append_to_vlist with single return value broken
Hi, according to the documentation for `append_to_vlist_filter`:
The prevdepth is also optional
so it should be allowed to only return a box in which case the prevdepth value shouldn't change. But if we actually try this: \directlua{ callback.register("append_to_vlist_filter", function(b) return b end) } abc \bye LuaTeX answers with warning (pdf backend): no pages of output. because it discards all boxes. This is caused by a bug in luanode.c, lua_appendtovlist_callback: The callback is called with lua_pcall(Luas, 4, 2, 0). Then LuaTeX tries to determine if one or two values have been returned by looking at the type of slot -1: If this is a number, the second return value have been a number and it is evaluated as new prevdepth. Otherwise else if (lua_type(Luas, -1) != LUA_TNIL) { p = check_isnode(Luas, -1); *result = *p; } is evaluated to scan for a single return value which is a node. But because lua_pcall(Luas, 4, 2, 0) explicitly requested two return values, a callback with one return values would result in a stack where the one return value is followed by `nil`. Therefore this `if` block is not entered. The problem can be fixed by always looking at stack slot -2 for the returned node: source/texk/web2c/luatexdir/lua/luanode.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/source/texk/web2c/luatexdir/lua/luanode.c b/source/texk/web2c/luatexdir/lua/luanode.c index a0c97e37d..d4baab96d 100644 --- a/source/texk/web2c/luatexdir/lua/luanode.c +++ b/source/texk/web2c/luatexdir/lua/luanode.c @@ -183,12 +183,9 @@ int lua_appendtovlist_callback(halfword box, int location, halfword prev_depth, if (lua_type(Luas,-1) == LUA_TNUMBER) { *next_depth = lua_roundnumber(Luas,-1); *prev_set = true; - if (lua_type(Luas, -2) != LUA_TNIL) { - p = check_isnode(Luas, -2); - *result = *p; - } - } else if (lua_type(Luas, -1) != LUA_TNIL) { - p = check_isnode(Luas, -1); + } + if (lua_type(Luas, -2) != LUA_TNIL) { + p = check_isnode(Luas, -2); *result = *p; } return 1; -- Best regards, Marcel
On Sat, Mar 7, 2020 at 2:13 PM Marcel Fabian Krüger
Hi,
according to the documentation for `append_to_vlist_filter`:
The prevdepth is also optional
so it should be allowed to only return a box in which case the prevdepth value shouldn't change.
But if we actually try this:
\directlua{ callback.register("append_to_vlist_filter", function(b) return b end) } abc \bye
LuaTeX answers with warning (pdf backend): no pages of output.
because it discards all boxes. This is caused by a bug in luanode.c, lua_appendtovlist_callback: The callback is called with lua_pcall(Luas, 4, 2, 0). Then LuaTeX tries to determine if one or two values have been returned by looking at the type of slot -1: If this is a number, the second return value have been a number and it is evaluated as new prevdepth. Otherwise
else if (lua_type(Luas, -1) != LUA_TNIL) { p = check_isnode(Luas, -1); *result = *p; }
is evaluated to scan for a single return value which is a node. But because lua_pcall(Luas, 4, 2, 0) explicitly requested two return values, a callback with one return values would result in a stack where the one return value is followed by `nil`. Therefore this `if` block is not entered.
The problem can be fixed by always looking at stack slot -2 for the returned node:
source/texk/web2c/luatexdir/lua/luanode.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/source/texk/web2c/luatexdir/lua/luanode.c b/source/texk/web2c/luatexdir/lua/luanode.c index a0c97e37d..d4baab96d 100644 --- a/source/texk/web2c/luatexdir/lua/luanode.c +++ b/source/texk/web2c/luatexdir/lua/luanode.c @@ -183,12 +183,9 @@ int lua_appendtovlist_callback(halfword box, int location, halfword prev_depth, if (lua_type(Luas,-1) == LUA_TNUMBER) { *next_depth = lua_roundnumber(Luas,-1); *prev_set = true; - if (lua_type(Luas, -2) != LUA_TNIL) { - p = check_isnode(Luas, -2); - *result = *p; - } - } else if (lua_type(Luas, -1) != LUA_TNIL) { - p = check_isnode(Luas, -1); + } + if (lua_type(Luas, -2) != LUA_TNIL) { + p = check_isnode(Luas, -2); *result = *p; } return 1; --
Thank you very much. Very likely I will see it this evening. -- luigi
On 3/7/2020 2:13 PM, Marcel Fabian Krüger wrote:
Hi,
according to the documentation for `append_to_vlist_filter`:
The prevdepth is also optional
so it should be allowed to only return a box in which case the prevdepth value shouldn't change.
But if we actually try this:
\directlua{ callback.register("append_to_vlist_filter", function(b) return b end) } abc \bye
LuaTeX answers with warning (pdf backend): no pages of output.
because it discards all boxes. This is caused by a bug in luanode.c, lua_appendtovlist_callback: The callback is called with lua_pcall(Luas, 4, 2, 0). Then LuaTeX tries to determine if one or two values have been returned by looking at the type of slot -1: If this is a number, the second return value have been a number and it is evaluated as new prevdepth. Otherwise
else if (lua_type(Luas, -1) != LUA_TNIL) { p = check_isnode(Luas, -1); *result = *p; }
is evaluated to scan for a single return value which is a node. But because lua_pcall(Luas, 4, 2, 0) explicitly requested two return values, a callback with one return values would result in a stack where the one return value is followed by `nil`. Therefore this `if` block is not entered.
The problem can be fixed by always looking at stack slot -2 for the returned node: actually we can as well accept nil then so that one can discard something
if (lua_type(Luas, -2) == LUA_TUSERDATA) { halfword* p = lmt_check_isnode(Luas, -2); *result = *p; } else if (lua_type(Luas, -2) == LUA_TNIL) { *result = null; } else { normal_warning("append to vlist","error: node or nil expected"); } if (lua_type(Luas, -1) == LUA_TNUMBER) { *next_depth = lmt_roundnumber(Luas, -1); *prev_set = 1; } ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------
On Sat, Mar 07, 2020 at 04:55:06PM +0100, Hans Hagen wrote:
The problem can be fixed by always looking at stack slot -2 for the returned node: actually we can as well accept nil then so that one can discard something
Returning `nil` is already supported: It is documented and also works fine because `result` is always initialized to `null` (in packaging.c). But I agree that handling that case explicitly in `lua_appendtovlist_callback` might be a bit cleaner and also in some cases slightly more efficient.
if (lua_type(Luas, -2) == LUA_TUSERDATA) { halfword* p = lmt_check_isnode(Luas, -2); *result = *p; } else if (lua_type(Luas, -2) == LUA_TNIL) { *result = null; } else { normal_warning("append to vlist","error: node or nil expected"); } if (lua_type(Luas, -1) == LUA_TNUMBER) { *next_depth = lmt_roundnumber(Luas, -1); *prev_set = 1; }
I assume lmt_... is the luametatex equivalent? Marcel
participants (3)
-
Hans Hagen -
luigi scarso -
Marcel Fabian Krüger