Sema: Explicitly check for 'inout' parameters on @objc functions

Previously we would produce a non-specific diagnostic about the
parameter type not being representable in Objective-C because
VarDecl::getType() wrapped the result in an InOutType.

Now that this is no longer the case we have to check for inout
independently of looking at the type.

Fixes <rdar://problem/41129106>.

Author: slavapestov

include/swift/AST/DiagnosticsSema.def

@@ -3522,6 +3522,9 @@ ERROR(objc_addressor, none,
 ERROR(objc_invalid_on_func_variadic,none,
       "method cannot be %" OBJC_ATTR_SELECT "0 because it has a variadic "
       "parameter", (unsigned))
+ERROR(objc_invalid_on_func_inout,none,
+      "method cannot be %" OBJC_ATTR_SELECT "0 because inout "
+      "parameters cannot be represented in Objective-C", (unsigned))
 ERROR(objc_invalid_on_func_param_type,none,
       "method cannot be %" OBJC_ATTR_SELECT "1 because the type of the "
       "parameter %0 cannot be represented in Objective-C", (unsigned, unsigned))

lib/Sema/TypeCheckType.cpp

@@ -3360,7 +3360,7 @@ static bool isParamListRepresentableInObjC(TypeChecker &TC,
   unsigned NumParams = PL->size();
   for (unsigned ParamIndex = 0; ParamIndex != NumParams; ParamIndex++) {
     auto param = PL->get(ParamIndex);
-    
+
     // Swift Varargs are not representable in Objective-C.
     if (param->isVariadic()) {
       if (Diagnose && shouldDiagnoseObjCReason(Reason, TC.Context)) {
@@ -3369,10 +3369,22 @@ static bool isParamListRepresentableInObjC(TypeChecker &TC,
           .highlight(param->getSourceRange());
         describeObjCReason(TC, AFD, Reason);
       }
-      
+
       return false;
     }
-    
+
+    // Swift inout parameters are not representable in Objective-C.
+    if (param->isInOut()) {
+      if (Diagnose && shouldDiagnoseObjCReason(Reason, TC.Context)) {
+        TC.diagnose(param->getStartLoc(), diag::objc_invalid_on_func_inout,
+                    getObjCDiagnosticAttrKind(Reason))
+          .highlight(param->getSourceRange());
+        describeObjCReason(TC, AFD, Reason);
+      }
+
+      return false;
+    }
+
     if (param->getType()->isRepresentableIn(
           ForeignLanguage::ObjectiveC,
           const_cast<AbstractFunctionDecl *>(AFD)))

test/attr/attr_objc.swift

@@ -354,6 +354,8 @@ class ConcreteContext3 {
 
   typealias NSCodingExistential = NSCoding.Type
 
+  @objc func inoutFunc(a: inout Int) {}
+  // expected-error@-1{{method cannot be marked @objc because inout parameters cannot be represented in Objective-C}}
   @objc func metatypeOfExistentialMetatypePram1(a: NSCodingExistential.Protocol) {}
   // expected-error@-1{{method cannot be marked @objc because the type of the parameter cannot be represented in Objective-C}}