WIP: "deprecated" attribute (#2698)

* Implement deprecated attribute

* Prevent duplicate deprecated diagnostic on non-overloaded functions

* Use FileCheck for deprecation test

* formatting

1 files changed, 40 insertions, 1 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 507b8c30f..119077eca 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -254,7 +254,42 @@ namespace Slang
         return SourceLoc();
     }
 
-    Expr* SemanticsVisitor::ConstructDeclRefExpr(
+    void SemanticsVisitor::diagnoseDeprecatedDeclRefUsage(
+        DeclRef<Decl> declRef,
+        SourceLoc loc,
+        Expr* originalExpr)
+    {
+        // This is slightly subtle, because we don't want to warn more than
+        // once for the same occurrence, however in some cases this function is
+        // called more than once for the same declref (specifically in the case
+        // of a non-overloaded function, once when the function is identified at
+        // first, and again when it's checked from
+        // CheckInvokeExprWithCheckedOperands).
+        //
+        // The correct fix is probably to make
+        // CheckInvokeExprWithCheckedOperands reuse the original declref,
+        // however that doesn't appear to be a simple change.
+        //
+        // What we do instead is see if there's already been a declRef
+        // constructed for this expression and rest assured that it's already
+        // had a diagnostic emitted.
+        auto originalAppExpr = as<AppExprBase>(originalExpr);
+        auto originalAppFunDecl = originalAppExpr ? as<DeclRefExpr>(originalAppExpr->functionExpr) : nullptr;
+        if(originalAppFunDecl && originalAppFunDecl->declRef)
+        {
+            return;
+        }
+        if (auto deprecatedAttr = declRef.getDecl()->findModifier<DeprecatedAttribute>())
+        {
+            getSink()->diagnose(
+                loc,
+                Diagnostics::deprecatedUsage,
+                declRef.getName(),
+                deprecatedAttr->message);
+        }
+    }
+
+    DeclRefExpr* SemanticsVisitor::ConstructDeclRefExpr(
         DeclRef<Decl>   declRef,
         Expr*    baseExpr,
         SourceLoc loc,
@@ -264,6 +299,10 @@ namespace Slang
         //
         auto type = GetTypeForDeclRef(declRef, loc);
 
+        // This is the bottleneck for using declarations which might be
+        // deprecated, diagnose here.
+        diagnoseDeprecatedDeclRefUsage(declRef, loc, originalExpr);
+
         // Construct an appropriate expression based on the structured of
         // the declaration reference.
         //