Expose and use labelMessage with pkg context

[philderbeast]

Fixes #12019.

• Rename warnMessage to labelMessage¹ and export from Distribution.Simple.Utils
• Add punctuation parameter and haddocks to labelMessage

The output of existing tests suffices to show and test this change.

I'll squash commits before applying the merge label if this pull request is approved.

Note

As can be seen in ppPackageCheck that returns the warning message, the Warning: package-name prefix is followed an [explanation-id] (like [no-default-language]) and then the explanation description:

cabal/Cabal/src/Distribution/PackageDescription/Check/Warning.hs

Lines 89 to 96 in 20fc9ba

	-- | Pretty printing 'PackageCheck'.
	ppPackageCheck :: PackageCheck -> String
	ppPackageCheck e =
	let ex = explanation e
	in "["
	++ (ppCheckExplanationId . checkExplanationId) ex
	++ "] "
	++ ppExplanation ex

QA Notes

Follow the reproduction in the issue, with this pull request checked out locally:

$ cabal install cabal-install:exe:cabal --overwrite-policy=always -j
$ cabal clean --project-file=cabal.validate.project
$ cabal build all --enable-tests --enable-benchmarks --project-file=cabal.validate.project 

The output from the build should contain Warning: Cabal-tests [no-default-language].

---

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added. (Ask for help if you don’t know how to write them! Ask for an exemption if tests are too complex for too little coverage!)

Footnotes

1. I didn't go with labelledMessage or labeledMessage because of the US versus UK, AU, NZ etc spelling differences. ↩