https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123738
Bug ID: 123738
Summary: "is not a constant expression" in code using a string
literal operator template
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: sberg.fun at gmail dot com
CC: nshead at gcc dot gnu.org
Target Milestone: ---
Starting with
<https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=c388d56a889469cf05a1512403e3267af7bb62be>
"c++: Fold non-ODR usages of potentially constant values early [PR120005]"
towards GCC 16,
> $ cat test.cc
> struct OStringLiteral {
> constexpr OStringLiteral(char const *) {}
> int str = 0;
> };
>
> template<OStringLiteral L> struct OStringHolder {
> static constexpr auto & literal = L;
> };
>
> struct OString {
> template<OStringLiteral L> constexpr OString(OStringHolder<L> const &
> holder):
> p(&holder.literal.str) {}
> int const * p;
> };
>
> template<OStringLiteral L> constexpr OStringHolder<L> operator ""_tstr() {
> return OStringHolder<L>();
> }
>
> constexpr OString s = ""_tstr;
started to fail with
> $ g++ -std=c++20 -fsyntax-only test.cc
> test.cc:20:23: error: ‘OString{(&<anonymous>.OStringLiteral::str)}’ is not a
> constant expression
> 20 | constexpr OString s = ""_tstr;
> | ^~~~~~~
> test.cc:20:23: error: ‘OString(operator""_tstr<OStringLiteral{0}>())’ is not
> a constant expression because it refers to an incompletely initialized
> variable
