https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86826
Bug ID: 86826
Summary: deduction fails on auto-returning function template
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Reduced from: https://stackoverflow.com/q/51643222/2069064
template <typename T> auto zero(T) { return 0; }
template <typename F> void deduce(F);
void ex() {
#ifdef VAR
auto x = &zero<int>;
#endif
#ifdef FUNC
deduce(&zero<int>);
#endif
}
Compiling with -DVAR succeds. With -DVAR -DFUNC also succeeds. But with just
-DFUNC fails:
<source>: In function 'void ex()':
<source>:9:20: error: no matching function for call to 'deduce(<unresolved
overloaded function type>)'
deduce(&zero<int>);
^
<source>:2:28: note: candidate: 'template<class F> void deduce(F)'
template <typename F> void deduce(F);
^~~~~~
<source>:2:28: note: template argument deduction/substitution failed:
<source>:9:20: note: couldn't deduce template parameter 'F'
deduce(&zero<int>);
^
Compiler returned: 1
If zero() didn't return auto (whether trailing return type or leading return
type), code compiles fine. clang accepts.
