Merge pull request swiftlang#67925 from beccadax/objcimpl-warning-main

Temporarily soften @objcImpl errors into warnings

Author: beccadax

include/swift/AST/DiagnosticsSema.def

@@ -1800,6 +1800,11 @@ NOTE(objc_implementation_one_matched_requirement,none,
      "'@objc(%3)' to use it}2",
      (ValueDecl *, ObjCSelector, bool, StringRef))
 
+WARNING(wrap_objc_implementation_will_become_error,none,
+        "%0; this will become an error before '@_objcImplementation' is "
+        "stabilized",
+        (DiagnosticInfo *))
+
 ERROR(cdecl_not_at_top_level,none,
       "@_cdecl can only be applied to global functions", ())
 ERROR(cdecl_empty_name,none,

lib/Sema/TypeCheckDeclObjC.cpp

@@ -2866,9 +2866,16 @@ namespace {
 class ObjCImplementationChecker {
   DiagnosticEngine &diags;
 
-  template<typename ...ArgTypes>
-  InFlightDiagnostic diagnose(ArgTypes &&...Args) {
-    auto diag = diags.diagnose(std::forward<ArgTypes>(Args)...);
+  template<typename Loc, typename ...ArgTypes>
+  InFlightDiagnostic diagnose(Loc loc, Diag<ArgTypes...> diagID,
+                        typename detail::PassArgument<ArgTypes>::type... Args) {
+    auto diag = diags.diagnose(loc, diagID, std::forward<ArgTypes>(Args)...);
+
+    // WORKAROUND (5.9): Soften newly-introduced errors to make things easier
+    // for early adopters.
+    if (diags.declaredDiagnosticKindFor(diagID.ID) == DiagnosticKind::Error)
+      diag.wrapIn(diag::wrap_objc_implementation_will_become_error);
+
     return diag;
   }