Add possibility to switch between unidiff and side-by-side-diff.

A new config option side-by-side-diffs added, defaulting to 0,
meaning unidiff. Also a query option (ss) is used toggle this.

In the commit page you can switch between the two diff formats by
clicking on the link on the "commit"-row, to the right of (patch).

In the diff page you can switch by using the link at the start
of the page.

All commit-links and diff-links will remember the choice.

Signed-off-by: Ragnar Ouchterlony <ragnar@lysator.liu.se>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/ui-diff.c b/ui-diff.c
index 0c6f8d7..42e81ac 100644
--- a/ui-diff.c
+++ b/ui-diff.c
@@ -85,7 +85,7 @@
 	}
 	htmlf("</td><td class='%s'>", class);
 	cgit_diff_link(info->new_path, NULL, NULL, ctx.qry.head, ctx.qry.sha1,
-		       ctx.qry.sha2, info->new_path);
+		       ctx.qry.sha2, info->new_path, 0);
 	if (info->status == DIFF_STATUS_COPIED || info->status == DIFF_STATUS_RENAMED)
 		htmlf(" (%s from %s)",
 		      info->status == DIFF_STATUS_COPIED ? "copied" : "renamed",
@@ -160,7 +160,7 @@
 
 	html("<div class='diffstat-header'>");
 	cgit_diff_link("Diffstat", NULL, NULL, ctx.qry.head, ctx.qry.sha1,
-		       ctx.qry.sha2, NULL);
+		       ctx.qry.sha2, NULL, 0);
 	html("</div>");
 	html("<table summary='diffstat' class='diffstat'>");
 	max_changes = 0;
@@ -250,6 +250,19 @@
 		cgit_ssdiff_header();
 }
 
+static void print_ssdiff_link()
+{
+	if (!strcmp(ctx.qry.page, "diff")) {
+		if (use_ssdiff)
+			cgit_diff_link("Unidiff", NULL, NULL, ctx.qry.head,
+				       ctx.qry.sha1, ctx.qry.sha2, NULL, 1);
+		else
+			cgit_diff_link("Side-by-side diff", NULL, NULL,
+				       ctx.qry.head, ctx.qry.sha1,
+				       ctx.qry.sha2, NULL, 1);
+	}
+}
+
 static void filepair_cb(struct diff_filepair *pair)
 {
 	unsigned long old_size = 0;
@@ -314,6 +327,11 @@
 		if (!commit2 || parse_commit(commit2))
 			cgit_print_error(fmt("Bad commit: %s", sha1_to_hex(old_rev_sha1)));
 	}
+
+	if ((ctx.qry.ssdiff && !ctx.cfg.ssdiff) || (!ctx.qry.ssdiff && ctx.cfg.ssdiff))
+		use_ssdiff = 1;
+
+	print_ssdiff_link();
 	cgit_print_diffstat(old_rev_sha1, new_rev_sha1);
 
 	html("<table summary='diff' class='diff'>");