[ClangImporter] Handle diagnostics about cast types in macros

The importer handles these by first trying to look up the type by name
using Clang's Sema, but that lookup can cause diagnostics to be
emitted (usually availability diagnostics). We could try to figure out
how to propagate that to the macro when we import it, but for now just
drop the macro instead if there are any diagnostics emitted when
looking up the type.

This will be a small source compatibility break if anyone was using a
macro defined in terms of a type that's deprecated or that has partial
availability; the macro will now silently not be imported instead of
producing an unsilenceable warning.

rdar://problem/36528212

Author: jrose-apple

lib/ClangImporter/ImportMacro.cpp

@@ -21,6 +21,7 @@
 #include "clang/AST/Expr.h"
 #include "clang/Lex/MacroInfo.h"
 #include "clang/Lex/Preprocessor.h"
+#include "clang/Sema/DelayedDiagnostic.h"
 #include "clang/Sema/Sema.h"
 #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
 #include "swift/AST/ASTContext.h"
@@ -361,10 +362,16 @@ static ValueDecl *importMacro(ClangImporter::Implementation &impl,
       }
       auto identifierName = identifierInfo->getName();
       auto &identifier = impl.getClangASTContext().Idents.get(identifierName);
+
+      clang::sema::DelayedDiagnosticPool diagPool{
+          impl.getClangSema().DelayedDiagnostics.getCurrentPool()};
+      auto diagState = impl.getClangSema().DelayedDiagnostics.push(diagPool);
       auto parsedType = impl.getClangSema().getTypeName(identifier,
                                                         clang::SourceLocation(),
                                                         /*scope*/nullptr);
-      if (parsedType) {
+      impl.getClangSema().DelayedDiagnostics.popWithoutEmitting(diagState);
+
+      if (parsedType && diagPool.empty()) {
         castType = parsedType.get();
       } else {
         return nullptr;

test/ClangImporter/macros.swift

@@ -172,3 +172,9 @@ func testRecursion() {
   _ = RECURSION_IN_EXPR2 // expected-error {{use of unresolved identifier 'RECURSION_IN_EXPR2'}}
   _ = RECURSION_IN_EXPR3 // expected-error {{use of unresolved identifier 'RECURSION_IN_EXPR3'}}
 }
+
+func testNulls() {
+  let _: Int = UNAVAILABLE_ONE // expected-error {{use of unresolved identifier 'UNAVAILABLE_ONE'}}
+  let _: Int = DEPRECATED_ONE // expected-error {{use of unresolved identifier 'DEPRECATED_ONE'}}
+  let _: Int = OKAY_TYPED_ONE // expected-error {{cannot convert value of type 'okay_t' (aka 'UInt32') to specified type 'Int'}}
+}

test/Inputs/clang-importer-sdk/usr/include/macros.h

@@ -144,3 +144,12 @@
 
 #define RECURSION_WITH_EXPR3 RECURSION_WITH_EXPR3_HELPER + 1
 #define RECURSION_WITH_EXPR3_HELPER RECURSION_WITH_EXPR3 + 1
+
+
+// Casts with problematic types
+#define UNAVAILABLE_ONE ((unavailable_t)1)
+typedef unsigned unavailable_t __attribute__((unavailable));
+#define DEPRECATED_ONE ((deprecated_t)1)
+typedef unsigned deprecated_t __attribute__((deprecated));
+#define OKAY_TYPED_ONE ((okay_t)1)
+typedef unsigned okay_t;