Sema: Fix interface type computation for observer parameters

Author: AnthonyLatsis

lib/Sema/TypeCheckDecl.cpp

@@ -1611,7 +1611,7 @@ bool TypeChecker::isAvailabilitySafeForConformance(
   return requirementInfo.isContainedIn(witnessInfo);
 }
 
-// Returns 'nullptr' if this is the setter's 'newValue' parameter;
+// Returns 'nullptr' if this is the 'newValue' or 'oldValue' parameter;
 // otherwise, returns the corresponding parameter of the subscript
 // declaration.
 static ParamDecl *getOriginalParamFromAccessor(AbstractStorageDecl *storage,
@@ -1623,11 +1623,9 @@ static ParamDecl *getOriginalParamFromAccessor(AbstractStorageDecl *storage,
   switch (accessor->getAccessorKind()) {
   case AccessorKind::DidSet:
   case AccessorKind::WillSet:
-      return nullptr;
-
   case AccessorKind::Set:
     if (param == accessorParams->get(0)) {
-      // This is the 'newValue' parameter.
+      // This is the 'newValue' or 'oldValue' parameter.
       return nullptr;
     }
 

test/decl/protocol/existential_member_accesses_self_assoctype_fixit.swift

@@ -189,10 +189,10 @@ struct Test {
   }
 
   subscript(p: any P & Q) -> any P {
-    _read { p.method(false) } // expected-error {{member 'method' cannot be used on value of protocol type 'P & Q'; consider using a generic constraint instead}} {{-1:20--1:25=<#generic parameter name#>}} {{-1:16--1:20=}} {{-1:12--1:12=<<#generic parameter name#>: P & Q>}} {{none}}
+    _read { p.method(false) }   // expected-error {{member 'method' cannot be used on value of protocol type 'P & Q'; consider using a generic constraint instead}} {{-1:20--1:25=<#generic parameter name#>}} {{-1:16--1:20=}} {{-1:12--1:12=<<#generic parameter name#>: P & Q>}} {{none}}
     _modify { p.method(false) } // expected-error {{member 'method' cannot be used on value of protocol type 'P & Q'; consider using a generic constraint instead}} {{-2:20--2:25=<#generic parameter name#>}} {{-2:16--2:20=}} {{-2:12--2:12=<<#generic parameter name#>: P & Q>}} {{none}}
-    willSet { p.method(false) } // expected-error {{member 'method' cannot be used on value of protocol type 'P'; consider using a generic constraint instead}} {{-3:20--3:25=<#generic parameter name#>}} {{-3:16--3:20=}} {{-3:12--3:12=<<#generic parameter name#>: P & Q>}} {{none}}
-    didSet { p.method(false) } // expected-error {{member 'method' cannot be used on value of protocol type 'P'; consider using a generic constraint instead}} {{-4:20--4:25=<#generic parameter name#>}} {{-4:16--4:20=}} {{-4:12--4:12=<<#generic parameter name#>: P & Q>}} {{none}}
+    willSet { p.method(false) } // expected-error {{member 'method' cannot be used on value of protocol type 'P & Q'; consider using a generic constraint instead}} {{-3:20--3:25=<#generic parameter name#>}} {{-3:16--3:20=}} {{-3:12--3:12=<<#generic parameter name#>: P & Q>}} {{none}}
+    didSet { p.method(false) }  // expected-error {{member 'method' cannot be used on value of protocol type 'P & Q'; consider using a generic constraint instead}} {{-4:20--4:25=<#generic parameter name#>}} {{-4:16--4:20=}} {{-4:12--4:12=<<#generic parameter name#>: P & Q>}} {{none}}
     // expected-error@-2 {{'willSet' is not allowed in subscripts}}
     // expected-error@-2 {{'didSet' is not allowed in subscripts}}
   }

test/decl/subscript/subscripting.swift

@@ -165,18 +165,22 @@ protocol ProtocolWillSetDidSet4 {
 }
 
 class DidSetInSubscript {
-  subscript(_: Int) -> Int {
+  subscript(x: Int) -> Bool {
     didSet { // expected-error {{'didSet' is not allowed in subscripts}}
       print("eek")
+      // Make sure implicit observer parameters pick up the right type.
+      let _: Int = x
     }
     get {}
   }
 }
 
 class WillSetInSubscript {
-  subscript(_: Int) -> Int {
+  subscript(x: Int) -> Bool {
     willSet { // expected-error {{'willSet' is not allowed in subscripts}}
       print("eek")
+      // Make sure implicit observer parameters pick up the right type.
+      let _: Int = x
     }
     get {}
   }