c++: diagnosing if-stmt with non-constant branches [PR105050]
When an if-stmt is determined to be non-constant because both of its
branches are non-constant, we issue a somewhat generic error which,
since the error also points to the 'if' token, misleadingly suggests
the condition is at fault:
constexpr-105050.C:8:3: error: expression ‘<statement>’ is not a constant expression
8 | if (p != q && *p < 0)
| ^~
This patch clarifies the error message to instead read:
constexpr-105050.C:8:3: error: neither branch of ‘if’ is a constant expression
8 | if (p != q && *p < 0)
| ^~
PR c++/105050
gcc/cp/ChangeLog:
* constexpr.cc (potential_constant_expression_1) <case IF_STMT>:
Clarify error message when a if-stmt is non-constant because its
branches are non-constant.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-105050.C: New test.