Fix circularity issue when checking multiple generic interface constraints. (#6121)

* Fix circularity issue with checking multiple generic interface constraints

* Create multi-generic-interface-constraint.slang

* Update multi-generic-interface-constraint.slang

* Update slang-check-inheritance.cpp

---------

Co-authored-by: Yong He <yonghe@outlook.com>

2 files changed, 48 insertions, 3 deletions

diff --git a/source/slang/slang-check-inheritance.cpp b/source/slang/slang-check-inheritance.cpp
index 7af2d2e81..b44858874 100644
--- a/source/slang/slang-check-inheritance.cpp
+++ b/source/slang/slang-check-inheritance.cpp
@@ -466,10 +466,14 @@ InheritanceInfo SharedSemanticsContext::_calcInheritanceInfo(
             if (constraintDeclRef.getDecl()->checkState.isBeingChecked())
                 continue;
 
-            ensureDecl(&visitor, constraintDeclRef.getDecl(), DeclCheckState::CanSpecializeGeneric);
+            ensureDecl(&visitor, constraintDeclRef.getDecl(), DeclCheckState::ScopesWired);
 
-            auto subType = getSub(astBuilder, constraintDeclRef);
-            auto superType = getSup(astBuilder, constraintDeclRef);
+            // Check only the sub-type.
+            visitor.CheckConstraintSubType(constraintDeclRef.getDecl()->sub);
+            auto sub = constraintDeclRef.getDecl()->sub;
+            if (!sub.type)
+                sub = visitor.TranslateTypeNodeForced(sub);
+            auto subType = constraintDeclRef.substitute(astBuilder, sub.type);
 
             // We only consider constraints where the type represented
             // by `declRef` is the subtype, since those
@@ -489,6 +493,11 @@ InheritanceInfo SharedSemanticsContext::_calcInheritanceInfo(
             if (subDeclRefType->getDeclRef() != declRef)
                 continue;
 
+            // Further check the constraint, since we now need the sup-type.
+            ensureDecl(&visitor, constraintDeclRef.getDecl(), DeclCheckState::CanSpecializeGeneric);
+
+            auto superType = getSup(astBuilder, constraintDeclRef);
+
             // Because the constraint is a declared inheritance relationship,
             // adding the base to our list of direct bases is as straightforward
             // as in all the preceding cases.
diff --git a/tests/language-feature/generics/multi-generic-interface-constraint.slang b/tests/language-feature/generics/multi-generic-interface-constraint.slang
new file mode 100644
index 000000000..9c6918ed2
--- /dev/null
+++ b/tests/language-feature/generics/multi-generic-interface-constraint.slang
@@ -0,0 +1,36 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -vk -shaderobj -output-using-type
+
+interface IFoo<T : __BuiltinFloatingPointType>
+{
+    bool requirement(T v1);
+}
+
+struct Bar<T : __BuiltinFloatingPointType, A : IFoo<T>, B : IFoo<T>>
+{
+    [Differentiable]
+    T doThing(T a)
+    {
+        return a * T(2.0);
+    }
+}
+
+struct Foo : IFoo<float>
+{
+    bool requirement(float v)
+    {
+        return v > 0.5;
+    }
+}
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[numthreads(1, 1, 1)]
+void computeMain(int3 dispatchThreadID : SV_DispatchThreadID)
+{
+    int tid = dispatchThreadID.x;
+    Bar<float, Foo, Foo> obj;
+    outputBuffer[tid] = obj.doThing(2.0f);
+    // CHECK: 4
+}