Bug 1810310 - When letter-spacing is present, disable all varieties of 'optional' ligatures, not only 'common' ones. r=emilio

This fixes behavior on css/css-fonts/font-feature-resolution-002.html.

Differential Revision: https://phabricator.services.mozilla.com/D166865

gfx/thebes/gfxFont.cpp

@@ -587,12 +587,18 @@ void gfxFontShaper::MergeFontFeatures(
     }
   }
 
+  auto disableOptionalLigatures = [&]() -> void {
+    mergedFeatures.InsertOrUpdate(HB_TAG('l', 'i', 'g', 'a'), 0);
+    mergedFeatures.InsertOrUpdate(HB_TAG('c', 'l', 'i', 'g'), 0);
+    mergedFeatures.InsertOrUpdate(HB_TAG('d', 'l', 'i', 'g'), 0);
+    mergedFeatures.InsertOrUpdate(HB_TAG('h', 'l', 'i', 'g'), 0);
+  };
+
   // Add features that are already resolved to tags & values in the style.
   if (styleRuleFeatures.IsEmpty()) {
-    // Disable common ligatures if non-zero letter-spacing is in effect.
+    // Disable optional ligatures if non-zero letter-spacing is in effect.
     if (aDisableLigatures) {
-      mergedFeatures.InsertOrUpdate(HB_TAG('l', 'i', 'g', 'a'), 0);
-      mergedFeatures.InsertOrUpdate(HB_TAG('c', 'l', 'i', 'g'), 0);
+      disableOptionalLigatures();
     }
   } else {
     for (const gfxFontFeature& feature : styleRuleFeatures) {
@@ -607,8 +613,7 @@ void gfxFontShaper::MergeFontFeatures(
       } else if (aDisableLigatures) {
         // Handle ligature-disabling setting at the boundary between high-
         // and low-level features.
-        mergedFeatures.InsertOrUpdate(HB_TAG('l', 'i', 'g', 'a'), 0);
-        mergedFeatures.InsertOrUpdate(HB_TAG('c', 'l', 'i', 'g'), 0);
+        disableOptionalLigatures();
       }
     }
   }

testing/web-platform/meta/css/css-fonts/font-feature-resolution-002.html.ini

@@ -1,2 +0,0 @@
-[font-feature-resolution-002.html]
-  expected: FAIL