Could we use a formatter for .cabal files in this project?

[philderbeast]

Could we use a formatter for .cabal files such as cabal-fmt? Nothing fancy, just a CI check to see that the .cabal files have been formated (by formatting again and checking for diffs).

I notice leading commas in cabal-install-solver.cabal and trailing commas in cabal-install.cabal.

cabal/cabal-install-solver/cabal-install-solver.cabal

Lines 101 to 113 in 03d7b42

	build-depends:
	, array >=0.4 && <0.6
	, base >=4.10 && <4.20
	, bytestring >=0.10.6.0 && <0.13
	, Cabal ^>=3.11
	, Cabal-syntax ^>=3.11
	, containers >=0.5.6.2 && <0.8
	, edit-distance ^>= 0.2.2
	, filepath ^>=1.4.0.0 || ^>=1.5.0.0
	, mtl >=2.0 && <2.4
	, pretty ^>=1.1
	, transformers >=0.4.2.0 && <0.7
	, text (>= 1.2.3.0 && < 1.3) || (>= 2.0 && < 2.2)

cabal/cabal-install/cabal-install.cabal

Lines 214 to 245 in 03d7b42

	build-depends:
	async >= 2.0 && < 2.3,
	array >= 0.4 && < 0.6,
	base16-bytestring >= 0.1.1 && < 1.1.0.0,
	binary >= 0.7.3 && < 0.9,
	bytestring >= 0.10.6.0 && < 0.13,
	containers >= 0.5.6.2 && < 0.8,
	cryptohash-sha256 >= 0.11 && < 0.12,
	directory >= 1.3.7.0 && < 1.4,
	echo >= 0.1.3 && < 0.2,
	edit-distance >= 0.2.2 && < 0.3,
	exceptions >= 0.10.4 && < 0.11,
	filepath >= 1.4.0.0 && < 1.6,
	hashable >= 1.0 && < 1.5,
	HTTP >= 4000.1.5 && < 4000.5,
	mtl >= 2.0 && < 2.4,
	network-uri >= 2.6.0.2 && < 2.7,
	pretty >= 1.1 && < 1.2,
	process >= 1.2.3.0 && < 1.7,
	random >= 1.2 && < 1.3,
	stm >= 2.0 && < 2.6,
	tar >= 0.5.0.3 && < 0.7,
	time >= 1.5.0.1 && < 1.13,
	zlib >= 0.5.3 && < 0.7,
	hackage-security >= 0.6.2.0 && < 0.7,
	text >= 1.2.3 && < 1.3 || >= 2.0 && < 2.2,
	parsec >= 3.1.13.0 && < 3.2,
	open-browser >= 0.2.1.0 && < 0.3,
	regex-base >= 0.94.0.0 && <0.95,
	regex-posix >= 0.96.0.0 && <0.97,
	safe-exceptions >= 0.1.7.0 && < 0.2,
	semaphore-compat >= 1.0.0 && < 1.1

[ulysses4ever]

I'm mildly supportive. We learned the downsides of auto formatting all too well with fourmolu: backports become very painful, contributor's life becomes harder. But cabal files are a tiny part of the code, so maybe these downsides don't quite apply.

[ffaf1]

Small gain with an increase of stuff that can break CI, not a fan.

[alt-romes]

FWIW I don't like the auto formatting. Having yet another one would be another hoop to jump through before being able to submit a patch that isn't add odds with CI for little gain.

[philderbeast]

I used cabal-fmt in production CI and found it pretty effortless to use. Before commiting, grab the relative path to the .cabal file in question and run $ cabal-fmt <paste> --inplace.

As for backporting, would that be easier if we ran cabal-fmt on the branch we're porting to first?

Disregarding cabal-fmt for the moment, won't we adopt automatic formatting when the exact printer, #7544, is ready?

[philderbeast]

There's now cabal-gild that can format .cabal and .project files.

I don't like having to hand-crank my editor to line up with the existing ad-hoc formatting, like this snippet that tries but fails to do column aligned version constraints;

cabal/Cabal-syntax/Cabal-syntax.cabal

Lines 30 to 46 in fe82d9b

	build-depends:
	array >= 0.4.0.1 && < 0.6,
	base >= 4.9 && < 5,
	binary >= 0.7 && < 0.9,
	bytestring >= 0.10.0.0 && < 0.13,
	containers >= 0.5.0.0 && < 0.8,
	deepseq >= 1.3.0.1 && < 1.6,
	directory >= 1.2 && < 1.4,
	filepath >= 1.3.0.1 && < 1.6,
	mtl >= 2.1 && < 2.4,
	parsec >= 3.1.13.0 && < 3.2,
	pretty >= 1.1.1 && < 1.2,
	text (>= 1.2.3.0 && < 1.3) || (>= 2.0 && < 2.2),
	time >= 1.4.0.1 && < 1.13,
	-- transformers-0.4.0.0 doesn't have record syntax e.g. for Identity
	-- See also https://github.com/ekmett/transformers-compat/issues/35
	transformers (>= 0.3 && < 0.4) || (>=0.4.1.0 && <0.7)

[philderbeast]

Take cabal-testsuite, it has leading commas and trailing commas, sort of sorted and really unsorted lists of dependencies.

cabal/cabal-testsuite/cabal-testsuite.cabal

Lines 126 to 136 in 2ee79c3

	build-depends: cabal-testsuite,
	base,
	directory,
	Cabal,
	Cabal-syntax,
	filepath,
	transformers,
	bytestring,
	time,
	process,
	exceptions

cabal/cabal-testsuite/cabal-testsuite.cabal

Lines 60 to 66 in 2ee79c3

	build-depends:
	, aeson ^>= 1.4.2.0 || ^>=1.5.0.0 || ^>= 2.0.0.0 || ^>= 2.1.0.0 || ^>= 2.2.1.0
	, async ^>= 2.2.1
	, attoparsec ^>= 0.13.2.2 || ^>=0.14.1
	, base16-bytestring ^>= 0.1.1.5 || ^>= 1.0
	, bytestring ^>= 0.10.0.2 || ^>= 0.11.0.0 || ^>= 0.12.0.0
	, containers ^>= 0.5.0.0 || ^>= 0.6.0.1 || ^>= 0.7