From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 23 Mar 2011 18:04:44 GMT
Subject: Re: [PATCH] pathspec: reserve some letters after a colon pathspec
Message-ID: <7vvcz9emrn.fsf@alter.siamese.dyndns.org>
In-Reply-To: <1300894353-19386-1-git-send-email-pclouds@gmail.com>

Nguyễn Thái Ngọc Duy <pclouds@gmail.com> writes:

> Pathspec ':something' means 'something' at top directory. Limit it a
> bit so that ':<non-alnum>something' can be reserved for future
> extensions. ':\<non-alnum>something' can be used to achieve
> ':something' before this patch.
>
> All non-alphanumeric chars on the en_US keyboard, except \ and ., are
> currently reserved.

While I was writing the other message, I really was hoping that people
would notice that trying to limit the magic signature (i.e. "which magic I
want" in my previous message) to a non-alnum letter that cannot easily be
remembered would be a bad direction.  A set of short mnemonic is fine, but
we probably should prepare the syntax framework to reserve spelled out
magic names for readability.

Here is a weather-baloon.  I will use colon below as the magic introducer,
as I don't care very deeply about the choice of it.

 - "^:([^\w\d]+)(.*)$", that is "a magic introducer followed by a sequence
   of non-alnum followed by the remainder" means that the part that is
   given to the matching engine is $2, and each gibberish character in $1
   determines what magic is requested when the matching engine does its
   work.  Among the gibberish that can be in $1, we currently would want
   to support:

    . '/' denotes that $2 is relative to root of the working tree, i.e. do
      not add 'prefix' to it at the left.

    . '!' denotes that the matching with $2 should not honor globbing.

   e.g.

    ":/*lib/**/foo.h", if '*' denoted recursive glob support for '**/' to
    mean "zero-or-more levels of any directory" [*1*], it would find any
    foo.h in a directory 'lib' or its subdirectory that is found in
    anywhere in the working tree.

 - "^:((?:[-a-z]+)(?:,[-a-z+]+)*):(.*)$", that is "a magic introducer,
   followed by one or more alpha-string separated with comma, followed
   by a magic terminator, and the remainder" means that the remainder is
   what is given to the matching engine, and the alpha-strings spell out
   the name of the magic.  We currently would want to support:

    . 'full-tree' means exactly the same as '/' mnemonic above.
    . 'noglob' means exactly the same as '!' mnemonic.

   e.g.

   ":full-tree,recursive-glob:lib/**/foo.h" would be how you fully spell
   the above example in the mnemonic section [*2*].


[Footnote]

*1* "man zshexpn" and look for "Recursive Globbing".

*2* It would be "/full-tree,recursive-glob/lib/**/foo.h" if the magic
introducer were '/', which might be easier to the eye.