Reject GAP function definitions containing huge list or record expressions (millions of entries) instead of silently discarding part of the data

[ChrisJefferson]

Fixes #5508 (GAP produces incorrect code when there are very large arrays inside functions). GAP will silently fail whenever there is a function with 2097152 or more elements given explicitly, inside a function (note a list must be this long, a list of lists whose sublists contain this many elements would be fine).

We could also look at increasing how much allowance we give, but I'm tempted to put this commit in as is (unless there are any small fixes / suggestions), because then if anyone has code that has hit this bug in the past, they will get a clear error message that an error has occurred (in fact, perhaps I should even extend the error to say "this code may have given incorrect answers in previous versions of GAP"?)

[fingolfin]

Why is this in testspecial and not part of the .tst file above?

gap> strlist := String(List([1..2097152], x -> x));;
gap> func := Concatenation("lf := function() return ", strlist, "; end;");;
gap> Read(InputTextString(func));;
Error, function too large for parser

should work fine there, no?

[ChrisJefferson]

The reason this was here is previously when this PRed "panic"ed, I couldn't do that in a normal test. Now it's an error, I can (I also added a record test as well. I don't know if anyone would ever create such a huge record in code, but it doesn't hurt to catch it!)

[fingolfin]

Just to say, despite my nitpicking, this is of course a good PR fixing a real issue in a sensible way -- thank you :-)

[fingolfin]

Running the above code changes the behavior of GAP in a way that breaks another test later in the test suite. In a nutshell:

gap> r:=rec();
rec(  )
gap> \.(r, 1000000);
Error, Record Element: <rnam> must be a valid rnam (not the integer 1000000)
not in any function at *stdin*:2
type 'quit;' to quit to outer loop
brk>
gap> r2 := rec();; for x in [1..2097150/2] do r2.(x) := x; od;;
gap> \.(r, 1000000);
Error, Record Element: '<rec>.992517' must have an assigned value
not in any function at *stdin*:5
type 'quit;' to quit to outer loop

Possible fix: modify tst/testinstall/recordname.tst to use, say MAX_SIZE_LIST_INTERNAL instead of 1000000, should fix this...

[fingolfin]

I've adjusted this test now, let's see if that is enough.

[ChrisJefferson]

Just wanted to point out this is now updated (just fixed tests for 32-bit GAP).