Re: package dependencies

[Ludovic Courtès]

Leo Famulari <address@hidden> skribis:

> On Sun, Dec 13, 2015 at 02:45:46PM +0100, Ludovic Courtès wrote:
>> Hello!
>> 
>> I’ve rephrased the doc in “package Reference” in a way that is hopefully
>> clearer:
>> 
>>      ‘inputs’ (default: ‘'()’)
>>      ‘native-inputs’ (default: ‘'()’)
>>      ‘propagated-inputs’ (default: ‘'()’)
>>           These fields list dependencies of the package.  Each one is a
>>           list of tuples, where each tuple has a label for the input (a
>>           string) as its first element, a package, origin, or derivation
>>           as its second element, and optionally the name of the output
>>           thereof that should be used, which defaults to ‘"out"’ (*note
>>           Packages with Multiple Outputs::, for more on package
>>           outputs).  For example, the list below specifies 3 inputs:
>> 
>>                `(("libffi" ,libffi)
>>                  ("libunistring" ,libunistring)
>>                  ("glib:bin" ,glib "bin"))  ;the "bin" output of Glib
>> 
>>           The distinction between ‘native-inputs’ and ‘inputs’ is
>>           necessary when considering cross-compilation.  When
>>           cross-compiling, dependencies listed in ‘inputs’ are built for
>>           the _target_ architecture; conversely, dependencies listed in
>>           ‘native-inputs’ are built for the architecture of the _build_
>>           machine.
>> 
>>           ‘native-inputs’ is typically where you would list tools needed
>>           at build time but not at run time, such as Autoconf, Automake,
>>           pkg-config, Gettext, or Bison.  ‘guix lint’ can report likely
>>           mistakes in this area (*note Invoking guix lint::).
>> 
>>           Lastly, ‘propagated-inputs’ is similar to ‘inputs’, but the
>>           specified packages will be force-installed alongside the
>>           package they belong to (*note ‘guix package’:
>>           package-cmd-propagated-inputs, for information on how ‘guix
>>           package’ deals with propagated inputs.)
>> 
>>           For example this is necessary when a library needs headers of
>>           another library to compile, or needs another shared library to
>>           be linked alongside itself when a program wants to link to it.
>
> I think it's a good improvement! This is a big obstacle for new
> packagers.
>
> It may be worth linking between the sections about propagated-inputs and
> the python-build-system, since the situation is somewhat different
> there. At least in a footnote.

Good point.  How about the patch below?  I’m not sure whether/how to
cross-reference from ‘python-build-system’ & co. since they don’t
mention the problem.

Thanks,
Ludo’.

diff --git a/doc/guix.texi b/doc/guix.texi
index 29cea5c..7b7e118 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2305,9 +2305,16 @@ belong to (@pxref{package-cmd-propagated-inputs, 
@command{guix
 package}}, for information on how @command{guix package} deals with
 propagated inputs.)
 
-For example this is necessary when a library needs headers of another
-library to compile, or needs another shared library to be linked
-alongside itself when a program wants to link to it.
+For example this is necessary when a C/C++ library needs headers of
+another library to compile, or when a pkg-config file refers to another
+one @i{via} its @code{Requires} field.
+
+Another example where @code{propagated-inputs} is useful is for
+languages that lack a facility to record the run-time search path akin
+to ELF's @code{RUNPATH}; this includes Guile, Python, Perl, GHC, and
+more.  To ensure that libraries written in those languages can find
+library code they depend on at run time, run-time dependencies must be
+listed in @code{propagated-inputs} rather than @code{inputs}.
 
 @item @code{self-native-input?} (default: @code{#f})
 This is a Boolean field telling whether the package should use itself as