Clean up fontconfig generic family map population

Track duplicate families by ID instead of name.

Also use filter_map to add all the generic families in one go. This also
lets us use the question mark operator in the iterator body, leading to
much cleaner code.

Author: valadaptive

fontique/src/backend/fontconfig.rs

@@ -3,7 +3,6 @@
 
 use core::{
     ffi::{CStr, c_char},
-    iter::once,
     marker::PhantomData,
     ptr::NonNull,
 };
@@ -488,7 +487,7 @@ impl SystemFonts {
 
         // Populate the generic family map.
         let mut generic_families = GenericFamilyMap::default();
-        for (generic_family, name) in GENERIC_FAMILY_NAMES {
+        for (generic_family, name) in GENERIC_FAMILY_NAMES.iter().copied() {
             let mut pattern = Pattern::new().unwrap();
             pattern.add_string(FC_FAMILY, name);
             // TODO: do we need FcConfigSetDefaultSubstitute?
@@ -499,34 +498,30 @@ impl SystemFonts {
             // they provide no new Unicode coverage.
             let font_set = config.font_sort(&pattern, true).unwrap();
 
-            // There are a lot of duplicate font names in the substituted
+            // There are a lot of duplicate font families in the substituted
             // pattern. Keep track of which ones have already been added to the
             // list.
-            let mut added_names = HashSet::new();
-
-            for font in font_set.iter() {
-                // Not sure if FcFontRenderPrepare performs any substitutions
-                // relevant to fallback family name matching, but it's a good
-                // idea to call it just in case.
-                let Some(font) = config.font_render_prepare(&pattern, &font) else {
-                    continue;
-                };
-                // Generic families can have more than one name, but the only
-                // one we care about is the first one.
-                let Ok(name) = font.get_string(FC_FAMILY, 0) else {
-                    continue;
-                };
-
-                if added_names.contains(name.as_ref()) {
-                    continue;
-                }
-                let Some(family_name) = name_map.get(name.as_ref()) else {
-                    continue;
-                };
-
-                added_names.insert(name.into_owned());
-                generic_families.append(*generic_family, once(family_name.id()));
-            }
+            let mut added_families = HashSet::new();
+
+            generic_families.append(
+                generic_family,
+                font_set.iter().filter_map(|font| {
+                    // Not sure if FcFontRenderPrepare performs any substitutions
+                    // relevant to fallback family name matching, but it's a good
+                    // idea to call it just in case.
+                    let font = config.font_render_prepare(&pattern, &font)?;
+                    // Generic families can have more than one name, but the only
+                    // one we care about is the first one.
+                    let name = font.get_string(FC_FAMILY, 0).ok()?;
+                    let family_name = name_map.get(name.as_ref())?;
+
+                    if !added_families.insert(family_name.id()) {
+                        return None;
+                    }
+
+                    Some(family_name.id())
+                }),
+            );
         }
 
         Self {