Add ghcup to PATH automatically

[hasufell]

https://discourse.haskell.org/t/haskell-and-vs-code-issues/7663

Comes up very frequently. The extension can probe for ghcup and if it's not in PATH, suggest to add it via haskell.serverEnvironment.

@fendor

[fendor]

How do we probe for ghcup?

We can guess all the locations ghcup installs itself into when installed via curl.
Further, we can guess locations by looking at XDG_DIR directories.
Should we also look at package managers to see to which location these install ghcup to, or is that a bad idea?

[hasufell]

We try to invoke it directly. If that works, then we run ghcup whereis bindir to get the actual binary dir (ghcup isn't guaranteed to reside there, e.g. when installed via package managers) and add that to PATH.

If that doesn't work, we follow this logic to guess the ghcup basedir: https://github.com/haskell/ghcup-hs/blob/371eda962f713fe483616310291004a82e5b029d/lib/GHCup/Utils/Dirs.hs#L202

Then check if a ghcup binary is in the bin/ subdir. If so, we add that to PATH.

[fendor]

We try to invoke it directly.

Doesn't that only work if it already is on the PATH?

The rest of the implementation roadmap looks sensible.

[hasufell]

Doesn't that only work if it already is on the PATH?

Yes, but it might be in /usr/bin, but the ghcup bindir is ~/.ghcup/bin.

[fendor]

Right, but if ghcup is on the PATH, then the extension will find it and ghcup works as expected.
The bindir of ghcup doesn't need to be on the PATH, since ghcup sets up all the tools in a tmpdir and adds that to the PATH.

Or is the point to unconditionally add ghcup bindir to the PATH via serverEnvironment?

[hasufell]

Or is the point to unconditionally add ghcup bindir to the PATH via serverEnvironment?

We probably should, since ghcup upgrade doesn't do an in-place upgrade, but puts it into GHCup bindir.

vscode-haskell/src/hlsBinaries.ts

Line 552 in aef73c2

await callGHCup(context, logger, ['upgrade'], 'Upgrading ghcup', true);

However, we need to make sure this doesn't take precedence over other user configurations, so I'm wondering if we should append to PATH, just in case of weird shenanigans (like someone putting ghcup binary into a custom dir and adding that via haskell.serverEnvironment to the PATH... then we don't want to overrule it).

[hasufell]

(like someone putting ghcup binary into a custom dir and adding that via haskell.serverEnvironment to the PATH... then we don't want to overrule it).

Although that case is fine, since we'll find the binary there anyway and won't guess the ghcup bindir.

Still think it's safer to append.

[hasufell]

Hm, but if we append, ghcup upgrade won't always take effect.

[hasufell]

Yeah, I guess most conservative method is to do nothing if we find a ghcup binary in PATH. Otherwise we probe and prepend to PATH.

[hasufell]

Actually we don't need to touch PATH at all, since we're only interested in the binary: #963

[hasufell]

Do we want to make a release?