[m-rev.] for review and benchmarking: speed up file name creation in write_deps_file.m

[Julien Fischer]

On Fri, 8 Sep 2023, Zoltan Somogyi wrote:

> On 2023-09-08 16:44 +10:00 AEST, "Peter Wang" <novalazy at gmail.com> wrote:
>> Making dir./ more understandable is good, but it's not about mangling.
>> 
>> dir./ tries to return a valid path for a given FileName relative to a
>> starting point of DirName. If FileName itself is an absolute path
>> (or a drive-relative path), it's not obvious what the result should be,
>> so dir./ throws an exception. You can't mangle an absolute path into a
>> relative path.
>> 
>> The other thing dir./ does is produce a normalised path, in that the
>> result path uses the standard separator for the platform, and does not
>> include redundant directory separators. (I had thought it might attempt
>> to do something with "." or ".." components but it does not.)
>
> This "other thing" is what I was referring to by "mangling". Sloppy usage, I know.
>
> I like the term "normalised"; it is (in this case) a synonym for "canonicalised",
> but shorter. We should include it in the name of any test predicate.
>
> There is something I don't understand about cygwin's use of directory separators.
> (I pretty much know nothing about cygwin in general, by design.) The comments
> say that cygwin distinguishes between // and \\ as the root directories of two
> different systems, but does it distinguish between / and \ in any other contexts?

According to documentation, there is a distinction as to whether a path
is treated as a Windows or or POSIX path.

See: <https://cygwin.com/cygwin-ug-net/using.html#using-pathnames.

Julien.