Warning if a file glob doesn't match anything

[michaelpj]

As a user, if I've got a file glob that doesn't match anything, that almost certainly means I've made a mistake.

[ffaf1]

Mhhh this should already be there in cabal check:

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

Lines 2367 to 2374 in 63b0f6f

	Right parsedGlob -> do
	results <- runDirFileGlob verbosity (root </> dir) parsedGlob
	let individualWarnings = results >>= getWarning field glob
	noMatchesWarning =
	[ PackageDistSuspiciousWarn (GlobNoMatch field glob)
	| all (not . suppressesNoMatchesWarning) results
	]
	return (noMatchesWarning ++ individualWarnings)

This is the test (added five years ago), added in #5403.

I am currently in the middle of a thorny rebase, an MRE would be quite welcome!