +661,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 
 	struct string_list range_list = STRING_LIST_INIT_NODUP;
 	int output_option = 0, opt = 0;
+	int fuzzy_lines = 0;
 	int show_stats = 0;
 	const char *revs_file = NULL;
 	const char *contents_from = NULL;
@@ -670,6 +671,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 		OPT_BOOL(0, "root", &show_root, N_("Do not treat root commits as boundaries (Default: off)")),
 		OPT_BOOL(0, "show-stats", &show_stats, N_("Show work cost statistics")),
 		OPT_BOOL(0, "progress", &show_progress, N_("Force progress reporting")),
+		OPT_BOOL(0, "fuzzy-lines", &fuzzy_lines, N_("Use fuzzy line ranges")),
 		OPT_BIT(0, "score-debug", &output_option, N_("Show output score for blame entries"), OUTPUT_SHOW_SCORE),
 		OPT_BIT('f', "show-name", &output_option, N_("Show original filename (Default: auto)"), OUTPUT_SHOW_NAME),
 		OPT_BIT('n', "show-number", &output_option, N_("Show original linenumber (Default: off)"), OUTPUT_SHOW_NUMBER),
@@ -878,6 +880,8 @@ 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 (fuzzy_lines && lno < top)
+			top = lno;
 		if (lno < top || ((lno || bottom) && lno < bottom))
 			die(Q_("file %s has only %lu line",
 			       "file %s has only %lu lines",
diff --git a/t/t8003-blame-corner-cases.sh b/t/t8003-blame-corner-cases.sh
index 661f9d430..6e7657df2 100755
--- a/t/t8003-blame-corner-cases.sh
+++ b/t/t8003-blame-corner-cases.sh
@@ -220,6 +220,12 @@ test_expect_success 'blame -L with invalid end' '
 	test_i18ngrep "has only 2 lines" errors
 '
 
+test_expect_success 'blame -L with invalid end and fuzzy-lines' '
+	git blame -L1,5 tres --fuzzy-lines >out &&
+	cat out &&
+	test $(wc -l < out) -eq 2
+'
+
 test_expect_success 'blame parses <end> part of -L' '
 	git blame -L1,1 tres >out &&
 	cat out &&
-- 
2.14.1