#2815 abs_integrate leads to infinite recursion

[Nils Bruin]

reported on sage-support; Robert Dodier confirms problematic behaviour.

See example below. On 5.30 the problem doesn't arise. If abs_integrate isn't loaded, the problem doesn't arise either.

Maxima 5.33.0 http://maxima.sourceforge.net
using Lisp ECL 12.12.1
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) load(abs_integrate);
(%o1) /usr/local/sage/sage-git/local/share/maxima/5.33.0/share/contrib/integration/abs_integrate.mac
(%i2) integrate(log(1-x)*log(1+x)/(1+x),x,0,1);
Maxima encountered a Lisp error:

BINDING-STACK overflow at size 10240. Stack can probably be resized.

[Aleksas]

On maxima 5.31.2 integration is correct:

(%i1) integrate(log(1-x)log(1+x)/(1+x),x,0,1),radcan;
(%o1) (3zeta(3)+8log(2)^3-2%pi^2*log(2))/24

(%i2) load(abs_integrate)$
(%i3) integrate(log(1-x)log(1+x)/(1+x),x,0,1),radcan;
(%o3) (3zeta(3)+8log(2)^3-2%pi^2*log(2))/24

(%i4) wxbuild_info()$
wxMaxima version: 13.4.0
Maxima version: 5.31.2
Maxima build date: 2013-10-07 23:05:06
Host type: i686-pc-mingw32
Lisp implementation type: GNU Common Lisp (GCL)
Lisp implementation version: GCL 2.6.8

best
Aleksas D

[Robert Dodier]

Error seems to be due to mishandling special variables VAR, VARLIST, MAINVAR, and/or GENVAR in TRYRISCH and/or TRYRISCH1 and/or some caller thereof.

git bisect seems to show that the bug appeared in commit [4ccaebaf56] although the bug is not in the abs_integrate code itself, but rather (it appears) a preexisting bug in the Risch code which is triggered by abs_integrate.

[Robert Dodier]

Fixed by commit [f7921c5265] which avoids recursions in TRYRISCH when VARLIST is empty. Closing this report.