https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67185
Bug ID: 67185
Summary: [concepts] Link error on ODR-use of constexpr
constrained variable template partial specialization
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: Casey at Carter dot net
Target Milestone: ---
Created attachment 36170
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36170&action=edit
Test case
r226750 compiles this program compiles correctly:
template <class T>
concept bool C = false;
template <class>
constexpr bool trait = false;
template <C T>
constexpr bool trait<T> = true;
const bool& f() { return trait<int>; }
int main() {}
since it uses the base template, but not this one:
template <class T>
concept bool C = true;
template <class>
constexpr bool trait = false;
template <C T>
constexpr bool trait<T> = true;
const bool& f() { return trait<int>; }
int main() {}
The error is:
~/gcc6-r226750/bin/g++ -std=gnu++1z foo2.cpp
/tmp/ccfAOK5N.o: In function `f()':
foo2.cpp:(.text+0x5): undefined reference to `trait'
collect2: error: ld returned 1 exit status
Inspection of the assembly output (target is Linux x64) shows that the first
program uses the symbol "_Z5traitIiE" for "trait<int>" and the second the
symbol "_ZL5trait". I suspect this discrepancy is the crux of the problem.
