[clang] Clang 19 regression "no member named" in templated class method

[vient]

template<class C>
class A {
  void call_f() {
      this->f();
  }
};

Compiles with Clang 18 but gives error: no member named 'f' in 'A<C>' with Clang 19 https://godbolt.org/z/vzjYf6Kxd

Caught while trying to compile code using simdjson

.conan2/p/simdjfa4aaa94b0935/p/include/simdjson.h:6101:13: error: no member named 'print_newline' in 'base_formatter<formatter>'
 6101 |       this->print_newline();
      |       ~~~~  ^

https://github.com/simdjson/simdjson/blob/v3.2.3/include/simdjson/dom/serialization.h#L59-L61

[DimitryAndric]

See also simdjson/simdjson#2187, and https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=280590

[DimitryAndric]

Either f061a39 or 8009bbe (both by @sdkrystian ) seems a likely cause, but not sure if this was the intended effect?

[MitalAshok]

Note that GCC15 also stops accepting this: https://godbolt.org/z/n1vrM44q5

Did this ever compile when the member function was used? A<T>{}.call_f() doesn't seem valid for any T so this does seem ill-formed (NDR)

[sdkrystian]

@DimitryAndric @vient Clang aims to diagnose uninstantiable templates prior to instantiation whenever possible. In the provided example, this->f() will never instantiate to a valid expression, hence the diagnostic. See the discussion here.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: vient (vient)

```c++ template<class C> class A { void call_f() { this->f(); } }; ``` Compiles with Clang 18 but gives `error: no member named 'f' in 'A<C>'` with Clang 19 https://godbolt.org/z/vzjYf6Kxd

Caught while trying to compile code using simdjson

.conan2/p/simdjfa4aaa94b0935/p/include/simdjson.h:6101:13: error: no member named 'print_newline' in 'base_formatter<formatter>'
 6101 |       this->print_newline();
      |       ~~~~  ^

https://github.com/simdjson/simdjson/blob/v3.2.3/include/simdjson/dom/serialization.h#L59-L61