tempfile related problems on MXE windows build

[cbm755]

from octave.discourse.group:

A couple of tests are failing in the CI with the nightly builds for Windows:
[freshly brewed Octave · gnu-octave/octave-buildbot@43f176e (github.com)](https://github.com/gnu-octave/octave-buildbot/runs/7238133932?check_suite_focus=true#step:13:15477)

Some of the errors seem to emit things like this:

  python: can't open file '/mingw64/share/octave/packages/symbolic-3.0.0/D:\a\_temp\oct-EEh6sa_octsympytmp.py': [Errno 2] No such file or directory

It looks like this could be two absolute paths that are concatenated. That is probably ok for most paths on a Linux file system. But it is failing on Windows.

Edit: That’s still with SymPy 1.5 in case that should matter.

updateI have trouble finding things later on discourse, not sure why, so I don't waste 5 mins in the future, here's the link https://octave.discourse.group/t/symbolic-3-0-0-released/2975/5

[cbm755]

@alexvong243f can you look into this?

[alexvong243f]

In private/python_ipc_system.m, we currently do

    %% Generate a temp .py file then execute it with system()
    % can be useful for debugging, or if "python -c" fails for you
    if (isempty (tmpfilename))
      tmpfilename = [tempname() '_octsympytmp.py'];
      if (verbose)
        disp (['This session will use the temp file "' tmpfilename '"'])
      end
    end
    fd = fopen (tmpfilename, 'w');
    fprintf(fd, '# temporary autogenerated code\n\n');
    % we just added two more lines at the top
    info.prelines = info.prelines + 2;
    fputs(fd, bigs);
    fclose(fd);
    [status, out] = system ([pyexec ' ' tmpfilename]);

[alexvong243f]

Could this be a tempname() problem? How should we reproduce it?

[cbm755]

I'm not sure :( I did run our test suite on a Windows machine (Octave 5.2.0) before releasing and I did not see this. Perhaps its something about cross-compiling? But I agree we're just using what tempname() gives us here, which is apparently

/mingw64/share/octave/packages/symbolic-3.0.0/D:\a\_temp\oct-EEh6sa_

That "D:" in the middle of a path seems invalid on Windows to me... @mmuetzel is it possible this is an upstream Octave / MXE builder problem...

[cbm755]

The other errors in that log look like:

   Traceback (most recent call last):
    File "<string>", line 1, in <module>
  FileNotFoundError: [Errno 2] No such file or directory: 'D:\x07\\octave-buildbot\\octave-buildbot\\octave-2022-07-07-00-12-w64\\mingw64\\share\\octave\\packages\\symbolic-3.0.0\\private\\python_header.py'

Note the very different paths which look more reasonably and don't have a mixture of slashes and backslashes... unlike what tempname is giving us: /mingw64/share/octave/packages/symbolic-3.0.0/D:\a\_temp\oct-EEh6sa_

[cbm755]

Hold on, this construction is maybe suspicious to me:

tmpfilename = [tempname() '_octsympytmp.py'];

Is there some problem about backslashes etc when you concatenate strings? Sounds familiar to me...

[cbm755]

Like does it help to use strcat(tempname(), '_octsympytmp.py') here? I can't see any difference...

[mmuetzel]

Hmm... It looks like the Python that is included in Octave for Windows is for Cygwin. But the Octave program itself is for native MinGW.
By the looks of it, that Cygwin Python has issues when it gets passed a native Windows path. It expects a Cygwin path instead.

I don't know why this is a Cygwin Python and not a MinGW Python.
@lostbard: Would it be possible to include a MinGW Python in MXE Octave? Or do you have an idea how that could be solved otherwise?

[cbm755]

For the record, I think the previous behaviour of Symbolic here was to create a temp file in the current working directory. Which is rude (see #1140). But that is presumably why previous versions did not hit this issue.

[lostbard]

@mmuetzel should already using msys2 python

in mxe: src/msys2-python.mk

At some point in the past we were using the embedded python rather than msys2, but have been with msys2 I believe for a while ?

in mxe:
changeset: 5493:dace3d372190
user: John Donoghue john.donoghue@ieee.org
date: Thu Jul 23 12:29:32 2020 -0400
summary: Use msys2 python3

That may have been after octave 5,2.0 ?