special treat __*

#2106

Author: sumneko

script/vm/compiler.lua

@@ -1341,8 +1341,8 @@ local compilerSwitch = util.switch()
             hasMarkDoc = vm.bindDocs(source)
         end
 
+        local key = guide.getKeyName(source)
         if not hasMarkDoc then
-            local key = guide.getKeyName(source)
             if key then
                 vm.compileByParentNode(source.node, key, function (src)
                     if src.type == 'doc.field'
@@ -1368,7 +1368,8 @@ local compilerSwitch = util.switch()
         end
 
         if source.value then
-            if not hasMarkDoc or source.value.type == 'table' then
+            if not hasMarkDoc
+            or (type(key) == 'string' and util.stringStartWith(key, '__')) then
                 vm.setNode(source, vm.compileNode(source.value))
             end
         end

test/type_inference/init.lua

@@ -4293,6 +4293,21 @@ local m = setmetatable({},{ __index = { a = 1 } })
 m.<?a?>
 ]]
 
+TEST 'integer' [[
+---@class metatable : table
+---@field __index table
+
+---@param table      table
+---@param metatable? metatable
+---@return table
+function setmetatable(table, metatable) end
+
+local mt = {a = 1 }
+local m = setmetatable({},{ __index = mt })
+
+m.<?a?>
+]]
+
 TEST 'integer' [[
 local x = 1
 repeat