Diagnose on attempt to specialize with interface type. (#2780)

* Diagnose on attempt to specialize with interface type.

Fixes ##1445.

* Enable fixed test.

* Fix test.

* Fix.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

5 files changed, 110 insertions, 7 deletions

diff --git a/source/slang/slang-check-constraint.cpp b/source/slang/slang-check-constraint.cpp
index f96b5a484..6e9d73b61 100644
--- a/source/slang/slang-check-constraint.cpp
+++ b/source/slang/slang-check-constraint.cpp
@@ -469,6 +469,16 @@ namespace Slang
             auto sub = getSub(m_astBuilder, constraintDeclRef);
             auto sup = getSup(m_astBuilder, constraintDeclRef);
 
+            if (sub->equals(sup))
+            {
+                // We are trying to use an interface type itself to conform to the
+                // type constraint. We can reach this case when the user code does
+                // not provide an explicit type parameter to specialize a generic
+                // and the type parameter cannot be inferred from any arguments.
+                // In this case, we should fail the constraint check.
+                return SubstitutionSet();
+            }
+
             // Search for a witness that shows the constraint is satisfied.
             auto subTypeWitness = tryGetSubtypeWitness(sub, sup);
             if(subTypeWitness)
diff --git a/tests/diagnostics/generic-type-inference-fail.slang b/tests/diagnostics/generic-type-inference-fail.slang
new file mode 100644
index 000000000..803c7584c
--- /dev/null
+++ b/tests/diagnostics/generic-type-inference-fail.slang
@@ -0,0 +1,81 @@
+//DIAGNOSTIC_TEST:SIMPLE:
+
+interface IAssoc
+{
+    int Compute();
+}
+
+interface IInterface
+{
+    associatedtype TAssoc : IAssoc;
+
+    [mutating]
+    void SetVal(int inVal);
+
+    TAssoc GetAssoc();
+};
+
+T.TAssoc CreateT_Assoc_Inner<T:IInterface>(int inVal)
+{
+    T obj;
+    obj.SetVal(inVal);
+    return obj.GetAssoc();
+}
+
+T.TAssoc CreateT_Assoc<T:IInterface>(int inVal)
+{
+    return CreateT_Assoc_Inner<T>(inVal);
+}
+
+T CreateT<T:IInterface>(int inVal)
+{
+    T obj;
+    obj.SetVal(inVal);
+    return obj;
+}
+
+struct Impl : IInterface
+{
+    struct TAssoc : IAssoc
+    {
+        int base;
+        int Compute()
+        {
+            return base;
+        }
+    };
+
+    TAssoc assoc;
+    [mutating]
+    void SetVal(int inVal)
+    {
+        assoc.base = inVal;
+    }
+
+    TAssoc GetAssoc()
+    {
+        return assoc;
+    }
+};
+
+int test()
+{
+    var obj = CreateT<Impl>(2);
+    var obj2 = CreateT_Assoc<Impl>(1);
+    
+    var obj3 = CreateT_Assoc_Inner(1); // ERROR.
+
+    return obj.GetAssoc().Compute() + obj2.Compute() + obj3.Compute();
+}
+
+
+//TEST_INPUT:ubuffer(data=[0 1 2 3], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer : register(u0);
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint tid = dispatchThreadID.x;
+    int outVal = test();
+    outputBuffer[tid] = outVal;
+}
\ No newline at end of file
diff --git a/tests/diagnostics/generic-type-inference-fail.slang.expected b/tests/diagnostics/generic-type-inference-fail.slang.expected
new file mode 100644
index 000000000..3f9753d68
--- /dev/null
+++ b/tests/diagnostics/generic-type-inference-fail.slang.expected
@@ -0,0 +1,9 @@
+result code = -1
+standard error = {
+tests/diagnostics/generic-type-inference-fail.slang(66): error 39999: could not specialize generic for arguments of type (int)
+    var obj3 = CreateT_Assoc_Inner(1); // ERROR.
+                                  ^
+tests/diagnostics/generic-type-inference-fail.slang(18): note 39999: see declaration of func CreateT_Assoc_Inner<T>(int) -> T.TAssoc
+}
+standard output = {
+}
diff --git a/tests/experiments/generic/type-to-value-4.slang b/tests/experiments/generic/type-to-value-4.slang
index 741b30791..8d768b54b 100644
--- a/tests/experiments/generic/type-to-value-4.slang
+++ b/tests/experiments/generic/type-to-value-4.slang
@@ -1,4 +1,4 @@
-//DISABLE_TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj
 
 /* Test here is to try and associate a value with a type
 
@@ -52,26 +52,25 @@ interface IGetE
 	static Enum getE();    
 };
 
-public struct A : IGetE
+struct A : IGetE
 {
     static Enum getE() { return Enum::A; }
 };
 
-public struct B : IGetE
+struct B : IGetE
 {
     static Enum getE() { return Enum::B; }
 };
 
 [numthreads(4, 1, 1)]
 void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
-{    
-    int index = dispatchThreadID.x;
+{
    
     // Err.. even though IGetE doesn't require an instanciation, not clear how to set it. So lets try with instanciation
     B b;
     IGetE g = b;
 
     let e = g.getE();
-    
+
     outputBuffer[dispatchThreadID.x] = int(e);
-}
\ No newline at end of file
+}
diff --git a/tests/experiments/generic/type-to-value-4.slang.expected.txt b/tests/experiments/generic/type-to-value-4.slang.expected.txt
new file mode 100644
index 000000000..98fb6a686
--- /dev/null
+++ b/tests/experiments/generic/type-to-value-4.slang.expected.txt
@@ -0,0 +1,4 @@
+1
+1
+1
+1