bpo-39468: Improve the site module's error handling while writing .python_history

[opensource-assist]

https://bugs.python.org/issue39468

[eryksun]

@eryksun
If I was to report this bug in the GNU readline's tracker, what should I have called the title?

I'd title it "errno not returned for some errors in write_history, append_history, and history_truncate_file". In particular these calls return -1 when the internal histfile_restore call fails because rename fails. It's fine for histfile_restore to return the result from rename, but this should be checked for failure (e.g. -1) and handled appropriately by the caller in history_do_write and history_truncate_file. For example, in history_do_write they do the following:

if (rv == 0 && histname && tempname)
    rv = histfile_restore (tempname, histname);

if (rv != 0)
    {
      if (tempname)
	unlink (tempname);
      history_lines_written_to_file = 0;
    }

This needs a simple fix to update the value of rv when histfile_restore fails:

if (rv == 0 && histname && tempname)
    rv = histfile_restore (tempname, histname);

if (rv != 0) {
    rv = errno;
    if (tempname)
        unlink(tempname);
    history_lines_written_to_file = 0;
}

[codecov]

Codecov Report

Merging #18299 into master will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18299      +/-   ##
==========================================
- Coverage   82.20%   82.12%   -0.08%     
==========================================
  Files        1957     1954       -3     
  Lines      589079   583367    -5712     
  Branches    44401    44401              
==========================================
- Hits       484247   479093    -5154     
+ Misses      95174    94636     -538     
+ Partials     9658     9638      -20     

Impacted Files	Coverage Δ
Lib/distutils/tests/test_bdist_rpm.py	30.00% <0.00%> (-65.00%)	⬇️
Lib/distutils/command/bdist_rpm.py	7.63% <0.00%> (-56.88%)	⬇️
Lib/test/test_urllib2net.py	76.92% <0.00%> (-13.85%)	⬇️
Lib/test/test_smtpnet.py	78.57% <0.00%> (-12.86%)	⬇️
Lib/ftplib.py	63.85% <0.00%> (-6.06%)	⬇️
Lib/test/test_ftplib.py	87.11% <0.00%> (-4.72%)	⬇️
Lib/dbm/__init__.py	66.66% <0.00%> (-4.45%)	⬇️
Tools/scripts/db2pickle.py	17.82% <0.00%> (-3.97%)	⬇️
Lib/test/test_socket.py	71.94% <0.00%> (-3.87%)	⬇️
Tools/scripts/pickle2db.py	16.98% <0.00%> (-3.78%)	⬇️
... and 312 more

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[opensource-assist]

I still want to notice the users that the .python_history file is not writable, so that they wouldn't guess there's something wrong somewhere else.

[iritkatriel]

You could use two except clauses:

except (FileNotFoundError, PermissionError):
   pass
except OsError:
    if e.errno == -1:
       print(...)
    else:
        raise

[iritkatriel]

That said, are you sure that printing to stdout is the right thing to do here?

[MaxwellDupre]

I am getting an error trying to check out this branch:
gh pr checkout 18299
From https://github.com/python/cpython
! [rejected] refs/pull/18299/head -> master (non-fast-forward)
exit status 1

My GH clone is up to date with cpython and my local repro is up to date with my clone.