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Don't redefine macros with OCaml 4.12 #30

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merged 1 commit into from Feb 24, 2021

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MisterDA
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Macros Val_none and Some_val are part of the standard library
starting with OCaml 4.12.

In some environments, redefining a macro triggers a compiler warning.
When warnings are treated as errors, the build fails.

Issue discussing the introduction of the macros, the problem, and the
fix: ocaml/ocaml#5154

Commit introducing the macros in the standard library:
ocaml/ocaml@973eeb1

Macros `Val_none` and `Some_val` are part of the standard library
starting with OCaml 4.12.

In some environments, redefining a macro triggers a compiler warning.
When warnings are treated as errors, the build fails.

Issue discussing the introduction of the macros, the problem, and the
fix: ocaml/ocaml#5154

Commit introducing the macros in the standard library:
ocaml/ocaml@973eeb1
MisterDA added a commit to MisterDA/ocaml that referenced this pull request Jul 2, 2020
If an OCaml C library already defines some of the new `Val_none`,
`Some_val`, `Is_none`, `Is_some`, `caml_alloc_some`, or `Tag_some`
macros; then the C compiler will likely warn for macro redefinition,
even if the macro definition are identical. In some setups that always
turn warnings to errors, this will block the compilation of the
library.

This problem happens in [ocaml-mccs][1].

The proposed [fix][2] for libraries is to only define the macros when
compiling with OCaml strictly older than 4.12, i.e.:

    #if OCAML_VERSION < 41200
    #define ...
    #endif

[1]: ocaml-opam/ocaml-mccs#30
[2]: ocaml#5154 (comment)
MisterDA added a commit to MisterDA/ocaml that referenced this pull request Jul 17, 2020
If an OCaml C library already defines some of the new `Val_none`,
`Some_val`, `Is_none`, `Is_some`, `caml_alloc_some`, or `Tag_some`
macros; then the C compiler will likely warn for macro redefinition,
even if the macro definition are identical.

This problem happens in [ocaml-mccs][1].

The proposed [fix][2] for libraries is to only define the macros when
compiling with OCaml strictly older than 4.12, i.e.:

    #if OCAML_VERSION < 41200
    #define ...
    #endif

[1]: ocaml-opam/ocaml-mccs#30
[2]: ocaml#5154 (comment)
@AltGr
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AltGr commented Feb 24, 2021

Thanks!

@AltGr AltGr merged commit 1d56d2f into ocaml-opam:master Feb 24, 2021
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#define Val_some
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