range-diff: adjust the output of the commit pairs

This not only uses "dashed stand-ins" for "pairs" where one side is
missing (i.e. unmatched commits that are present only in one of the two
commit ranges), but also adds onelines for the reader's pleasure.

This change brings `git range-diff` yet another step closer to
feature parity with tbdiff: it now shows the oneline, too, and indicates
with `=` when the commits have identical diffs.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

range-diff.c

@@ -7,6 +7,8 @@
 #include "xdiff-interface.h"
 #include "linear-assignment.h"
 #include "diffcore.h"
+#include "commit.h"
+#include "pretty.h"
 
 struct patch_util {
 	/* For the search for an exact match */
@@ -255,9 +257,49 @@ static void get_correspondences(struct string_list *a, struct string_list *b,
 	free(b2a);
 }
 
-static const char *short_oid(struct patch_util *util)
+static void output_pair_header(struct strbuf *buf,
+			       struct strbuf *dashes,
+			       struct patch_util *a_util,
+			       struct patch_util *b_util)
 {
-	return find_unique_abbrev(&util->oid, DEFAULT_ABBREV);
+	struct object_id *oid = a_util ? &a_util->oid : &b_util->oid;
+	struct commit *commit;
+
+	if (!dashes->len)
+		strbuf_addchars(dashes, '-',
+				strlen(find_unique_abbrev(oid,
+							  DEFAULT_ABBREV)));
+
+	strbuf_reset(buf);
+	if (!a_util)
+		strbuf_addf(buf, "-:  %s ", dashes->buf);
+	else
+		strbuf_addf(buf, "%d:  %s ", a_util->i + 1,
+			    find_unique_abbrev(&a_util->oid, DEFAULT_ABBREV));
+
+	if (!a_util)
+		strbuf_addch(buf, '>');
+	else if (!b_util)
+		strbuf_addch(buf, '<');
+	else if (strcmp(a_util->patch, b_util->patch))
+		strbuf_addch(buf, '!');
+	else
+		strbuf_addch(buf, '=');
+
+	if (!b_util)
+		strbuf_addf(buf, " -:  %s", dashes->buf);
+	else
+		strbuf_addf(buf, " %d:  %s", b_util->i + 1,
+			    find_unique_abbrev(&b_util->oid, DEFAULT_ABBREV));
+
+	commit = lookup_commit_reference(the_repository, oid);
+	if (commit) {
+		strbuf_addch(buf, ' ');
+		pp_commit_easy(CMIT_FMT_ONELINE, commit, buf);
+	}
+	strbuf_addch(buf, '\n');
+
+	fwrite(buf->buf, buf->len, 1, stdout);
 }
 
 static struct diff_filespec *get_filespec(const char *name, const char *p)
@@ -286,6 +328,7 @@ static void patch_diff(const char *a, const char *b,
 static void output(struct string_list *a, struct string_list *b,
 		   struct diff_options *diffopt)
 {
+	struct strbuf buf = STRBUF_INIT, dashes = STRBUF_INIT;
 	int i = 0, j = 0;
 
 	/*
@@ -307,32 +350,30 @@ static void output(struct string_list *a, struct string_list *b,
 
 		/* Show unmatched LHS commit whose predecessors were shown. */
 		if (i < a->nr && a_util->matching < 0) {
-			printf("%d: %s < -: --------\n",
-			       i + 1, short_oid(a_util));
+			output_pair_header(&buf, &dashes, a_util, NULL);
 			i++;
 			continue;
 		}
 
 		/* Show unmatched RHS commits. */
 		while (j < b->nr && b_util->matching < 0) {
-			printf("-: -------- > %d: %s\n",
-			       j + 1, short_oid(b_util));
+			output_pair_header(&buf, &dashes, NULL, b_util);
 			b_util = ++j < b->nr ? b->items[j].util : NULL;
 		}
 
 		/* Show matching LHS/RHS pair. */
 		if (j < b->nr) {
 			a_util = a->items[b_util->matching].util;
-			printf("%d: %s ! %d: %s\n",
-			       b_util->matching + 1, short_oid(a_util),
-			       j + 1, short_oid(b_util));
+			output_pair_header(&buf, &dashes, a_util, b_util);
 			if (!(diffopt->output_format & DIFF_FORMAT_NO_OUTPUT))
 				patch_diff(a->items[b_util->matching].string,
 					   b->items[j].string, diffopt);
 			a_util->shown = 1;
 			j++;
 		}
 	}
+	strbuf_release(&buf);
+	strbuf_release(&dashes);
 }
 
 int show_range_diff(const char *range1, const char *range2,