[DeclPrinter] Fix two cases that crash clang -ast-print.

[tra]

Summary

Both crashes are related to handling anonymous structures.

• clang didn't handle () around an anonymous struct variable.
• clang also crashed on syntax errors that could lead to other syntactic constructs following the declaration of an anonymous struct. While the code is invalid, that's not a good reason to panic compiler.

[jlebar]

I strongly approve of fixing these crashes, but I don't think I can say with confidence whether this change is correct.

[tra]

@arphaman: ping.

[tra]

@bkramer Can you take a look at the patch?

[bkramer]

This should be fine.

clang/lib/AST/DeclPrinter.cpp

DeclPrinter Printer(Out, Policy, getASTContext(), Indentation,
                       PrintInstantiation);
   Printer.Visit(const_cast<Decl*>(this));
 }
 
 static QualType GetBaseType(QualType T) {
   // FIXME: This should be on the Type class!
   QualType BaseType = T;
   while (!BaseType->isSpecifierType()) {
-    if (isa<TypedefType>(BaseType))
-      break;
-    else if (const PointerType* PTy = BaseType->getAs<PointerType>())
+    if (const PointerType *PTy = BaseType->getAs<PointerType>())
       BaseType = PTy->getPointeeType();
     else if (const BlockPointerType *BPy = BaseType->getAs<BlockPointerType>())
       BaseType = BPy->getPointeeType();
     else if (const ArrayType* ATy = dyn_cast<ArrayType>(BaseType))
       BaseType = ATy->getElementType();
     else if (const FunctionType* FTy = BaseType->getAs<FunctionType>())
       BaseType = FTy->getReturnType();
     else if (const VectorType *VTy = BaseType->getAs<VectorType>())
       BaseType = VTy->getElementType();
     else if (const ReferenceType *RTy = BaseType->getAs<ReferenceType>())
       BaseType = RTy->getPointeeType();
     else if (const AutoType *ATy = BaseType->getAs<AutoType>())
       BaseType = ATy->getDeducedType();
+    else if (const ParenType *PTy = BaseType->getAs<ParenType>())
+      BaseType = PTy->desugar();
     else
-      llvm_unreachable("Unknown declarator!");
+      // This must be a syntax error.
+      break;
   }
   return BaseType;
 }
 
 static QualType getDeclType(Decl* D) {
   if (TypedefNameDecl* TDD = dyn_cast<TypedefNameDecl>(D))
     return TDD->getUnderlyingType();
   if (ValueDecl* VD = dyn_cast<ValueDecl>(D))

clang/test/Sema/ast-print.c

 struct blah {
   struct {
     struct {
       int b;
     };
   };
 };
 
+// This used to crash clang.
+struct {
+}(s1);
+
 int foo(const struct blah *b) {
   // CHECK: return b->b;
   return b->b;
 }
 
 int arr(int a[static 3]) {
   // CHECK: int a[static 3]
   return a[2];

clang/test/SemaCXX/ast-print-crash.cpp

+// RUN: not %clang_cc1 -triple %ms_abi_triple -ast-print %s -std=gnu++11 \
+// RUN:     | FileCheck %s
+
+// The test compiles a file with a syntax error which used to cause a crash with
+// -ast-print. Compilation fails due to the syntax error, but compiler should
+// not crash and print out whatever it manager to parse.
+
+// CHECK:      struct {
+// CHECK-NEXT: } dont_crash_on_syntax_error;
+// CHECK-NEXT: decltype(nullptr) p;
+struct {
+} dont_crash_on_syntax_error /* missing ; */ decltype(nullptr) p;