On Sun, 27 Nov 2022 at 14:59, Marcel Fabian Krüger 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