This provides temporary life support to the `validate-old-ghcs` action
until node16 will be finally axed by GHA in May 2024.

Workaround for:
- https://github.com/haskell/cabal/issues/9858

Add “Add default-language” suggestion

As a warning (“Hackage would reject this package”), to prepare users
to GHC language editions.

Ignore testdb/intree generated files

Use package groups

* Remove cabal.project.libonly

It was only referenced once in a stale Makefile comment about doctests.

* Remove weeder

- remove weeder's configuration
- remove its recipe from Makefile
- remove its project

* Delete cabal.project.doctest

- Adding --ghc-options="-Wwarn" is sufficient to avoid the numerous <interactive> failures seen otherwise
- write-ghc-environment-files has a default of never

- Reduce duplication in test flag setup
- Avoid "New config" picking cabal's own project

Before this change, this was the test failure:

Unit Tests
  UnitTests.Distribution.Client.Configure
    Configure tests
      New config:                     FAIL
        Exception: project-cabal/pkgs/cabal.config: withBinaryFile: does not exist (No such file or directory)
        Use -p '/New config/' to rerun this test only.
      Replacement + new config:       OK
      Old + new config:               OK
      Old + new config, no appending: OK
      Old + new config, backup check: OK
      Local program options:          OK

1 out of 6 tests failed (0.02s)

- Satisfy -Wmissing-signatures in test-runtime-deps
- Satisfy -Wx-partial in HackageBenchmark
- Satisfy -Wunused-imports in QuickCheck.Instances.Cabal
- Use partial pattern for filtering in list comprehension
- Don't error on deprecated import

- Move constraints to project-cabal/constraints.config
- Remove duplicate package groups
- Groups coverage, doctest and validate are the same as the default group
- Remove duplicate validate-libonly package group
- Both validate and validate-libonly are the same
- Move Cabal & Cabal-syntax to pkgs/cabal.config
- Add install package group
- Add benchmarks package group
- Add tests package group
- Both default and libonly groups were the same set of packages that I renamed to tests
- Put install group before tests and benchmarks
- Don't repeat packages
- Add TODO and REVIEW comments on allow-newer exceptions
- Move latest.ghc configuration
- Put program-options first & separate imports
- Remove optional-packages
- Don't reiterate default value for tests and benchmarks
- Don't reiterate default value for optimization
- Add ghc-options.config
- Rename to ghc-latest.config
- Use -Werror in ghc-options.config
- Don't include ghc-options.config for doctest project
- Add project-config/pkgs.config
- Add project-config/pkgs.config importing all package groups
- Move Cabal-described to the cabal package group
- Remove cabal.project.buildinfo
- Have cabal.project.doctest import cabal.project
- Split integration tests into their own package group.
- Add back trailing newlines at EOF in projects
- Integration-tests.config needed for libonly
- Add a README for projects.

Fix --project-file option for boostrap

Text file, newlines at end of files

Add required-fields to changelog.d config

Conform BSD-2-Clause and BSD-3-Clause text to SPDX

`cabal init` text for BSD-2-Clause and BSD-3-Clause licence differed
slightly from the one published at SPDX. [1] [2]

This caused some problems to users when dealing with licence-recognition
software. [3]

[1] https://spdx.org/licenses/BSD-2-Clause.html
[2] https://spdx.org/licenses/BSD-3-Clause.html
[3] https://discourse.haskell.org/t/non-standard-license-generated-by-stack-new/9059

Add a --dry-run build check of cabal.project.release

Co-authored-by: brandon s allbery kf8nh <allbery.b@gmail.com>

Needed for POSIX compliance for text files

- Fix whitespace in cabal-testsuite + other tests

The release project disables tests and benchmarks.

- Cache of ~/.cabal/store not needed for --dry-run
- Remove workaround for the new job only

Support GHC2024 (fixes #9736)

* Add tests for #9742

`main-is` not picked up when inside a multibranch CondNode.

* Fix comments

* Add simplifyBranch to Distribution.Types.CondTree

Goes hand in hand with with simplifyCondTree.

* Make `check` deal correctly with multiple branches

`cabal check` had a problem recognising fields in presence of
multiple branches. This patch fixes the problem and does not
meaningfully increases CI time of particularly taxing tests
(like “duplicate flagged dependencies” from MemoryUsage).

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Testsuite: pass -i argument to runghc invocations