CI doesn't ensure cabal install cabal-install from previous major series works

[ezyang]

Self-explanatory. Probably should just make a separate job in the matrix for testing this case.

[phadej]

Do you have an example? AFAICS cabal check should say aloud if cabal-version is too low, also we have setup-deps...

[23Skidoo]

To clarify: this means cabal-install-1.24 install cabal-install-1.26, not cabal-install-1.26 install cabal-install-1.24.

[23Skidoo]

In general, we need a more systematic pre-release testing procedure.

[ezyang]

The way the Travis script works is by first bootstrapping cabal-install using bootstrap.sh, and then using the resulting cabal for the rest of the operations. So this won't check if cabal-install-1.24 install cabal-install-1.26 works, as @23Skidoo says. I noticed this when I was working on the internal libraries PR, because for cabal-install to use internal libraries requires a sufficiently new version of Cabal, but the CI wasn't failing.

[jneira]

Now github workflows does:

• cabal-${lastReleaseVersion} v2-build cabal-head
• uses the cabal-head to run all the tests suites
• cabal-head v2-build cabal head (only in windows for now but it will be extended soon, see Extend new dogfooding ci job to linux and macos #7742)

So the issue request was being done since time ago and we check cabal-head too (As travis did when this issue was opened)