Assume compatibility with minor / patch compiler releases

[milesfrain]

Since the latest compiler version is not yet listed in latest-compatible-sets.json, new users starting today will encounter the following error:

npm i -g purescript spago

purs --version
0.14.1
spago --version
0.20.0

spago init
[info] Initializing a sample project or migrating an existing one..
[error] It seems that you're using a compiler version that is not supported by package-sets at the moment.
Please install one of the following versions of the compiler and try again: 
- 0.14.0
- 0.13.8
- 0.13.6
...

Could spago assume that minor compiler version bumps maintain compatibility with the latest package set? For example, I suspect that purs 0.14.1 is still compatible with psc-0.14.0-20210409.

[JordanMartinez]

I suspect that purs 0.14.1 is still compatible with psc-0.14.0-20210409.

It still is compatible.

One can workaround this issue by updating their packages.dhall file to the latest package set manually (as spago currently complains when one runs spago upgrade-set) and then add the below with metadata.version = "v0.14.1" part to the file. For example...

let upstream =
      https://github.com/purescript/package-sets/releases/download/psc-0.14.0-20210409/packages.dhall sha256:e81c2f2ce790c0e0d79869d22f7a37d16caeb5bd81cfda71d46c58f6199fd33f

in  upstream
    with metadata.version = "v0.14.1"

[f-f]

This is fixed for this release, but we have to do something otherwise we'll encounter this again with the next minor. The logic that handled this compatibility has been there for a while, but got overriden by the newer logic. We could make it so that if the compiler "not in the list" is "semver compatible" with a compiler in the list, then we could use its set.

We have some logic already implemented for this here:

spago/src/Spago/PackageSet.hs

Lines 201 to 218 in 456be94

	-- | The check is successful only when the installed compiler is "slightly"
	-- greater (or equal of course) to the minimum version. E.g. fine cases are:
	-- - current is 0.12.2 and package-set is on 0.12.1
	-- - current is 1.4.3 and package-set is on 1.3.4
	-- Not fine cases are e.g.:
	-- - current is 0.1.2 and package-set is 0.2.3
	-- - current is 1.2.3 and package-set is 1.3.4
	-- - current is 1.2.3 and package-set is 0.2.3
	performCheck :: Version.SemVer -> Version.SemVer -> RIO env ()
	performCheck actualPursVersion minPursVersion = do
	let versionList semver = semver ^.. (Version.major <> Version.minor <> Version.patch)
	case (versionList actualPursVersion, versionList minPursVersion) of
	([0, b, c], [0, y, z]) | b == y && c >= z -> pure ()
	([a, b, _c], [x, y, _z]) | a /= 0 && a == x && b >= y -> pure ()
	_ -> die [ display
	$ Messages.pursVersionMismatch
	(Version.prettySemVer actualPursVersion)
	(Version.prettySemVer minPursVersion) ]

[f-f]

Fix up in #782, @milesfrain @JordanMartinez could you take a look at it?

[JordanMartinez]

@f-f LGTM!

[milesfrain]

It will be a bit tough to test until we get another compiler bump beyond the latest package set, but I don't see anything looks problematic in that PR. So I'm thinking we can consider this resolved.

[f-f]

Great, thank you for taking a look at it. I thought about adding some tests for the change, but the code involved here is fairly "IO-heavy", and disentangling the whole thing might not be worth it at this stage. We'll have another minor release soon so we'll likely just test it then.