GitLab

- Add availableSince to language/extension fields
   - Also autogen-modules once we are on that.
- Remove default-language check for cabal-version: 3.4

We cannot make the field `uniqueFieldAlaDef`, as that would require
specifying `default-language` in each subconditional.
I leave it for https://github.com/haskell/cabal/issues/6925

Note: the default language is whatever is the compiler's default.
The GHC-8.10 default is its variant of Haskell2010
with NondecreasingIndentation and without DatatypeContexts

This is preparation to solve #6083.
As such, this shouldn't affect anything yet.

Now it re-exports a collection of modules,
not individual symbols.

I.e. find out where we don't yet
used `Distribution.Client.Compat.Prelude`.

- If the module is small I added direct `Prelude` imports.
- Add Exception, deepseq stuff to Cabal Prelude
- Add Parsec, Pretty and Verbosity to Client Prelude
- use for, for_, traverse and traverse_ (removes need for Control.Monad)

Also add a test for current behaviour
of https://github.com/haskell/cabal/issues/6083

And variant with mixin, for https://github.com/haskell/cabal/issues/6281

The tests are disable for GHC older than 8.8
Should they work?

This makes type-signatures awful, but using _ one can infer them.
Parsing performance doesn't seem to be affected.

Also move Newtypes to Distribution.FieldGrammar.Newtypes as that is
more correct place.

There was three Flag's. Now they are
- `Flag` (cli parsing)
- `PackageFlag`
- `CompilerFlag`

This allows wild-imports without `hiding (Flag)`, and make tags
navigaton work!

cabal-install support is very WIP

- We had to add gpdScannedVersion to permit solver to report
  about too new packages in the index.
  https://github.com/haskell/cabal/issues/6652
- It's hard to track what happening with Setup interface selection in
  ProjectPlanning.
  https://github.com/haskell/cabal/issues/6651 would help to
  make sense of it.

Do this already in the Parsec instance parser.
This allows removing checks from `D.PD.Check`.
Later this would also allow removing non-relevant
constructors from `VersionRange`, allowing easier testing.

This change causes 10% slowdown: from

```
135768 files processed
  7350 files contained warnings
113156 files have check warnings
     0 files failed to parse

120.901201s elapsed
117.640431s elapsed
119.663620s elapsed
119.454329s elapsed
119.785214s elapsed
```

to

```
135768 files processed
 31912 files contained warnings
113109 files have check warnings
     0 files failed to parse

130.969593s elapsed
132.016403s elapsed
134.214536s elapsed
128.753382s elapsed
131.503804s elapsed
```

I hope the slowdown is acceptable, and I have an idea which may mitigate
this. I'll try out it after I done further refactorings.

Note how (parser) warnings grew by a factor. There are plenty of (old)
files on Hackage, which don't use correct cabal-version.  For that
reason we only issue warnings, and not fail.  Quirks approach won't
scale for these. In comparison, there are even more files
with check warnings

Partially fixes https://github.com/haskell/cabal/issues/6587
For local files, there might be invalid UTF8; but if
file comes from Hackage, we can assume they are valid UTF8.

So we do with many other stuff

These are only supported properly starting with
cabal-version:3.0 (which has been enforced by
Hackage as well -- via this very patch).

See #6033 for details

While those buildinfo fields were added to the parser some time
ago via 57d7f28e and
4a287659 that work was never completed
by implementing the necessary build/sdist logic in Cabal.

This commit remedies this oversight by implementing and wiring up the
missing build logic.

*WARNING* this commit is still very WIP; ASM works mostly; C--
          support is still incomplete

Add safe alternatives to some partial functions in
Distribution.Utils.Generic, and removes the originals from
Distribution.Compat.Prelude

Uncomment versions of functions in Distribution.Compat.Parsing
that return non-empty lists
Co-authored-by: Dale Wijnand <dale.wijnand@gmail.com>

Before:

130113 files processed
7304 have lexer/parser warnings
332 build impossible
9742 build warning
49779 build dist suspicious
38666 build dist suspicious warning
11834 build dist inexcusable

After:

130113 files processed
7304 have lexer/parser warnings
332 build impossible
10063 build warning
49779 build dist suspicious
38666 build dist suspicious warning
11834 build dist inexcusable

i.e. 321 build warnings on all Hackage

Examples:

NO_DEBUG_MODE                       -- forgotten -D?
-traditional                        -- doesn't work, nor needed
-fallow-undecidable-instances       -- wrong -options?
-fno-exceptions
-Wall
-Werror
--include=include/config.h          -- doesn't work
-maes                               -- cpp is not C++ ?
-mpclmul
-mssse3

This would trip up the improved pattern match checker from [!963](ghc/ghc!963).

The removed code is related to maintaining the round-trip property, so
should be re-introduced at some point. This is tracked in #6193.

The pseudo-`NonEmpty` was temporarily introduced in
b4a96aab

[ci skip]

autogen-includes aren't searched nor packages by `sdist`.

This is relatively small code patch, but there are
- change in file-format
- short documentation of the field
- `cabal check`
- test-suite noise due new field in `BuildInfo`