Fix dereferencing null pointer

[zloyrobot]

Summary

All callers of Demangler::parseTagUniqueName check 'Demangler.Error' and assume that 'Error is false' means 'return value is not null'

[thakis]

test?

[zloyrobot]

In D60963#1474783, @thakis wrote:

test?

Would you please advise me on what kind of test I should add for such fix?

[zloyrobot]

kind reminder

[thakis]

Add a test that fails without the code change and that passes with it. I don't know under which conditions this change is needed, so I apologize that I can't make a more concrete suggestion.

[kwk]

llvm/lib/Demangle/MicrosoftDemangle.cpp

737

Why not change the return type to llvm::Expected<TagTypeNode>? Then you have one return value that is either an error (when return value evaluates to false) or the value. On top of just a boolean Error variable you then can also use the return value to store error texts if you need them. Now, I don't know if the Error member is used anywhere else.

[thakis]

llvm/lib/Demangle/MicrosoftDemangle.cpp

737

Error is not a parameter, it's class-level state that's used pervasively in this file.

[kwk]

llvm/lib/Demangle/MicrosoftDemangle.cpp

737

Okay, was just a thought. Thanks for explaining.

llvm/lib/Demangle/MicrosoftDemangle.cpp

SymbolNode *Demangler::parse(StringView &MangledName) {
   }
 
   if (Error)
     return nullptr;
 
   return Symbol;
 }
 
 TagTypeNode *Demangler::parseTagUniqueName(StringView &MangledName) {
-  if (!MangledName.consumeFront(".?A"))
+  if (!MangledName.consumeFront(".?A")) {
+    Error = true;
     return nullptr;
+  }
   MangledName.consumeFront(".?A");
-  if (MangledName.empty())
+  if (MangledName.empty()) {
+    Error = true;
     return nullptr;
+  }
 
   return demangleClassType(MangledName);
 }
 
 // <type-encoding> ::= <storage-class> <variable-type>
 // <storage-class> ::= 0  # private static member
 //                 ::= 1  # protected static member
 //                 ::= 2  # public static member