Reland "Give NullabilityKind a printing operator<<"

This reverts commit 5326c9e480d70e16c2504cb5143524aff3ee2605.

The problem that caused the revert was downstream
(missing dep in user of clang).

clang/include/clang/Basic/Specifiers.h

@@ -19,6 +19,9 @@
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/ErrorHandling.h"
 
+namespace llvm {
+class raw_ostream;
+} // namespace llvm
 namespace clang {
 
   /// Define the meaning of possible values of the kind in ExplicitSpecifier.
@@ -333,6 +336,8 @@ namespace clang {
     // parameters are assumed to only get null on error.
     NullableResult,
   };
+  /// Prints human-readable debug representation.
+  llvm::raw_ostream &operator<<(llvm::raw_ostream&, NullabilityKind);
 
   /// Return true if \p L has a weaker nullability annotation than \p R. The
   /// ordering is: Unspecified < Nullable < NonNull.

clang/lib/Basic/Diagnostic.cpp

@@ -43,28 +43,12 @@ using namespace clang;
 
 const StreamingDiagnostic &clang::operator<<(const StreamingDiagnostic &DB,
                                              DiagNullabilityKind nullability) {
-  StringRef string;
-  switch (nullability.first) {
-  case NullabilityKind::NonNull:
-    string = nullability.second ? "'nonnull'" : "'_Nonnull'";
-    break;
-
-  case NullabilityKind::Nullable:
-    string = nullability.second ? "'nullable'" : "'_Nullable'";
-    break;
-
-  case NullabilityKind::Unspecified:
-    string = nullability.second ? "'null_unspecified'" : "'_Null_unspecified'";
-    break;
-
-  case NullabilityKind::NullableResult:
-    assert(!nullability.second &&
-           "_Nullable_result isn't supported as context-sensitive keyword");
-    string = "_Nullable_result";
-    break;
-  }
-
-  DB.AddString(string);
+  DB.AddString(
+      ("'" +
+       getNullabilitySpelling(nullability.first,
+                              /*isContextSensitive=*/nullability.second) +
+       "'")
+          .str());
   return DB;
 }
 

clang/lib/Basic/IdentifierTable.cpp

@@ -849,6 +849,20 @@ StringRef clang::getNullabilitySpelling(NullabilityKind kind,
   llvm_unreachable("Unknown nullability kind.");
 }
 
+llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, NullabilityKind NK) {
+  switch (NK) {
+  case NullabilityKind::NonNull:
+    return OS << "NonNull";
+  case NullabilityKind::Nullable:
+    return OS << "Nullable";
+  case NullabilityKind::NullableResult:
+    return OS << "NullableResult";
+  case NullabilityKind::Unspecified:
+    return OS << "Unspecified";
+  }
+  llvm_unreachable("Unknown nullability kind.");
+}
+
 diag::kind
 IdentifierTable::getFutureCompatDiagKind(const IdentifierInfo &II,
                                          const LangOptions &LangOpts) {

clang/test/SemaObjC/nullable-result.m

@@ -25,9 +25,9 @@ void test_conversion(void) {
 }
 
 void test_dup(void) {
-  id _Nullable_result _Nullable_result a; // expected-warning {{duplicate nullability specifier _Nullable_result}}
-  id _Nullable _Nullable_result b; // expected-error{{nullability specifier _Nullable_result conflicts with existing specifier '_Nullable'}}
-  id _Nullable_result _Nonnull c; // expected-error{{nullability specifier '_Nonnull' conflicts with existing specifier _Nullable_result}}
+  id _Nullable_result _Nullable_result a; // expected-warning {{duplicate nullability specifier '_Nullable_result'}}
+  id _Nullable _Nullable_result b; // expected-error{{nullability specifier '_Nullable_result' conflicts with existing specifier '_Nullable'}}
+  id _Nullable_result _Nonnull c; // expected-error{{nullability specifier '_Nonnull' conflicts with existing specifier '_Nullable_result'}}
 }
 
 @interface NoContextSensitive