https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94894
Bug ID: 94894 Summary: Premature instantiation of conversion function template during overload resolution Product: gcc Version: 10.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: ppalka at gcc dot gnu.org Target Milestone: --- The following testcase was reduced from a build failure with GCC 10 when compiling LLVM. When considering the overload candidate 'void f(int&)' for the overloaded call 'f(S{})', we try to build up a conversion sequence from 'S' to 'int&' that goes through the conversion operator template with T=int. In doing so we instantiate the conversion operator template, which triggers an instantiation of F<int>::k which triggers a hard error. $ cat testcase.C template <typename T, bool B = false> struct F { static_assert(B); }; struct S { template <typename T, int = F<T>::k> operator T(); }; void f(int&); void f(S); void foo() { f(S{}); } $ g++ testcase.C testcase.C: In instantiation of ‘struct F<int, false>’: testcase.C:9:37: required by substitution of ‘template<class T, int <anonymous> > S::operator T() [with T = int; int <anonymous> = <missing>]’ testcase.C:18:6: required from here testcase.C:4:17: error: static assertion failed 4 | static_assert(B); | ^