OCaml < 4.14, Fedora 42 and GCC 15

Late last week, @MisterDA added Fedora 42 support to the Docker base image builder. The new base images attempted to build over the weekend, but there have been a few issues!

The code I had previously added to force Fedora 41 to use the DNF version 5 syntax was specifically for version 41. For reference, the old syntax was yum groupinstall -y 'C Development Tools and Libraries’, and the new syntax is yum group install -y 'c-development'. Note the extra space.

let c_devtools_libs : (t, unit, string, t) format4 =
  match d with
  | `Fedora `V41 -> {|"c-development"|}
  | `Fedora _ -> {|"C Development Tools and Libraries"|}
  | _ -> {|"Development Tools”|}
...
let dnf_version = match d with `Fedora `V41 -> 5 | _ -> 3

To unburden ourselves of this maintenance in future releases, I have inverted the logic so unmatched versions will use the new syntax.

let (dnf_version, c_devtools_libs) : int * (t, unit, string, t) format4 =
  match d with
  | `Fedora
    ( `V21 | `V22 | `V23 | `V24 | `V25 | `V26 | `V27 | `V28 | `V29
    | `V30 | `V31 | `V32 | `V33 | `V34 | `V35 | `V36 | `V37 | `V38
    | `V39 | `V40 ) ->
    (3, {|"C Development Tools and Libraries"|})
  | `Fedora _ -> (5, {|"c-development"|})
  | _ -> (3, {|"Development Tools"|})

Fedora 42 also removed awk, so it now needs to be specifically included as a dependency. However, this code is shared with Oracle Linux, which does not have a package called awk. Fortunately, both have a package called gawk!

The next issue is that Fedora 42 is the first of the distributions we build base images for that has moved to GCC 15, specifically GCC 15.0.1. This breaks all versions of OCaml < 4.14.

The change is that the code below, which previously gave no information about the number or type of parameters. (see runtime/caml/prims.h)

typedef value (*c_primitive)();

Now means that there are no parameters, aka:

typedef value (*c_primitive)(void);

This is caused by a change of the default compilter language version. See GCC change log

C23 by default: GCC 15 changes the default language version for C compilation from -std=gnu17 to -std=gnu23. If your code relies on older versions of the C standard, you will need to either add -std= to your build flags, or port your code; see the porting notes.

Also see the porting notes, and this bug report.

This is not an immediate problem as OCaml-CI and opam-repo-ci only test against OCaml 4.14.2 and 5.3.0 on Fedora. I have opened issue#320 to track this problem.

OCaml < 4.14, Fedora 42 and GCC 15

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