gh-37573: Doctester: Abbreviate tracebacks in warnings
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Warnings during doctesting show tracebacks that include too much of the
irrelevant details of the doctester. In particular, in the CI, where we
run the doctester under the Coverage.py framework, we see
```
Failed example:: Got: doctest:warning
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File "/sage/local/var/lib/sage/venv-python3.11.1/lib/python3.11/site-
packages/coverage/__main__.py", line 10, in <module>
sys.exit(main())
File "/sage/local/var/lib/sage/venv-python3.11.1/lib/python3.11/site-
packages/coverage/cmdline.py", line 970, in main
status = CoverageScript().command_line(argv)
File "/sage/local/var/lib/sage/venv-python3.11.1/lib/python3.11/site-
packages/coverage/cmdline.py", line 681, in command_line
return self.do_run(options, args)
File "/sage/local/var/lib/sage/venv-python3.11.1/lib/python3.11/site-
packages/coverage/cmdline.py", line 858, in do_run
runner.run()
File "/sage/local/var/lib/sage/venv-python3.11.1/lib/python3.11/site-
packages/coverage/execfile.py", line 211, in run
exec(code, main_mod.__dict__)
File "/sage/src/bin/sage-runtests", line 166, in <module>
err = DC.run()
File "/sage/src/sage/doctest/control.py", line 1565, in run
self.run_doctests()
File "/sage/src/sage/doctest/control.py", line 1177, in run_doctests
self.dispatcher.dispatch()
File "/sage/src/sage/doctest/forker.py", line 2156, in dispatch
self.parallel_dispatch()
File "/sage/src/sage/doctest/forker.py", line 2049, in
parallel_dispatch
w.start() # This might take some time
File "/sage/src/sage/doctest/forker.py", line 2329, in start
super().start()
File "/sage/local/var/lib/sage/venv-
python3.11.1/lib/python3.11/multiprocessing/process.py", line 121, in
start
self._popen = self._Popen(self)
File "/sage/local/var/lib/sage/venv-
python3.11.1/lib/python3.11/multiprocessing/context.py", line 224, in
_Popen
return _default_context.get_context().Process._Popen(process_obj)
File "/sage/local/var/lib/sage/venv-
python3.11.1/lib/python3.11/multiprocessing/context.py", line 281, in
_Popen
return Popen(process_obj)
File "/sage/local/var/lib/sage/venv-
python3.11.1/lib/python3.11/multiprocessing/popen_fork.py", line 19, in
__init__
self._launch(process_obj)
File "/sage/local/var/lib/sage/venv-
python3.11.1/lib/python3.11/multiprocessing/popen_fork.py", line 71, in
_launch
code = process_obj._bootstrap(parent_sentinel=child_r)
File "/sage/local/var/lib/sage/venv-python3.11.1/lib/python3.11/site-
packages/coverage/multiproc.py", line 50, in _bootstrap
return original_bootstrap(self, *args, **kwargs)
File "/sage/local/var/lib/sage/venv-
python3.11.1/lib/python3.11/multiprocessing/process.py", line 314, in
_bootstrap
self.run()
File "/sage/src/sage/doctest/forker.py", line 2300, in run
task(self.options, self.outtmpfile, msgpipe, self.result_queue,
File "/sage/src/sage/doctest/forker.py", line 2622, in __call__
doctests, extras = self._run(runner, options, results)
File "/sage/src/sage/doctest/forker.py", line 2670, in _run
result = runner.run(test)
File "/sage/src/sage/doctest/forker.py", line 911, in run
return self._run(test, compileflags, out)
File "/sage/src/sage/doctest/forker.py", line 712, in _run
self.compile_and_execute(example, compiler, test.globs)
File "/sage/src/sage/doctest/forker.py", line 1147, in
compile_and_execute
exec(compiled, globs)
File "<doctest sage.combinat.chas.fsym.FreeSymmetricFunctions[7]>",
line 1, in <module>
all(FF(G[t].coproduct()) == F(G[t]).coproduct()
File "<doctest sage.combinat.chas.fsym.FreeSymmetricFunctions[7]>",
line 1, in <genexpr>
all(FF(G[t].coproduct()) == F(G[t]).coproduct()
File "/sage/src/sage/categories/coalgebras.py", line 124, in coproduct
return self.parent().coproduct(self)
File "/sage/src/sage/modules/with_basis/morphism.py", line 404, in
__call__
return self.codomain().linear_combination(
File "/sage/src/sage/combinat/free_module.py", line 1067, in
linear_combination
return self._from_dict(blas.linear_combination(((element._monomial_c
oefficients, coeff)
File "/sage/src/sage/combinat/free_module.py", line 1067, in <genexpr>
return self._from_dict(blas.linear_combination
```
Here we omit all of the irrelevant frames.
### :memo: Checklist
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- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.
### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/37573
Reported by: Matthias Köppe
Reviewer(s): Frédéric Chapoton
