Re: PATCH: Allow empty targets in unaccent dictionary - Mailing list pgsql-hackers

Hi.

At 2014-04-20 01:06:43 +0200, alhashash@alhashash.net wrote:
>
> To use unaccent dictionary for these languages, we need to allow empty
> targets to remove diacritics instead of replacing them.

Your patch should definitely add a test case or two to sql/unaccent.sql
and expected/unaccent.out showing the behaviour that didn't work before
the change.

> The attached patch modfies unaacent.c so that dictionary parser uses
> zero-length target when the line has no target.

The basic idea seems sensible.

> diff --git a/contrib/unaccent/unaccent.c b/contrib/unaccent/unaccent.c
> old mode 100644
> new mode 100755
> index a337df6..4e72829
> --- a/contrib/unaccent/unaccent.c
> +++ b/contrib/unaccent/unaccent.c
> @@ -58,7 +58,9 @@ placeChar(TrieChar *node, unsigned char *str, int lenstr, char *replaceTo, int r
>          {
>              curnode->replacelen = replacelen;
>              curnode->replaceTo = palloc(replacelen);
> -            memcpy(curnode->replaceTo, replaceTo, replacelen);
> +            /* palloc(0) returns a valid address, not NULL */
> +            if (replaceTo) /* memcpy() is undefined for NULL pointers*/
> +                memcpy(curnode->replaceTo, replaceTo, replacelen);
>          }
>      }

I think these comments confuse the issue, and should be removed. In
fact, I think this part of the code can remain unchanged (see below).

> @@ -105,10 +107,10 @@ initTrie(char *filename)
>              while ((line = tsearch_readline(&trst)) != NULL)
>              {
>                  /*
> -                 * The format of each line must be "src trg" where src and trg
> +                 * The format of each line must be "src [trg]" where src and trg
>                   * are sequences of one or more non-whitespace characters,
>                   * separated by whitespace.  Whitespace at start or end of
> -                 * line is ignored.
> +                 * line is ignored. If no trg added, a zero-length string is used.
>                   */
>                  int            state;

I suggest "If trg is empty, a zero-length string is used" for the last
sentence.

> @@ -160,6 +162,13 @@ initTrie(char *filename)
>                      }
>                  }
>  
> +                /* if no trg (loop stops at state 1 or 2), use zero-length target */
> +                if (state == 1 || state == 2)
> +                {
> +                    trglen = 0;
> +                    state = 5;
> +                }

If I understand the code correctly, "src" alone will leave state == 1,
and "src " will leave state == 2, and in both cases trg and trglen will
be unchanged (from NULL and 0 respectively).

In that case, I think it would be clearer to do something like this:
   char *trg = "";
   …
   /* It's OK to have a valid src and empty trg. */   if (state > 0 && trglen == 0)       state = 5;

That way, you don't have the NULL pointer, and you don't have to add a
NULL-pointer test in placeChar() above.

What do you think? If you submit a revised patch along these lines, I'll
mark it ready for committer.

Thank you.

-- Abhijit