Sema: Improve requirement indicator note for actor_isolated_witness

`x declared here` is not helpful and clear enough, especially when there
are other notes attached. Swap it for a new note that says
`requirement x declared here`. While we are here, also make sure we do
not emit this note unless the requirement has a valid location.

Author: AnthonyLatsis

include/swift/AST/DiagnosticsSema.def

@@ -42,6 +42,8 @@ NOTE(opaque_return_type_declared_here,none,
      "opaque return type declared here", ())
 NOTE(default_value_declared_here,none,
      "default value declared here", ())
+NOTE(protocol_requirement_declared_here,none,
+     "requirement %0 declared here", (const ValueDecl *))
 
 //------------------------------------------------------------------------------
 // MARK: Constraint solver diagnostics

lib/Sema/TypeCheckProtocol.cpp

@@ -3439,8 +3439,12 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
   // If there are remaining options, they are missing async/throws on the
   // requirement itself. If we have a source location for the requirement,
   // provide those in a note.
-  if (missingOptions && requirement->getLoc().isValid() &&
-      isa<AbstractFunctionDecl>(requirement)) {
+
+  if (requirement->getLoc().isInvalid()) {
+    return std::nullopt;
+  }
+
+  if (missingOptions && isa<AbstractFunctionDecl>(requirement)) {
     int suggestAddingModifiers = 0;
     std::string modifiers;
     if (missingOptions.contains(MissingFlags::RequirementAsync)) {
@@ -3486,7 +3490,8 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
         diag.fixItInsert(insertLoc, modifiers);
     }
   } else {
-    requirement->diagnose(diag::decl_declared_here, requirement);
+    requirement->diagnose(diag::protocol_requirement_declared_here,
+                          requirement);
   }
 
   return std::nullopt;

test/Concurrency/actor_isolation.swift

@@ -1612,7 +1612,7 @@ class OverridesNonsiolatedInit: SuperWithNonisolatedInit {
 class NonSendable {}
 
 protocol NonisolatedProtocol {
-  var ns: NonSendable { get } // expected-note {{'ns' declared here}}
+  var ns: NonSendable { get } // expected-note {{requirement 'ns' declared here}}
 }
 
 actor ActorWithNonSendableLet: NonisolatedProtocol {

test/Concurrency/global_actor_inference.swift

@@ -120,7 +120,7 @@ func testNotAllInP1(nap1: NotAllInP1) { // expected-note{{add '@SomeGlobalActor'
 // Make sure we don't infer 'nonisolated' for stored properties.
 @MainActor
 protocol Interface {
-  nonisolated var baz: Int { get } // expected-note{{'baz' declared here}}
+  nonisolated var baz: Int { get } // expected-note{{requirement 'baz' declared here}}
 }
 
 @MainActor

test/Concurrency/preconcurrency_conformances.swift

@@ -130,7 +130,7 @@ struct GlobalActor {
 protocol WithIndividuallyIsolatedRequirements {
   @MainActor var a: Int { get set }
   @GlobalActor var b: Int { get set }
-  // expected-note@-1 {{'b' declared here}}
+  // expected-note@-1 {{requirement 'b' declared here}}
 
   @GlobalActor func test()
   // expected-note@-1 {{mark the protocol requirement 'test()' 'async' to allow actor-isolated conformances}}
@@ -158,7 +158,7 @@ do {
 @MainActor
 protocol WithNonIsolated {
   var prop: Int { get set }
-  // expected-note@-1 {{'prop' declared here}}
+  // expected-note@-1 {{requirement 'prop' declared here}}
   nonisolated func test()
   // expected-note@-1 {{mark the protocol requirement 'test()' 'async' to allow actor-isolated conformances}}
 }

test/decl/class/actor/conformance.swift

@@ -15,8 +15,8 @@ extension MyActor: AsyncProtocol {
 }
 
 protocol SyncProtocol {
-  var propertyA: Int { get } // expected-note{{'propertyA' declared here}}
-  var propertyB: Int { get set } // expected-note{{'propertyB' declared here}}
+  var propertyA: Int { get } // expected-note{{requirement 'propertyA' declared here}}
+  var propertyB: Int { get set } // expected-note{{requirement 'propertyB' declared here}}
 
   func syncMethodA() // expected-note{{mark the protocol requirement 'syncMethodA()' 'async' to allow actor-isolated conformances}}{{21-21= async}}
 
@@ -28,7 +28,7 @@ protocol SyncProtocol {
 
   func syncMethodG() throws -> Void // expected-note{{mark the protocol requirement 'syncMethodG()' 'async' to allow actor-isolated conformances}}{{22-22=async }}
 
-  subscript (index: Int) -> String { get } // expected-note{{'subscript(_:)' declared here}}
+  subscript (index: Int) -> String { get } // expected-note{{requirement 'subscript(_:)' declared here}}
 
   static func staticMethod()
   static var staticProperty: Int { get }

test/decl/protocol/special/DistributedActor.swift

@@ -55,7 +55,7 @@ distributed actor D4 {
 
 protocol P1: DistributedActor {
   distributed func dist() -> String
-  // expected-note@-1{{'dist()' declared here}}
+  // expected-note@-1{{requirement 'dist()' declared here}}
 }
 
 distributed actor D5: P1 {