Parse suppressed-conformance constraints in expressions and validate them

Ensure that we're properly parsing suppressed-conformance constraints
in expression contents and in metatypes. This allows types like `any
~Copyable` in expression context as well as types like `any
~Copyable.Type`.

While we're here, ensure that existentials that involve
suppressed-conformance constraints are spelled with `any`.

Fixes rdar://123728228.

(cherry picked from commit 533a744)

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -5694,6 +5694,8 @@ ERROR(incorrect_optional_any,none,
 ERROR(existential_requires_any,none,
       "use of %select{protocol |}2%0 as a type must be written %1",
       (Type, Type, bool))
+ERROR(inverse_requires_any,none,
+      "constraint that suppresses conformance requires 'any'", ())
 
 ERROR(nonisolated_let,none,
       "'nonisolated' is meaningless on 'let' declarations because "

include/swift/Parse/Parser.h

@@ -1239,12 +1239,19 @@ class Parser {
     // the following token is something that can introduce a type. Thankfully
     // none of these tokens overlap with the set of tokens that can follow an
     // identifier in a type production.
-    return (Tok.is(tok::identifier) &&
-            peekToken().isAny(tok::at_sign, tok::kw_inout, tok::l_paren,
-                              tok::identifier, tok::l_square, tok::kw_Any,
-                              tok::kw_Self, tok::kw__, tok::kw_var,
-                              tok::kw_let)) ||
-           isLifetimeDependenceToken();
+    if (Tok.is(tok::identifier)) {
+      auto next = peekToken();
+      if (next.isAny(tok::at_sign, tok::kw_inout, tok::l_paren,
+                     tok::identifier, tok::l_square, tok::kw_Any,
+                     tok::kw_Self, tok::kw__, tok::kw_var,
+                     tok::kw_let))
+        return true;
+
+      if (next.is(tok::oper_prefix) && next.getText() == "~")
+        return true;
+    }
+
+    return isLifetimeDependenceToken();
   }
 
   struct ParsedTypeAttributeList {

lib/Parse/ParseExpr.cpp

@@ -479,7 +479,8 @@ ParserResult<Expr> Parser::parseExprSequenceElement(Diag<> message,
 
   // 'any' followed by another identifier is an existential type.
   if (Tok.isContextualKeyword("any") &&
-      peekToken().is(tok::identifier) &&
+      (peekToken().is(tok::identifier) ||
+       peekToken().isContextualPunctuator("~")) &&
       !peekToken().isAtStartOfLine()) {
     ParserResult<TypeRepr> ty = parseType();
     auto *typeExpr = new (Context) TypeExpr(ty.get());

lib/Sema/TypeCheckType.cpp

@@ -170,6 +170,7 @@ static unsigned getGenericRequirementKind(TypeResolutionOptions options) {
   case TypeResolverContext::ImmediateOptionalTypeArgument:
   case TypeResolverContext::AbstractFunctionDecl:
   case TypeResolverContext::CustomAttr:
+  case TypeResolverContext::Inverted:
     break;
   }
 
@@ -5150,6 +5151,7 @@ NeverNullType TypeResolver::resolveImplicitlyUnwrappedOptionalType(
   case TypeResolverContext::GenericParameterInherited:
   case TypeResolverContext::AssociatedTypeInherited:
   case TypeResolverContext::CustomAttr:
+  case TypeResolverContext::Inverted:
     doDiag = true;
     break;
   }
@@ -5740,10 +5742,30 @@ NeverNullType TypeResolver::buildMetatypeType(
 
 NeverNullType TypeResolver::resolveInverseType(InverseTypeRepr *repr,
                                                TypeResolutionOptions options) {
-  auto ty = resolveType(repr->getConstraint(), options);
+  auto subOptions = options.withoutContext(true)
+      .withContext(TypeResolverContext::Inverted);
+  auto ty = resolveType(repr->getConstraint(), subOptions);
   if (ty->hasError())
     return ErrorType::get(getASTContext());
 
+  // If the inverted type is an existential metatype, unwrap the existential
+  // metatype so we can look at the instance type. We'll re-wrap at the end.
+  ExistentialMetatypeType *existentialTy =
+      dyn_cast<ExistentialMetatypeType>(ty.get().getPointer());
+  if (existentialTy) {
+    ty = existentialTy->getInstanceType();
+  }
+
+  auto wrapInExistential = [existentialTy](Type type) -> Type {
+    if (!existentialTy)
+      return type;
+
+    std::optional<MetatypeRepresentation> repr;
+    if (existentialTy->hasRepresentation())
+      repr = existentialTy->getRepresentation();
+    return ExistentialMetatypeType::get(type, repr);
+  };
+
   if (auto kp = ty->getKnownProtocol()) {
     if (auto kind = getInvertibleProtocolKind(*kp)) {
 
@@ -5752,13 +5774,16 @@ NeverNullType TypeResolver::resolveInverseType(InverseTypeRepr *repr,
           !getASTContext().LangOpts.hasFeature(Feature::NonescapableTypes)) {
         diagnoseInvalid(repr, repr->getLoc(),
                         diag::escapable_requires_feature_flag);
-        return ErrorType::get(getASTContext());
+        return wrapInExistential(ErrorType::get(getASTContext()));
       }
 
-      return ProtocolCompositionType::getInverseOf(getASTContext(), *kind);
+      return wrapInExistential(
+          ProtocolCompositionType::getInverseOf(getASTContext(), *kind));
     }
   }
 
+  // Rewrap for diagnostic purposes.
+  ty = wrapInExistential(ty);
   diagnoseInvalid(repr, repr->getLoc(), diag::inverse_type_not_invertible, ty);
   return ErrorType::get(getASTContext());
 }
@@ -5917,6 +5942,23 @@ class ExistentialTypeSyntaxChecker : public ASTWalker {
     if (isa<ExistentialTypeRepr>(T))
       return Action::SkipNode();
 
+    // Suppressed conformance needs to be within any/some.
+    if (auto inverse = dyn_cast<InverseTypeRepr>(T)) {
+      // Find an enclosing protocol composition, if there is one, so we
+      // can insert 'any' before that.
+      SourceLoc anyLoc = inverse->getTildeLoc();
+      if (!reprStack.empty()) {
+        if (isa<CompositionTypeRepr>(reprStack.back())) {
+          anyLoc = reprStack.back()->getStartLoc();
+        }
+      }
+
+      Ctx.Diags.diagnose(inverse->getTildeLoc(), diag::inverse_requires_any)
+        .highlight(inverse->getConstraint()->getSourceRange())
+        .fixItInsert(anyLoc, "any ");
+      return Action::SkipNode();
+    }
+
     reprStack.push_back(T);
 
     auto *declRefTR = dyn_cast<DeclRefTypeRepr>(T);

lib/Sema/TypeCheckType.h

@@ -202,6 +202,9 @@ enum class TypeResolverContext : uint8_t {
 
   /// Whether this is a custom attribute.
   CustomAttr,
+
+  /// Whether this is the argument of an inverted constraint (~).
+  Inverted,
 };
 
 /// Options that determine how type resolution should work.
@@ -298,6 +301,7 @@ class TypeResolutionOptions {
     case Context::GenericParameterInherited:
     case Context::AssociatedTypeInherited:
     case Context::CustomAttr:
+    case Context::Inverted:
       return false;
     }
     llvm_unreachable("unhandled kind");
@@ -316,6 +320,7 @@ class TypeResolutionOptions {
     case Context::GenericRequirement:
     case Context::ExistentialConstraint:
     case Context::MetatypeBase:
+    case Context::Inverted:
       return false;
     case Context::None:
     case Context::ScalarGenericArgument:
@@ -353,6 +358,7 @@ class TypeResolutionOptions {
     case Context::PackElement:
     case Context::TupleElement:
     case Context::VariadicGenericArgument:
+    case Context::Inverted:
       return true;
     case Context::None:
     case Context::PatternBindingDecl:
@@ -425,6 +431,7 @@ class TypeResolutionOptions {
     case Context::ImmediateOptionalTypeArgument:
     case Context::AbstractFunctionDecl:
     case Context::CustomAttr:
+    case Context::Inverted:
       return false;
     }
   }

test/Parse/inverses.swift

@@ -81,15 +81,18 @@ func ownership2(_ t: ~ borrowing Int) {} // expected-error {{cannot find type 'b
 
 func ownership3(_ t: consuming some ~Clone) {}
 
-func what(one: ~Copyable..., // expected-error {{type 'any Copyable' cannot be suppressed}}
+func what(one: ~Copyable..., // expected-error {{noncopyable type '~Copyable' cannot be used within a variadic type yet}}
           two: ~(Copyable...) // expected-error {{variadic parameter cannot appear outside of a function parameter list}}
-                              // expected-error@-1 {{type 'any Copyable' cannot be suppressed}}
+                              // expected-error@-1 {{parameter of noncopyable type '~Copyable' must specify ownership}}
+              // expected-note@-2{{add 'borrowing' for an immutable reference}}
+              // expected-note@-3{{add 'inout' for a mutable reference}}
+              // expected-note@-4{{add 'consuming' to take the value from the caller}}
           ) {}
 
 struct A { struct B { struct C {} } }
 
-typealias Z1 = (~Copyable).Type // FIXME: should be an error
-typealias Z1 = ~Copyable.Type // expected-error {{type 'any Copyable.Type' cannot be suppressed}}
+typealias Z0 = (~Copyable).Type // expected-error{{constraint that suppresses conformance requires 'any'}}{{17-17=any }}
+typealias Z1 = ~Copyable.Type // expected-error{{constraint that suppresses conformance requires 'any'}}{{16-16=any }}
 typealias Z2 = ~A.B.C // expected-error {{type 'A.B.C' cannot be suppressed}}
 typealias Z3 = ~A? // expected-error {{type 'A?' cannot be suppressed}}
 typealias Z4 = ~Rope<Int> // expected-error {{type 'Rope<Int>' cannot be suppressed}}
@@ -106,11 +109,22 @@ struct Bad: ~NotAProtocol {} // expected-error {{type 'NotAProtocol' cannot be s
 struct X<T: ~Copyable>: ~Copyable { }
 
 func typeInExpression() {
-  _ = [~Copyable]()  // expected-error{{type 'any Copyable' cannot be suppressed}}
+  _ = [~Copyable]()  // expected-error{{type '~Copyable' does not conform to protocol 'Copyable'}}
   _ = X<any ~Copyable>()
 
   _ = X<any ~Copyable & Foo>()
   _ = X<any Foo & ~Copyable>()
 
   _ = X<(borrowing any ~Copyable) -> Void>()
+
+  _ = ~Copyable.self // expected-error{{unary operator '~' cannot be applied to an operand of type '(any Copyable).Type'}}
+  _ = (~Copyable).self // expected-error{{constraint that suppresses conformance requires 'any'}}{{8-8=any }}
+  _ = (any ~Copyable).self
 }
+
+func param1(_ t: borrowing ~Copyable) {} // expected-error{{constraint that suppresses conformance requires 'any'}}{{28-28=any }}
+func param2(_ t: ~Copyable.Type) {} // expected-error{{constraint that suppresses conformance requires 'any'}}{{18-18=any }}
+func param3(_ t: borrowing any ~Copyable) {}
+func param4(_ t: any ~Copyable.Type) {}
+
+func param3(_ t: borrowing ExtraNoncopyProto & ~Copyable) {} // expected-error{{constraint that suppresses conformance requires 'any'}}{{28-28=any }}