Stack should intelligently select a resolver based on a installed GHC version

[drwebb]

It would be nice to have resolver automatically prefer a nightly (at the moment until LTS 3.x is rolled out at least) snapshot if GHC7.10 is already installed on the user's system. If multiple versions are present I suppose we could go with what is most stable, i.e. the current LTS version.

[DanBurton]

I think "current LTS" is the preferable default, regardless of what is
already installed.

I'm not entirely opposed to a temporary hack to ease people onto ghc 7.10
if they already have it, though, since LTS 3 is so imminent.

-- Dan Burton

On Tue, Jun 30, 2015 at 6:48 PM, Tristan Webb notifications@github.com
wrote:

It would be nice to have resolver automatically prefer a nightly (at the
moment until LTS 3.x is rolled out at least) snapshot if GHC7.10 is already
installed on the user's system. If multiple versions are present I suppose
we could go with what is most stable, i.e. the current LTS version.

—
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#468.

[snoyberg]

For the record, I asked @drwebb to open this issue. Your point is valid @DanBurton, it really isn't clear that any change from our current behavior would be a good one. An example of a downside would be a user being pushed to a stale LTS just because he/she has a distribution provided GHC.

Does anyone feel strongly that we should change the default? If not, let's attack this with better documentation.

[drwebb]

I agree with the better docs suggestion, I'm not sure how it works at the moment, but stack initshould do more than just suggesting downloading GHC 7.8 through stack setup if the user has GHC 7.10 already, and pose another option to be to use an appropriate nightly resolver. Apologies if this is already the case, I haven't tested on a fresh system.

[snoyberg]

We want stack init to avoid getting in your face. If it can't find a matching snapshot, it gives you options for choosing one explicitly. You can give it command line parameters to let it know what your preferences are. I think we should include this in #489. I'm going to close this and we'll focus on #489 instead.