Segfault in plural

[mantepse]

Steps To Reproduce

1. Ubuntu 22.04.5 LTS
2. SageMath version 10.5.beta5, Release Date: 2024-09-22, develop branch compiled from source
3. sage -t src/sage/rings/polynomial/plural.pyx
4. segfault

Expected Behavior

all tests pass

Actual Behavior

bug.txt

Additional Information

Might be related to #29528, but the segfault occured every time I ran the test.

Environment

• OS: Ubuntu 22.04.5 LTS
• Sage Version: 10.5.beta5, Release Date: 2024-09-22, develop branch compiled from source

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide

[fchapoton]

I have that on all machines running gcc13

EDIT: no, in fact. I was thinking to pbori failures.

[dimpase]

no problem on Fedora with gcc 14, and on macOS with its usual clang toolchain

[fchapoton]

I can see that segfault on Ubuntu 22.04.4 LTS running gcc 11.4.0

[tobiasdiez]

Stacktrace:

sage -t --warn-long 5.0 --random-seed=121929766104423602556012623849278420179 src/sage/rings/polynomial/plural.pyx
    SignalError in doctesting framework
**********************************************************************

Tests run before exception:
sage: A.<x,y,z> = FreeAlgebra(QQ, 3) ## line 50 ##
sage: P.<x,y,z> = A.g_algebra(relations={y*x:-x*y}, order = 'lex') ## line 51 ##
sage: P ## line 53 ##
Noncommutative Multivariate Polynomial Ring in x, y, z over Rational Field, nc-relations: {y*x: -x*y}
sage: y*x + 1/2 ## line 56 ##
-x*y + 1/2
sage: A.<x,y,z> = FreeAlgebra(GF(17), 3) ## line 59 ##
sage: P.<x,y,z> = A.g_algebra(relations={y*x:-x*y}, order = 'lex') ## line 60 ##
sage: P ## line 61 ##
Noncommutative Multivariate Polynomial Ring in x, y, z over Finite Field of size 17, nc-relations: {y*x: -x*y}
sage: y*x + 7 ## line 64 ##
-x*y + 7
sage: from sage.matrix.constructor import Matrix ## line 71 ##
sage: c = Matrix(3) ## line 72 ##
sage: c[0,1] = -2 ## line 73 ##
sage: c[0,2] = 1 ## line 74 ##
sage: c[1,2] = 1 ## line 75 ##
sage: d = Matrix(3) ## line 77 ##
sage: d[0, 1] = 17 ## line 78 ##
sage: P = QQ['x','y','z'] ## line 79 ##
sage: c = c.change_ring(P) ## line 80 ##
sage: d = d.change_ring(P) ## line 81 ##
sage: from sage.rings.polynomial.plural import NCPolynomialRing_plural ## line 83 ##
sage: R.<x,y,z> = NCPolynomialRing_plural(QQ, c = c, d = d, order=TermOrder('lex',3),category=Algebras(QQ)) ## line 84 ##
sage: R ## line 85 ##
Noncommutative Multivariate Polynomial Ring in x, y, z over Rational Field, nc-relations: {y*x: -2*x*y + 17}
sage: R.term_order() ## line 88 ##
Lexicographic term order
sage: a,b,c = R.gens() ## line 91 ##
sage: f = 57 * a^2*b + 43 * c + 1; f ## line 92 ##
57*x^2*y + 43*z + 1
sage: A.<x,y,z> = FreeAlgebra(QQ, 3) ## line 97 ##
sage: P = A.g_algebra(relations={y*x:-x*y}, order = 'lex') ## line 98 ##
sage: TestSuite(P).run() ## line 99 ##
sage: loads(dumps(P)) is P ## line 100 ##
True
sage: A.<x,y,z> = FreeAlgebra(QQ, 3) ## line 103 ##
sage: P = A.g_algebra(relations={y*x:-x*y}, order = 'lex') ## line 104 ##
sage: P.is_commutative() ## line 105 ##
False
sage: R.<x,y,z> = FreeAlgebra(QQ, 3) ## line 108 ##
sage: P = R.g_algebra(relations={}, order='lex') ## line 109 ##
sage: P.is_commutative() ## line 110 ##
True
sage: sig_on_count() # check sig_on/off pairings (virtual doctest) ## line 112 ##
0
sage: A.<x,y,z> = FreeAlgebra(QQ, 3) ## line 156 ##
sage: H = A.g_algebra({y*x:x*y-z, z*x:x*z+2*x, z*y:y*z-2*y}) ## line 157 ##

**********************************************************************
Traceback (most recent call last):
  File "parent.pyx", line 895, in sage.structure.parent.Parent.__call__
  File "coerce_dict.pyx", line 650, in sage.structure.coerce_dict.MonoDict.get
KeyError: Free Algebra on 3 generators (x, y, z) over Rational Field

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "parent.pyx", line 2501, in sage.structure.parent.Parent._internal_convert_map_from
  File "coerce_dict.pyx", line 650, in sage.structure.coerce_dict.MonoDict.get
KeyError: Free Algebra on 3 generators (x, y, z) over Rational Field

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/doctest/forker.py", line 2596, in __call__
    doctests, extras = self._run(runner, options, results)
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/doctest/forker.py", line 2644, in _run
    result = runner.run(test)
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/doctest/forker.py", line 905, in run
    return self._run(test, compileflags, out)
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/doctest/forker.py", line 716, in _run
    self.compile_and_execute(example, compiler, test.globs)
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/doctest/forker.py", line 1137, in compile_and_execute
    exec(compiled, globs)
  File "<doctest sage.rings.polynomial.plural.G_AlgFactory[1]>", line 1, in <module>
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/algebras/free_algebra.py", line 1018, in g_algebra
    dmat[v2_ind, v1_ind] = polynomial_ring(d_poly)
  File "parent.pyx", line 897, in sage.structure.parent.Parent.__call__
  File "parent.pyx", line 2503, in sage.structure.parent.Parent._internal_convert_map_from
  File "parent.pyx", line 2524, in sage.structure.parent.Parent.discover_convert_map_from
  File "parent.pyx", line 2146, in sage.structure.parent.Parent._internal_coerce_map_from
  File "parent.pyx", line 2238, in sage.structure.parent.Parent._internal_coerce_map_from
  File "parent.pyx", line 2383, in sage.structure.parent.Parent.discover_coerce_map_from
  File "module.pyx", line 132, in sage.modules.module.Module._coerce_map_from_
  File "/home/runner/miniconda3/envs/sage-dev/lib/python3.10/site-packages/sage/algebras/free_algebra.py", line 771, in _coerce_map_from_
    if isinstance(R, (FreeAlgebra_generic, FreeAlgebra_letterplace)):
  File "lazy_import.pyx", line 966, in sage.misc.lazy_import.LazyImport.__instancecheck__
  File "lazy_import.pyx", line 224, in sage.misc.lazy_import.LazyImport.get_object
  File "lazy_import.pyx", line 259, in sage.misc.lazy_import.LazyImport._get_object
  File "free_algebra_letterplace.pyx", line 1, in init sage.algebras.letterplace.free_algebra_letterplace
  File "free_algebra_element_letterplace.pyx", line 25, in init sage.algebras.letterplace.free_algebra_element_letterplace
  File "function.pyx", line 1809, in sage.libs.singular.function.lib
cysignals.signals.SignalError: Segmentation fault

https://github.com/sagemath/sage/actions/runs/12456108227/job/34769264987