Support relative_to on URNs (#1423)

Signed-off-by: Juan Cruz Viotti <jv@jviotti.com>

src/uri/uri.cc

@@ -514,6 +514,12 @@ auto URI::relative_to(const URI &base) -> URI & {
   }
 
   uriFreeUriMembersMmA(&result, nullptr);
+
+  // TODO: Why do we even need to do this?
+  if (copy.data.starts_with('/')) {
+    copy.data.erase(0, 1);
+  }
+
   copy.parse();
 
   // `uriparser` has this weird thing where it will only look at scheme and

test/uri/uri_relative_to_test.cc

@@ -77,3 +77,10 @@ TEST(URI_relative_to, relative_relative_1) {
   uri.relative_to(base);
   EXPECT_EQ(uri.recompose(), "foo/bar/baz");
 }
+
+TEST(URI_relative_to, urn_1) {
+  const sourcemeta::jsontoolkit::URI base{"schema:"};
+  sourcemeta::jsontoolkit::URI uri{"schema:myschema"};
+  uri.relative_to(base);
+  EXPECT_EQ(uri.recompose(), "myschema");
+}