[libgroff]: Make `spacewidth` mandatory.

* src/libs/libgroff/font.cpp (font::load): Throw error if a font
  description file is missing a `spacewidth` directive, since it is now
  re-documented as mandatory.  Atypically, we don't return false in this
  scenario; instead we proceed with the existing logic to compute a
  space width for the font based on typical practices for Western
  alphabetic fonts (see, e.g., <https://type.today/en/journal/spaces>.

Thanks to Deri James for the discussion.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/libs/libgroff/font.cpp b/src/libs/libgroff/font.cpp
index b774fe7a1..9f578478e 100644
--- a/src/libs/libgroff/font.cpp
+++ b/src/libs/libgroff/font.cpp
@@ -1018,6 +1018,8 @@ bool font::load(bool load_header_only)
     return false;
   }
   if (space_width == 0) {
+    t.error("font description 'spacewidth' directive missing");
+    // _Don't_ return false; compute a typical one for Western glyphs.
     if (zoom)
       space_width = scale_round(unitwidth, res, 72 * 3 * sizescale,
 				zoom);