Merge invalid async decl + attribute

This patch merges the two diagnostics complaining about asynchronous
function declarations with incompatible attributes. The two are cdecl
and ibaction at the moment.

include/swift/AST/DiagnosticsSema.def

@@ -1433,8 +1433,6 @@ ERROR(invalid_ibinspectable,none,
       "only instance properties can be declared @%0", (StringRef))
 ERROR(invalid_ibaction_decl,none,
       "only instance methods can be declared @%0", (StringRef))
-ERROR(invalid_ibaction_decl_async,none,
-      "@%0 instance methods cannot be async", (StringRef))
 ERROR(invalid_ibaction_result,none,
       "methods declared @%0 must %select{|not }1return a value", (StringRef, bool))
 ERROR(invalid_ibaction_argument_count,none,
@@ -1466,11 +1464,12 @@ ERROR(cdecl_empty_name,none,
       "@_cdecl symbol name cannot be empty", ())
 ERROR(cdecl_throws,none,
       "raising errors from @_cdecl functions is not supported", ())
-ERROR(cdecl_async,none,
-      "@_cdecl functions cannot be asynchronous", ())
 
 ERROR(attr_methods_only,none,
       "only methods can be declared %0", (DeclAttribute))
+ERROR(attr_decl_async,none,
+      "@%0 %1 cannot be asynchronous", (StringRef, DescriptiveDeclKind))
+
 ERROR(access_control_in_protocol,none,
       "%0 modifier cannot be used in protocols", (DeclAttribute))
 NOTE(access_control_in_protocol_detail,none,

lib/Sema/TypeCheckAttr.cpp

@@ -501,6 +501,12 @@ validateIBActionSignature(ASTContext &ctx, DeclAttribute *attr,
     valid = false;
   }
 
+  if (FD->isAsyncContext()) {
+    ctx.Diags.diagnose(FD->getAsyncLoc(), diag::attr_decl_async,
+        attr->getAttrName(), FD->getDescriptiveKind());
+    valid = false;
+  }
+
   // We don't need to check here that parameter or return types are
   // ObjC-representable; IsObjCRequest will validate that.
 
@@ -530,12 +536,6 @@ void AttributeChecker::visitIBActionAttr(IBActionAttr *attr) {
     return;
   }
 
-  if (FD->isAsyncContext()) {
-    diagnoseAndRemoveAttr(attr, diag::invalid_ibaction_decl_async,
-                          attr->getAttrName());
-    return;
-  }
-
   if (isRelaxedIBAction(Ctx))
     // iOS, tvOS, and watchOS allow 0-2 parameters to an @IBAction method.
     validateIBActionSignature(Ctx, attr, FD, /*minParams=*/0, /*maxParams=*/2);

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2973,7 +2973,9 @@ public:
         if (FD->hasAsync()) {
           FD->setForeignAsyncConvention(*asyncConvention);
           getASTContext().Diags.diagnose(CDeclAttr->getLocation(),
-                                         diag::cdecl_async);
+                                         diag::attr_decl_async,
+                                         CDeclAttr->getAttrName(),
+                                         FD->getDescriptiveKind());
         } else if (FD->hasThrows()) {
           FD->setForeignErrorConvention(*errorConvention);
           getASTContext().Diags.diagnose(CDeclAttr->getLocation(),

test/attr/attr_cdecl_async.swift

@@ -2,6 +2,6 @@
 
 // REQUIRES: concurrency
 
-@_cdecl("async") // expected-error{{@_cdecl functions cannot be asynchronous}}
+@_cdecl("async") // expected-error{{@_cdecl global function cannot be asynchronous}}
 func asynchronous() async { }
 

test/attr/attr_ibaction.swift

@@ -43,7 +43,7 @@ class IBActionWrapperTy {
   func evenMoreMagic(_: AnyObject) -> () {} // no-warning
 
   @available(macOS 10.15, *)
-  @IBAction // expected-error {{@IBAction instance methods cannot be async}}
+  @IBAction // expected-error@+1 {{@IBAction instance method cannot be async}}
   func asyncIBAction(_: AnyObject) async -> () {}
 }