Allow interface requirements to reference to the interface type itself. (#2398)

* Allow interface requirements to reference to the interface type itself.

* add comment explaining the change.

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

5 files changed, 77 insertions, 19 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 4d55669e2..b988fac60 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -157,8 +157,6 @@ namespace Slang
             openedType->originalInterfaceType = expr->type.type;
             openedType->originalInterfaceDeclRef = interfaceDeclRef;
 
-            DeclRef<InterfaceDecl> substDeclRef = openedType->getSpecializedInterfaceDeclRef();
-
             ExtractExistentialValueExpr* openedValue = m_astBuilder->create<ExtractExistentialValueExpr>();
             openedValue->declRef = varDeclRef;
             openedValue->type = QualType(openedType);
diff --git a/source/slang/slang-syntax.cpp b/source/slang/slang-syntax.cpp
index 9a7200e9d..5b4b61849 100644
--- a/source/slang/slang-syntax.cpp
+++ b/source/slang/slang-syntax.cpp
@@ -838,28 +838,40 @@ Index getFilterCountImpl(const ReflectClassInfo& clsInfo, MemberFilterStyle filt
                 // Otherwise, check if we are trying to apply
                 // a this-type substitution to the given interface
                 //
-                for(auto s = substsToApply; s; s = s->outer)
+                // Note: We want to skip the ThisTypeSubstitution that specializes
+                // declToSpecialize itself (when declToSpecialize is an interface
+                // decl and the subst specializes it), and only pull the
+                // ThisTypeSubstitution when the decl is referencing a child of
+                // the interface decl being specialized. This is because
+                // by default an interface declref type is a "free" existential
+                // type that shouldn't be specialized by someone else, unless
+                // there is an "implicit" ThisType reference preceeding a child
+                // reference.
+                if (declToSpecialize != ancestorInterfaceDecl)
                 {
-                    auto appThisTypeSubst = as<ThisTypeSubstitution>(s);
-                    if(!appThisTypeSubst)
-                        continue;
+                    for (auto s = substsToApply; s; s = s->outer)
+                    {
+                        auto appThisTypeSubst = as<ThisTypeSubstitution>(s);
+                        if (!appThisTypeSubst)
+                            continue;
 
-                    if(appThisTypeSubst->interfaceDecl != ancestorInterfaceDecl)
-                        continue;
+                        if (appThisTypeSubst->interfaceDecl != ancestorInterfaceDecl)
+                            continue;
 
-                    int diff = 0;
-                    auto restSubst = specializeSubstitutions(
-                        astBuilder,
-                        ancestorInterfaceDecl->parentDecl,
-                        substsToSpecialize,
-                        substsToApply,
-                        &diff);
+                        int diff = 0;
+                        auto restSubst = specializeSubstitutions(
+                            astBuilder,
+                            ancestorInterfaceDecl->parentDecl,
+                            substsToSpecialize,
+                            substsToApply,
+                            &diff);
 
-                    ThisTypeSubstitution* firstSubst = astBuilder->getOrCreateThisTypeSubstitution(
-                        ancestorInterfaceDecl, appThisTypeSubst->witness, restSubst);
+                        ThisTypeSubstitution* firstSubst = astBuilder->getOrCreateThisTypeSubstitution(
+                            ancestorInterfaceDecl, appThisTypeSubst->witness, restSubst);
 
-                    (*ioDiff)++;
-                    return firstSubst;
+                        (*ioDiff)++;
+                        return firstSubst;
+                    }
                 }
             }
         }
diff --git a/source/slang/slang.natvis b/source/slang/slang.natvis
index 4d5bad2d3..6c8f15ec9 100644
--- a/source/slang/slang.natvis
+++ b/source/slang/slang.natvis
@@ -239,6 +239,7 @@
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::AndTypeExpr">(Slang::AndTypeExpr*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::ModifiedTypeExpr">(Slang::ModifiedTypeExpr*)&amp;astNodeType</ExpandedItem>
             <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::PointerTypeExpr">(Slang::PointerTypeExpr*)&amp;astNodeType</ExpandedItem>
+            <Item Name="[type]">type</Item>
             <Item Name="[Expr]">(Slang::Expr*)this,nd</Item>
         </Expand>
     </Type>
@@ -477,4 +478,14 @@
             <Item Name="[Members]">members</Item>
         </Expand>
     </Type>
+    <Type Name="Slang::Val" Inheritable="false">
+        <DisplayString>{astNodeType}</DisplayString>
+        <Expand>
+            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::ConstantIntVal">(Slang::ConstantIntVal*)&amp;astNodeType</ExpandedItem>
+            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::PolynomialIntVal">(Slang::PolynomialIntVal*)&amp;astNodeType</ExpandedItem>
+            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::GenericParamIntVal">(Slang::GenericParamIntVal*)&amp;astNodeType</ExpandedItem>
+            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::DeclaredSubtypeWitness">(Slang::DeclaredSubtypeWitness*)&amp;astNodeType</ExpandedItem>
+            <ExpandedItem Condition="astNodeType == Slang::ASTNodeType::TransitiveSubtypeWitness">(Slang::TransitiveSubtypeWitness*)&amp;astNodeType</ExpandedItem>
+        </Expand>
+    </Type>
 </AutoVisualizer>
\ No newline at end of file
diff --git a/tests/bugs/interface-type-self-ref.slang b/tests/bugs/interface-type-self-ref.slang
new file mode 100644
index 000000000..e3b1fe7cc
--- /dev/null
+++ b/tests/bugs/interface-type-self-ref.slang
@@ -0,0 +1,32 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+interface IFoo
+{
+    int compute(out IFoo param);
+}
+
+struct Impl : IFoo
+{
+    int compute(out IFoo param)
+    {
+        param = this;
+        return 0;
+    }
+}
+
+int f(IFoo p)
+{
+    IFoo r;
+    return p.compute(r);
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(int3 dispatchThreadID: SV_DispatchThreadID)
+{
+    int index = dispatchThreadID.x;
+    Impl impl;
+    outputBuffer[index] = f(impl);
+}
diff --git a/tests/bugs/interface-type-self-ref.slang.expected.txt b/tests/bugs/interface-type-self-ref.slang.expected.txt
new file mode 100644
index 000000000..b9efb5a97
--- /dev/null
+++ b/tests/bugs/interface-type-self-ref.slang.expected.txt
@@ -0,0 +1,5 @@
+type: int32_t
+0
+0
+0
+0