Skip redecl errors for inits that conflict with an inherited init

This can only happen when the conflicting init is within an extension.
It is the override checker's responsibility to emit a sensible diagnostic here.

Author: AnthonyLatsis

include/swift/AST/DiagnosticsSema.def

@@ -668,8 +668,8 @@ ERROR(reserved_member_name,none,
 
 ERROR(invalid_redecl,none,"invalid redeclaration of %0", (DeclName))
 ERROR(invalid_redecl_init,none,
-      "invalid redeclaration of %select{synthesized|"
-      "synthesized memberwise|inherited}1 %0", (DeclName, unsigned))
+      "invalid redeclaration of synthesized %select{|memberwise }1%0",
+      (DeclName, bool))
 WARNING(invalid_redecl_swift5_warning,none,
         "redeclaration of %0 is deprecated and will be an error in Swift 5",
         (DeclName))

lib/Sema/TypeCheckDecl.cpp

@@ -917,16 +917,14 @@ static void checkRedeclaration(TypeChecker &tc, ValueDecl *current) {
         const auto *otherInit = dyn_cast<ConstructorDecl>(other);
         // Provide a better description for implicit initializers.
         if (otherInit && otherInit->isImplicit()) {
-          enum {
-            Synthetic, SyntheticMemberwise, Inherited
-          } kind = Synthetic;
-          if (otherInit->isMemberwiseInitializer())
-            kind = SyntheticMemberwise;
-          else if (otherInit->getOverriddenDecl())
-            kind = Inherited;
-
-          tc.diagnose(current, diag::invalid_redecl_init,
-                      current->getFullName(), kind);
+          // Skip conflicts with inherited initializers, which only happen
+          // when the current declaration is within an extension. The override
+          // checker should have already taken care of emitting a more
+          // productive diagnostic.
+          if (!other->getOverriddenDecl())
+            tc.diagnose(current, diag::invalid_redecl_init,
+                        current->getFullName(),
+                        otherInit->isMemberwiseInitializer());
         } else {
           tc.diagnose(current, diag::invalid_redecl, current->getFullName());
           tc.diagnose(other, diag::invalid_redecl_prev, other->getFullName());

test/decl/init/basic_init.swift

@@ -19,12 +19,18 @@ extension Foo {
 
 class InitClass {
   init(arg: Bool) {} // expected-note{{add '@objc' to make this declaration overridable}}
+  @objc init(baz: Int) {} // expected-note{{overridden declaration is here}}
+  @objc dynamic init(bar: Int) {}
 }
 class InitSubclass: InitClass {}
+// expected-note@-1 {{'init(bar:)' previously overridden here}}
+// expected-note@-2 {{'init(baz:)' previously overridden here}}
 extension InitSubclass {
-  convenience init(arg: Bool) {}
-  // expected-error@-1{{invalid redeclaration of inherited 'init(arg:)'}}
-  // expected-error@-2{{overriding non-@objc declarations from extensions is not supported}}
+  convenience init(arg: Bool) {} // expected-error{{overriding non-@objc declarations from extensions is not supported}}
+  convenience override init(baz: Int) {}
+  // expected-error@-1 {{cannot override a non-dynamic class declaration from an extension}}
+  // expected-error@-2 {{'init(baz:)' has already been overridden}}
+  convenience override init(bar: Int) {} // expected-error{{'init(bar:)' has already been overridden}}
 }
 
 struct InitStruct {