On Sun, 27 Nov 2022 at 14:59, Marcel Fabian Krüger <t...@2krueger.de> wrote:
> Hi,
>
> in LuaTeX node.ligaturing should return the head and the tail of the
> list after ligatures got applied. But in the case that the tail of the new
> list is a discretionary the current code returns the passed in tail
> instead, assuming that it didn't change. This breaks if the
> discretionary node wasn't the tail before the ligature pass:.
>
> Take for example
>
> \directlua{
> local b = token.scan_list()
> local h = b.head
> local t = node.tail(h)
> local post_h, post_t = node.ligaturing(h, node.tail(t))
> print(node.tail(post_h), post_t)
> }\hpack{a\discretionary{}{f}{f}f}
> \bye
>
> Here the `f`s in the discretionary form ligatures with the `f` after the
> discretionary, so after node.ligaturing the list if effectively
> `a\discretionary{}{ff}{ff}` and therefore `post_t` should point to the
> discretionary node. But as the output shows, post_t instead is a glyph
> node while node.tail(post_h) is the expected disc node.
>
> This is caused by `handle_lig_word` in luafont.c. `handle_lig_word` is
> used in `handle_ligaturing` as
>
> while (cur != null) {
> if (type(cur) == glyph_node || (type(cur) == boundary_node)) {
> cur = handle_lig_word(cur);
> }
> prev = cur;
> cur = vlink(cur);
> }
>
> so it is expected that handle_lig_word returns the last node already
> handled
> so that afterwards the loop can continue at vlink(cur). But if the handled
> segment ends with a discretionary `handle_lig_word` returns the node
> `after`
> the last already handled node instead. This is fine if the last node is a
> non glyph/non boundary node, but if the discretionary ends the segment
> passed
> to handle_ligaturing than this means that `handle_lig_word` returns null,
> therefore settings `prev` to `null` instead of tracking the tail.
> Also this relies on `vlink(null)` being null, causing issues if this
> ever gets corrupted (see my next mail for an example...).
>
> It can be fixed by making sure that handle_lig_word always returns the
> last handled node, e.g. using
>
> diff --git a/source/texk/web2c/luatexdir/font/luafont.c
> b/source/texk/web2c/luatexdir/font/luafont.c
> index 2e08facb1..c33037244 100644
> --- a/source/texk/web2c/luatexdir/font/luafont.c
> +++ b/source/texk/web2c/luatexdir/font/luafont.c
> @@ -2242,6 +2242,7 @@ static halfword handle_lig_nest(halfword root,
> halfword cur)
> static halfword handle_lig_word(halfword cur)
> {
> halfword right = null;
> + halfword last = null;
> if (type(cur) == boundary_node) {
> halfword prev = alink(cur);
> halfword fwd = vlink(cur);
> @@ -2481,9 +2482,10 @@ static halfword handle_lig_word(halfword cur)
>
> } else {
> /*tex We have glyph nor disc. */
> - return cur;
> + return last;
> }
> /*tex Goto the next node, where |\par| allows |vlink(cur)| to be
> NULL. */
> + last = cur;
> cur = vlink(cur);
> }
> return cur;
> --
>
Sorry for the delay, I will check it this evening .
--
luigi
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