#5484 [xlabel,5] gives a Lisp error and [ylabel,abc] writes invalid gnuplot

[David Scherfgen]

This bug was discovered by Claude Opus 5.5 and reproduced on Maxima Git commit c62924c (2026-09-26) with SBCL 2.2.9.

Where: src/plot.lisp, PLOT-OPTIONS-PARSER

PLOT-OPTIONS-PARSER checks xlabel, ylabel and zlabel with #'STRING, which converts instead of testing. A number signals a Lisp type error, and a symbol is accepted and later written as set ylabel $ABC.

Steps

1. Verify that the existing behavior is incorrect: run the reproducer below; it gives the result under "Before the fix". Judge for yourself that this is wrong instead of relying on the ticket: where the bug allows it, try some related inputs of your own, or check the result another way, for example numerically or against the documentation. A Lisp error is wrong in itself.
2. Edit the file src/plot.lisp as described under "Fix".
3. Rebuild Maxima.
4. Verify that the behavior is now correct: the reproducer gives the result under "Correct result". Judge for yourself that this is right, not only that it matches: where the bug allows it, try some related inputs of your own, including some that the fix should leave unchanged.
5. Add the test case(s) under "Test cases" to tests/rtest_plotoptions.mac, at the end of the file.
6. Run the complete test suite, share tests included (make check, or run_testsuite(share_tests=true); in ./maxima-local), and check that the change breaks no test. Failures that also occur without the change (a run on the unchanged build shows which) are pre-existing and can be ignored.
7. Add the line * \#5484 [xlabel,5] gives a Lisp error and [ylabel,abc] writes invalid gnuplot to ChangeLog, under "Bug fixes for numbered bugs:".
8. Commit the fix; a proposed Git commit message is under "Commit message".
9. Push the commit. Then set this ticket's status to "closed" and add a comment naming the commit, for example Fixed by commit [1a2b3c]., with the first six characters of the commit's SHA in the brackets (git rev-parse HEAD | cut -c1-6 prints them). SourceForge links this to the commit.

Reproducer

set_plot_option([xlabel,5]); set_plot_option([ylabel,abc]);

Before the fix:

Maxima encountered a Lisp error: 5 is not a string designator; the second call is accepted

Correct result:

Wrong argument for plot option "xlabel" (and "ylabel"). Expecting a string

Fix

In src/plot.lisp (PLOT-OPTIONS-PARSER, clause "($xlabel (setf (getf options '$xlabel)"), replace

         ($xlabel (setf (getf options '$xlabel)
                        (check-option (cdr opt) #'string "a string" 1)))

with

         ($xlabel (setf (getf options '$xlabel)
                        (check-option (cdr opt) #'stringp "a string" 1)))

In src/plot.lisp (PLOT-OPTIONS-PARSER, clause "($ylabel (setf (getf options '$ylabel)"), replace

         ($ylabel (setf (getf options '$ylabel)
                        (check-option (cdr opt) #'string "a string" 1)))

with

         ($ylabel (setf (getf options '$ylabel)
                        (check-option (cdr opt) #'stringp "a string" 1)))

In src/plot.lisp (PLOT-OPTIONS-PARSER, clause "($zlabel (setf (getf options '$zlabel)"), replace

         ($zlabel (setf (getf options '$zlabel)
                        (check-option (cdr opt) #'string "a string" 1)))

with

         ($zlabel (setf (getf options '$zlabel)
                        (check-option (cdr opt) #'stringp "a string" 1)))

Test cases

Add these lines to tests/rtest_plotoptions.mac, separated from the tests before them by two empty lines:

/* Bug #5484: "[xlabel,5] gives a Lisp error and [ylabel,abc] writes invalid gnuplot" */

block ([r],
  reset_plot_options (),
  r: [errcatch (set_plot_option ([xlabel, 5])),
      errcatch (set_plot_option ([ylabel, abc])),
      errcatch (set_plot_option ([zlabel, 1/2])),
      (set_plot_option ([xlabel, "t"]), get_plot_option (xlabel))],
  reset_plot_options (),
  r);
[[], [], [], [xlabel, "t"]]$

Commit message

plot.lisp: require strings for xlabel, ylabel and zlabel

PLOT-OPTIONS-PARSER checked xlabel, ylabel and zlabel with #'STRING,
which converts instead of testing, so [xlabel, 5] signaled a Lisp error
and [ylabel, abc] wrote invalid gnuplot commands. Check with #'STRINGP.

This fixes bug #5484.

Found and fixed by Claude Opus 5.5.