mavgen: protect for too deep inlcude trees

[olliw42]

protect against too deep include trees
useful for mavlink/mavlink#1537 (the include trees tend to become deeper and deeper ...)

[hamishwillee]

@peterbarker This looks like a very good idea to me (eventually we'll hit the limit of inclusion, and this will save us a lot of time explaining to people why their dialect doesn't work)

[peterbarker]

Perhaps this would be neater as:

count = 0
while True:
    if not expand_one_iteration():
       break;
    count += 1
    if count >= MAXIMUM_INCLUDE_FILE_NESTING:
        print("ERROR include tree is too deeply nested!")
        sys.exit(1)

Give-or-take an off-by-one error or two.

My reasoning is just that for loops are usually used for bounded iterations, so checking the number of times you iterated looks a little odd.

[lightmare]

The original PR won't abort, because i will never be set to MAXIMUM_INCLUDE_FILE_NESTING. range(N) does not contain N.
(In other words, for i in range(N) is not the same thing as for(i = 0; i < N; ++i) ;))

The variant suggested by @peterbarker will work. I'd only note that while True: ... if something: break seems awkward, and the comparison should probably be strict, so as to not abort after doing exactly the allowed amount.

count = 0
while expand_one_iteration():
    count += 1
    if count > MAXIMUM_INCLUDE_FILE_NESTING:
        print("ERROR include tree is too deeply nested!")
        sys.exit(1)

[olliw42]

strange
I certainly had tested it for that occasion (by simply reducing the limit to a small value like 1 or 2 which triggers) and it worked for me (otherwise I wouldn't have dared to offer it). I just double checked again and still found it to work for me.
But I agree it's not so nice for python

the simplest probably would be

    for n in range(MAXIMUM_INCLUDE_FILE_NESTING+1):
        if n >= MAXIMUM_INCLUDE_FILE_NESTING:
            print("ERROR include tree is too deeply nested!")
            sys.exit(1)
        if not expand_oneiteration():
            break

works for me

[lightmare]

Yeah if the range is extended by +1, it will get to the max. If you really want to use a for loop, put the error in its else branch, you don't need to check "are we past max rounds" each time.

for _ in range(MAXIMUM_INCLUDE_FILE_NESTING+1):
    if not expand_oneiteration():
        break
else:
    print("ERROR include tree is too deeply nested!")
    sys.exit(1)

But I still think the while loop is more easily understood, especially to people not familiar with nuances of how ranges and for-break-else work in Python.