Allow returning a Promise in blocks without wrapping it again.

Author: gdotdesign

src/type_checker.cr

@@ -27,6 +27,7 @@ module Mint
     VOID_FUNCTION  = Type.new("Function", [Variable.new("a")] of Checkable)
     TEST_CONTEXT   = Type.new("Test.Context", [Variable.new("a")] of Checkable)
     STYLE_MAP      = Type.new("Map", [STRING, STRING] of Checkable)
+    PROMISE        = Type.new("Promise", [Variable.new("a")] of Checkable)
 
     getter records, scope, artifacts, formatter, web_components
 

src/type_checkers/block.cr

@@ -11,8 +11,14 @@ module Mint
       last =
         statements.last
 
+      last_type = cache[last]
+
       if node.async?
-        Type.new("Promise", [cache[last]] of Checkable)
+        if Comparer.compare(last_type, PROMISE)
+          last_type
+        else
+          Type.new("Promise", [cache[last]] of Checkable)
+        end
       else
         cache[last]
       end