Const-ify pointers

[nicoonoclaste]

Many pointers are only set once before going out-of-scope, and could be constified.

Example at https://reviewable.io/reviews/toktok/toxcore/143#-KRuxior-8qxWa2CFtp5

[iphydf]

What's special about pointers? Why should we only const-ify pointers? I understand you mean to make the pointers themselves const, not make them pointers to const.

[nicoonoclaste]

You have a point there: there is no reason not to constify things that are constantm regardless of whether they are pointers.

However, that's pretty likely a large undertaking, and starting with pointers might make sense.

[iphydf]

If we want to go forward with this, we'll need a static analysis to tell us where to add const. There is https://github.com/TokTok/tokstyle that aims to provide some simple checks. This would involve checking that a name is only set once, so a simple heuristic would be:

1. for each function:
   1. vars = get all variable names
   2. get all assignment operators, including the initialiser if it exists (int i; is not assigned, int i = 0; is)
   3. group assignment operators by LHS
   4. for each group:
      1. if group size greater than 1, remove LHS from vars
   5. print out all the vars remaining as diagnostic "can be const"

[iphydf]

Pointers-to-nonconst are more important than local variables, and have a broader impact. I've randomly found some instances of ptrs-to-nonconst that should be ptrs-to-const.

[iphydf]

This is now mostly done. There's a non-blocking check provided by sonarcube that helps us find these.