Fix issue of missing scope for 'Differential' type (#7433)

* Fix issue of missing scope for 'Differential' type

When we synthesize the struct decl for Differential type, we should
add the ownedScope for this decl, because the scope is used in lots
of locations in the following synthesized processes, e.g. constructor
synthesize. And that could cause surprising behavior, e.g. the 'this'
expression could access the members of parent struct decl.

Fix the issue by adding the scope. The containerDecl will be the
Differential struct decl itself, parent scope will be the parent struct.

* Add a unit-test

2 files changed, 34 insertions, 0 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index a530eb8f0..43987132e 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -674,6 +674,9 @@ Expr* SemanticsVisitor::maybeUseSynthesizedDeclForLookupResult(
                 conformanceDecl->base.type = m_astBuilder->getDiffInterfaceType();
                 structDecl->addMember(conformanceDecl);
                 structDecl->parentDecl = parent;
+                structDecl->ownedScope = m_astBuilder->create<Scope>();
+                structDecl->ownedScope->containerDecl = structDecl;
+                structDecl->ownedScope->parent = getScope(parent);
 
                 synthesizedDecl = structDecl;
                 auto typeDef = m_astBuilder->create<TypeAliasDecl>();
diff --git a/tests/bugs/gh-6756.slang b/tests/bugs/gh-6756.slang
new file mode 100644
index 000000000..ab1e5aa98
--- /dev/null
+++ b/tests/bugs/gh-6756.slang
@@ -0,0 +1,31 @@
+//TEST:SIMPLE(filecheck=CHECK):-target spirv -emit-spirv-via-glsl
+
+// This test is to test that PartlyDiffable.Differential is synthesized
+// with correct scope. If not, the constructor for it will be wrong, and
+// slang will generate wrong code, the downstream compiler will fail to
+// compile.
+
+// CHECK: OpEntryPoint Fragment
+
+struct PartlyDiffable : IDifferentiable
+{
+    int i;
+    float q;
+}
+
+
+func breaker(x:PartlyDiffable.Differential) {
+    return;
+}
+
+
+[shader("fragment")]
+float4 fragment(float4 in: SV_Position)
+    : SV_Target
+{
+    if (PartlyDiffable.Differential(0).q == 0) {
+        return float4(0);
+    } else {
+        return float4(1);
+    }
+}