parser: Avoid dropping modifiers when splitting list (#8546)

Fix for a linked list usage bug; avoids dropping any modifiers when
moving type modifiers from a linked list of modifiers into their own
linked list. Since this change results in no_diff modifiers to
traditional functions ending up on the return type instead of the
function (due to the order they're parsed in), we duplicate the no_diff
modifier onto the function declaration after the fact.

Includes a test for the original issue. The no_diff redistribution case
is covered by a slangpy device test case.

Fixes #8332

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 4bfbde584..867c1daad 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -10241,6 +10241,17 @@ void SemanticsDeclHeaderVisitor::checkInterfaceRequirement(Decl* decl)
     }
 }
 
+bool doesTypeHaveNoDiffModifier(Type* type)
+{
+    if (auto modifiedType = as<ModifiedType>(type))
+    {
+        if (modifiedType->findModifier<NoDiffModifierVal>() != nullptr)
+            return true;
+        return doesTypeHaveNoDiffModifier(modifiedType->getBase());
+    }
+    return false;
+}
+
 void SemanticsDeclHeaderVisitor::checkCallableDeclCommon(CallableDecl* decl)
 {
     for (auto paramDecl : decl->getParameters())
@@ -10259,6 +10270,13 @@ void SemanticsDeclHeaderVisitor::checkCallableDeclCommon(CallableDecl* decl)
     }
     decl->errorType = errorType;
 
+    if (doesTypeHaveNoDiffModifier(decl->returnType.type))
+    {
+        auto noDiffMod = m_astBuilder->create<NoDiffModifier>();
+        noDiffMod->loc = decl->loc;
+        addModifier(decl, noDiffMod);
+    }
+
     checkDifferentiableCallableCommon(decl);
 
     // If this method is intended to be a CUDA kernel, verify that the return type is void.