Re-visit re-writing variable declarations with a typedefed type

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#49

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Let's say you have a typedef that looks like this:

typedef struct _A { 
  int a;
  int b;
} A, *PA;

There are two variable declarations somewhere in the program:

PA p1 = foo();

and

PA p2 = bar(); 

In one scenario, both foo and bar are unconstrained and can be PTR. The re-writer could make one edit, in the typedef, to change the definition of PA to be ptr<struct _A> PA. Then this will just work.

However, let's say that the return value of foo is PTR but bar is constrained to not PTR. So one of these will be re-written to ptr and another won't. Can we do better? One option is to create a new typedef, but there are questions to be answered. What is this typedef called? How do we disambiguate it from the old one? And so on.

Come up with a spectrum of answers to this question and implement them.

[secure-sw-dev-bot]

Comment from @mgrang:

Issue filed with 3C: correctcomputation/checkedc-clang#418