#5486 The documented keyword ztics is rejected as unknown

[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

The symbol branch of PLOT-OPTIONS-PARSER has clauses for the keywords xtics and ytics, which remove the option, but none for ztics, although the documentation lists ztics and noztics.

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.
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 * \#5486 The documented keyword ztics is rejected as unknown 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([ztics,1,2,3])$ set_plot_option(ztics);

Before the fix:

Unknown plot option "ztics".

Correct result:

ztics is removed from the options

Fix

In src/plot.lisp (PLOT-OPTIONS-PARSER, line "($ytics (remf options '$ytics))"), replace

         ($ytics (remf options '$ytics))

with

         ($ytics (remf options '$ytics))
         ($ztics (remf options '$ztics))

Test cases

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

/* Bug #5486: "The documented keyword ztics is rejected as unknown" */

block ([r],
  reset_plot_options (),
  set_plot_option ([ztics, 1, 2, 3]),
  set_plot_option (ztics),
  r: get_plot_option (ztics),
  reset_plot_options (),
  r);
false$

Commit message

plot.lisp: accept the ztics keyword

PLOT-OPTIONS-PARSER had clauses for the keywords xtics and ytics, which
remove the option, but none for ztics, so the documented keyword ztics
was rejected as unknown. Add the clause.

This fixes bug #5486.

Found and fixed by Claude Opus 5.5.