Build simplifications

[samuelpilz]

This pull-request is the result of my review of the install.hs file.

Following improvements were made:

• hoogle-database is only generated once. The same file was generated every time.
• cabal-install is not installed via stack if the executable cabal can already be found.

A review from @fendor has been conducted and the suggestions have been included.

[nponeccop]

@fendor Tastes differ. My eyes bleed when I see these maybe-cases and return Just. My opinion is that <$> isn't exotic at all, it's idiomatic in day-to-day Haskell code, and it's almost always improves readability. It's used 78 times in 16 files in hie. It's not the right place to discuss coding guidelines here though, so I closed the conversation so it doesn't seem like an outstanding issue preventing the PR from merging.

[alanz]

I just checked out this branch, deleted my .stack-work and gave it ./install.hs build-all.

It first built and ran hoogle, and then started building Cabal-2.4.1.0, which was not built by the prior version, and is already on my machine, as far as I know.

It then started building cabal-install-2.0.0.0, which as far as I am concerned should not be installed, as it is an old version. This is for the hie-8.2.1 target, I think.

Stopping the build and restarting it does not re-install Cabal or cabal-install, so I guess they are used for the specific hoogle in use. Which should probably be build against the hie-8.6.4 baseline, rather than the hie-8.2.1 one.

[samuelpilz]

@alanz Thank you for testing my PR.

cabal-install and hoogle are runtime-dependencies that need to be built if not already present on the system. To minimize the number of downloaded ghcs, they are built using the same ghc as the install.hs file is beeing executed. It should not build cabal-install or hoogle if the are already present in the path.

I am unable to reproduce the behavior that cabal-install-2.0.0.0 is installed. For me, it is the version as provided in the resolver from the shake.yaml, which is cabal-install-2.4.1.0.

[fendor]

You changed the API of install.hs, the README must be adapted before merge.

[samuelpilz]

Following additional features are implemented:

• building with 8.6.3 is no option windows systems. (closes New install.sh builds hie-8.6.3 on Windows... and fails #1155)
• check if installed stack version is too old
• install cabal-install via stack if the found cabal executable is too old

[fendor]

LGTM, ready to merge in my opinion, I tested it on windows.

[alanz]

If you guys are happy with this, then merge it.

[Anrock]

I see it also closes #1008 and #1155

[fendor]

In the short help message, the nightly ghc version seems to be excluded. If this is fine, then we can merge, otherwise this needs to be added to the short-help message.