[llvm-bugs] [Bug 97365] clang++-19: Incorrect warning `unused-private-field` even though member is used in constructor.

[LLVM Bugs via llvm-bugs]

Issue	97365
Summary	clang++-19: Incorrect warning `unused-private-field` even though member is used in constructor.
Labels	clang
Assignees
Reporter	greg7mdp

    ### test program: `Wunused-private-field.cpp`

```
// compiling this with `clang++-19 -Wall -c Wunused-private-field.cpp`
//
// produces a warning (even though `c` is used in the lambda)
//   `Wunused-private-field.cpp:19:13: warning: private field 'c' is not used [-Wunused-private-field]`
// ----------------------------------------------------------------------------------------------------
#include <functional>

struct node;

struct cluster {
   void ping();
};

void register_cb(std::function<void()>);

struct node {
   node(cluster&);
private:
   cluster &c;
};

node::node(cluster& c) : c(c) {
   register_cb([&]() { c.ping(); });
   c.ping();
}
```

### compiler output:

```
~/test ❯ clang++-19 -Wall -c Wunused-private-field.cpp                                                                                                                                     
Wunused-private-field.cpp:19:13: warning: private field 'c' is not used [-Wunused-private-field]
   19 |    cluster &c;
      |             ^
1 warning generated.
```

### compiler version

```
~/test ❯ clang++-19 --version                                                                                                                                                              
Ubuntu clang version 19.0.0 (++20240630031615+ac84ada9a169-1~exp1~20240630151739.1777)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-19/bin
```

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