Lowercase drive letter in URIs for Windows (#1441)

If a LSP client on Windows sends a capital drive letter in a URI, then the compiler diagnostics end up sending the wrong position/range.

This is because of this line. It checks that the path from the compiler matches the URI path. The path from the compiler has a lowercase drive letter, so they don't match and the diagnostics are treated as if they are coming from an include.

I've fixed this in els_uri:path, but there might be a better place to do it, I'm not sure.

apps/els_core/src/els_uri.erl

@@ -49,9 +49,10 @@ path(Uri, IsWindows) ->
     case {IsWindows, Host} of
         {true, <<>>} ->
             % Windows drive letter, have to strip the initial slash
-            re:replace(
+            Path1 = re:replace(
                 Path, "^/([a-zA-Z]:)(.*)", "\\1\\2", [{return, binary}]
-            );
+            ),
+            lowercase_drive_letter(Path1);
         {true, _} ->
             <<"//", Host/binary, Path/binary>>;
         {false, <<>>} ->
@@ -113,6 +114,13 @@ percent_decode(Str) ->
     http_uri:decode(Str).
 -endif.
 
+-spec lowercase_drive_letter(binary()) -> binary().
+lowercase_drive_letter(<<Drive0, ":", Rest/binary>>) ->
+    Drive = string:to_lower(Drive0),
+    <<Drive, ":", Rest/binary>>;
+lowercase_drive_letter(Path) ->
+    Path.
+
 -ifdef(TEST).
 -include_lib("eunit/include/eunit.hrl").