mkhelper.mk.in: an example of two-step Fortran compilation.

.gitignore

@@ -21,6 +21,7 @@ Makefile
 
 # Build stage files
 *.a
+*.modstamp
 *.o
 /main
 /mod

configure

@@ -616,6 +616,9 @@ FC_INC_ORDER_PP_f90
 FC_INC_FLAG_PP_f90
 FC_INC_ORDER
 FC_INC_FLAG
+SEPARATE_MODS_DISABLED
+SEPARATE_MODS_ENABLED
+FC_MOD_ONLY
 FC_ROOT_SMOD
 FC_SMOD_FILE_EXT
 FC_SMOD_FILE_INFIX
@@ -687,6 +690,7 @@ ac_subst_files=''
 ac_user_opts='
 enable_option_checking
 enable_rpaths
+enable_separate_mods
 enable_silent_rules
 enable_additional_mods
 enable_openmp
@@ -1356,6 +1360,8 @@ Optional Features:
   --enable-rpaths         prepend LDFLAGS with additional linker flags to add
                           directories specified with -L flags to the runtime
                           library search path (RPATH) [default=yes]
+  --enable-separate-mods  enable the two-step compilation of the Fortran
+                          source files [default=yes]
   --enable-silent-rules   less verbose build output (undo: "make V=1")
                           [default=yes]
   --enable-additional-mods
@@ -3599,6 +3605,75 @@ else
 
 fi
 
+# Check whether --enable-separate-mods was given.
+if test "${enable_separate_mods+set}" = set; then :
+  enableval=$enable_separate_mods;
+else
+  enable_separate_mods=yes
+fi
+
+if test "x$enable_separate_mods" = xyes; then :
+        { $as_echo "$as_me:${as_lineno-$LINENO}: checking for Fortran compiler flag needed to generate module files but no object files" >&5
+$as_echo_n "checking for Fortran compiler flag needed to generate module files but no object files... " >&6; }
+if ${acx_cv_fc_module_only_flag+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  acx_cv_fc_module_only_flag=unknown
+      as_dir=conftest.dir; as_fn_mkdir_p
+      cd conftest.dir
+      cat > conftest.$ac_ext <<_ACEOF
+      module conftest_module
+      end module
+_ACEOF
+      if test "x$acx_cv_fc_module_naming_upper" = xyes; then :
+  acx_tmp="CONFTEST_MODULE.$acx_cv_fc_module_naming_ext"
+else
+  acx_tmp="conftest_module.$acx_cv_fc_module_naming_ext"
+fi
+      acx_save_FCFLAGS=$FCFLAGS
+      for acx_flag in '-syntax-only' '-fsyntax-only' '-Msyntax-only' '-otype=mod' '-M' '-dB -M2179'; do
+        FCFLAGS="$acx_save_FCFLAGS $acx_flag"
+        if { { ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:${as_lineno-$LINENO}: $ac_try_echo\""
+$as_echo "$ac_try_echo"; } >&5
+  (eval "$ac_compile") 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; } && test -f $acx_tmp && test ! -f conftest.$ac_objext; then :
+  acx_cv_fc_module_only_flag=$acx_flag; break
+else
+  rm -f $acx_tmp conftest.$ac_objext
+fi
+      done
+      FCFLAGS=$acx_save_FCFLAGS
+      cd ..
+      rm -rf conftest.dir
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $acx_cv_fc_module_only_flag" >&5
+$as_echo "$acx_cv_fc_module_only_flag" >&6; }
+   if test "x$acx_cv_fc_module_only_flag" = xunknown; then :
+  { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
+$as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
+as_fn_error $? "unable to detect Fortran compiler flag needed to generate module files but no object files
+See \`config.log' for more details" "$LINENO" 5; }
+else
+  FC_MOD_ONLY=$acx_cv_fc_module_only_flag
+fi
+   SEPARATE_MODS_ENABLED=''
+   SEPARATE_MODS_DISABLED='#'
+else
+  FC_MOD_ONLY=
+   SEPARATE_MODS_ENABLED='#'
+   SEPARATE_MODS_DISABLED=''
+fi
+
+
+
+
       { $as_echo "$as_me:${as_lineno-$LINENO}: checking for Fortran compiler flag needed to specify search paths for the \"INCLUDE\" statement" >&5
 $as_echo_n "checking for Fortran compiler flag needed to specify search paths for the \"INCLUDE\" statement... " >&6; }
 if ${acx_cv_fc_ftn_include_flag+:} false; then :

configure.ac

@@ -73,6 +73,22 @@ ACX_FC_MODULE_SNAMING(
 ACX_FC_MODULE_ROOT_SMOD(
   [AC_SUBST([FC_ROOT_SMOD], [$acx_cv_fc_module_root_smod])])
 
+AC_ARG_ENABLE([separate-mods],
+  [AS_HELP_STRING([--enable-separate-mods],
+     [enable the two-step compilation of the Fortran source files
+@<:@default=yes@:>@])], [],
+  [enable_separate_mods=yes])
+AS_VAR_IF([enable_separate_mods], [yes],
+  [ACX_FC_MODULE_ONLY_FLAG([FC_MOD_ONLY=$acx_cv_fc_module_only_flag])
+   SEPARATE_MODS_ENABLED=''
+   SEPARATE_MODS_DISABLED='#'],
+  [FC_MOD_ONLY=
+   SEPARATE_MODS_ENABLED='#'
+   SEPARATE_MODS_DISABLED=''])
+AC_SUBST([FC_MOD_ONLY])
+AC_SUBST([SEPARATE_MODS_ENABLED])
+AC_SUBST([SEPARATE_MODS_DISABLED])
+
 ACX_FC_INCLUDE_FLAG(
   [AC_SUBST([FC_INC_FLAG], [$acx_cv_fc_ftn_include_flag])])
 ACX_FC_INCLUDE_ORDER(

mkhelper.mk.in

@@ -17,6 +17,7 @@ bundled_subdirs:= \
 
 # Path to the directory with the Fortran module files:
 moddir:= mod
+@SEPARATE_MODS_ENABLED@moddir_null:= $(moddir)/null
 
 # Paths to the installation directories:
 prefix= @prefix@
@@ -36,7 +37,7 @@ SHELL= @SHELL@
 
 # Fortran compiler flags:
 FCFLAGS= @FCFLAGS@
-makefile_FCFLAGS= @FC_MOD_IN@$(moddir) @FC_MOD_OUT@$(moddir) @FC_INC_FLAG@$(srcdir)/src/include @FC_INC_FLAG_PP_f90@$(srcdir)/src/include @config_FCFLAGS@ @BUNDLED_FCFLAGS@ @NETCDF_FCFLAGS@
+makefile_FCFLAGS= @FC_MOD_IN@$(moddir) @FC_INC_FLAG@$(srcdir)/src/include @FC_INC_FLAG_PP_f90@$(srcdir)/src/include @config_FCFLAGS@ @BUNDLED_FCFLAGS@ @NETCDF_FCFLAGS@
 
 # Archiver flags:
 ARFLAGS= @ARFLAGS@
@@ -62,6 +63,7 @@ silent_DEPGEN= @echo "  DEPGEN  " $@;
 silent_FC=     @echo "  FC      " $@;
 silent_FCLD=   @echo "  FCLD    " $@;
 silent_MKDIR=  @echo "  MKDIR   " $(@D);
+silent_MOD=    @echo "  MOD    <" $<;
 endif
 
 # Path suffixes (i.e. without $(srcdir) prefix) of the source files:
@@ -119,6 +121,7 @@ mostlyclean: $(bundled_subdirs)
 	rm -f $(moddir)/*.@FC_MOD_FILE_EXT@ $(moddir)/*.@[email protected]
 	rm -f $(moddir)/*.@FC_SMOD_FILE_EXT@ $(moddir)/*.@[email protected]
 	rm -f $(lib_files) $(exe_files) $(exe_files:=.dSYM)
+@SEPARATE_MODS_ENABLED@	rm -rf $(moddir_null) $(src_files:.f90=.modstamp)
 
 # Delete files generated at the building stage:
 clean: mostlyclean
@@ -162,9 +165,15 @@ $(exe_files): | $(dir_files)
 	$(silent_FCLD)$(FC) -o $@ $(makefile_FCFLAGS) $(FCFLAGS) $(LDFLAGS) $+ $(makefile_LIBS) $(LIBS)
 
 # Fortran compilation rule:
-%.@OBJEXT@: %.f90 | $(dir_files) $(bundled_subdirs) sanitize-mod-proxies
-	$(silent_FC)$(FC) -o $@ -c $(makefile_FCFLAGS) $(FCFLAGS) @FCFLAGS_f90@ $<
+@SEPARATE_MODS_ENABLED@%.@OBJEXT@: %.f90 | $(dir_files) $(bundled_subdirs) sanitize-mod-proxies
+@SEPARATE_MODS_ENABLED@	$(silent_FC)@MKDIR_P@ $(moddir_null)/$@ && $(FC) -o $@ -c @FC_MOD_OUT@$(moddir_null)/$@ $(makefile_FCFLAGS) $(FCFLAGS) @FCFLAGS_f90@ $<
 
+@SEPARATE_MODS_DISABLED@%.@OBJEXT@: %.f90 | $(dir_files) $(bundled_subdirs) sanitize-mod-proxies
+@SEPARATE_MODS_DISABLED@	$(silent_FC)$(FC) -o $@ -c @FC_MOD_OUT@$(moddir) $(makefile_FCFLAGS) $(FCFLAGS) @FCFLAGS_f90@ $<
+
+# Fortran module generation rule:
+@SEPARATE_MODS_ENABLED@%.modstamp: %.f90 | $(dir_files) $(bundled_subdirs) sanitize-mod-proxies
+@SEPARATE_MODS_ENABLED@	$(silent_MOD)$(FC) -c @FC_MOD_OUT@$(moddir) $(makefile_FCFLAGS) $(FCFLAGS) @FC_MOD_ONLY@ @FCFLAGS_f90@ $< && touch $@
 
 # Fortran module file tracking rule:
 $(moddir)/%.@[email protected]:
@@ -197,8 +206,11 @@ sanitize-mod-proxies:
 	$(silent_MKDIR)@MKDIR_P@ $(@D) && touch $@
 
 # Fortran dependency generation rule:
+@SEPARATE_MODS_ENABLED@fc_mod_stamp_name= $(@:.f90.d=.modstamp)
+@SEPARATE_MODS_DISABLED@fc_mod_stamp_name= $(@:.f90.d=.o)
+
 %.f90.d: %.f90 mkhelper.mk | $(dir_files)
-	$(silent_DEPGEN)$(DEPGEN) $(DEPGEN_args) -o $@ --obj-name $(@:.f90.d=.@OBJEXT@) -i $< -- $(DEPGEN_FCFLAGS) $(makefile_FCFLAGS) $(FCFLAGS)
+	$(silent_DEPGEN)$(DEPGEN) $(DEPGEN_args) -o $@ --obj-name $(@:.f90.d=.o) --fc-mod-stamp-name $(fc_mod_stamp_name) -i $< -- $(DEPGEN_FCFLAGS) @FC_MOD_OUT@$(moddir) $(makefile_FCFLAGS) $(FCFLAGS)
 
 # Dependency generation rule for undetectable Fortran dependencies:
 extra_f90.d: mkhelper.mk