Map of repo-name to repo-url/path is global, which breaks git-worktree workflows

I use git worktree fairly heavily, to concurrently work on multiple branches on our monorepo. Unfortunately, this means our opam repo — which exists in that monorepo — doesn't play nice.

Our initial git-repository setup does something a lil' like this:

$ opam repo add --dont-select theproj "./backend/opam" || \
      opam repo set-url theproj "./backend/opam"
$ opam repo add --dont-select mirror "https://opam.oursite.net" || \
      opam repo set-url mirror "https://opam.oursite.net"

Unfortunately, if I run this initial setup in ~/code/monorepo, that means opam now has this understanding:

$ opam repo list --all
# Repository # Url                                                 # Switches(rank)
theproj      file:///home/elliott.cable/code/monorepo/backend/opam /home/elliott.cable/code/monorepo(1/2)
default      https://opam.ocaml.org                                <default> _globals our-placeholder
mirror       https://opam.oursite.net                              /home/elliott.cable/code/monorepo(2/2)

Note that the path ~/code/monorepo is now hard-coded in a global way.

Meanwhile, if someone subsequently sets up another clone of the repository and attempts to give it a clean copy of the switch (which is the entire point of directory-local switches, yes?) ...

$ git worktree add ~/code/monorepo.worktrees/alt && cd !#3
$ opam repo add --dont-select theproj "./backend/opam" || \
      opam repo set-url theproj "./backend/opam"

Wait, hold up. Now the theproj repo points at the alt worktree; both for us, and for the original git-clone. That's bad.

One fix I attempted, was setting the repo during switch-creation; so it's hopefully locally to only that switch:

$ git worktree add ~/code/monorepo.worktrees/alt && cd !#3
$ make init
rm -rf _opam backend/_build
opam init --bare --enable-shell-hook 
make opam-setup
make[1]: Entering directory '/home/elliott.cable/code/monorepo.worktrees/alt'
# adding the repo if it doesn't exist || setting the url of the repo
opam repo add --dont-select mirror  || opam repo set-url mirror "https://opam.oursite.net"
opam update -a # we need to update the repo to make sure that the latest version of the compiler package is detected

<><> Updating package repositories ><><><><><><><><><><><><><><><><><><><><><><>
[theproj] no changes from file:///home/elliott.cable/code/monorepo/backend/opam
[default] no changes from https://opam.ocaml.org
[mirror] no changes from https://opam.oursite.net
# setting theproj-setup and theproj-dev-tools-deps as invariant so that they aren't uninstalled by accident later on
opam sw -y --repositories "theproj=./backend/opam,mirror" create . --packages=theproj-setup,theproj-dev-tools-deps,ocaml-base-compiler.4.14.0 --no-install
Creating repository theproj...
[ERROR] Repository theproj is already set up and points to file:///home/elliott.cable/code/monorepo/backend/opam. To change that, use 'opam repository set-url theproj
        file:///home/elliott.cable/code/monorepo.worktrees/alt/backend/opam'.
make[1]: *** [Makefile:26: opam-setup] Error 2
make[1]: Leaving directory '/home/elliott.cable/code/monorepo.worktrees/alt'
make: *** [Makefile:32: init] Error 2

Okay, nope, no suck luck — even if I attempt to create a new theproj repo in opam switch create, it still conflicts with a completely separate theproj repo in another switch.

My last attempt involved using $PWD as the name of the repo, because that's somewhat honest — it is, indeed, a directory-local repo specific to that worktree. Something like the following:

$ opam repo add --dont-select "$PWD" "./backend/opam" || \
      opam repo set-url "$PWD" "./backend/opam"

Unfortunately, this leads — somewhat unsurprisingly — to build-failures like the following, due to non-existent directories like /tmp/opam-NNN//home/elliott.cable/code/monorepo.worktrees/alt/packages...:

#=== ERROR while compiling ragel.6.8+20190930 =================================#
Sys_error("/tmp/opam-25708-888da3//home/elliott.cable/code/monorepo.worktrees/alt/packages/ragel.6.8+20190930/files/ragel.install: No such file or directory")

<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
┌─ The following actions failed
│ ⬇ fetch   sqlgg    20220401+git
│ λ build   camlp4   4.14+1
│ λ build   ctypes   0.20.1
│ λ build   lwt      5.5.0
│ λ build   ocamlmod 0.0.9
│ λ build   ocamlnet 4.1.9-2
│ λ build   ptime    1.0.0
│ λ build   ragel    6.8+20190930
│ λ build   rresult  0.7.0
│ ∗ install geoip    0.0.3
└─

So, tl;dr, I'd love to see one of the following:

Lowering the 'name'-to-'url' map of opam repositories into individual switches, or …
allow some opam repo 'names' to have different values in different switches, or …
allow repo 'names' to have slashes in them, and automatically make that play nice with the filesystem.

opam config report

``` $ opam config report # opam config report # opam-version 2.1.2 # self-upgrade no # system arch=x86_64 os=linux os-distribution=debian os-version=10 [ERROR] No switch is currently set. Please use 'opam switch' to set or install a switch # read-state OpamStd.OpamSys.Exit(50) ```

ocaml / opam

Map of repo-name to repo-url/path is global, which breaks git-worktree workflows #5126