Crash in Transform f addargs(1,last) if f appears with no arguments

[jodavies]

Hello,

This is not really a bug as such, but something I found and thought I should report. I would expect the following code to simply "do nothing",

#-
CFunction f;
Local test = f;
Transform f addargs(1,last);
Print +s;
.end

but rather it gives the misleading error

Illegal $ value in range while executing transform statement.

Of course one can avoid it with

Identify f = 0;

or similar, before the transform statement.

Thanks,
Josh.

[jodavies]

Now I hit this again with mulargs. Let's make this give a sensible error message at least, but I would prefer it to just "do nothing" in the 0-arg cases. Any thoughts?

[jodavies]

For this I will prepare a PR which "does nothing" if transform encounters a function with no args and "last" has been used. Experimenting more, this is consistent with the behaviour if a fixed number of args is provided, for eg Transform f addargs(1,2); just ignores f (and f(1)). Also I will give a better error message if the user passes a range spec that is <= 0 directly (currently it also complains about dollar vars).

While looking at the functions in transform I also saw that there is a LOCK placed and not released in RunPermute if a dollar var is used for the cycles and a moduleoption is present that is not "local". The following leads to a deadlock, for example (honestly I am not sure when such dollar variable use is what you would want...)

CFunction f;
Symbol a1,...,a7;
Symbol x,n;

Local test = f(a1,a2,a3,a4,a5,a6,a7);
.sort

$doln = 1;
Transform f permute($doln,3,5)(2,6);

ModuleOption maximum $doln;
Print;
.end

[jodavies]

The commits here fix up the main part of the issue: https://github.com/jodavies/form/tree/transform-noargs

I actually don't like the discrepancies in how addargs and mulargs treat their ranges. Compare:

form/sources/transform.c

Lines 2717 to 2720 in 2073865

	if ( arg2 < arg1 ) { n = arg1; arg1 = arg2; arg2 = n; }
	if ( arg2 > totarg ) return(0);
	num = arg2-arg1+1;
	if ( num == 1 ) return(0);

to

form/sources/transform.c

Lines 2795 to 2800 in 2073865

	if ( arg2 < arg1 ) { n = arg1; arg1 = arg2; arg2 = n; }
	if ( arg1 > totarg ) return(0);
	if ( arg2 < 1 ) return(0);
	if ( arg1 < 1 ) arg1 = 1;
	if ( arg2 > totarg ) arg2 = totarg;
	if ( arg1 == arg2 ) return(0);

Specifically, addargs ignores functions which have fewer arguments than the upper range limit, but mulargs treats it like "last". This should probably be considered a bug, but fixing it may well break user code.

Any thoughts?