spkg/bin/sage: do not change directory

[jdemeyer]

Remove all unneeded "cd" statements from spkg/bin/sage.

Apply:

1. 13459_no_cd.patch​ to the SAGE_ROOT repository.
2. 13459_no_cd_scripts.patch​ to the SCRIPTS repository.

[jdemeyer]

There is a problem with

import sage

when the current directory is $SAGE_ROOT/devel/sage (or more generally, when a directory sage exists).

[jhpalmieri]

Why are there still some "cd"s in spkg/bin/sage? At least some of them (sync-build, bdist, upgrade) don't look like they're needed. I don't know about the patchbot.

[jdemeyer]

Replying to jhpalmieri:

Why are there still some "cd"s in spkg/bin/sage? At least some of them (sync-build, bdist, upgrade) don't look like they're needed. I don't know about the patchbot.

I wanted to err on the safe side. When unsure, I put the cd statement (or left it). bdist seems to require the cd, for the rest I don't know.

[jhpalmieri]

Can you explain the change in sage-ipython? I don't see any lines corresponding to import sage in the old version. I guess I don't know the mechanics of how sage gets imported when you run sage from the command line.

[jdemeyer]

Replying to jhpalmieri:

Can you explain the change in sage-ipython? I don't see any lines corresponding to import sage in the old version. I guess I don't know the mechanics of how sage gets imported when you run sage from the command line.

When running Sage through IPython (but not through plain Python when running a script for example), the current working directory is always added to sys.path (the empty string is added as zeroth entry, which means the current working directory). So when doing

import sage    # or sage.foo.bar....

the current working directory will be checked first for the existence of a "sage" module. If the current working directory happens to be $SAGE_ROOT/devel/sage, that contains a "sage" subdirectory which Python will happily import. But this is the wrong directory, it should be imported from site-packages instead. This creates problems for Cython modules, as these exist only in site-packages.

So we avoid this problem by first fixing sys.path, then importing Sage so any future imports of Sage submodules will work fine.

[jdemeyer]

I just realized that there is no need to change sys.path in sage-ipython, because we simply import sage before IPython is started. I also added some more comments, needs_review.

[jhpalmieri]

Okay, this looks pretty good to me. I might prefer some more comments in spkg/bin/sage, for example pointing out that sage-bdist needs to be run from SAGE_ROOT. (I'm not actually sure that it does, actually: if run from somewhere else, it just creates the temporary directories in the current working directory, but maybe it will still work. I guess for the principle of least surprise, we shouldn't change the behavior of building in SAGE_ROOT/tmp/.)