Fix LDFLAGS definition and usage

`ld` flags are currently specified incorrectly. For example:
1. `-lnetcdf` is not required since it is a dependency of the netCDF
Fortran library - only `-lnetcdff` is needed.
2. `ld` flags are being split across two variables: `LDFLAGS` and `LD`
when there should only be one (`LD` typically refers to the path  to the
`ld` executable). Having the flags split across two variables allows for
the flags to be passed to the compiler in an inconsistent way.
See #198 for more details.

This change removes the `LD` variable and any hard-coded linker flags or
include flags in the Makefile or build script. Linker flags and include
flags are replaced with a query to `pkg-config` so that the build system
is insulated from changes to library versions and dependencies.

Fixes #198

src/offline/Makefile

@@ -147,9 +147,6 @@ PROG_MPI = cable-mpi
 # from the compiled object files
 OBJS := ${LSRC:.F90=.o}
 
-#compiler switches and flags
-CINC = -I$(NCMOD)
-
 #suffixes we use
 .SUFFIXES:
 .SUFFIXES: .F90 .o
@@ -162,11 +159,11 @@ SUPPRESS_FLAGS := -warn nostderrors -diag-disable 10145
 # the first target is the default target
 .PHONY: serial
 serial: cable_driver.F90 $(OBJS)
-	$(FC) $(SUPPRESS_FLAGS) $(CFLAGS) $(LDFLAGS) $(LD) -o $(PROG_SERIAL) $^ $(CINC)
+	$(FC) $(SUPPRESS_FLAGS) $(CFLAGS) -o $(PROG_SERIAL) $^ $(CINC) $(LDFLAGS)
 
 .PHONY: mpi
 mpi: cable_mpidrv.F90 cable_mpicommon.o cable_mpimaster.o cable_mpiworker.o pop_mpi.o $(OBJS)
-	$(FC) $(SUPPRESS_FLAGS) $(CFLAGS) $(LDFLAGS) -o $(PROG_MPI) $^ $(CINC) $(LD)
+	$(FC) $(SUPPRESS_FLAGS) $(CFLAGS) -o $(PROG_MPI) $^ $(CINC) $(LDFLAGS)
 
 cable_mpicommon.o: cable_mpicommon.F90 $(OBJS)
 pop_mpi.o: pop_mpi.F90 cable_mpicommon.o $(OBJS)

src/offline/build3.sh

@@ -15,12 +15,22 @@ host_gadi()
    module purge
    module add intel-compiler/2019.5.281
    module add netcdf/4.6.3
+   # This is required so that the netcdf-fortran library is discoverable by
+   # pkg-config (Note, we manually prepend to PKG_CONFIG_PATH instead of
+   # using `module prepend-path` so that we can invoke this script successfully
+   # in benchcab):
+   export PKG_CONFIG_PATH=${NETCDF_BASE}/lib/Intel/pkgconfig/:$PKG_CONFIG_PATH
+
+   if ! pkg-config --exists netcdf-fortran; then
+       echo ''
+       echo 'Unable to find netcdf-fortran via pkg-config. Exiting...'
+       echo ''
+       exit 1
+   fi
 
-   export NCDIR=$NETCDF_ROOT'/lib/Intel'
-   export NCMOD=$NETCDF_ROOT'/include/Intel'
    export CFLAGS='-O2 -fp-model precise '
-   export LDFLAGS='-L'$NCDIR
-   export LD='-lnetcdf -lnetcdff'
+   export LDFLAGS=`pkg-config --libs netcdf-fortran`
+   export CINC=`pkg-config --cflags netcdf-fortran`
 
    if [[ $1 = 'mpi' ]]; then
       module add intel-mpi/2019.5.281
@@ -144,9 +154,6 @@ build_status()
       echo  ''
       echo 'Oooops. Something went wrong'
       echo  ''
-      echo 'Other than compiler messages, known build issues:'
-      echo 'Some systems require additional library. '
-      echo 'e.g. Edit Makefile; add -lnetcdff to LD = ...'
    fi
    exit
 }