Fix datadir path in generated Paths_ file

[JoshMeredith]

The generated datadir path can be incorrect if a project is configured for a single component as per #5862

Since the install command uses the non-component variant of the paths for the datadir,

cabal/Cabal/Distribution/Simple/Install.hs

Lines 98 to 114 in 27ef964

	InstallDirs {
	datadir = dataPref,
	-- NB: The situation with Haddock is a bit delicate. On the
	-- one hand, the easiest to understand Haddock documentation
	-- path is pkgname-0.1, which means it's per-package (not
	-- per-component). But this means that it's impossible to
	-- install Haddock documentation for internal libraries. We'll
	-- keep this constraint for now; this means you can't use
	-- Cabal to Haddock internal libraries. This does not seem
	-- like a big problem.
	docdir = docPref,
	htmldir = htmlPref,
	haddockdir = interfacePref}
	-- Notice use of 'absoluteInstallDirs' (not the
	-- per-component variant). This means for non-library
	-- packages we'll just pick a nondescriptive foo-0.1
	= absoluteInstallDirs pkg_descr lbi copydest

this patch changes the generated path to use the same function.

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[phadej]

Can we refactor so "consistency" is obvious via code sharing?

[JoshMeredith]

Can we refactor so "consistency" is obvious via code sharing?

Yes, I think it would be a good idea to make for example absoluteMixedInstallDirs, although I don't know which variant would be a better default for the fields of InstallDirs that are unused by the install command and the generated file.