range-diff: first rudimentary implementation

At this stage, `git range-diff` can determine corresponding commits
of two related commit ranges. This makes use of the recently introduced
implementation of the linear assignment algorithm.

The core of this patch is a straight port of the ideas of tbdiff, the
apparently dormant project at https://github.com/trast/tbdiff.

The output does not at all match `tbdiff`'s output yet, as this patch
really concentrates on getting the patch matching part right.

Note: due to differences in the diff algorithm (`tbdiff` uses the Python
module `difflib`, Git uses its xdiff fork), the cost matrix calculated
by `range-diff` is different (but very similar) to the one calculated
by `tbdiff`. Therefore, it is possible that they find different matching
commits in corner cases (e.g. when a patch was split into two patches of
roughly equal length).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 44 insertions, 1 deletions

diff --git a/builtin/range-diff.c b/builtin/range-diff.c
index 36788ea4f2..94c1f362cc 100644
--- a/builtin/range-diff.c
+++ b/builtin/range-diff.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "builtin.h"
 #include "parse-options.h"
+#include "range-diff.h"
 
 static const char * const builtin_range_diff_usage[] = {
 N_("git range-diff [<options>] <old-base>..<old-tip> <new-base>..<new-tip>"),
@@ -17,9 +18,51 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 			    N_("Percentage by which creation is weighted")),
 		OPT_END()
 	};
+	int res = 0;
+	struct strbuf range1 = STRBUF_INIT, range2 = STRBUF_INIT;
 
 	argc = parse_options(argc, argv, NULL, options,
 			     builtin_range_diff_usage, 0);
 
-	return 0;
+	if (argc == 2) {
+		if (!strstr(argv[0], ".."))
+			die(_("no .. in range: '%s'"), argv[0]);
+		strbuf_addstr(&range1, argv[0]);
+
+		if (!strstr(argv[1], ".."))
+			die(_("no .. in range: '%s'"), argv[1]);
+		strbuf_addstr(&range2, argv[1]);
+	} else if (argc == 3) {
+		strbuf_addf(&range1, "%s..%s", argv[0], argv[1]);
+		strbuf_addf(&range2, "%s..%s", argv[0], argv[2]);
+	} else if (argc == 1) {
+		const char *b = strstr(argv[0], "..."), *a = argv[0];
+		int a_len;
+
+		if (!b) {
+			error(_("single arg format must be symmetric range"));
+			usage_with_options(builtin_range_diff_usage, options);
+		}
+
+		a_len = (int)(b - a);
+		if (!a_len) {
+			a = "HEAD";
+			a_len = strlen(a);
+		}
+		b += 3;
+		if (!*b)
+			b = "HEAD";
+		strbuf_addf(&range1, "%s..%.*s", b, a_len, a);
+		strbuf_addf(&range2, "%.*s..%s", a_len, a, b);
+	} else {
+		error(_("need two commit ranges"));
+		usage_with_options(builtin_range_diff_usage, options);
+	}
+
+	res = show_range_diff(range1.buf, range2.buf, creation_factor);
+
+	strbuf_release(&range1);
+	strbuf_release(&range2);
+
+	return res;
 }