allow __len to override # (#1034)

Fixes #1031.

Author: mbartlett21

spec/lang/code_gen/macroexp_spec.lua

@@ -222,5 +222,27 @@ describe("macroexp code generation", function()
 
       print('arg1', 'arg2', nil)
    ]]))
+
+   it("overrides array __len", util.gen([[
+      local interface Foo is {integer}
+         sz: integer
+         metamethod __len: function(self) = macroexp(self: Foo)
+            return self.sz
+         end
+      end
+
+      local f: Foo = {sz = 10}
+      print(#f)
+   ]], [[
+
+
+
+
+
+
+
+      local f = {sz = 10}
+      print(f.sz)
+   ]]))
 end)
 

tl.lua

@@ -14109,6 +14109,15 @@ self:expand_type(node, values, elements) })
                local tn = types_op[ra.typename]
                local t = tn and a_type(node, tn, {})
 
+
+               local meta_on_operator
+               if not t then
+                  local mt_name = unop_to_metamethod[node.op.op]
+                  if mt_name then
+                     t, meta_on_operator = self:check_metamethod(node, mt_name, ra, nil, ua, nil)
+                  end
+               end
+
                if not t and ra.fields then
                   if ra.interface_list then
                      for _, iface in ipairs(ra.interface_list) do
@@ -14120,14 +14129,6 @@ self:expand_type(node, values, elements) })
                   end
                end
 
-               local meta_on_operator
-               if not t then
-                  local mt_name = unop_to_metamethod[node.op.op]
-                  if mt_name then
-                     t, meta_on_operator = self:check_metamethod(node, mt_name, ra, nil, ua, nil)
-                  end
-               end
-
                if ra.typename == "map" then
                   if ra.keys.typename == "number" or ra.keys.typename == "integer" then
                      self.errs:add_warning("hint", node, "using the '#' operator on a map with numeric key type may produce unexpected results")

tl.tl

@@ -14109,6 +14109,15 @@ do
                local tn = types_op[ra.typename]
                local t = tn and a_type(node, tn, {})
 
+               -- we need to check if we have a macroexp that overrides any interfaces first
+               local meta_on_operator: integer
+               if not t then
+                  local mt_name = unop_to_metamethod[node.op.op]
+                  if mt_name then
+                     t, meta_on_operator = self:check_metamethod(node, mt_name, ra, nil, ua, nil)
+                  end
+               end
+
                if not t and ra is RecordLikeType then
                   if ra.interface_list then
                      for _, iface in ipairs(ra.interface_list) do
@@ -14120,14 +14129,6 @@ do
                   end
                end
 
-               local meta_on_operator: integer
-               if not t then
-                  local mt_name = unop_to_metamethod[node.op.op]
-                  if mt_name then
-                     t, meta_on_operator = self:check_metamethod(node, mt_name, ra, nil, ua, nil)
-                  end
-               end
-
                if ra is MapType then
                   if ra.keys.typename == "number" or ra.keys.typename == "integer" then
                       self.errs:add_warning("hint", node, "using the '#' operator on a map with numeric key type may produce unexpected results")