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From: "klaus.doldinger64 at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109718] New: Dependency generation for header-units and
 modules not possible
Date: Wed, 03 May 2023 16:16:15 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109718

            Bug ID: 109718
           Summary: Dependency generation for header-units and modules not
                    possible
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: klaus.doldinger64 at googlemail dot com
  Target Milestone: ---

To generate make-dependencies I use the following command line:

g++ -c -MD -MG -std=3Dc++23 -fconcepts -fmodules-ts test.cc

where test.cc is:

-----------------
import <array>;

int main() {
}
-----------------


It gives the error:

cc1plus: error: '-MG' may only be used with '-M' or '-MM'

Removing -MG gives also an error, because the precompiled header does not y=
et
exist:

/usr/local/include/c++/14.0.0/iostream: error: failed to read compiled modu=
le:
No such file or directory
/usr/local/include/c++/14.0.0/iostream: note: compiled module file is
'gcm.cache/./usr/local/include/c++/14.0.0/iostream.gcm'
/usr/local/include/c++/14.0.0/iostream: note: imports must be built before
being imported
/usr/local/include/c++/14.0.0/iostream: fatal error: returning to the gate =
for
a mechanical issue

So, it looks that there is no possiblity to create a valid dependency file =
with
gcc.=