diags without usable source location after #127338

[nico]

$ cat repro.cc
class Location {
 public:
  static Location CurrentWithoutFunctionName(
      const char* file_name = __builtin_FILE(),
      int line_number = __builtin_LINE());
};

class NotReachedNoreturnError {
 public:
  explicit NotReachedNoreturnError(
      const Location& location =
          Location::CurrentWithoutFunctionName());

  [[noreturn]] [[clang::nomerge]] [[clang::noinline]] [[clang::not_tail_called]]
      ~NotReachedNoreturnError();
};

#define NOTREACHED() NotReachedNoreturnError()

int f() {
  NOTREACHED();
  return 4;
}

int g() {
  return 4;
  NOTREACHED();
}

$ out/gn/bin/clang -c repro.cc -Wunreachable-code-aggressive
repro.cc:22:10: warning: 'return' will never be executed [-Wunreachable-code-return]
   22 |   return 4;
      |          ^
repro.cc:12:11: warning: code will never be executed [-Wunreachable-code]
   12 |           Location::CurrentWithoutFunctionName());
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings generated.

The first diag points at the line that has the problem. That's good.

The second diag doesn't point even close to the problem. If the macro is in a header and the diag is in a file that uses the macro 20+ times, it's very hard to see where the problem is.

[nico]

Also, it's weird that the diagnostic goes away if e.g. the NotReachedNoreturnError ctor takes an int i = default_int_value() argument instead of the Location argument.

[llvmbot]

@llvm/issue-subscribers-clang-static-analyzer

Author: Nico Weber (nico)

``` $ cat repro.cc class Location { public: static Location CurrentWithoutFunctionName( const char* file_name = __builtin_FILE(), int line_number = __builtin_LINE()); };

class NotReachedNoreturnError {
public:
explicit NotReachedNoreturnError(
const Location& location =
Location::CurrentWithoutFunctionName());

[[noreturn]] [[clang::nomerge]] [[clang::noinline]] [[clang::not_tail_called]]
~NotReachedNoreturnError();
};

#define NOTREACHED() NotReachedNoreturnError()

int f() {
NOTREACHED();
return 4;
}

int g() {
return 4;
NOTREACHED();
}

$ out/gn/bin/clang -c repro.cc -Wunreachable-code-aggressive
repro.cc:22:10: warning: 'return' will never be executed [-Wunreachable-code-return]
22 | return 4;
| ^
repro.cc:12:11: warning: code will never be executed [-Wunreachable-code]
12 | Location::CurrentWithoutFunctionName());
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2 warnings generated.

The first diag points at the line that has the problem. That's good.

The second diag doesn't point even close to the problem. If the macro is in a header and the diag is in a file that uses the macro 20+ times, it's very hard to see where the problem is.

</details>