Incorrect behavior for install rule and py-compile for _PYTHON targets

[Sander Niemeijer]

Hi all,

I've run into the following (AFAICS incorrect) behavior:

Consider a project with a conditional python_PYTHON target.
When the conditional is false and a 'make install' is issued then the 
rule install-pythonPYTHON is executed with 0 files to install (i.e. the 
dlist variable in the install rule will be empty).
In automake 1.7.9 this resulted in an error since the py-compile script 
did not allow 0 zero input files.
In automake 1.8.0 and 1.8.1 the py-compile script does not complain 
anymore. The reason why it does not complain with this version is 
because the script does not correctly check the amount of input files 
it receives. When you provide only a --basedir option to py-compile 
(which is what happens in the install-pythonPYTHON rule) the py-compile 
script will happely execute and start compiling 0 files. If you would 
try to do the same thing without the --basedir option the py-compile 
script would complain and terminate with an error code.

Although the current behavior in automake 1.8.x will probably not 
result in any problems for users, IMHO I think it would be a good idea 
to make the following changes in order to evade future problems:

- change 'PYTHON=$(PYTHON) $(py_compile) --basedir 
$(DESTDIR)$(pythondir) $$dlist' for each python install target to 'test 
-z "$$dlist" || PYTHON=$(PYTHON) $(py_compile) --basedir 
$(DESTDIR)$(pythondir) $$dlist'
- revert the check for the amount of files given to py-compile to the 
way it was done in automake 1.7.9 (i.e. using the 'if [ $# = 0 ]' check 
after checking for basedir/help/version flags.

This has the advantage that py-compile isn't executed at all anymore 
when a 'make install' is run for an excluded conditional _PYTHON target.

Regards,
Sander Niemeijer