[Sema] Diagnose redundant any on existential type

Author: LucianoPAlmeida

include/swift/AST/DiagnosticsSema.def

@@ -4708,7 +4708,9 @@ ERROR(unchecked_not_inheritance_clause,none,
       "'unchecked' attribute only applies in inheritance clauses", ())
 ERROR(unchecked_not_existential,none,
       "'unchecked' attribute cannot apply to non-protocol type %0", (Type))
-
+ERROR(redundant_any_in_existential,none,
+       "redundant 'any' has no effect on existential type %0",
+       (Type))
 ERROR(any_not_existential,none,
        "'any' has no effect on %select{concrete type|type parameter}0 %1",
        (bool, Type))

lib/Sema/TypeCheckType.cpp

@@ -3987,6 +3987,14 @@ TypeResolver::resolveExistentialType(ExistentialTypeRepr *repr,
   if (constraintType->hasError())
     return ErrorType::get(getASTContext());
 
+  // Diagnose redundant `any` on an already existential type e.g. any (any P)
+  // with a fix-it to remove first any.
+  if (constraintType->is<ExistentialType>()) {
+    diagnose(repr->getLoc(), diag::redundant_any_in_existential, constraintType)
+        .fixItRemove(repr->getAnyLoc());
+    return constraintType;
+  }
+
   if (!constraintType->isExistentialType()) {
     // Emit a tailored diagnostic for the incorrect optional
     // syntax 'any P?' with a fix-it to add parenthesis.
@@ -4002,13 +4010,9 @@ TypeResolver::resolveExistentialType(ExistentialTypeRepr *repr,
       return constraintType;
     }
 
-    auto anyStart = repr->getAnyLoc();
-    auto anyEnd = Lexer::getLocForEndOfToken(getASTContext().SourceMgr,
-                                             anyStart);
     diagnose(repr->getLoc(), diag::any_not_existential,
-             constraintType->isTypeParameter(),
-             constraintType)
-      .fixItRemove({anyStart, anyEnd});
+             constraintType->isTypeParameter(), constraintType)
+        .fixItRemove(repr->getAnyLoc());
     return constraintType;
   }
 

test/type/explicit_existential.swift

@@ -329,3 +329,15 @@ func testEnumAssociatedValue() {
     case c3((P) -> Void)
   }
 }
+
+// https://github.com/apple/swift/issues/58920
+typealias Iterator = any IteratorProtocol
+var example: any Iterator = 5 // expected-error{{redundant 'any' has no effect on existential type 'Iterator' (aka 'IteratorProtocol')}} {{14-18=}} 
+// expected-error@-1{{value of type 'Int' does not conform to specified type 'IteratorProtocol'}}
+var example1: any (any IteratorProtocol) = 5 // expected-error{{redundant 'any' has no effect on existential type 'any IteratorProtocol'}} {{15-19=}}
+// expected-error@-1{{value of type 'Int' does not conform to specified type 'IteratorProtocol'}}
+
+protocol P {}
+struct A : P {}
+var a: any P = A() // Ok
+var b: any (any P) = A() // expected-error{{redundant 'any' has no effect on existential type 'any P'}} {{8-12=}}