Reintroduce nil type check for stub value cast

src/spectator/mocks/stubbable.cr

@@ -130,7 +130,7 @@ module Spectator
         if %stub = _spectator_find_stub(%call)
           # Cast the stub or return value to the expected type.
           # This is necessary to match the expected return type of the original method.
-          _spectator_cast_stub_value(%stub, %call, typeof({{original}}))
+          _spectator_cast_stub_value(%stub, %call, typeof({{original}}), {{method.return_type && method.return_type.resolve < Nil || false}})
         else
           # Delegate missing stub behavior to concrete type.
           _spectator_stub_fallback(%call, typeof({{original}})) do
@@ -221,7 +221,7 @@ module Spectator
           # This is necessary to match the expected return type of the original method.
           {% if method.return_type %}
             # Return type restriction takes priority since it can be a superset of the original implementation.
-            _spectator_cast_stub_value(%stub, %call, {{method.return_type}})
+            _spectator_cast_stub_value(%stub, %call, {{method.return_type}}, {{method.return_type.resolve < Nil}})
           {% elsif !method.abstract? %}
             # The method isn't abstract, infer the type it returns without calling it.
             _spectator_cast_stub_value(%stub, %call, typeof({{original}}))
@@ -328,7 +328,8 @@ module Spectator
     # *stub* is the variable holding the stub.
     # *call* is the variable holding the captured method call.
     # *type* is the expected type to cast the value to.
-    private macro _spectator_cast_stub_value(stub, call, type)
+    # *nullable* indicates whether *type* can be nil or not.
+    private macro _spectator_cast_stub_value(stub, call, type, nullable = true)
       # Attempt to cast the stub to the method's return type.
       # If successful, return the value of the stub.
       # This is a common usage where the return type is simple and matches the stub type exactly.
@@ -348,9 +349,12 @@ module Spectator
         # Attempt to cast the value to the method's return type.
         # If successful, which it will be in most cases, return it.
         # The caller will receive a properly typed value without unions or other side-effects.
-        begin
-          %value.as({{type}})
-        rescue TypeCastError
+        if %cast = %value.as?({{type}})
+          %cast
+        else
+          {% if nullable %}
+            nil
+          {% else %}
           # The stubbed value was something else entirely and cannot be cast to the return type.
           # There's something weird going on (compiler bug?) that sometimes causes this class lookup to fail.
           %type = begin
@@ -359,6 +363,7 @@ module Spectator
             "<Unknown>"
           end
           raise TypeCastError.new("#{_spectator_stubbed_name} received message #{ {{call}} } and is attempting to return a `#{%type}`, but returned type must be `#{ {{type}} }`.")
+          {% end %}
         end
       end
     end