I believe the path to add is enough (<CWD>/_opam/bin), but is there anything I missed?

It's a nice simple idea, but this doesn't work, I'm afraid (it will be brittle):

• Some time in the next few months, msvc will start adding other directories to PATH (so compiler in PATH won't work)
• The other environment variables set by opam exec matter - for example, CAML_LD_LIBRARY_PATH in opam-repository's current setup could cause problems

I think it's important if the action exports the environment that it exports the same one as opam exec would give. There are a few solutions which could work:

• Pick a shell (for example opam env --shell=bash) and parse the output. The annoying thing here is that you have to find the existing value of environment variables to work out the change. For example, on my system:

dra@thor:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/dra/.dotnet/tools
dra@thor:~$ opam env --shell=bash | grep ^PATH
PATH='/home/dra/.opam/dev-4.11/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/dra/.dotnet/tools'; export PATH;

So you have to post-process the PATH= line to work out that it's really PATH="/home/dra/.opam/dev-4.11/bin:/usr/local/sbin:$PATH" (and remember that switches can append items to variables as well).

• Parse _opam/.opam-switch/environment. This is probably the best solution right now, though it's tedious to have to parse the file
• Update opam to support JSON export of the environment updates.

Indeed - and I think there is a cleaner solution with opam 2.2, so I'm closing this for now.

What's in opam 2.2 to help with this?