Diagnose on use of struct inheritance. (#7419)

* Diagnose on use of struct inheritance.

* fix test.

* Fix tests.

* fix.

---------

Co-authored-by: ArielG-NV <159081215+ArielG-NV@users.noreply.github.com>

1 files changed, 22 insertions, 2 deletions

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 2865188b4..ddc4ec4d5 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -7811,7 +7811,7 @@ void SemanticsDeclBasesVisitor::visitStructDecl(StructDecl* decl)
         {
             getSink()->diagnose(
                 inheritanceDecl,
-                Diagnostics::baseOfStructMustBeStructOrInterface,
+                Diagnostics::baseOfStructMustBeInterface,
                 decl,
                 baseType);
             continue;
@@ -7823,6 +7823,26 @@ void SemanticsDeclBasesVisitor::visitStructDecl(StructDecl* decl)
         }
         else if (auto baseStructDeclRef = baseDeclRef.as<StructDecl>())
         {
+            if (!isFromCoreModule(decl))
+            {
+                // In Slang 2026, we no longer allow structs to inherit from other structs.
+                if (isSlang2026OrLater(this))
+                {
+                    getSink()->diagnose(
+                        inheritanceDecl,
+                        Diagnostics::baseOfStructMustBeInterface,
+                        decl,
+                        baseType);
+                }
+                else
+                {
+                    // For legacy langauge versions, we still allow struct inheritance to avoid
+                    // breaking existing code, but we will emit a warning to inform the user
+                    // that this feature is unstable and may be removed in the future.
+                    getSink()->diagnose(inheritanceDecl, Diagnostics::inheritanceUnstable);
+                }
+            }
+
             // To simplify the task of reading and maintaining code,
             // we require that when a `struct` inherits from another
             // `struct`, the base `struct` is the first item in
@@ -7845,7 +7865,7 @@ void SemanticsDeclBasesVisitor::visitStructDecl(StructDecl* decl)
         {
             getSink()->diagnose(
                 inheritanceDecl,
-                Diagnostics::baseOfStructMustBeStructOrInterface,
+                Diagnostics::baseOfStructMustBeInterface,
                 decl,
                 baseType);
             continue;