InstalledPackageInfo parser roundtrip test

Warn if -- token is found. Don't warn if it's "--".

Resolves #2681

Cabal files don't have trailing line comments. In many fields they
simply cause parse errors, but e.g. in extra-source-files
virtually everything is accepted. As there is simple
work around if people actually want double-dash, let's warn
about bare one.

Leading comma 2

Tag Backpack fields (mixins, signatures) to `availableSince [2,0]`.
This "fixes" https://github.com/haskell/cabal/issues/4448, as fields
are recognised, warned, but parsed as empty if cabal-version < 2.0
(actual cut-off is ! (>= 1.25). For example, a file with

    cabal-version: >=1.10
    library:
      mixins: foo-indef requires (Foo42 as FooImpl)

will be accepted, yet warned, and parsed `mixins` in `BuildInfo` will be
an empty list.

Also availableSince is removed from `build-tool-depends`,
as we **want** to parse (and not warn) it in old Cabal files.
It can be thought as added retrospectively to old specs, but old `Cabal`
s don't know how to use it.

CabalSpecVersion type-class will allow to gather per-spec conditionals.
Currently it's used for selecting parsers / grammatical structure.

Leading (or trailing commas) for CommaFSep/CommaVSep fields,
i.e. fields with mandatory comma are (atm):

- build-depends
- build-tool-depends
- build-tools
- mixins
- pkgconfig-depends
- reexported-modules
- setup-depends

[WIP] Distribution.SPDX.LicenseId generation

Distribution.SDPX.LicenseId and Distribution.SDPX.LicenceExceptionId are
generated.

Enable 'make lexer' in travis-meta.

Kill trailing whitespaces in `.cabal` file emitted by `cabal init`

`cabal init` currently generates trailing whitespaces; this patch
simply adds a final post-processing step filtering out any such trailing
whitespace.

Changes to `cabal check` for `-O0` with tests or benchmarks.

 cabal-install: Remove support for building with GHC < 7.10.

This is to address #4551.

GHC 7.8.4 was released in Dec 2014, so this is in accordance with our
support policy. NB: doesn't affect lib:Cabal.

Fixes #4856.

[ci skip]

Adds --enable-tests and --enable-benchmarks to 'cabal fetch'.

Travis: use 8.2.2 to compile configurations with expensive asserts.

Unbreak the build with directory < 1.2.3.0.

Solver still sometimes picks 1.6.14 for some reason, and that version
is broken on older GHCs.

See https://github.com/haskell/cabal/pull/4950#issuecomment-352753882
for context.

Dave Laing authored 7 years ago and Mikhail Glushenkov committed 7 years ago

This is to address #1375.

Previously they were updated in the post install phase, which
would mean that the sources did not have their timestamps
updated unless the package being installed completed successfully.

This change moves the updating of the timestamps to the end of
the install phase, so that the add-source packages that are
successfully installed get their timestamps updated regardless of
the overall outcome of the installation.

[ci skip]

[ci skip]

[ci skip]

Peter authored 7 years ago and Mikhail Glushenkov committed 7 years ago

Resolves: #4444

Solver: Deduplicate flags and stanzas in DependencyReason.

The issue is fixed now.

Fix NondecreasingIndentation filtering

Improve `build-type` defaulting 

(see 9fb03d73 and #4958 for details)