Re: [PATCH] config.c: change the function signature of `git_config_string()`

On Tue, Jul 22, 2014 at 03:49:56AM -0700, Tanay Abhra wrote:

`git_config_string()` output parameter `dest` is declared as a const
which is unnecessary as the caller of the function is given a strduped
string which can be modified without causing any harm.

Thus, remove the const from the function signature.

You are correct that it is unnecessary. However, this patch alone is not
sufficient because of the way const-ness in C works. If I have:

  static const char *some_global;

then with your patch, calling:

  git_config_string(&some_global, var, value);

will complain that we are passing a pointer to "const char *", not a
pointer to "char *". And indeed, compiling with your patch introduces a
ton of compiler warnings.

We would have to convert each of the variables we pass to it to:

  static char *some_global;

That's not so bad, but:

  static char *some_global = "some_default_value";

is wrong. Such a global sometimes points to const storage (i.e.,
initially), and sometimes to allocated storage (if it was loaded from
config). We simply keep the latter as a const pointer (since we would
not bother to free it at the end of the program anyway), and that
decision influences git_config_string, which is just a helper for
setting such variables anyway.

So I would not mind lifting this unnecessary restriction on
git_config_string, but I do not see a way to do it without making the
rest of the code much uglier (and I do not see a particular advantage in
modifying git_config_string here that would make it worth the trouble).

-Peff