From 5b9e2f2588164c54570cf8a51440296a0aaf76b8 Mon Sep 17 00:00:00 2001
From: Andy Terra <152812+airstrike@users.noreply.github.com>
Date: Thu, 5 Mar 2026 15:31:16 -0500
Subject: [PATCH] Fix variable font weight matching in FontMatchKey
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Add variable_weight_match flag to FontMatchKey: when a face has a
wght axis covering the requested weight, let it pass the
font_weight_diff == 0 filter without altering sort priority.

The check is done inline via db.with_face_data() in FontMatchKey::new()
so it participates in the existing font_matches_cache invalidation —
no separate caching needed.
---
 src/font/fallback/mod.rs |  8 ++++----
 src/font/system.rs       | 18 ++++++++++++++----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/font/fallback/mod.rs b/src/font/fallback/mod.rs
index 00b7218..3b9aaaf 100644
--- a/src/font/fallback/mod.rs
+++ b/src/font/fallback/mod.rs
@@ -282,7 +282,7 @@ impl<'a> FontFallbackIter<'a> {
 
         self.font_match_keys
             .iter()
-            .filter(|m_key| m_key.font_weight_diff == 0)
+            .filter(|m_key| m_key.font_weight_diff == 0 || m_key.variable_weight_match)
             .find(|m_key| self.face_contains_family(m_key.id, default_family_name))
     }
 
@@ -297,9 +297,9 @@ impl<'a> FontFallbackIter<'a> {
         }
 
         let font_match_keys_iter = |is_mono| {
-            self.font_match_keys
-                .iter()
-                .filter(move |m_key| m_key.font_weight_diff == 0 || is_mono)
+            self.font_match_keys.iter().filter(move |m_key| {
+                m_key.font_weight_diff == 0 || m_key.variable_weight_match || is_mono
+            })
         };
 
         'DEF_FAM: while self.default_i < self.default_families.len() {
diff --git a/src/font/system.rs b/src/font/system.rs
index 2d19743..6542289 100644
--- a/src/font/system.rs
+++ b/src/font/system.rs
@@ -8,6 +8,7 @@ use core::fmt;
 use core::ops::{Deref, DerefMut};
 use fontdb::{FaceInfo, Query, Style};
 use skrifa::raw::{ReadError, TableProvider as _};
+use skrifa::MetadataProvider;
 
 // re-export fontdb and harfrust
 pub use fontdb;
@@ -25,14 +26,22 @@ pub struct FontMatchKey {
     pub(crate) font_weight: u16,
     pub(crate) font_stretch: u16,
     pub(crate) id: fontdb::ID,
+    pub(crate) variable_weight_match: bool,
 }
 
 impl FontMatchKey {
-    fn new(attrs: &Attrs, face: &FaceInfo) -> FontMatchKey {
+    fn new(attrs: &Attrs, face: &FaceInfo, db: &fontdb::Database) -> FontMatchKey {
         // TODO: smarter way of detecting emoji
         let not_emoji = !face.post_script_name.contains("Emoji");
-        // TODO: correctly take variable axes into account
         let font_weight_diff = attrs.weight.0.abs_diff(face.weight.0);
+
+        let variable_weight_match = font_weight_diff != 0
+            && db.with_face_data(face.id, |font_data, face_index| {
+                let font_ref = skrifa::FontRef::from_index(font_data, face_index).ok()?;
+                let axis = font_ref.axes().get_by_tag(skrifa::Tag::new(b"wght"))?;
+                let w = attrs.weight.0 as f32;
+                Some(w >= axis.min_value() && w <= axis.max_value())
+            }) == Some(Some(true));
         let font_weight = face.weight.0;
         let font_stretch_diff = attrs.stretch.to_number().abs_diff(face.stretch.to_number());
         let font_stretch = face.stretch.to_number();
@@ -55,6 +64,7 @@ impl FontMatchKey {
             font_weight,
             font_stretch,
             id,
+            variable_weight_match,
         }
     }
 }
@@ -363,7 +373,7 @@ impl FontSystem {
                 let mut font_match_keys = self
                     .db
                     .faces()
-                    .map(|face| FontMatchKey::new(attrs, face))
+                    .map(|face| FontMatchKey::new(attrs, face, &self.db))
                     .collect::<Vec<_>>();
 
                 // Sort so we get the keys with weight_offset=0 first
@@ -389,7 +399,7 @@ impl FontSystem {
                         font_match_keys.insert(0, match_key);
                     } else if let Some(face) = self.db.face(id) {
                         // else insert in front
-                        let match_key = FontMatchKey::new(attrs, face);
+                        let match_key = FontMatchKey::new(attrs, face, &self.db);
                         font_match_keys.insert(0, match_key);
                     } else {
                         log::error!("Could not get face from db, that should've been there.");