[Sema] Null check in BuildDeclarationNameExpr

[kongyi]

Summary

Qualtype may point to null if we cannot infer its type yet.

Fixes PR33843

[kongyi]

ping...

[rnk]

lgtm

lib/Sema/SemaExpr.cpp

ExprResult Sema::BuildDeclarationNameExpr(
   // must be the subject of a pointer-to-member expression.
   if (IndirectFieldDecl *indirectField = dyn_cast<IndirectFieldDecl>(VD))
     if (!indirectField->isCXXClassMember())
       return BuildAnonymousStructUnionMemberReference(SS, NameInfo.getLoc(),
                                                       indirectField);
 
   {
     QualType type = VD->getType();
+    if (type.isNull())
+      return ExprError();
     if (auto *FPT = type->getAs<FunctionProtoType>()) {
       // C++ [except.spec]p17:
       //   An exception-specification is considered to be needed when:
       //   - in an expression, the function is the unique lookup result or
       //     the selected member of a set of overloaded functions.
       ResolveExceptionSpec(Loc, FPT);
       type = VD->getType();
     }

test/SemaCXX/typo-correction-crash.cpp

-// RUN: %clang_cc1 -fsyntax-only -std=c++14 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify %s
 auto check1() {
   return 1;
   return s; // expected-error {{use of undeclared identifier 's'}}
 }
 
 int test = 11; // expected-note {{'test' declared here}}
 auto check2() {
   return "s";
   return tes; // expected-error {{use of undeclared identifier 'tes'; did you mean 'test'?}}
 }
 
 namespace BarNamespace {
 namespace NestedNamespace { // expected-note {{'BarNamespace::NestedNamespace' declared here}}
 typedef int type;
 }
 }
 struct FooRecord { };
 FooRecord::NestedNamespace::type x; // expected-error {{no member named 'NestedNamespace' in 'FooRecord'; did you mean 'BarNamespace::NestedNamespace'?}}
 
 void cast_expr(int g) { +int(n)(g); } // expected-error {{undeclared identifier 'n'}}
+
+void bind() { for (const auto& [test,_] : _test_) { }; } // expected-error {{undeclared identifier '_test_'}}