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