Fix URI.merge/2 handling of base without authority

Author: marcelotto

lib/elixir/lib/uri.ex

@@ -919,6 +919,15 @@ defmodule URI do
     %{base | query: rel.query || base.query, fragment: rel.fragment}
   end
 
+  def merge(%URI{host: nil, path: nil} = base, %URI{} = rel) do
+    %{
+      base
+      | path: remove_dot_segments_from_path(rel.path),
+        query: rel.query,
+        fragment: rel.fragment
+    }
+  end
+
   def merge(%URI{} = base, %URI{} = rel) do
     new_path = merge_paths(base.path, rel.path)
     %{base | path: new_path, query: rel.query, fragment: rel.fragment}

lib/elixir/test/elixir/uri_test.exs

@@ -465,6 +465,15 @@ defmodule URITest do
     assert URI.merge("tag:example", "#fragment") |> to_string == "tag:example#fragment"
   end
 
+  test "merge/2 with non-hierarchical base without host and path" do
+    assert URI.merge("ex:", "test") |> to_string() == "ex:test"
+    assert URI.merge("ex:", "a/b/c") |> to_string() == "ex:a/b/c"
+    assert URI.merge("ex:", "a/b/./../c") |> to_string() == "ex:a/c"
+    assert URI.merge("ex:", "test?query=value") |> to_string() == "ex:test?query=value"
+    assert URI.merge("mailto:", "[email protected]") |> to_string() == "mailto:[email protected]"
+    assert URI.merge("urn:isbn", "0451450523") |> to_string() == "urn:0451450523"
+  end
+
   test "merge/2 (with RFC examples)" do
     # These are examples from:
     #