[Sema] Improved dynamic replacement diagnostic.

Make use of swift::getAccessorNameForDiagnostic instead of having a
parallel list of accessor names in DiagnosticsSema.def.

Author: nate-chandler

include/swift/AST/DiagnosticsSema.def

@@ -6584,8 +6584,8 @@ ERROR(dynamic_with_transparent,none,
 ERROR(dynamic_replacement_accessor_not_dynamic, none,
       "replaced accessor for %0 is not marked dynamic", (DeclName))
 ERROR(dynamic_replacement_accessor_not_explicit, none,
-      "replaced accessor %select{get|set|_read|_modify|willSet|didSet|unsafeAddress|addressWithOwner|addressWithNativeOwner|unsafeMutableAddress|mutableAddressWithOwner|}0 for %1 is not explicitly defined",
-      (unsigned, DeclName))
+      "replaced %0 for %1 is not explicitly defined",
+      (StringRef, DeclName))
 ERROR(dynamic_replacement_function_not_dynamic, none,
       "replaced function %0 is not marked dynamic", (DeclName))
 ERROR(dynamic_replacement_function_not_found, none,

lib/Sema/TypeCheckAttr.cpp

@@ -3623,7 +3623,8 @@ static FuncDecl *findSimilarAccessor(DeclNameRef replacedVarName,
         origStorage->getWriteImpl() == WriteImplKind::Stored)) {
     Diags.diagnose(attr->getLocation(),
                    diag::dynamic_replacement_accessor_not_explicit,
-                   (unsigned)origAccessor->getAccessorKind(),
+                   getAccessorNameForDiagnostic(origAccessor->getAccessorKind(),
+                                                /*article=*/false),
                    origStorage->getName());
     attr->setInvalid();
     return nullptr;

test/attr/dynamicReplacement.swift

@@ -75,3 +75,23 @@ extension P {
   func replacement_f() {
   }
 }
+
+struct ImplicitModifier {
+  var i: Int {
+    get { 1 }
+    set {}
+  }
+}
+
+extension ImplicitModifier {
+  @_dynamicReplacement(for: i) // expected-error{{replaced 'modify' accessor for 'i' is not explicitly defined}}
+  var _i: Int {
+    get {
+      0
+    }
+    _modify {
+      var i: Int = 0
+      yield &i
+    }
+  }
+}