Failing length/2 test

Running the Logtalk bundled tests for the de facto standard length/2 predicate, a single test fails:

?- length([1, 2, 3, 4, 5| _], 2).
limit exceeded ;

In the this related thread, I provide a Prolog implementation of the predicate. But the actual fix for Tau Prolog may be simpler.

P.S. Running all the Logtalk standards compliance tests with 153145aa0862d5643826e2bdd223d825be0cfe41 gives:

% 182 test sets: 165 completed, 12 skipped, 1 broken, 0 timedout, 4 crashed
% 2651 tests: 93 skipped, 2200 passed, 358 failed (0 flaky)

The four crashes are fixed by #287. The reported broken test is for the length/2 predicate due to the bug above. Of the 358 failed tests, 285 are for the format/2-3 predicates (a far from trivial predicate to implement). Several of the remaining 73 failed tests should be easily fixed.

[jariazavalverde]

Fixed.

@UWN Thanks for the link. I think I fixed all cases (except number 26).

[pmoura]

Before there was a single failing test. Now:

% tests started at 2022-03-26, 20:37:16
% 
% running tests from object tests
% file: logtalk3/tests/prolog/predicates/length_2/tests.lgt
% 
% commons_length_2_01: success (in 0.0 seconds)
% commons_length_2_02: success (in 0.0 seconds)
% commons_length_2_03: success (in 0.0 seconds)
% commons_length_2_04: success (in 0.0 seconds)
% commons_length_2_05: success (in 0.0 seconds)
% commons_length_2_06: success (in 0.0 seconds)
% commons_length_2_07: success (in 0.0 seconds)
% commons_length_2_08: success (in 0.0 seconds)
% commons_length_2_09: success (in 0.0 seconds)
!     commons_length_2_10: failure (in 0.0 seconds)
!       test assertion failed: variant([[]-0,[A]-1,[A,B]-2,[A,B,C]-3],[[]-0,[D]-1,[E,F]-2,[G,H,I]-3])
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 66-69
!     commons_length_2_11: failure (in 0.0 seconds)
!       test assertion failed: variant([[]-3,[A]-4,[A,B]-5,[A,B,C]-6],[[]-3,[D]-4,[E,F]-5,[G,H,I]-6])
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 69-72
% commons_length_2_12: success (in 0.0 seconds)
% commons_length_2_13: success (in 0.0 seconds)
!     commons_length_2_14: failure (in 0.0 seconds)
!       test goal failed but should have thrown an error:
!         expected error(type_error(list,a),A)
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 78-81
!     commons_length_2_15: failure (in 0.0 seconds)
!       test goal failed but should have thrown an error:
!         expected error(type_error(list,a),A)
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 81-84
!     commons_length_2_16: failure (in 0.0 seconds)
!       test goal failed but should have thrown an error:
!         expected error(type_error(list,1),A)
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 84-87
!     commons_length_2_17: failure (in 0.0 seconds)
!       test goal failed but should have thrown an error:
!         expected error(type_error(list,[A,B|a]),C)
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 87-90
!     commons_length_2_18: failure (in 0.0 seconds)
!       test goal failed but should have thrown an error:
!         expected error(type_error(list,[A,B|a]),C)
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 90-93
!     commons_length_2_19: failure (in 0.0 seconds)
!       test goal failed but should have thrown an error:
!         expected error(type_error(list,[A,B|a]),C)
!       in file logtalk3/tests/prolog/predicates/length_2/tests.lgt between lines 93-96
% commons_length_2_20: success (in 0.0 seconds)
% commons_length_2_21: success (in 0.0 seconds)
% commons_length_2_22: success (in 0.0 seconds)
% commons_length_2_23: success (in 0.0 seconds)
% commons_length_2_24: success (in 0.0 seconds)
% commons_length_2_25: skipped
% commons_length_2_26: skipped
% commons_length_2_27: skipped
% 
% 27 tests: 3 skipped, 16 passed, 8 failed (0 flaky)
% completed tests from object tests
% 
% no code coverage information collected
% tests ended at 2022-03-26, 20:37:22