Difficulties installing plplot in ocaml 5.2.1

Ecosystem
1

I cannot install plplot due the dune build process failing, with seemingly an issue occurring due to a dropped const qualifier in the plplot c source.

  • Is there any way to coax the dune build to be more permissive with types?
  • Alternatively, what plotting libraries actually work with ocaml > 5.0?

opam switch: 5.2.1+options
dune: 3.17.2
fedora version: 41
plplot-devel: 5.15.0-72

dune build output:
<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
[ERROR] The compilation of plplot.5.12.0 failed at “dune build -p plplot -j 15”.

#=== ERROR while compiling plplot.5.12.0 ======================================#

context 2.3.0 | linux/x86_64 | ocaml-variants.5.2.1+options | pinned(file:///home/jacobw/Downloads/plplot-5.12.0)

path ~/.opam/5.2.1+options/.opam-switch/build/plplot.5.12.0

command ~/.opam/opam-init/hooks/sandbox.sh build dune build -p plplot -j 15

exit-code 1

env-file ~/.opam/log/plplot-44177-3a679f.env

output-file ~/.opam/log/plplot-44177-3a679f.out

output

plplot_impl.c:351:17: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]

[…]

plplot_impl.c: In function ‘ml_plparseopts’:

plplot_impl.c:704:41: error: passing argument 2 of ‘c_plparseopts’ from incompatible pointer type [-Wincompatible-pointer-types]

704 | result = plparseopts( &argv_length, c_argv, combined_parse_method );

| ^~~~~~

| |

| const char **

In file included from /usr/include/plplot/plplotP.h:151,

from plplot_impl.c:29:

/usr/include/plplot/plplot.h:2305:46: note: expected ‘PLCHAR_NC_MATRIX’ {aka ‘char **’} but argument is of type ‘const char **’

2305 | c_plparseopts( int *p_argc, PLCHAR_NC_MATRIX argv, PLINT mode );

| ~~~~~~~~~~~~~~~^~

2

Before going any further, are you able to install plplot with any other OCaml > 5.0 ? Does it install with OCaml 5.0.0 ?

3

Hello, I don’t know if this is useful or not, but:

(1) on Ubuntu 24.04
(2) dune 3.17.2
(3) OCaml 5.2.1 (a completely vanilla switch)

5.2.1 ocaml-base-compiler.5.2.1,ocaml-options-vanilla.1

(4) with plplot installed by Ubuntu:

ii libplplot-dev 5.15.0+dfsg2-9build1.1 amd64 Scientific plotting library (development files)

(5) I was able to cleanly with no complaints install it:

plplot 5.12.0 Bindings for the PLplot library

(6) When I THEN went to build the OCaml plplot library from source, I got the -same- warning you posted (but the build went thru fine):

plplot_impl.c: In function ‘ml_plparseopts’:
plplot_impl.c:704:41: warning: passing argument 2 of ‘c_plparseopts’ from incompatible pointer type [-Wincompatible-pointer-types]
  704 |     result = plparseopts( &argv_length, c_argv, combined_parse_method );
      |                                         ^~~~~~
      |                                         |
      |                                         const char **

(7) Also, here’s my gcc:

$ gcc --version
gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0

To debug further, I might look at the dune “log” file, in “_build/log” and see what the “gcc” command that blew up was.

4

This is a C compiler warning you can ignore. I’m guessing it’s caused by ctypes and I don’t think it’s worth the effort to fix it if it would make ctypes more complicated. (const here leads to a warning rather than an error, the datatype is correct.)

5

Thanks for replying!

the provided error warning was given when the ‘opam install plplot’ command failed. I did try later to manually build the plplot-ocaml github repository, but received the same warning.

I have since tested the opam install plplot command with switches ( 4.08.1, 5.0.0, 5.3.1+options) to the same effect,

looking at the _build/log for the local repository
the build command/s for the external library where
$ /home/jacobw/.opam/4.14.2/bin/ocamlc.opt -config > /tmp/dune_c97c72_output
$ (cd _build/default/src && /usr/lib64/ccache/gcc -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC -D_FILE_OFFSET_BITS=64 -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC -g -O2 -I/usr/include/plplot -g -I /home/jacobw/.opam/4.14.2/lib/ocaml -o idlalloc.o -c idlalloc.c)
$ (cd _build/default/src && /usr/lib64/ccache/gcc -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC -D_FILE_OFFSET_BITS=64 -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC -g -O2 -I/usr/include/plplot -g -I /home/jacobw/.opam/4.14.2/lib/ocaml -o plplot_impl.o -c plplot_impl.c)

I’ve tried changing the flag configurations within the src/dune file : removing :standard , and adding -w. to no particular effect.

dune seems to still be using the flags given to it by ocamlc.opt -options (which includes -fno-strict-aliasing) for the gcc command, and I am not certain how to prevent dune from passing them in.

6

I looked in the _build/log for my 5.2.1 switch, compiling plplot.5.12.0 (as before) and found:

$ (cd _build/default/src && /usr/bin/gcc -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC -pthread -D_FILE_OFFSET_BITS=64 -O2 -fno-strict-aliasing -fwrapv -pthread -fPIC -pthread -g -O2 -I/usr/include/plplot -g -I /home/chet/Hack/Opam-2.3.0/GENERIC/5.2.1/lib/ocaml -o plplot_impl.o -c plplot_impl.c)

Squinting, that looks pretty much like your gcc invocation, doesn’t it? I don’t see the difference.

So I thought: why don’t I run the command? And yeah, the command goes thru without any trouble. Could I suggest that you do the same? That is, take the command from your build/log and run it in a shell?

And also, what’s the output of “gcc --version” on your machine?

Last: can you turn off this “ccache” stuff? Is that perhaps related to your problem?

7

Since GCC 14, passing pointers with incompatible types is no longer just a warning, it is a hard error. You need to pass the option -Wno-error=incompatible-pointer-types to revert to the old behavior of GCC.

8

I was able to build plplot successfully by adding both
-w and -Wno-error=incompatible-pointer-types
to the src/dune flags list
neither of the flags individually resolved the build failure.

Thank you for the help and time

9

Probably worth opening an issue with the plplot package, so they fix it there also.