Re: [PATCH v5 1/1] cat-file: quote-format name in error when using -z

> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> On 12/05/2023 17:57, Junio C Hamano wrote:
>>> Toon Claes <toon@iotcl.com> writes:
>>> Stepping back a bit, how big a problem is this in real life?  It
>>> certainly is possible to create a pathname with funny byte values in
>>> it, and in some environments,letters like single-quote that are
>>> considered cumbersome to handle by those who are used to CLI
>>> programs may be commonplace.  But a path with newline?  Or any
>>> control character for that matter?  And this is not even the primary
>>> output from the program but is an error message for consumption by
>>> humans, no?
>>> I am wondering if it is simpler to just declare that the paths
>>> output in error messages have certain bytes, probably all control
>>> characters other than HT, replaced with a dot, and tell the users
>>> not to rely on the pathnames being intact if they contain funny
>>> bytes in them.
>>
>> We could only c-quote the name when it contains a control character
>> other that HT. That way names containing double quotes and backslashes
>> are unchanged but it will still be possible to parse the path from the
>> error message. If we're going to munge the name we might as well use
>> our standard quoting rather than some ad-hoc scheme.
> 
> In the above suggestion, I gave up and no longer aim to do
> "quoting".  A more appropriate word for the approach is "redacting".
> The message essentially is: If you use truly problematic bytes in
> your path, they are redacted (so do not use them if it hurts).
> 
> This is because I am not sure how "names containing dq and bs are
> unchanged" can be done without ambiguity.

>  If I see a message that
> comes out of this:
> 
> 	printf("%s missing\n", obj_name);
> 
> and it looks like
> 
> 	"a\nb" missing
> 
> how do I tell if it is complaining about the object the user named
> with a three-byte string (i.e. lowercase-A, newline, lowercase-B),
> or a six-byte string (i.e. dq, lowercase-A, bs, lowercase-N,
> lowercase-B, dq)?
> 
> If we were forbidding '"' to appear in a refname, then we could take
> advantage of the fact that the name of an object inside a tree at a
> funny path would not start with '"', to disambiguate.  For the
> three- and six-byte string cases above, the formatting function will
> give these messages (referred to as "sample output" below):
> 
> 	"master:a\nb" missing
> 	master:"a\nb" missing
> 
> because of your "we do not exactly do our standard c-quote; we
> exempt dq and bs from the bytes to be quoted" rule.
> 
> But it still feels a bit misleading.  This codepath may have the
> whole objectname as a single string so that c-quoting the entire
> "<commit> <colon> <path>" inside a single c-quoted string that
> begins with a dq is easy, but not all codepaths are lucky and some
> may have to show <commit> and <path> separately, concatenated with
> <colon> at the outermost output layer, which means that the second
> one from the sample output may still mean the path with three-byte
> name in the tree of 'master' commit.
> 
> And worse yet, because
> 
> 	git branch '"master'
> 
> is possible (even though nobody sane would do that), so "treat the
> string as c-quoted only if the object name as a whole begins with a
> dq", this disambiguation idea would not work.  The first one from
> the sample output could be the blob at the path with a five-byte
> string name (i.e. lowercase-A, bs, lowercase-N, lowercase-B, dq)
> in the tree of the commit at the tip of branch with seven-byte
> string name (i.e. dq followed by 'master').
> 
> So, I dunno.