[Macros] Narrow the carve-out for DebugDescription’s use of symbol

linkage markers.

Author: hborla

lib/Frontend/CompilerInvocation.cpp

@@ -1606,10 +1606,6 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DisableDynamicActorIsolation |=
       Args.hasArg(OPT_disable_dynamic_actor_isolation);
 
-  // @DebugDescription uses @_section and @_used attributes.
-  if (Opts.hasFeature(Feature::DebugDescriptionMacro))
-    Opts.enableFeature(Feature::SymbolLinkageMarkers);
-
 #if SWIFT_ENABLE_EXPERIMENTAL_PARSER_VALIDATION
   /// Enable round trip parsing via the new swift parser unless it is disabled
   /// explicitly. The new Swift parser can have mismatches with C++ parser -

lib/Sema/TypeCheckAttr.cpp

@@ -2376,8 +2376,36 @@ void AttributeChecker::visitExternAttr(ExternAttr *attr) {
   }
 }
 
+static bool allowSymbolLinkageMarkers(ASTContext &ctx, Decl *D) {
+  if (ctx.LangOpts.hasFeature(Feature::SymbolLinkageMarkers))
+    return true;
+
+  auto *sourceFile = D->getDeclContext()->getParentModule()
+      ->getSourceFileContainingLocation(D->getStartLoc());
+  if (!sourceFile)
+    return false;
+
+  auto expansion = sourceFile->getMacroExpansion();
+  auto *macroAttr = sourceFile->getAttachedMacroAttribute();
+  if (!expansion || !macroAttr)
+    return false;
+
+  auto *decl = expansion.dyn_cast<Decl *>();
+  if (!decl)
+    return false;
+
+  auto *macroDecl = decl->getResolvedMacro(macroAttr);
+  if (!macroDecl)
+    return false;
+
+  if (macroDecl->getParentModule()->isStdlibModule() &&
+      macroDecl->getName().getBaseIdentifier()
+          .str().equals("_DebugDescriptionProperty"))
+    return true;
+}
+
 void AttributeChecker::visitUsedAttr(UsedAttr *attr) {
-  if (!Ctx.LangOpts.hasFeature(Feature::SymbolLinkageMarkers)) {
+  if (!allowSymbolLinkageMarkers(Ctx, D)) {
     diagnoseAndRemoveAttr(attr, diag::section_linkage_markers_disabled);
     return;
   }
@@ -2403,7 +2431,7 @@ void AttributeChecker::visitUsedAttr(UsedAttr *attr) {
 }
 
 void AttributeChecker::visitSectionAttr(SectionAttr *attr) {
-  if (!Ctx.LangOpts.hasFeature(Feature::SymbolLinkageMarkers)) {
+  if (!allowSymbolLinkageMarkers(Ctx, D)) {
     diagnoseAndRemoveAttr(attr, diag::section_linkage_markers_disabled);
     return;
   }