Subject: bug#52888: 29.0.50; font_{delete_unmatched,score} do not handle nil FONT_WEIGHT_INDEX

From: Sean Whitton <[email-masked]>
Date: Wed, 29 Dec 2021 22:28:37 -0700

Hello,

On my system I have a variable weight .ttf font[1] installed somewhere.
When I build with --enable-check-lisp-object-type, the line

    int candidate = XFIXNUM (AREF (entity, prop)) >> 8;

in font_delete_unmatched and the expression

   EMACS_INT diff = ((XFIXNUM (AREF (entity, i)) >> 8)
                     - (XFIXNUM (spec_prop[i]) >> 8));

in font_score have failed assertions because the FONT_WEIGHT_INDEX for
this .ttf file is nil:

    #<font-entity ftcrhb CYRE Inconsolata nil iso10646-1 nil normal nil
     0 nil 100 0 ((:font-entity
     "/usr/share/fonts/inconsolata/Inconsolata-VariableFont_wdth,wght.ttf"
     . 0))>

I don't believe Emacs really knows how to handle these multi-weight .ttf
files?  Thus I propose the attached patch, to handle the value.

[1]  https://github.com/googlefonts/Inconsolata/tree/main/fonts/variable

-- 
Sean Whitton
>From b7eff2c3e1d09f44b1d5790275fc92c11e9be88f Mon Sep 17 00:00:00 2001
From: Sean Whitton <[email-masked]>
Date: Wed, 29 Dec 2021 21:18:07 -0700
Subject: [PATCH] Handle nil FONT_WEIGHT_INDEX

* src/font.c (font_delete_unmatched, font_score): Handle nil entity
property.  In particular, FONT_WEIGHT_INDEX is nil for some variable
weight fonts.
---
 src/font.c | 42 ++++++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/src/font.c b/src/font.c
index fa831f2861..cb057abca6 100644
--- a/src/font.c
+++ b/src/font.c
@@ -2183,7 +2183,8 @@ font_score (Lisp_Object entity, Lisp_Object *spec_prop)
 
   /* Score three style numeric fields.  Maximum difference is 127. */
   for (i = FONT_WEIGHT_INDEX; i <= FONT_WIDTH_INDEX; i++)
-    if (! NILP (spec_prop[i]) && ! EQ (AREF (entity, i), spec_prop[i]))
+    if (! NILP (spec_prop[i]) && ! NILP (AREF (entity, i))
+	&& ! EQ (AREF (entity, i), spec_prop[i]))
       {
 	EMACS_INT diff = ((XFIXNUM (AREF (entity, i)) >> 8)
 			  - (XFIXNUM (spec_prop[i]) >> 8));
@@ -2764,26 +2765,31 @@ font_delete_unmatched (Lisp_Object vec, Lisp_Object spec, int size)
 	{
 	  if (FIXNUMP (AREF (spec, prop)))
 	    {
-	      int required = XFIXNUM (AREF (spec, prop)) >> 8;
-	      int candidate = XFIXNUM (AREF (entity, prop)) >> 8;
+	      if (NILP (AREF (entity, prop)))
+		  prop = FONT_SPEC_MAX;
+	      else {
+		int required = XFIXNUM (AREF (spec, prop)) >> 8;
+		int candidate = XFIXNUM (AREF (entity, prop)) >> 8;
 
-	      if (candidate != required
+		if (candidate != required
 #ifdef HAVE_NTGUI
-		  /* A kludge for w32 font search, where listing a
-		     family returns only 4 standard weights: regular,
-		     italic, bold, bold-italic.  For other values one
-		     must specify the font, not just the family in the
-		     :family attribute of the face.  But specifying
-		     :family in the face attributes looks for regular
-		     weight, so if we require exact match, the
-		     non-regular font will be rejected.  So we relax
-		     the accuracy of the match here, and let
-		     font_sort_entities find the best match.  */
-		  && (prop != FONT_WEIGHT_INDEX
-		      || eabs (candidate - required) > 100)
+		    /* A kludge for w32 font search, where listing a
+		       family returns only 4 standard weights:
+		       regular, italic, bold, bold-italic.  For other
+		       values one must specify the font, not just the
+		       family in the :family attribute of the face.
+		       But specifying :family in the face attributes
+		       looks for regular weight, so if we require
+		       exact match, the non-regular font will be
+		       rejected.  So we relax the accuracy of the
+		       match here, and let font_sort_entities find the
+		       best match.  */
+		    && (prop != FONT_WEIGHT_INDEX
+			|| eabs (candidate - required) > 100)
 #endif
-		  )
-		prop = FONT_SPEC_MAX;
+		    )
+		  prop = FONT_SPEC_MAX;
+	      }
 	    }
 	}
       if (prop < FONT_SPEC_MAX
-- 
2.30.2