Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

I've rewritten the test suite to be more concise and "correct by
construction".  The primary method that this is achieved by
is introducing the 'TestM' monad, which carries around the
important state for the tests so that (1) we don't have to
pass it as an argument all around, and (2) we can automatically
make the correct decisions about how to do things.  This new
method emphasises "configuration by convention": we assume
that a test-case named "Foo" has its test packages in the
directory "tests/PackageTests/Foo".

A secondary change is that all command functions automatically fail if
they have a non-zero exit code (unless you use the 'shouldFail'
combinator which inverts the sense.)  This saves a lot of typing
on test-cases.  (In fact, I've reorganized all of the commands
related here.)

In the process, I've tightened up the logic for how to find the
LocalBuildInfo of the Cabal we've testing, so we should now
reliably be testing the inplace Cabal library, and not the
system library (as was often the case.)

Because things are a lot shorter, there is no good reason to
make Check modules except for the biggest test cases.  Most
test-cases have been folded into PackageTests.Tests; if you
have a small test-case you should just put it there.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Clean up FIXMEs

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Also probe in canonicalized path, if binary was a symlink.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Introduce ignore-expiry cmdline arg

Make sure 'tarEntriesList' does not create thunks

If used, this will instruct the hackage-security library to ignore expiry dates
on TUF metadata (to be used only if, say, the main server is down and we need
to rely on mirrors that have not been updated for longer than the expiry period
on the timestamp).

Define Semigroup instances

GHC 8.0.1 is going to ship with time-1.6

Separate out reading index from building cache

And clarify the lazy nature of the algorithm.

This makes the code `-Wcompat`-clean with GHC 8.0

Due to the amount of `Monoid` instances, a compat-layer is used
rather than flooding the code-base with CPP conditionals.

Type refactoring

Program.Find: Fix on Win32

ee0ed0b9 added another codepath to
Distribution.Simple.Program.Find for Win32 platforms however did not add
correct imports or a dependency on the Win32 library. Fix this.

This changes the definition of `Index` to

``` haskell
data Index =
    -- | The main index for the specified repository
    RepoIndex Repo

    -- | A sandbox-local repository
    -- Argument is the location of the index file
  | SandboxIndex FilePath
```

with

```
cacheFile (SandboxIndex index) = index `replaceExtension` "cache"
```

This also renames `repoRemote'` to `maybeRepoRemote`.

I believe this addresses all comments.

In other words, give it a callback, changing the type from

    globalRepos :: GlobalFlags -> [Repo]

to

    Verbosity -> GlobalFlags -> ([Repo] -> IO a) -> IO a

This will be necessary for repositories that need to do some
repository-specific initialization (even if we don't currently have any, we
will soon). The Verbosity flag is not used yet, but will be.

This just changes the type and deals with the fallout.

The old Repo type has a repoKind

    repoKind     :: Either RemoteRepo LocalRepo,

where LocalRepo was isomorphic to unit:

    data LocalRepo = LocalRepo

This commit changes Repo to

    data Repo =
        -- | Local repositories
        RepoLocal {
            repoLocalDir :: FilePath
          }

        -- | Standard (unsecured) remote repositores
      | RepoRemote {
            repoRemote   :: RemoteRepo
          , repoLocalDir :: FilePath
          }

instead, which is a little more idiomatic and will make adding more repository
types easier.

Right now this just wraps the list of cache entries, but this might make it
easier in the future to change the structure of the cache.

In particular, distinguish between the repo-global index and a (sandbox-)local
index.

GHC 8.0 changed the `ErrorCall` type to have an extended constructor,
and backward compatibility has been provided via PatternSynonyms:

    data ErrorCall = ErrorCallWithLocation String String
        deriving (Eq, Ord)

    pattern ErrorCall :: String -> ErrorCall
    pattern ErrorCall err <- ErrorCallWithLocation err _ where
            ErrorCall err  = ErrorCallWithLocation err ""

However, due to https://ghc.haskell.org/ticket/8779 the
exhaustive-checker doesn't cope well with pattern-synonyms yet, and so
we get a non-exhaustive pattern-match failure when matching on
'ErrorCall' now.

As the matching on the constructor 'ErrorCall' is done here to help
infer the Exception instance, we can also just annotate the type
directly, and eschew the problematic pattern match.

While at it, this commit also makes this module CPP-free.

Cabal lib for nix local build

Extend repo config with security settings

Remove magic value from `globalCommand`

About the ghc package dbs in particular.

For supporting multi instance registrations on older GHC versions.

This extends `RemoteRepo` with new fields

``` haskell
-- | Enable secure access to Hackage?
remoteRepoSecure :: Bool,

-- | Root key IDs (for bootstrapping)
remoteRepoRootKeys :: [String],

-- | Threshold for verification during bootstrapping
remoteRepoKeyThreshold :: Int,
```

and modifies the parser accordingly. This does not yet require a dependency on
the security library.

NOTE: We suggest to make the security functionality opt-in, rather than
opt-out, for the first official release. Thus, the 'secure' field will be set
to 'False' when initializing a `~/.cabal/config` file, and existing
`~/.cabal/config` files will be interpreted as if they had `secure: False`.