Depends on:
* https://github.com/llvm/llvm-project/pull/177921
* https://github.com/llvm/llvm-project/pull/177926
(only last commit is relevant for this review)
This patch emits a workaround suggestion (in the form of a `note:`
diagnostic) when an expression fails due to trying to mutate state/call
functions with CV-qualifiers that are disallowed by C++ language rules
based on the context the expression is evaluated in. The note looks as
follows:
```
(lldb) expr next.method()
˄
╰─ error: 'this' argument to member function 'method' has type 'const Bar', but function is not marked const
note: Ran expression as 'C++14'.
note: note: 'method' declared here
note: Possibly trying to mutate object in a const context. Try running the expression with: expression --c++-ignore-context-qualifiers -- <your expression>
```
We stopped marking `__lldb_expr` with the function qualifiers of the
method LLDB is stopped in ever since
`8bdcd522510f923185cdfaec66c4a78d0a0d38c0`. The assumption was that it
wasn't ever required for correctness (i.e., LLDB should just always
pretend it's in a mutable context). But since function qualifiers affect
overloading in C++, this assumption can lead to unexpected expression
evaluator behaviour. E.g., if a function is overloaded on qualifiers
(`const` vs. `non-const`), the expression evaluator would currently
always call the non-CV qualified overload.
This patch adds function qualifiers to `$__lldb_class::$__lldb_expr`
that resemble the qualifiers of the method that we're stopped in.
However, mutating variables or calling arbitrary member functions from
CV-qualified methods can be useful/is something users already may be
used to. To provide users with the ability to ignore the CV-qualifiers
of the current context, we will provide an expression evaluator flag
that switches this off in a follow-up patch.
