[aux] fix units lookup prevent crash with AFM fonts

With the new loader, the ``units_per_em`` field resides under the
toplevel TFM structure with the key ``units``. For AFM fonts, it is not
fount under the metadata table too, which we are currently querying.
Thus we prefer the main value, falling back on metadata only in case it
is missing.

At this occasion, tidy up our unit lookup helper and use that wherever
we need access to the values ourselves.

1 files changed, 16 insertions, 10 deletions

diff --git a/src/luaotfload-auxiliary.lua b/src/luaotfload-auxiliary.lua
index e544dd7..e482aba 100644
--- a/src/luaotfload-auxiliary.lua
+++ b/src/luaotfload-auxiliary.lua
@@ -100,17 +100,21 @@ luaotfload_callbacks [#luaotfload_callbacks + 1] = {
   "patch_font", set_sscale_dimens, "set_sscale_dimens",
 }
 
+local default_units = 1000
+
 --- fontobj -> int
 local lookup_units = function (fontdata)
-  local metadata = fontdata.shared and fontdata.shared.rawdata.metadata
-  if metadata and metadata.units then
-    return metadata.units
-  elseif fontdata.parameters and fontdata.parameters.units then
-    return fontdata.parameters.units
-  elseif fontdata.units then --- v1.x
-    return fontdata.units
+  local units = fontdata.units
+  if units and units > 0 then return units end
+  local shared     = fontdata.shared    if not shared     then return default_units end
+  local rawdata    = shared.rawdata     if not rawdata    then return default_units end
+  local metadata   = rawdata.metadata   if not metadata   then return default_units end
+  local capheight  = metadata.capheight if not capheight  then return default_units end
+  local units      = metadata.units or fontdata.units
+  if not units or units == 0 then
+    return default_units
   end
-  return 1000
+  return units
 end
 
 --[[doc--
@@ -213,8 +217,9 @@ local query_ascender = function (fontdata)
   local metadata   = rawdata.metadata    if not metadata   then return false end
   local ascender   = parameters.ascender
                   or metadata.ascender   if not ascender   then return false end
-  local units      = metadata.units      if units == 0     then return false end
   local size       = parameters.size     if not size       then return false end
+  local units = lookup_units (fontdata)
+  if not units or units == 0 then return false end
   return ascender * size / units
 end
 
@@ -224,8 +229,9 @@ local query_capheight = function (fontdata)
   local rawdata    = shared.rawdata       if not rawdata    then return false end
   local metadata   = rawdata.metadata     if not metadata   then return false end
   local capheight  = metadata.capheight   if not capheight  then return false end
-  local units      = metadata.units       if units == 0     then return false end
   local size       = parameters.size      if not size       then return false end
+  local units = lookup_units (fontdata)
+  if not units or units == 0 then return false end
   return capheight * size / units
 end