Re: [gentoo-portage-dev] has_version and built_with_use ignore package.provided

[Edward Catmur]

On Sun, 2006-08-06 at 22:08 +0100, Paul Bredbury wrote:
> > Other cases would want it to return TRUE.
>
> Got an example of those? I expect to be able to show that they're
> incorrect.

Sorry to keep this alive.

Example: subversion.eclass has
	if built_with_use dev-util/subversion nowebdav; then
		die "need webdav support in subversion"
		...
Clearly, where an ebuild requires that a package be merged *without* a
USE flag set, a FALSE return from built_with_use is expected to indicate
that that package was merged with that USE flag unset.

Looking at this logically, you're interpreting built_with_use as the
Russell definite designator:

built_with_use (A, Fl) := Fl set_on (i P. P matches A)
    == Ex P. (All P'. (P' matches A <=> P' = P) ^ Fl set_on P)

where A denotes an atom, Fl a flag, P, P' a package.

Yes, the Russell definite designator has value FALSE if it lacks a
referent; however there is no need for built_with_use to behave as the
definite designator, since we have a trinary logic (TRUE, FALSE, die)
available. The big problem with the Russell definite designator is that
it is not self-dual under negation (and its dual under negation is not
useful); a trinary definite designator /is/ self-dual. (That is,
"built_with_use app-foo/bar shiney" is equivalent to "! built_with_use
app-foo/bar -shiney". Which is what ebuild authors want.)

HTH,

Ed

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