https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120676
Nathaniel Shead <nshead at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |DUPLICATE
CC| |nshead at gcc dot gnu.org
--- Comment #1 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
Thanks for the report! The root cause appears to be due to this known
deficiency GCC's module implementation, see
https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Modules.html:
Textual merging of reachable GM entities
Entities may be multiply defined across different header-units. These must
be de-duplicated, and this is implemented across imports, or when an import
redefines a textually-defined entity. However the reverse is not
implemented—textually redefining an entity that has been defined in an imported
header-unit. A redefinition error is emitted.
---
In this example, the issue is that the 'import CompilerVersions' at the top of
'FunctionTraits.h' declares (hidden) names from e.g. <type_traits>, that are
then redeclared by the '#include <type_traits>' later on in the file. This
confuses the compiler and things go awry.
In general, for now try to ensure that all #includes come before any imports
that may declare the same entities; this will be particularly relevant for
standard library headers of course.
*** This bug has been marked as a duplicate of bug 99000 ***
