Re: [RFC PATCH 3/3] list-objects-filter: implement composite filters

[Matthew DeVore <matvore@comcast.net>]

> On 2019/05/17, at 6:17, Matthew DeVore <matvore@comcast.net> wrote:
> 
> We do have to require the combine operator (& or +) and % be encoded. For other operators, there are three options:
> 
> ...
> 3. Require encoding of a couple of "reserved" characters that don't appear in filters now, and don't typically appear in UNIX path names. This would allow for expansion later. For instance, "~&%*+|(){}!\" plus the ASCII range [0, 0x20] and single and double quotes - do not allow encoding of anything else.
> 
> 4. Same requirements as 3, but permit encoding of other arbitrary characters.

I tried implementing the reserved characters idea, and considering that
it was a small amount of code, I think it's worth it:

+static const char *RESERVED_NON_WS = "\"\\'[]{}!@#$^~*+";
+
+static int has_reserved_character(
+       struct strbuf *sub_spec, struct strbuf *errbuf)
+{
+       const char *c = sub_spec->buf;
+       while (*c) {
+               if (*c <= ' ' || *strchr(RESERVED_NON_WS, *c))
+                       goto found_reserved;
+               c++;
+       }
+
+       return 0;
+
+found_reserved:
+       if (errbuf)
+               strbuf_addf(errbuf, "must escape char in sub-spec: %c", *c);
+       return 1;
+}
+