Re: [PATCH v5 1/5] setup: add gentle version of read_gitfile

Jeff King wrote:

But the NULL does not carry the information about _which_ error, and
Erik is suggesting that the caller may need to change behavior based on
that information. IOW, his current patch (return NULL and set the
specific integer code in a variable) allows this, but switching the
integer code out for a human-readable strbuf does not.

Right.  Two ways to handle that are:

 - two out parameters: an integer code and a human-readable string, or

 - an integer code returned using the ERR_PTR method and a
   human-readable string out parameter

The point I was trying to make clear is that the human-readable error
message and the integer to affect control flow have different purposes
and are not tightly related except in that they are produced at the
same time.

Using an integer to convey the human-readable error message (like errno
does) unnecessarily forces the message to be more vague (by not being
parameterized, and by always using the same error message for the same
integer error).