The leading underscore has the notion that this would be a private function.
It really isn't, and it would be fine for the user to call it directly.

Just like we have g_slice_free() and g_slice_free1().

  $ find * -type f |xargs perl contrib/scripts/spdx.pl
  $ git rm contrib/scripts/spdx.pl

It is like strcmp(), but has a signature suitable for GCompareDataFunc.

This is necessary with nm_utils_ptrarray_find_binary_search()
to search a sorted strv array.

The fault is here really C, which doesn't allow inline static functions.
So, you need all kinds of slightly different flavors for the same
callbacks (with or without user-data).

Note that glib2 internally just casts strcmp() to GCompareDataFunc ([1]),
relying on the fact how arguments are passed to the function and
ignoring the additional user-data argument. But I find that really
ugly and probably not permissible in general C. Dunno whether POSIX
would guarantee for this to work. I'd rather not do such function
pointer casts.

[1] https://gitlab.gnome.org/GNOME/glib/blob/0c0cf59858abb3f8464bc55f596f9fbf599ac251/glib/garray.c#L1792

If there is only one argument, we can assume this is a plain string.

That is especially the case, because g_set_error() is G_GNUC_PRINTF()
and would warn if this would be a format string with missing parameters.

This is for convenience. Previously, one was compelled to explicitly
choose between nm_utils_error_set_literal() and nm_utils_error_set().
Now, it automatically chooses.

Note that there are a few things that won't work, like

  nm_utils_error_set (error, code, "bogus %u escape");

But that's good. You get a compiler warning (as you used to)
and it's clear in this case you really need
nm_utils_error_set_literal().