Merge pull request swiftlang#81104 from Azoy/value-generic-namelookup-warning

[AST] Temporarily downgrade value generic redeclaration to warning

Author: MaxDesiatov

include/swift/AST/Decl.h

@@ -310,6 +310,9 @@ struct OverloadSignature {
   /// Whether this is a macro.
   unsigned IsMacro : 1;
 
+  /// Whether this is a generic argument.
+  unsigned IsGenericArg : 1;
+
   /// Whether this signature is part of a protocol extension.
   unsigned InProtocolExtension : 1;
 
@@ -323,8 +326,10 @@ struct OverloadSignature {
   OverloadSignature()
       : UnaryOperator(UnaryOperatorKind::None), IsInstanceMember(false),
         IsVariable(false), IsFunction(false), IsAsyncFunction(false),
-        IsDistributed(false), InProtocolExtension(false),
-        InExtensionOfGenericType(false), HasOpaqueReturnType(false) { }
+        IsDistributed(false), IsEnumElement(false), IsNominal(false),
+        IsTypeAlias(false), IsMacro(false), IsGenericArg(false),
+        InProtocolExtension(false), InExtensionOfGenericType(false),
+        HasOpaqueReturnType(false) { }
 };
 
 /// Determine whether two overload signatures conflict.

lib/AST/Decl.cpp

@@ -3859,6 +3859,13 @@ bool swift::conflicting(ASTContext &ctx,
   if (sig1.IsFunction != sig2.IsFunction)
     return true;
 
+  // Gracefully handle the case where value generic arguments were introduced
+  // as a conflicting value with static variables of the same name.
+  if (sig1.IsGenericArg != sig2.IsGenericArg) {
+    *wouldConflictInSwift5 = true;
+    return true;
+  }
+
   // Variables always conflict with non-variables with the same signature.
   // (e.g variables with zero argument functions, variables with type
   //  declarations)
@@ -4037,6 +4044,7 @@ OverloadSignature ValueDecl::getOverloadSignature() const {
   signature.IsNominal = isa<NominalTypeDecl>(this);
   signature.IsTypeAlias = isa<TypeAliasDecl>(this);
   signature.IsMacro = isa<MacroDecl>(this);
+  signature.IsGenericArg = isa<GenericTypeParamDecl>(this);
   signature.HasOpaqueReturnType =
                        !signature.IsVariable && (bool)getOpaqueResultTypeDecl();
 

test/Sema/value_generics.swift

@@ -121,7 +121,7 @@ func testC4<let T: Int>(with c: C<T, T>) {
 struct D<let N: Int & P> {} // expected-error {{non-protocol, non-class type 'Int' cannot be used within a protocol-constrained type}}
 
 struct E<A, let b: Int> { // expected-note {{'b' previously declared here}}
-  static var b: Int { // expected-error {{invalid redeclaration of 'b'}}
+  static var b: Int { // expected-warning {{redeclaration of 'b' is deprecated and will be an error in Swift 5}}
                       // expected-note@-1 {{'b' declared here}}
     123
   }
@@ -183,7 +183,7 @@ func testTypeOf2<let c: Int>(_: E<Int, c>.Type) -> Int {
 }
 
 struct H<let I: Int> { // expected-note {{'I' previously declared here}}
-  struct I {} // expected-error {{invalid redeclaration of 'I'}}
+  struct I {} // expected-warning {{redeclaration of 'I' is deprecated and will be an error in Swift 5}}
 }
 
 typealias J = E<Int, 123>.b // expected-error {{static property 'b' is not a member type of 'E<Int, 123>'}}