Add 'store-dir' global flag for custom store location

[alexbiehl]

This is also a nice workaround for #4515 since I can easily define store-dir=C:\cabal-store in my global configuration.

This also propagates the global logs-dir configuration instead of hard-coding the logs dir to cabalDir </> logs.

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.

[mention-bot]

@alexbiehl, thanks for your PR! By analyzing the history of the files in this pull request, we identified @dcoutts, @ezyang and @hvr to be potential reviewers.

[23Skidoo]

Haven't looked at the code, but the general idea is good.

[ezyang]

LGTM. CI failures are because you've forgotten some test/monoid-y code for the config change. Look at an old diff which added a field to figure out exactly what.

[alexbiehl]

OK, this is ready for review now! Tests should work pass now!

[alexbiehl]

Hmm. I am not sure what is causing some of the tests to fail.

[ezyang]

It doesn't look like it's your fault, looks like CI is in trouble right now.

[ezyang]

FYI I cancelled your most recent build because it was definitely going to fail

[ezyang]

CI is unwedged, I restarted it.

[ezyang]

Hi @alexbiehl, can you rebase your PR on master and repush? It doesn't look like Travis is successfully merging with master (which has fixed contbuild.)

[alexbiehl]

Almost...

[alexbiehl]

Yeah! CI is happy!

[23Skidoo]

@alexbiehl Can you please add some docs and update the changelog? Otherwise the patch seems okay.

[23Skidoo]

@alexbiehl NB: you can use [ci skip] anywhere in the commit message body to avoid triggering CI for documentation-only commits.

[hvr]

@23Skidoo are the changelog conflicts the only thing keeping this from being merged, or was there something else that needs doing?

[ezyang]

Yes it's just the changelog conflict.

[Mistuke]

I've been trying to use this but it always results in a weird path:

$ cabal --store-dir=/e/cabal-store new-test
Build profile: -w ghc-8.0.2 -O1
In order, the following will be built (use -v for more details):
 - base-compat-0.9.3 (lib) (requires build)
....
Configuring library for base-compat-0.9.3..
cabal.exe: ghc-pkg dump failed: dieVerbatim: user error (cabal.exe:
'E:\msys64\mingw64\bin\ghc-pkg.exe' exited with an error:
ghc-pkg.exe: C:cabal-store\ghc-8.0.2\package.db:
getDirectoryContents:findFirstFile: does not exist (The system cannot find the
path specified.)
)

No matter what path I give it, the resulting path seems to always be rooted in C: even though I gave it E: and the path itself is invalid because it's missing the \ after the colon...

[23Skidoo]

@Mistuke Can you please file a new issue?