Fix bug with overload resolution under nested generics (shader-slang#3107)

* Add test for generic param inference bug for nested generics

* Change description & simplify test

* Add expected file

* Check parent decl before unifying type parameters

Author: saipraveenb25

source/slang/slang-check-constraint.cpp

@@ -705,14 +705,16 @@ namespace Slang
             auto fstDeclRef = fstDeclRefType->getDeclRef();
 
             if (auto typeParamDecl = as<GenericTypeParamDecl>(fstDeclRef.getDecl()))
-                return TryUnifyTypeParam(constraints, typeParamDecl, snd);
+                if (typeParamDecl->parentDecl == constraints.genericDecl)
+                    return TryUnifyTypeParam(constraints, typeParamDecl, snd);
 
             if (auto sndDeclRefType = as<DeclRefType>(snd))
             {
                 auto sndDeclRef = sndDeclRefType->getDeclRef();
 
                 if (auto typeParamDecl = as<GenericTypeParamDecl>(sndDeclRef.getDecl()))
-                    return TryUnifyTypeParam(constraints, typeParamDecl, fst);
+                    if (typeParamDecl->parentDecl == constraints.genericDecl)
+                        return TryUnifyTypeParam(constraints, typeParamDecl, fst);
 
                 // can't be unified if they refer to different declarations.
                 if (fstDeclRef.getDecl() != sndDeclRef.getDecl()) return false;
@@ -816,7 +818,7 @@ namespace Slang
 
             if (auto typeParamDecl = as<GenericTypeParamDecl>(fstDeclRef.getDecl()))
             {
-                if(typeParamDecl->parentDecl == constraints.genericDecl )
+                if(typeParamDecl->parentDecl == constraints.genericDecl)
                     return TryUnifyTypeParam(constraints, typeParamDecl, snd);
             }
         }
@@ -827,7 +829,7 @@ namespace Slang
 
             if (auto typeParamDecl = as<GenericTypeParamDecl>(sndDeclRef.getDecl()))
             {
-                if(typeParamDecl->parentDecl == constraints.genericDecl )
+                if(typeParamDecl->parentDecl == constraints.genericDecl)
                     return TryUnifyTypeParam(constraints, typeParamDecl, fst);
             }
         }

tests/compute/generics-overload-2.slang

@@ -0,0 +1,38 @@
+//TEST(smoke,compute):COMPARE_COMPUTE: -shaderobj
+//TEST(smoke,compute):COMPARE_COMPUTE:-cpu -shaderobj
+
+// Test overload resolution for nested generic definitions
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+
+__generic<T : __BuiltinFloatingPointType>
+struct Foo
+{
+	T test(uint index, T x)
+    {
+        return __realCast<T, float>(1.f);
+	}
+
+	__generic<let N: int>
+	T test(vector<uint, N> index, T x)
+    {
+        return __realCast<T, float>(2.f);
+	}
+};
+
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+	uint tid = dispatchThreadID.x + 2;
+	
+	Foo<float> obj;
+
+	float outVal = obj.test(tid, 0.f);
+	outputBuffer[0] = outVal; // Expect: 1
+
+	float outVal2 = obj.test(uint2(tid, tid), 0.f);
+	outputBuffer[1] = outVal2; // Expect: 2
+}

tests/compute/generics-overload-2.slang.expected.txt

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