Fix substitution for associatedtype.

fixes shader-slang#341

When a typedef definition is used to satisfy an associated type, we must also substitute the resulting typedef type using parent substitution, in the case that the typedef is a generic application.

Author: csyonghe

source/slang/syntax.cpp

@@ -503,7 +503,7 @@ void Type::accept(IValVisitor* visitor, void* extra)
                         if (aggTypeDeclRef.getDecl()->memberDictionary.TryGetValue(assocTypeDecl->getName(), targetType))
                         {
                             if (auto typeDefDecl = dynamic_cast<TypeDefDecl*>(targetType))
-                                return typeDefDecl->type.type;
+                                return typeDefDecl->type.type->Substitute(aggTypeDeclRef.substitutions);
                             else
                                 return DeclRefType::Create(getSession(), DeclRef<Decl>(targetType, aggTypeDeclRef.substitutions));
                         }

tests/compute/assoctype-func-param.slang

@@ -0,0 +1,53 @@
+//TEST(compute):COMPARE_COMPUTE:-xslang -use-ir
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):dxbinding(0),glbinding(0),out
+
+// Test type checking of associatedtype and typedef
+
+RWStructuredBuffer<float> outputBuffer;
+
+interface IBase
+{
+    associatedtype SubTypeT;
+    associatedtype RetT;
+    RetT getVal(SubTypeT t);
+    SubTypeT setVal(RetT v);
+}
+
+struct SubType<T>
+{
+    T x;
+};
+
+struct GenStruct<T> : IBase
+{
+    typedef T RetT;
+    typedef SubType<RetT> SubTypeT;
+    SubTypeT setVal(T val)
+    {
+        SubTypeT rs;
+        rs.x = val;
+        return rs;
+    }
+    T getVal(SubTypeT v)
+    {
+        return v.x;
+    }
+};
+
+U.RetT test<U:IBase>(U.RetT val)
+{
+    U obj;
+    U.SubTypeT sb = obj.setVal(val);
+    return obj.getVal(sb);
+}
+
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint tid = dispatchThreadID.x;
+    float inVal = float(tid);
+    /* wrong error message for the following line */
+    float outVal = test<GenStruct<float> >(inVal);
+    outputBuffer[tid] = outVal.x;
+}

tests/compute/assoctype-func-param.slang.expected.txt

@@ -0,0 +1,4 @@
+0
+3F800000
+40000000
+40400000