Do not suggest moving any or some to the beginning of a composition if the first type is already an existential or opaque type.

Author: moritzdietsche

lib/Parse/ParseType.cpp

@@ -881,13 +881,20 @@ Parser::parseTypeSimpleOrComposition(Diag<> MessageID, ParseTypeReason reason) {
         Tok.isContextualKeyword("any")) {
       auto keyword = Tok.getText();
       auto badLoc = consumeToken();
+                
+      // Suggest moving `some` or `any` in front of the first type unless
+      // the first type is an opaque or existential type.
+      if (opaqueLoc.isValid() || anyLoc.isValid()) {
+        diagnose(badLoc, diag::opaque_mid_composition, keyword)
+            .fixItRemove(badLoc);
+      } else {
+        diagnose(badLoc, diag::opaque_mid_composition, keyword)
+            .fixItRemove(badLoc)
+            .fixItInsert(FirstTypeLoc, keyword.str() + " ");
+      }
 
       const bool isAnyKeyword = keyword.equals("any");
 
-      diagnose(badLoc, diag::opaque_mid_composition, keyword)
-          .fixItRemove(badLoc)
-          .fixItInsert(FirstTypeLoc, keyword.str() + " ");
-
       if (isAnyKeyword) {
         if (anyLoc.isInvalid()) {
           anyLoc = badLoc;

test/type/explicit_existential.swift

@@ -156,15 +156,17 @@ func anyAny() {
 
 protocol P1 {}
 protocol P2 {}
+protocol P3 {}
 do {
   // Test that we don't accidentally misparse an 'any' type as a 'some' type
   // and vice versa.
-  let _: P1 & any P2 // expected-error {{'any' should appear at the beginning of a composition}}
-  let _: any P1 & any P2 // expected-error {{'any' should appear at the beginning of a composition}}
-  let _: any P1 & some P2 // expected-error {{'some' should appear at the beginning of a composition}}
+  let _: P1 & any P2 // expected-error {{'any' should appear at the beginning of a composition}} {{15-19=}} {{10-10=any }}
+  let _: any P1 & any P2 // expected-error {{'any' should appear at the beginning of a composition}} {{19-23=}}
+  let _: any P1 & P2 & any P3 // expected-error {{'any' should appear at the beginning of a composition}} {{24-28=}}
+  let _: any P1 & some P2 // expected-error {{'some' should appear at the beginning of a composition}} {{19-24=}}
   let _: some P1 & any P2
   // expected-error@-1 {{'some' type can only be declared on a single property declaration}}
-  // expected-error@-2 {{'any' should appear at the beginning of a composition}}
+  // expected-error@-2 {{'any' should appear at the beginning of a composition}} {{20-24=}}
 }
 
 struct ConcreteComposition: P1, P2 {}

test/type/opaque.swift

@@ -488,8 +488,11 @@ func foo_repl<S>(_ s: S) -> some Proto {
 
 protocol SomeProtocolA {}
 protocol SomeProtocolB {}
-struct SomeStructC: SomeProtocolA, SomeProtocolB {}
+protocol SomeProtocolC {}
+struct SomeStructC: SomeProtocolA, SomeProtocolB, SomeProtocolC {}
 let someProperty: SomeProtocolA & some SomeProtocolB = SomeStructC() // expected-error {{'some' should appear at the beginning of a composition}}{{35-40=}}{{19-19=some }}
+let someOtherProperty: some SomeProtocolA & some SomeProtocolB = SomeStructC() // expected-error {{'some' should appear at the beginning of a composition}}{{45-50=}}
+let someThirdProperty: some SomeProtocolA & SomeProtocolB & some SomeProtocolC = SomeStructC() // expected-error {{'some' should appear at the beginning of a composition}}{{61-66=}}
 
 // An opaque result type on a protocol extension member effectively
 // contains an invariant reference to 'Self', and therefore cannot