Don't fix access of an 'open' decl in a 'public' extension

This is reasonable to diagnose with a warning, but dropping the 'open'
down to 'public' isn't the right fix, because now it's not a valid
override. The declaration has to get moved to another extension instead,
or the extension has to not set a default access level.

This turned out to be a source compat issue because the same logic
that emits the fix-it also updates the access of the member, which
then resulted in "must be as accessible as the declaration it
overrides" in the /same/ build. It's not immediately clear what caused
this; probably something's just being validated in a different order
than it was before. The change makes sense either way.

Stepping back, it's weird that a warning would change how the compiler
saw the code, and while we could check for 'override' explicitly, we
can't know if the member might be satisfying a protocol requirement.
Better to just not guess at the right answer here.

rdar://problem/47557376&28493971

Author: jrose-apple

lib/Sema/TypeCheckAttr.cpp

@@ -1641,8 +1641,10 @@ void AttributeChecker::visitAccessControlAttr(AccessControlAttr *attr) {
                                 diag::access_control_ext_member_more,
                                 attr->getAccess(),
                                 extAttr->getAccess());
-        swift::fixItAccess(diag, cast<ValueDecl>(D), defaultAccess, false,
-                           true);
+        // Don't try to fix this one; it's just a warning, and fixing it can
+        // lead to diagnostic fights between this and "declaration must be at
+        // least this accessible" checking for overrides and protocol
+        // requirements.
         return;
       } else if (attr->getAccess() == defaultAccess) {
         TC.diagnose(attr->getLocation(),

test/ClangImporter/Inputs/custom-modules/ObjCParseExtras.h

@@ -241,3 +241,11 @@ struct NonTrivialToCopyWrapper {
 struct TrivialToCopy {
   __unsafe_unretained id field;
 };
+
+@interface OverrideInExtensionBase : NSObject
+- (void)method;
+- (void)accessWarning;
+@end
+
+@interface OverrideInExtensionSub : OverrideInExtensionBase
+@end

test/ClangImporter/objc_override.swift

@@ -116,6 +116,16 @@ class MyHashableNSObject: NSObject {
   }
 }
 
+// rdar://problem/47557376
+// Adding an override to someone else's class in an extension like this isn't
+// really sound, but it's allowed in Objective-C too.
+extension OverrideInExtensionSub {
+  open override func method() {}
+}
+public extension OverrideInExtensionSub {
+  open override func accessWarning() {} // expected-warning {{'open' modifier conflicts with extension's default access of 'public'}}
+}
+
 // FIXME: Remove -verify-ignore-unknown.
 // <unknown>:0: error: unexpected note produced: overridden declaration is here
 // <unknown>:0: error: unexpected note produced: setter for 'boolProperty' declared here

test/Compatibility/accessibility.swift

@@ -80,17 +80,17 @@ public extension PublicStruct {
   private func extImplPublic() {}
 }
 internal extension PublicStruct {
-  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{3-10=}}
+  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{none}}
   fileprivate func extFuncInternal() {}
   private func extImplInternal() {}
 }
 fileprivate extension PublicStruct {
-  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{3-10=}}
+  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{none}}
   fileprivate func extFuncFilePrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a fileprivate extension}} {{3-15=}}
   private func extImplFilePrivate() {}
 }
 private extension PublicStruct {
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   fileprivate func extFuncPrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a private (equivalent to fileprivate) extension}} {{3-15=}}
   private func extImplPrivate() {}
 }
@@ -100,17 +100,17 @@ public extension InternalStruct { // expected-error {{extension of internal stru
   private func extImplPublic() {}
 }
 internal extension InternalStruct {
-  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{3-10=}}
+  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{none}}
   fileprivate func extFuncInternal() {}
   private func extImplInternal() {}
 }
 fileprivate extension InternalStruct {
-  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{3-10=}}
+  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{none}}
   fileprivate func extFuncFilePrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a fileprivate extension}} {{3-15=}}
   private func extImplFilePrivate() {}
 }
 private extension InternalStruct {
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   fileprivate func extFuncPrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a private (equivalent to fileprivate) extension}} {{3-15=}}
   private func extImplPrivate() {}
 }
@@ -120,17 +120,17 @@ public extension FilePrivateStruct { // expected-error {{extension of fileprivat
   private func extImplPublic() {}
 }
 internal extension FilePrivateStruct { // expected-error {{extension of fileprivate struct cannot be declared internal}} {{1-10=}}
-  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{3-10=}}
+  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{none}}
   fileprivate func extFuncInternal() {}
   private func extImplInternal() {}
 }
 fileprivate extension FilePrivateStruct {
-  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{3-10=}}
+  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{none}}
   fileprivate func extFuncFilePrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a fileprivate extension}} {{3-15=}}
   private func extImplFilePrivate() {}
 }
 private extension FilePrivateStruct {
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   fileprivate func extFuncPrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a private (equivalent to fileprivate) extension}} {{3-15=}}
   private func extImplPrivate() {}
 }
@@ -140,17 +140,17 @@ public extension PrivateStruct { // expected-error {{extension of private struct
   private func extImplPublic() {}
 }
 internal extension PrivateStruct { // expected-error {{extension of private struct cannot be declared internal}} {{1-10=}}
-  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{3-10=}}
+  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{none}}
   fileprivate func extFuncInternal() {}
   private func extImplInternal() {}
 }
 fileprivate extension PrivateStruct { // expected-error {{extension of private struct cannot be declared fileprivate}} {{1-13=}}
-  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{3-10=}}
+  public func extMemberFilePrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'fileprivate'}} {{none}}
   fileprivate func extFuncFilePrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a fileprivate extension}} {{3-15=}}
   private func extImplFilePrivate() {}
 }
 private extension PrivateStruct {
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   fileprivate func extFuncPrivate() {} // expected-warning {{'fileprivate' modifier is redundant for instance method declared in a private (equivalent to fileprivate) extension}} {{3-15=}}
   private func extImplPrivate() {}
 }
@@ -175,10 +175,10 @@ public class Base {
 
 
 public extension Base {
-  open func extMemberPublic() {} // expected-warning {{'open' modifier conflicts with extension's default access of 'public'}}
+  open func extMemberPublic() {} // expected-warning {{'open' modifier conflicts with extension's default access of 'public'}} {{none}}
 }
 internal extension Base {
-  open func extMemberInternal() {} // expected-warning {{'open' modifier conflicts with extension's default access of 'internal'}}
+  open func extMemberInternal() {} // expected-warning {{'open' modifier conflicts with extension's default access of 'internal'}} {{none}}
 }
 
 public class PublicSub: Base {

test/SILGen/accessibility_warnings.swift

@@ -65,35 +65,35 @@ public extension PublicStruct {
 }
 
 internal extension PublicStruct {
-  // CHECK-DAG: sil hidden [ossa] @$s22accessibility_warnings12PublicStructV17extMemberInternalyyF
-  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{3-10=}}
+  // CHECK-DAG: sil [ossa] @$s22accessibility_warnings12PublicStructV17extMemberInternalyyF
+  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{none}}
   // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings12PublicStructV15extImplInternal33_5D2F2E026754A901C0FF90C404896D02LLyyF
   private func extImplInternal() {}
 }
 private extension PublicStruct {
-  // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings12PublicStructV16extMemberPrivate33_5D2F2E026754A901C0FF90C404896D02LLyyF
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  // CHECK-DAG: sil [ossa] @$s22accessibility_warnings12PublicStructV16extMemberPrivateyyF
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings12PublicStructV14extImplPrivate33_5D2F2E026754A901C0FF90C404896D02LLyyF
   private func extImplPrivate() {}
 }
 
 internal extension InternalStruct {
   // CHECK-DAG: sil hidden [ossa] @$s22accessibility_warnings14InternalStructV09extMemberC0yyF
-  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{3-10=}}
+  public func extMemberInternal() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'internal'}} {{none}}
   // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings14InternalStructV07extImplC033_5D2F2E026754A901C0FF90C404896D02LLyyF
   private func extImplInternal() {}
 }
 private extension InternalStruct {
-  // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings14InternalStructV16extMemberPrivate33_5D2F2E026754A901C0FF90C404896D02LLyyF
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  // CHECK-DAG: sil hidden [ossa] @$s22accessibility_warnings14InternalStructV16extMemberPrivateyyF
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings14InternalStructV14extImplPrivate33_5D2F2E026754A901C0FF90C404896D02LLyyF
   private func extImplPrivate() {}
 }
 
 
 private extension PrivateStruct {
   // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings13PrivateStruct33_5D2F2E026754A901C0FF90C404896D02LLV09extMemberC0yyF
-  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{3-10=}}
+  public func extMemberPrivate() {} // expected-warning {{'public' modifier conflicts with extension's default access of 'private'}} {{none}}
   // CHECK-DAG: sil private [ossa] @$s22accessibility_warnings13PrivateStruct33_5D2F2E026754A901C0FF90C404896D02LLV07extImplC0yyF
   private func extImplPrivate() {}
 }