conf-perl.3, conf-perl-{string-shellquote,ipc-system-simple}.4: Cygwin/MSYS2 support

[smorimoto]

Summary

Add Cygwin and MSYS2 support for conf-perl-* packages. These Perl modules have no corresponding system packages in either Cygwin or MSYS2 package repositories, so depexts alone cannot satisfy the dependency.

Changes

conf-perl.3 (new version):

• Creates a self-contained CPAN configuration (MyConfig.pm) inside the opam switch, avoiding conflicts with any existing user CPAN configuration
• Uses %{prefix}% to locate the switch directory and normalizes backslashes to forward slashes for Windows compatibility (opam → Cygwin command-line → Perl requires triple-layer escaping)
• Exports perl5lib and cpan_config_dir via .config file so dependent packages can find installed modules and use the switch-local CPAN config
• Sets SHELL, PERL_MM_USE_DEFAULT, and PERL5LIB via setenv for dependent packages
• On MSYS2, the MyConfig.pm sets make to /usr/bin/make to avoid the mingw make (/mingw64/bin/make.EXE) which cannot handle POSIX paths
• On MSYS2, adds perl-devel to depexts (provides Config.pm required by ExtUtils::MakeMaker)

conf-perl-{string-shellquote,ipc-system-simple}.4 (new versions):

• Depend on conf-perl >= 3
• On Cygwin/MSYS2, install the required Perl module via perl -I <cpan_config_dir> -MCPAN using the switch-local CPAN configuration
• SHELL, PERL_MM_USE_DEFAULT, and PERL5LIB are propagated from conf-perl via setenv
• Verify the module is available via perl -MModule -e 1

Background

Since setup-ocaml v3.5.0, opam uses --cygwin-internal-install which manages its own internal Cygwin. This means opam uses the internal Cygwin perl for conf-perl-* verification. The corresponding Cygwin/MSYS2 system packages for these Perl modules (perl-String-ShellQuote, etc.) do not exist in the Cygwin or MSYS2 package repositories, so depexts cannot resolve them.

The fix installs modules via the CPAN client bundled with perl, with platform-specific handling:

• Cygwin: SHELL=/bin/sh must be set to work around a fileparse() crash in CPAN::FirstTime (RT #131313)
• MSYS2: Additionally requires a custom MyConfig.pm that points make to /usr/bin/make (the MSYS2 POSIX make), because opam's PATH ordering places /mingw64/bin/make.EXE (mingw make) first, which cannot handle POSIX paths

Windows path handling

On Windows, %{prefix}% returns a path with backslashes (e.g. D:\a\opam-repository\opam-repository\_opam). Since opam's .config file parser treats \ as an escape character, the generated conf-perl.config must use forward slashes. The Perl script normalizes backslashes via s{\\}{/}g, but this requires 8 backslashes (\\\\\\\\) in the opam file to survive three escaping layers: opam string unescaping, Cygwin command-line processing, and Perl regex parsing.

Also requires setup-ocaml v3.6.0+ which installs the opam base packages (make, tar, unzip, rsync) on MSYS2 (ocaml/setup-ocaml#1096).

ref: ocaml/setup-ocaml#1094

[a2line]

Hello smorimoto,

I’ve successfully tested your branch on our Windows CI by replacing the Perl module installation step with:

opam repo add conf-perl-fix https://github.com/ocaml/opam-repository.git#conf-perl-cygwin-cpan --all --rank=1

conf-perl.3, conf-perl-ipc-system-simple.4, and conf-perl-string-shellquote.4 resolved and installed transparently — no manual steps required. The modules are picked up automatically during opam install . --deps-only, just like on Unix.

This is exactly what we needed. It makes maintaining manual workarounds for conf-perl on Windows CI completely obsolete.

Thank you for the thorough work and the quick turnaround, especially over the weekend!