[Macros] Disallow declaration of codeItem macros

Author: ahoppen

include/swift/AST/DiagnosticsCommon.def

@@ -223,7 +223,7 @@ ERROR(unknown_attribute,none,
 NOTE(in_macro_expansion,none,
      "in expansion of macro %0 here", (DeclName))
 ERROR(macro_experimental,none,
-      "%0 macros are an experimental feature that is not enabled (%1)",
+      "%0 macros are an experimental feature that is not enabled %select{|(%1)}1",
       (StringRef, StringRef))
 ERROR(ambiguous_macro_reference,none,
       "ambiguous reference to macro %0", (DeclName))

include/swift/AST/MacroDeclaration.h

@@ -83,6 +83,9 @@ bool isAttachedMacro(MacroRoles contexts);
 
 MacroRoles getAttachedMacroRoles();
 
+/// Checks if the macro is supported or guarded behind an experimental flag.
+bool isMacroSupported(MacroRole role, ASTContext &ctx);
+
 enum class MacroIntroducedDeclNameKind {
   Named,
   Overloaded,

lib/AST/Decl.cpp

@@ -10182,6 +10182,21 @@ MacroRoles swift::getAttachedMacroRoles() {
   return attachedMacroRoles;
 }
 
+bool swift::isMacroSupported(MacroRole role, ASTContext &ctx) {
+  switch (role) {
+  case MacroRole::Expression:
+  case MacroRole::Declaration:
+  case MacroRole::Accessor:
+  case MacroRole::MemberAttribute:
+  case MacroRole::Member:
+  case MacroRole::Peer:
+  case MacroRole::Conformance:
+    return true;
+  case MacroRole::CodeItem:
+    return ctx.LangOpts.hasFeature(Feature::CodeItemMacros);
+  }
+}
+
 void MissingDecl::forEachMacroExpandedDecl(MacroExpandedDeclCallback callback) {
   auto macroRef = unexpandedMacro.macroRef;
   auto *baseDecl = unexpandedMacro.baseDecl;

lib/Parse/ParseDecl.cpp

@@ -2257,6 +2257,11 @@ Parser::parseMacroRoleAttribute(
         status.setIsParseError();
         return status;
       }
+      if (!isMacroSupported(*role, Context)) {
+        diagnose(roleNameLoc, diag::macro_experimental, roleName.str(), "");
+        status.setIsParseError();
+        return status;
+      }
 
       // Check that the role makes sense.
       if (isAttached == !isAttachedMacro(*role)) {

test/Macros/macro_codeitems_disabled.swift

@@ -0,0 +1,4 @@
+// RUN: %target-typecheck-verify-swift -swift-version 5 %s
+
+@freestanding(codeItem)  // expected-error {{codeItem macros are an experimental feature that is not enabled}}
+macro codeItems() // expected-error {{macro 'codeItems()' requires a definition}}

test/Macros/macros_diagnostics.swift

@@ -1,6 +1,6 @@
 // REQUIRES: swift_swift_parser
 
-// RUN: %target-typecheck-verify-swift -swift-version 5 -enable-experimental-feature FreestandingMacros -module-name MacrosTest
+// RUN: %target-typecheck-verify-swift -swift-version 5 -enable-experimental-feature FreestandingMacros -enable-experimental-feature CodeItemMacros -module-name MacrosTest
 
 @expression macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroDefinition", type: "StringifyMacro")
 // expected-note@-1 2{{'stringify' declared here}}