fonts: adopt CSS Fonts Level 3 compatible font matching

wezterm-font/src/db.rs

@@ -2,7 +2,7 @@
 
 use crate::ftwrap::Library;
 use crate::locator::FontDataSource;
-use crate::parser::{load_built_in_fonts, parse_and_collect_font_info, FontMatch, ParsedFont};
+use crate::parser::{load_built_in_fonts, parse_and_collect_font_info, ParsedFont};
 use anyhow::Context;
 use config::{Config, FontAttributes};
 use rangeset::RangeSet;
@@ -50,14 +50,12 @@ impl Entry {
 }
 
 pub struct FontDatabase {
-    by_family: HashMap<String, Vec<Arc<Entry>>>,
     by_full_name: HashMap<String, Arc<Entry>>,
 }
 
 impl FontDatabase {
     pub fn new() -> Self {
         Self {
-            by_family: HashMap::new(),
             by_full_name: HashMap::new(),
         }
     }
@@ -69,13 +67,6 @@ impl FontDatabase {
                 coverage: Mutex::new(None),
             });
 
-            if let Some(family) = entry.parsed.names().family.as_ref() {
-                self.by_family
-                    .entry(family.to_string())
-                    .or_insert_with(Vec::new)
-                    .push(Arc::clone(&entry));
-            }
-
             self.by_full_name
                 .entry(entry.parsed.names().full_name.clone())
                 .or_insert(entry);
@@ -182,23 +173,20 @@ impl FontDatabase {
     }
 
     pub fn resolve(&self, font_attr: &FontAttributes) -> Option<&ParsedFont> {
-        if let Some(entry) = self.by_full_name.get(&font_attr.family) {
+        let candidates: Vec<&ParsedFont> = self
-            if entry.parsed.matches_attributes(font_attr) == FontMatch::FullName {
+            .by_full_name
-                return Some(&entry.parsed);
+            .values()
-            }
+            .filter_map(|entry| {
+                if entry.parsed.matches_name(font_attr) {
+                    Some(&entry.parsed)
+                } else {
+                    None
                 }
+            })
+            .collect();
 
-        if let Some(family) = self.by_family.get(&font_attr.family) {
+        if let Some(idx) = ParsedFont::best_matching_index(font_attr, &candidates) {
-            let mut candidates = vec![];
+            return candidates.get(idx).map(|&p| p);
-            for entry in family {
-                let res = entry.parsed.matches_attributes(font_attr);
-                if res != FontMatch::NoMatch {
-                    candidates.push((res, entry));
-                }
-            }
-            candidates.sort_by(|a, b| a.0.cmp(&b.0));
-            let best = candidates.first()?;
-            return Some(&best.1.parsed);
         }
 
         None

wezterm-font/src/locator/core_text.rs

@@ -89,8 +89,7 @@ impl FontLocator for CoreTextFontLocator {
         for attr in fonts_selection {
             if let Ok(descriptor) = descriptor_from_attr(attr) {
                 let handles = handles_from_descriptor(&descriptor);
-                let ranked = ParsedFont::rank_matches(attr, handles);
+                if let Some(parsed) = ParsedFont::best_match(attr, handles) {
-                for parsed in ranked {
                     fonts.push(parsed);
                     loaded.insert(attr.clone());
                 }

wezterm-font/src/locator/font_config.rs

@@ -1,6 +1,6 @@
 use crate::fcwrap;
 use crate::locator::{FontDataHandle, FontDataSource, FontLocator};
-use crate::parser::{FontMatch, ParsedFont};
+use crate::parser::ParsedFont;
 use anyhow::Context;
 use config::FontAttributes;
 use fcwrap::{to_fc_weight, to_fc_width, CharSet, Pattern as FontPattern};
@@ -98,7 +98,7 @@ impl FontLocator for FontConfigFontLocator {
                             // so we need to parse the returned font
                             // here to see if we got what we asked for.
                             if let Ok(parsed) = crate::parser::ParsedFont::from_locator(&handle) {
-                                if parsed.matches_attributes(attr) != FontMatch::NoMatch {
+                                if parsed.matches_name(attr) {
                                     log::trace!("found font-config match for {:?}", parsed.names());
                                     fonts.push(parsed);
                                     loaded.insert(attr.clone());

wezterm-font/src/locator/gdi.rs

@@ -1,7 +1,7 @@
 #![cfg(windows)]
 
 use crate::locator::{FontDataSource, FontLocator};
-use crate::parser::{parse_and_collect_font_info, rank_matching_fonts, FontMatch, ParsedFont};
+use crate::parser::{best_matching_font, parse_and_collect_font_info, ParsedFont};
 use config::{FontAttributes, FontStretch, FontWeight as WTFontWeight};
 use dwrote::{FontDescriptor, FontStretch, FontStyle, FontWeight};
 use std::borrow::Cow;
@@ -63,7 +63,7 @@ fn extract_font_data(font: HFONT, attr: &FontAttributes) -> anyhow::Result<Parse
 
         let mut font_info = vec![];
         parse_and_collect_font_info(&source, &mut font_info)?;
-        let matches = ParsedFont::rank_matches(attr, font_info);
+        let matches = ParsedFont::best_match(attr, font_info);
 
         for m in matches {
             return Ok(m);
@@ -145,11 +145,9 @@ fn handle_from_descriptor(
 
             log::debug!("{} -> {}", family_name, path.display());
             let source = FontDataSource::OnDisk(path);
-            match rank_matching_fonts(&source, attr) {
+            match best_matching_font(&source, attr) {
-                Ok(matches) => {
+                Ok(parsed) => {
-                    for p in matches {
+                    return Some(parsed);
-                        return Some(p);
-                    }
                 }
                 Err(err) => log::warn!("While parsing: {:?}: {:#}", source, err),
             }
@@ -176,7 +174,7 @@ impl FontLocator for GdiFontLocator {
                 fonts: &mut Vec<ParsedFont>,
                 loaded: &mut HashSet<FontAttributes>,
             ) -> bool {
-                if parsed.matches_attributes(font_attr) != FontMatch::NoMatch {
+                if parsed.matches_name(font_attr) {
                     fonts.push(parsed);
                     loaded.insert(font_attr.clone());
                     true

wezterm-font/src/parser.rs

@@ -87,57 +87,164 @@ impl ParsedFont {
         self.italic
     }
 
-    pub fn matches_attributes(&self, attr: &FontAttributes) -> FontMatch {
+    pub fn matches_name(&self, attr: &FontAttributes) -> bool {
         if let Some(fam) = self.names.family.as_ref() {
             if attr.family == *fam {
-                if attr.stretch == self.stretch {
+                return true;
-                    let wanted_weight = attr.weight.to_opentype_weight();
-                    let weight = self.weight.to_opentype_weight();
-
-                    if weight >= wanted_weight {
-                        if attr.italic == self.italic {
-                            return FontMatch::Weight(weight - wanted_weight);
             }
         }
+        self.matches_full_or_ps_name(attr)
+    }
 
+    pub fn matches_full_or_ps_name(&self, attr: &FontAttributes) -> bool {
         if attr.family == self.names.full_name {
-                        return FontMatch::FullName;
+            return true;
         }
-                }
+        if let Some(ps) = self.names.postscript_name.as_ref() {
-            }
-        }
-
-        if attr.family == self.names.full_name {
-            FontMatch::FullName
-        } else if let Some(ps) = self.names.postscript_name.as_ref() {
             if attr.family == *ps {
-                FontMatch::FullName
+                return true;
-            } else {
-                FontMatch::NoMatch
             }
-        } else {
-            FontMatch::NoMatch
         }
+        false
     }
 
-    pub fn rank_matches(attr: &FontAttributes, fonts: Vec<Self>) -> Vec<Self> {
+    /// Perform CSS Fonts Level 3 font matching.
-        let mut candidates = vec![];
+    /// This implementation is derived from the `find_best_match` function
-        for p in fonts {
+    /// in the font-kit crate which is
-            let res = p.matches_attributes(attr);
+    /// Copyright © 2018 The Pathfinder Project Developers.
-            if res != FontMatch::NoMatch {
+    /// https://drafts.csswg.org/css-fonts-3/#font-style-matching says
-                candidates.push((res, p));
+    pub fn best_matching_index<P: std::ops::Deref<Target = Self> + std::fmt::Debug>(
-            }
+        attr: &FontAttributes,
-        }
+        fonts: &[P],
-        candidates.sort_by(|a, b| a.0.cmp(&b.0));
+    ) -> Option<usize> {
-        candidates.into_iter().map(|(_, p)| p).collect()
+        if fonts.is_empty() {
-    }
+            return None;
         }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
+        let mut candidates: Vec<usize> = (0..fonts.len()).collect();
-pub enum FontMatch {
+
-    Weight(u16),
+        // First, filter by stretch
-    FullName,
+        let stretch_value = attr.stretch.to_opentype_stretch();
-    NoMatch,
+        let stretch = if candidates
+            .iter()
+            .any(|&idx| fonts[idx].stretch == attr.stretch)
+        {
+            attr.stretch
+        } else if attr.stretch <= FontStretch::Normal {
+            // Find the closest stretch, looking at narrower first before
+            // looking at wider candidates
+            match candidates
+                .iter()
+                .filter(|&&idx| fonts[idx].stretch < attr.stretch)
+                .min_by_key(|&&idx| stretch_value - fonts[idx].stretch.to_opentype_stretch())
+            {
+                Some(&idx) => fonts[idx].stretch,
+                None => {
+                    let idx = *candidates.iter().min_by_key(|&&idx| {
+                        fonts[idx].stretch.to_opentype_stretch() - stretch_value
+                    })?;
+                    fonts[idx].stretch
+                }
+            }
+        } else {
+            // Look at wider values, then narrower values
+            match candidates
+                .iter()
+                .filter(|&&idx| fonts[idx].stretch > attr.stretch)
+                .min_by_key(|&&idx| fonts[idx].stretch.to_opentype_stretch() - stretch_value)
+            {
+                Some(&idx) => fonts[idx].stretch,
+                None => {
+                    let idx = *candidates.iter().min_by_key(|&&idx| {
+                        stretch_value - fonts[idx].stretch.to_opentype_stretch()
+                    })?;
+                    fonts[idx].stretch
+                }
+            }
+        };
+
+        // Reduce to matching stretches
+        candidates.retain(|&idx| fonts[idx].stretch == stretch);
+
+        // Now match style: italics
+        let styles = [attr.italic, !attr.italic];
+        let italic = *styles
+            .iter()
+            .filter(|&&italic| candidates.iter().any(|&idx| fonts[idx].italic == italic))
+            .next()?;
+
+        // Reduce to matching italics
+        candidates.retain(|&idx| fonts[idx].italic == italic);
+
+        // And now match by font weight
+        let query_weight = attr.weight.to_opentype_weight();
+        let weight = if candidates
+            .iter()
+            .any(|&idx| fonts[idx].weight == attr.weight)
+        {
+            // Exact match for the requested weight
+            attr.weight
+        } else if attr.weight == FontWeight::Regular
+            && candidates
+                .iter()
+                .any(|&idx| fonts[idx].weight == FontWeight::Medium)
+        {
+            // https://drafts.csswg.org/css-fonts-3/#font-style-matching says
+            // that if they want weight=400 and we don't have 400,
+            // look at weight 500 first
+            FontWeight::Medium
+        } else if attr.weight == FontWeight::Medium
+            && candidates
+                .iter()
+                .any(|&idx| fonts[idx].weight == FontWeight::Regular)
+        {
+            // Similarly, look at regular before Medium if they wanted
+            // Medium and we didn't have it
+            FontWeight::Regular
+        } else if attr.weight <= FontWeight::Medium {
+            // Find best lighter weight, else best heavier weight
+            match candidates
+                .iter()
+                .filter(|&&idx| fonts[idx].weight <= attr.weight)
+                .min_by_key(|&&idx| query_weight - fonts[idx].weight.to_opentype_weight())
+            {
+                Some(&idx) => fonts[idx].weight,
+                None => {
+                    let idx = *candidates.iter().min_by_key(|&&idx| {
+                        fonts[idx].weight.to_opentype_weight() - query_weight
+                    })?;
+                    fonts[idx].weight
+                }
+            }
+        } else {
+            // Find best heavier weight, else best lighter weight
+            match candidates
+                .iter()
+                .filter(|&&idx| fonts[idx].weight >= attr.weight)
+                .min_by_key(|&&idx| fonts[idx].weight.to_opentype_weight() - query_weight)
+            {
+                Some(&idx) => fonts[idx].weight,
+                None => {
+                    let idx = *candidates.iter().min_by_key(|&&idx| {
+                        query_weight - fonts[idx].weight.to_opentype_weight()
+                    })?;
+                    fonts[idx].weight
+                }
+            }
+        };
+
+        // Reduce to matching weight
+        candidates.retain(|&idx| fonts[idx].weight == weight);
+
+        // The first one in this set is our best match
+        candidates.into_iter().next()
+    }
+
+    pub fn best_match(attr: &FontAttributes, mut fonts: Vec<Self>) -> Option<Self> {
+        let refs: Vec<&Self> = fonts.iter().collect();
+        let idx = Self::best_matching_index(attr, &refs)?;
+        fonts.drain(idx..=idx).next()
+    }
 }
 
 /// In case the user has a broken configuration, or no configuration,
@@ -186,13 +293,13 @@ pub(crate) fn load_built_in_fonts(font_info: &mut Vec<ParsedFont>) -> anyhow::Re
     Ok(())
 }
 
-pub fn rank_matching_fonts(
+pub fn best_matching_font(
     source: &FontDataSource,
     font_attr: &FontAttributes,
-) -> anyhow::Result<Vec<ParsedFont>> {
+) -> anyhow::Result<Option<ParsedFont>> {
     let mut font_info = vec![];
     parse_and_collect_font_info(source, &mut font_info)?;
-    Ok(ParsedFont::rank_matches(font_attr, font_info))
+    Ok(ParsedFont::best_match(font_attr, font_info))
 }
 
 pub(crate) fn parse_and_collect_font_info(