[Bug fortran/114922] New: fsyntax-only need the modules

[axel.ehrich--- via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114922

Bug ID: 114922
   Summary: fsyntax-only need the modules
   Product: gcc
   Version: 13.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: fortran
  Assignee: unassigned at gcc dot gnu.org
  Reporter: axel.ehr...@tu-clausthal.de
  Target Milestone: ---

Created attachment 58087
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58087&action=edit
Short Example for this problem

I encounter the following problem with gfortran: When I try to compile a file
(such as the one attached) with the options -c -fsyntax-only,
that is

"gfortran -c -fsyntax-only syntax-only_test.f90"

I receive the following error message:
--
syntax-only_test.f90:2:5:

2 | use module
  | 1
Fatal Error: Cannot open module file 'module.mod' for reading at (1): No such
file or directory
compilation terminated.
---

One purpose of the option "-fsyntax-only" is to create the module files (.mod),
however, without doing the compilation that would require module files. The
observed behaviour appears like a bug in gfortran.

I used 
https://aoterodelaroza.github.io/devnotes/modern-fortran-makefiles/
to look how i can solve the problem with the depends of mod files.

Best regards,
Axel

[Bug fortran/114922] fsyntax-only need the modules

[axel.ehrich--- via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114922

--- Comment #3 from Axel Ehrich  ---
The question is related to the actual purpose of the option -fsyntax only:

In my understanding, the intention of the option -fsyntax-only is to construct
the module files needed to compile the code. A  build process would involve two
steps: Step 1: construct all module files with gfortran -fsyntax only. Step 2:
construct the object files without this option, while relying on the presence
of all module files. (I have found this recipe on the internet and consider it
valuable.)

Alternatively, the purpose of -fsyntax-only could be to save compile time by a
doing quick first check before entering the time consuming parts of the
compilation.  If this syntax check goes so far that it requires the module
files already, the goal mentioned above cannot be reached.

[Bug fortran/114922] fsyntax-only need the modules

[axel.ehrich--- via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114922

--- Comment #5 from Axel Ehrich  ---
Thank you for the explanation. This resolves the issue.