gnulib-tool: conditional dependencies calculation

[Dmitry Selyutin]

During implementing support for --conditional-dependencies option I've found a 
strange behavior, which makes me thinking that I don't quite get how module's 
conditional state is being calculated. Let's consider the following gnulib-
tool invocation:

gnulib-tool --with-tests --conditional-dependencies --no-changelog --aux-dir 
build-aux --doc-base doc --lib libgnu --m4-base m4/ --source-base lib/ --
tests-base tests --local-dir gl --makefile-name=gnulib.mk --libtool --import 
fnmatch vasnprintf

Upon executing the same command with pygnulib.py from "python" branch, I 
clearly see the difference between way how modules are treat as conditional. 
For example, module configmake is considered to be conditional by pygnulib.py 
and unconditional by gnulib-tool. Here are all the possible paths which lead 
to configmake module, collected via TransitiveClosure.paths("configmake") 
invocation):

('configmake', 'localcharset', 'mbrtowc', 'mbsinit-tests')
('configmake', 'localcharset', 'mbrtowc', 'mbsrtowcs-tests')
('configmake', 'localcharset', 'mbrtowc', 'mbsinit', 'mbrtowc-tests')
('configmake', 'localcharset', 'mbrtowc', 'mbsinit', 'fnmatch')
('configmake', 'localcharset', 'mbrtowc', 'mbsinit', 'mbsrtowcs-tests')
('configmake', 'localcharset', 'mbrtowc', 'mbsinit', 'wcrtomb', 'wctomb', 
'wctob', 'mbrtowc-tests')
('configmake', 'localcharset', 'mbrtowc', 'mbsinit', 'wcrtomb', 'wctomb', 
'wctob', 'mbsrtowcs-tests')
('configmake', 'localcharset', 'mbrtowc', 'mbsrtowcs', 'fnmatch')
('configmake', 'localcharset', 'mbrtowc', 'mbtowc', 'btowc', 'wcrtomb-tests')

The relationship between configmake and localcharset is an unconditional 
dependency; however, localcharset is listed as a conditional dependency in 
mbrtowc "Depends-on" section, and thus it seems reasonable that not only 
localcharset is a conditional dependency, but all modules required by it.

No other module seem to require localcharset except of mbrtowc.
1) mbrtowc is the only one module which requires localcharset;
2) mbrtowc requires localcharset conditionally;
3) all the dependencies of localcharset shall be considered conditional.

Is the following assumption correct and I've found a bug in gnulib-tool, or am 
I misunderstanding the whole concept of conditional dependencies? I'd be very 
grateful if someone could help me with this issue, currently it is the last 
part of the support for --conditional-dependencies in Python.

Thank you!

-- 
With best regards,
Dmitry Selyutin

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