[Diagnostics] Adjust the description of existential types for the

type_cannot_conform diagnostic message.

Author: hborla

include/swift/AST/DiagnosticsSema.def

@@ -1661,7 +1661,7 @@ ERROR(use_of_equal_instead_of_equality,none,
       "use of '=' in a boolean context, did you mean '=='?", ())
 
 ERROR(type_cannot_conform, none,
-      "%select{|protocol }0type %1 cannot conform to %2; "
+      "%select{|value of protocol }0type %1 cannot conform to %2; "
       "only struct/enum/class types can conform to protocols",
       (bool, Type, Type))
 NOTE(required_by_opaque_return,none,

test/Constraints/generics.swift

@@ -191,7 +191,7 @@ func r22459135() {
 
 // <rdar://problem/19710848> QoI: Friendlier error message for "[] as Set"
 // <rdar://problem/22326930> QoI: "argument for generic parameter 'Element' could not be inferred" lacks context
-_ = [] as Set  // expected-error {{protocol type 'Any' cannot conform to 'Hashable'; only struct/enum/class types can conform to protocols}}
+_ = [] as Set  // expected-error {{value of protocol type 'Any' cannot conform to 'Hashable'; only struct/enum/class types can conform to protocols}}
 // expected-note@-1 {{required by generic struct 'Set' where 'Element' = 'Any'}}
 
 

test/Constraints/operator.swift

@@ -220,7 +220,7 @@ func rdar46459603() {
   // expected-error@-1 {{binary operator '==' cannot be applied to operands of type 'Dictionary<String, E>.Values' and '[E]'}}
   // expected-note@-2  {{expected an argument list of type '(Self, Self)'}}
   _ = [arr.values] == [[e]]
-  // expected-error@-1 {{protocol type 'Any' cannot conform to 'Equatable'; only struct/enum/class types can conform to protocols}}
+  // expected-error@-1 {{value of protocol type 'Any' cannot conform to 'Equatable'; only struct/enum/class types can conform to protocols}}
   // expected-note@-2 {{requirement from conditional conformance of '[Any]' to 'Equatable'}}
 }
 

test/Generics/conditional_conformances_literals.swift

@@ -128,9 +128,9 @@ func combined() {
 
     // Needs self conforming protocols:
     let _: Conforms = [[0: [1 : [works]] as Conforms]]
-    // expected-error@-1 {{protocol type 'Conforms' cannot conform to 'Conforms'; only struct/enum/class types can conform to protocols}}
+    // expected-error@-1 {{value of protocol type 'Conforms' cannot conform to 'Conforms'; only struct/enum/class types can conform to protocols}}
 
     let _: Conforms = [[0: [1 : [fails]] as Conforms]]
     // expected-error@-1 {{protocol 'Conforms' requires that 'Fails' conform to 'Conforms'}}
-    // expected-error@-2 {{protocol type 'Conforms' cannot conform to 'Conforms'; only struct/enum/class types can conform to protocols}}
+    // expected-error@-2 {{value of protocol type 'Conforms' cannot conform to 'Conforms'; only struct/enum/class types can conform to protocols}}
 }

test/Generics/existential_restrictions.swift

@@ -20,7 +20,7 @@ func fAOE(_ t: AnyObject) { }
 func fT<T>(_ t: T) { }
 
 func testPassExistential(_ p: P, op: OP, opp: OP & P, cp: CP, sp: SP, any: Any, ao: AnyObject) {
-  fP(p) // expected-error{{protocol type 'P' cannot conform to 'P'; only struct/enum/class types can conform to protocols}}
+  fP(p) // expected-error{{value of protocol type 'P' cannot conform to 'P'; only struct/enum/class types can conform to protocols}}
   fAO(p) // expected-error{{cannot invoke 'fAO' with an argument list of type '(P)'}} // expected-note{{expected an argument list of type '(T)'}}
   fAOE(p) // expected-error{{argument type 'P' does not conform to expected type 'AnyObject'}}
   fT(p)
@@ -34,8 +34,8 @@ func testPassExistential(_ p: P, op: OP, opp: OP & P, cp: CP, sp: SP, any: Any,
   fAOE(cp)
   fT(cp)
 
-  fP(opp) // expected-error{{protocol type 'OP & P' cannot conform to 'P'; only struct/enum/class types can conform to protocols}}
-  fOP(opp) // expected-error{{protocol type 'OP & P' cannot conform to 'OP'; only struct/enum/class types can conform to protocols}}
+  fP(opp) // expected-error{{value of protocol type 'OP & P' cannot conform to 'P'; only struct/enum/class types can conform to protocols}}
+  fOP(opp) // expected-error{{value of protocol type 'OP & P' cannot conform to 'OP'; only struct/enum/class types can conform to protocols}}
   fAO(opp) // expected-error{{cannot invoke 'fAO' with an argument list of type '(OP & P)'}} // expected-note{{expected an argument list of type '(T)'}}
   fAOE(opp)
   fT(opp)
@@ -61,9 +61,9 @@ class GAO<T : AnyObject> {} // expected-note 2{{requirement specified as 'T' : '
 func blackHole(_ t: Any) {}
 
 func testBindExistential() {
-  blackHole(GP<P>()) // expected-error{{protocol type 'P' cannot conform to 'P'; only struct/enum/class types can conform to protocols}}
+  blackHole(GP<P>()) // expected-error{{value of protocol type 'P' cannot conform to 'P'; only struct/enum/class types can conform to protocols}}
   blackHole(GOP<OP>())
-  blackHole(GCP<CP>()) // expected-error{{protocol type 'CP' cannot conform to 'CP'; only struct/enum/class types can conform to protocols}}
+  blackHole(GCP<CP>()) // expected-error{{value of protocol type 'CP' cannot conform to 'CP'; only struct/enum/class types can conform to protocols}}
   blackHole(GAO<P>()) // expected-error{{'GAO' requires that 'P' be a class type}}
   blackHole(GAO<OP>())
   blackHole(GAO<CP>()) // expected-error{{'GAO' requires that 'CP' be a class type}}
@@ -89,5 +89,5 @@ func foo() {
   // generic no overloads error path. The error should actually talk
   // about the return type, and this can happen in other contexts as well;
   // <rdar://problem/21900971> tracks improving QoI here.
-  allMine.takeAll() // expected-error{{protocol type 'Mine' cannot conform to 'Mine'; only struct/enum/class types can conform to protocols}}
+  allMine.takeAll() // expected-error{{value of protocol type 'Mine' cannot conform to 'Mine'; only struct/enum/class types can conform to protocols}}
 }

test/decl/protocol/conforms/error_self_conformance.swift

@@ -11,15 +11,15 @@ func testSimple(error: Error) {
 
 protocol ErrorRefinement : Error {}
 func testErrorRefinment(error: ErrorRefinement) {
-  wantsError(error) // expected-error {{protocol type 'ErrorRefinement' cannot conform to 'Error'; only struct/enum/class types can conform to protocols}}
+  wantsError(error) // expected-error {{value of protocol type 'ErrorRefinement' cannot conform to 'Error'; only struct/enum/class types can conform to protocols}}
 }
 
 protocol OtherProtocol {}
 func testErrorComposition(error: Error & OtherProtocol) {
-  wantsError(error) // expected-error {{protocol type 'Error & OtherProtocol' cannot conform to 'Error'; only struct/enum/class types can conform to protocols}}
+  wantsError(error) // expected-error {{value of protocol type 'Error & OtherProtocol' cannot conform to 'Error'; only struct/enum/class types can conform to protocols}}
 }
 
 class C {}
 func testErrorCompositionWithClass(error: Error & C) {
-  wantsError(error) // expected-error {{protocol type 'C & Error' cannot conform to 'Error'; only struct/enum/class types can conform to protocols}}
+  wantsError(error) // expected-error {{value of protocol type 'C & Error' cannot conform to 'Error'; only struct/enum/class types can conform to protocols}}
 }

test/stmt/foreach.swift

@@ -179,7 +179,7 @@ func testOptionalSequence() {
 
 // Crash with (invalid) for each over an existential
 func testExistentialSequence(s: Sequence) { // expected-error {{protocol 'Sequence' can only be used as a generic constraint because it has Self or associated type requirements}}
-  for x in s { // expected-error {{protocol type 'Sequence' cannot conform to 'Sequence'; only struct/enum/class types can conform to protocols}}
+  for x in s { // expected-error {{value of protocol type 'Sequence' cannot conform to 'Sequence'; only struct/enum/class types can conform to protocols}}
     _ = x
   }
 }

test/type/subclass_composition.swift

@@ -413,7 +413,7 @@ func conformsTo<T1 : P2, T2 : Base<Int> & P2>(
   // expected-note@-2 {{expected an argument list of type '(T)'}}
 
   conformsToP1(p1)
-  // expected-error@-1 {{protocol type 'P1' cannot conform to 'P1'; only struct/enum/class types can conform to protocols}}
+  // expected-error@-1 {{value of protocol type 'P1' cannot conform to 'P1'; only struct/enum/class types can conform to protocols}}
 
   // FIXME: Following diagnostics are not great because when
   // `conformsTo*` methods are re-typechecked, they loose information

validation-test/compiler_crashers_fixed/00017-llvm-foldingset-llvm-attributesetnode-nodeequals.swift

@@ -20,4 +20,4 @@ extension Bool : BooleanProtocol {
 func f<T : BooleanProtocol>(_ b: T) {}
 // expected-note@-1 {{required by global function 'f' where 'T' = 'BooleanProtocol'}}
 
-f(true as BooleanProtocol) // expected-error {{protocol type 'BooleanProtocol' cannot conform to 'BooleanProtocol'; only struct/enum/class types can conform to protocols}}
+f(true as BooleanProtocol) // expected-error {{value of protocol type 'BooleanProtocol' cannot conform to 'BooleanProtocol'; only struct/enum/class types can conform to protocols}}