Replace the cycle breaker for pattern bindings

Author: CodaFi

include/swift/AST/Decl.h

@@ -2226,6 +2226,9 @@ class PatternBindingDecl final : public Decl,
   /// \returns the way 'static'/'class' should be spelled for this declaration.
   StaticSpellingKind getCorrectStaticSpelling() const;
 
+  /// Is the pattern binding entry for this variable  currently being computed?
+  bool isComputingPatternBindingEntry(const VarDecl *vd) const;
+
   static bool classof(const Decl *D) {
     return D->getKind() == DeclKind::PatternBinding;
   }

lib/AST/Decl.cpp

@@ -1735,6 +1735,13 @@ bool PatternBindingDecl::isDefaultInitializable(unsigned i) const {
   return false;
 }
 
+bool PatternBindingDecl::isComputingPatternBindingEntry(
+    const VarDecl *vd) const {
+  unsigned i = getPatternEntryIndexForVarDecl(vd);
+  return getASTContext().evaluator.hasActiveRequest(
+      PatternBindingEntryRequest{const_cast<PatternBindingDecl *>(this), i});
+}
+
 SourceLoc TopLevelCodeDecl::getStartLoc() const {
   return Body->getStartLoc();
 }
@@ -2761,7 +2768,7 @@ bool ValueDecl::isRecursiveValidation() const {
 
   if (auto *vd = dyn_cast<VarDecl>(this))
     if (auto *pbd = vd->getParentPatternBinding())
-      if (pbd->isBeingValidated())
+      if (pbd->isComputingPatternBindingEntry(vd))
         return true;
 
   auto *dc = getDeclContext();

test/decl/overload.swift

@@ -610,10 +610,27 @@ enum SR_10084_E_16 {
   case Z // expected-error {{invalid redeclaration of 'Z'}}
 }
 
-// N.B. Validating the pattern binding initializer for `raw` used to cause
+// N.B. Validating the pattern binding initializer for `pickMe` used to cause
 // recursive validation of the VarDecl. Check that we don't regress now that
 // this isn't the case.
 public struct Cyclic {
   static func pickMe(please: Bool) -> Int { return 42 }
   public static let pickMe = Cyclic.pickMe(please: true)
 }
+
+struct Node {}
+struct Parameterized<Value, Format> {
+  func please<NewValue>(_ transform: @escaping (_ otherValue: NewValue) -> Value) -> Parameterized<NewValue, Format> {
+    fatalError()
+  }
+}
+
+extension Parameterized where Value == [Node], Format == String {
+  static var pickMe: Parameterized {
+    fatalError()
+  }
+}
+
+extension Parameterized where Value == Node, Format == String {
+  static let pickMe = Parameterized<[Node], String>.pickMe.please { [$0] }
+}

test/decl/protocol/conforms/circular_validation.swift

@@ -4,13 +4,12 @@
 // not crash.
 
 protocol P {
-  var x: Int { get set }
+  var x: Int { get set } // expected-note {{protocol requires property 'x' with type 'Int'; do you want to add a stub?}}
 }
 
-struct S : P {
-  static var x = 0
-  var x = S.x // expected-error {{circular reference}}
-  // expected-note@-1 {{through reference here}}
+struct S : P { // expected-error {{type 'S' does not conform to protocol 'P'}}
+  static var x = 0 // expected-note {{candidate operates on a type, not an instance as required}}
+  var x = S.x // expected-note {{candidate references itself}}
 }
 
 // FIXME: Lousy diagnostics on this case.

test/decl/protocol/req/associated_type_inference.swift

@@ -185,8 +185,8 @@ struct XCollectionLikeP0a<T> : CollectionLikeP0 {
 struct XCollectionLikeP0b : CollectionLikeP0 {
 // expected-error@-1 {{type 'XCollectionLikeP0b' does not conform to protocol 'CollectionLikeP0'}}
   var startIndex: XCollectionLikeP0b.Index
-  // expected-error@-1{{circular reference}}
-  // expected-note@-2{{through reference here}}
+  // There was an error @-1 ("'startIndex' used within its own type"),
+  // but it disappeared and doesn't seem like much of a loss.
   var startElement: XCollectionLikeP0b.Element
 }