forbid records inside interfaces

Fixes #870.

spec/lang/declaration/record_spec.lua

@@ -1061,4 +1061,14 @@ describe("abstract check", function()
    ]], {
       { y = 7, x = 9, msg = "interfaces are abstract", }
    }))
+
+   it("for record definitions inside interfaces", util.check_syntax_error([[
+      local interface X
+         record Y
+            z: number
+         end
+      end
+   ]], {
+      { y = 2, x = 10, msg = "interfaces cannot contain record definitions", }
+   }))
 end)

tl.lua

@@ -4019,7 +4019,11 @@ do
 
             store_field_in_record(ps, iv, v.tk, nt.newtype, def.fields, def.field_order)
          elseif parse_type_body_fns[tn] and ps.tokens[i + 1].tk ~= ":" then
-            i = parse_nested_type(ps, i, def, tn)
+            if def.typename == "interface" and tn == "record" then
+               i = failskip(ps, i, "interfaces cannot contain record definitions", skip_type_body)
+            else
+               i = parse_nested_type(ps, i, def, tn)
+            end
          else
             local is_metamethod = false
             if ps.tokens[i].tk == "metamethod" and ps.tokens[i + 1].tk ~= ":" then

tl.tl

@@ -4019,7 +4019,11 @@ parse_record_body = function(ps: ParseState, i: integer, def: RecordLikeType): i
 
          store_field_in_record(ps, iv, v.tk, nt.newtype, def.fields, def.field_order)
       elseif parse_type_body_fns[tn] and ps.tokens[i+1].tk ~= ":" then
-         i = parse_nested_type(ps, i, def, tn)
+         if def.typename == "interface" and tn == "record" then
+            i = failskip(ps, i, "interfaces cannot contain record definitions", skip_type_body)
+         else
+            i = parse_nested_type(ps, i, def, tn)
+         end
       else
          local is_metamethod = false
          if ps.tokens[i].tk == "metamethod" and ps.tokens[i+1].tk ~= ":" then