https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125230
Nathaniel Shead <nshead at gcc dot gnu.org> changed:
What |Removed |Added
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See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=101126
CC| |nshead at gcc dot gnu.org
--- Comment #11 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
(In reply to Rainer Deyke from comment #8)
> Consensus at [email protected] seems to be that the set of
> "importable headers" is meant to be a finite closed set of
> implementation-provided headers that does not include user-provided headers.
> a.hpp in my example is not supposed to be an "importable header". Importing
> it should not turn it into an importable header. Precompiling it should not
> turn it into turn it into an "importable header". An #include of this
> header be turned into an import.
The actual issue here is PR101126; we don't support precompiled headers with
modules currently. When you compile a header with modules support enabled, you
are promising the compiler that this is an importable header and are building a
CMI for it.
The default module mapper (for simple command-line usage, not really intended
for proper build systems) then assumes that any header it can see that's been
built is a valid importable header. If you choose to instead use a custom
module mapper you can indicate which headers are intended to be importable (and
thus should undergo include translation) and which are not. See also
https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Module-Preprocessing.html:
> Include translation converts #include, #include_next and #import directives
> to internal import declarations. Whether a particular directive is translated
> is controlled by the module mapper.
The mapper protocol itself is described in
https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Module-Mapper.html and
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1184r2.pdf; see
section 4.9 of the latter to determine whether given headers are meant to be
part of the importable header list or not.
