Fix l-value computation for subscript call. (#5177)

1 files changed, 20 insertions, 0 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 1b9725a8c..bdf8721e9 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -436,6 +436,26 @@ namespace Slang
                     // of a GLSL buffer interface block which isn't marked as
                     // read_only
                     expr->type.isLeftValue = isMutableGLSLBufferBlockVarExpr(baseExpr) && (expr->type.hasReadOnlyOnTarget == false);
+
+                    // Another exception is if we are accessing a property
+                    // that provides a [nonmutating] setter.
+                    if (!expr->type.isLeftValue &&
+                        as<PropertyDecl>(declRef.getDecl()))
+                    {
+                        bool isLValue = false;
+                        for (auto member : as<ContainerDecl>(declRef.getDecl())->members)
+                        {
+                            if (as<SetterDecl>(member) || as< RefAccessorDecl>(member))
+                            {
+                                if (member->findModifier<NonmutatingAttribute>())
+                                {
+                                    isLValue = true;
+                                }
+                                break;
+                            }
+                        }
+                        expr->type.isLeftValue = isLValue;
+                    }
                 }
                 else
                 {