[Concurrency] Allow ActorIsolation in diagnostic messages.

ActorIsolation is rendered as a descriptive phrase before an entity,
e.g, "actor-independent" or "global actor 'UIActor'-isolated" when
used in diagnostics.

include/swift/AST/ActorIsolation.h

@@ -16,6 +16,7 @@
 #ifndef SWIFT_AST_ACTORISOLATIONSTATE_H
 #define SWIFT_AST_ACTORISOLATIONSTATE_H
 
+#include "swift/AST/Type.h"
 #include "llvm/ADT/Hashing.h"
 
 namespace llvm {

include/swift/AST/DiagnosticEngine.h

@@ -18,6 +18,7 @@
 #ifndef SWIFT_BASIC_DIAGNOSTICENGINE_H
 #define SWIFT_BASIC_DIAGNOSTICENGINE_H
 
+#include "swift/AST/ActorIsolation.h"
 #include "swift/AST/DeclNameLoc.h"
 #include "swift/AST/DiagnosticConsumer.h"
 #include "swift/AST/TypeLoc.h"
@@ -93,6 +94,7 @@ namespace swift {
     DeclAttribute,
     VersionTuple,
     LayoutConstraint,
+    ActorIsolation,
   };
 
   namespace diag {
@@ -122,6 +124,7 @@ namespace swift {
       const DeclAttribute *DeclAttributeVal;
       llvm::VersionTuple VersionVal;
       LayoutConstraint LayoutConstraintVal;
+      ActorIsolation ActorIsolationVal;
     };
 
   public:
@@ -209,6 +212,12 @@ namespace swift {
     DiagnosticArgument(LayoutConstraint L)
       : Kind(DiagnosticArgumentKind::LayoutConstraint), LayoutConstraintVal(L) {
     }
+
+    DiagnosticArgument(ActorIsolation AI)
+      : Kind(DiagnosticArgumentKind::ActorIsolation),
+        ActorIsolationVal(AI) {
+    }
+
     /// Initializes a diagnostic argument using the underlying type of the
     /// given enum.
     template<
@@ -299,6 +308,11 @@ namespace swift {
       assert(Kind == DiagnosticArgumentKind::LayoutConstraint);
       return LayoutConstraintVal;
     }
+
+    ActorIsolation getAsActorIsolation() const {
+      assert(Kind == DiagnosticArgumentKind::ActorIsolation);
+      return ActorIsolationVal;
+    }
   };
 
   struct DiagnosticFormatOptions {

lib/AST/DiagnosticEngine.cpp

@@ -660,6 +660,26 @@ static void formatDiagnosticArgument(StringRef Modifier,
     Out << FormatOpts.OpeningQuotationMark << Arg.getAsLayoutConstraint()
         << FormatOpts.ClosingQuotationMark;
     break;
+  case DiagnosticArgumentKind::ActorIsolation:
+    switch (auto isolation = Arg.getAsActorIsolation()) {
+    case ActorIsolation::ActorInstance:
+      Out << "actor-isolated";
+      break;
+
+    case ActorIsolation::GlobalActor:
+      Out << "global actor " << FormatOpts.OpeningQuotationMark
+        << isolation.getGlobalActor().getString()
+        << FormatOpts.ClosingQuotationMark << "-isolated";
+      break;
+
+    case ActorIsolation::Independent:
+      Out << "actor-independent";
+      break;
+
+    case ActorIsolation::Unspecified:
+      Out << "non-actor-isolated";
+      break;
+    }
   }
 }