dblaikie added inline comments.

================
Comment at: 
lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string/main.cpp:101
     S.assign(L"!!!!!"); // Set break point at this line.
+    std::string *not_a_string = (std::string *) 0x0;
+    touch_string(*not_a_string);
----------------
This cast isn't needed, right? This could be rewritten more traditionally as:
```
std::string &not_a_string = nullptr;
```
?


================
Comment at: 
lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string/main.cpp:102
+    std::string *not_a_string = (std::string *) 0x0;
+    touch_string(*not_a_string);
     return 0;
----------------
JDevlieghere wrote:
> shafik wrote:
> > This is undefined behavior and I AFAICT this won't pass a sanitized build, 
> > amazingly even if I use `__attribute__((no_sanitize("address", 
> > "undefined")))` : https://godbolt.org/z/4TGPbrYhq
> Definitely UB, but the sanitized bot builds LLDB with the sanitizers, not the 
> test cases, so this should be "fine". 
Seems best avoided if possible though, yeah? What's trying to be demonstrated 
by this test?

What if the function took a std::string* instead of std::string&, and the 
caller doesn't need to dereference that pointer - it could call some other, 
unrelated function to act as a stop-point for the debugger?

& then the "printing a bad string" Could be tested by printing an expression, 
like "p *str" that dereferences in the expression?

Or is the issue only present through the auto-printing of variables in 
parameters in a stack trace, and not present when using the user-defined 
expression evaluator?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D108228/new/

https://reviews.llvm.org/D108228

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