Share common ghc options and other fields in `postgrest.cabal`

[taimoorzaeem]

Problem

Right now there is a lot of duplication in postgrest.cabal between different project components. This includes common build information, ghc-options, default language extensions and more.

Duplicated flags:

postgrest/postgrest.cabal

Lines 176 to 177 in ca4a6d9

	ghc-options: -j -Werror -Wall -fwarn-identities
	-fno-spec-constr -optP-Wno-nonportable-include-path

postgrest/postgrest.cabal

Lines 205 to 207 in ca4a6d9

	ghc-options: -j -threaded -rtsopts "-with-rtsopts=-N -I0 -qg"
	-O2 -Werror -Wall -fwarn-identities
	-fno-spec-constr -optP-Wno-nonportable-include-path

Duplicated language extensions:

postgrest/postgrest.cabal

Lines 41 to 44 in ca4a6d9

	default-language: Haskell2010
	default-extensions: OverloadedStrings
	NoImplicitPrelude
	NumericUnderscores

postgrest/postgrest.cabal

Lines 221 to 224 in ca4a6d9

	default-extensions: OverloadedStrings
	QuasiQuotes
	NoImplicitPrelude
	NumericUnderscores

... and more.

Also discussed in #5139 (comment)

Solution

We can use common stanzas to group these options and reuse in different places.

It would look something like:

common common-lang-edition
  default-language:   Haskell2010

common common-exts
  default-extensions: OverloadedStrings
                      NoImplicitPrelude
                      NumericUnderscores

common common-ghc-options
  ghc-options:        -j -Werror -Wall -fwarn-identities
                      -fno-spec-constr -optP-Wno-nonportable-include-path

.
.
.

library
  import:             common-lang-edition, common-exts, common-ghc-options
  ...

executable postgrest
  import:             common-lang-edition, common-exts, common-ghc-options
  ...

test-suite spec
  import:             common-lang-edition, common-exts, common-ghc-options
  default-extensions: QuasiQuotes
  ...

Notes

We should discuss how to group these effectively, the above is just an example.