fonts: Have CoreTextFontCache::core_text_font return a PlatformFont (#38758)

This will make it easier in a followup to include the normalized font
variations in the return value. This also make
`PlatformFont::ensure_h_kern_subtable` work on the instance instead of
being a struct method. Finally, all `PlatformFont` methods are combined
into a single impl block.

Testing: This should not change behavior and is thus covered by existing
tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/fonts/platform/macos/core_text_font_cache.rs

@@ -17,6 +17,7 @@ use core_text::font_descriptor::kCTFontURLAttribute;
 use parking_lot::RwLock;
 
 use crate::FontData;
+use crate::platform::font::PlatformFont;
 use crate::system_font_service::FontIdentifier;
 
 /// A cache of `CTFont` to avoid having to create `CTFont` instances over and over. It is
@@ -36,7 +37,7 @@ impl CoreTextFontCache {
         font_identifier: FontIdentifier,
         data: Option<&FontData>,
         pt_size: f64,
-    ) -> Option<CTFont> {
+    ) -> Option<PlatformFont> {
         //// If you pass a zero font size to one of the Core Text APIs, it'll replace it with
         //// 12.0. We don't want that! (Issue #10492.)
         let clamped_pt_size = pt_size.max(0.01);
@@ -49,7 +50,7 @@ impl CoreTextFontCache {
                 .get(&font_identifier)
                 .and_then(|identifier_cache| identifier_cache.get(&au_size))
             {
-                return Some(core_text_font.clone());
+                return Some(PlatformFont::new_with_ctfont(core_text_font.clone()));
             }
         }
 
@@ -60,7 +61,7 @@ impl CoreTextFontCache {
         // on the cache has been acquired, the cache was populated with the data that we need. Thus
         // check again and return the CTFont if it is is already cached.
         if let Some(core_text_font) = identifier_cache.get(&au_size) {
-            return Some(core_text_font.clone());
+            return Some(PlatformFont::new_with_ctfont(core_text_font.clone()));
         }
 
         let core_text_font = match font_identifier {
@@ -98,6 +99,6 @@ impl CoreTextFontCache {
         };
 
         identifier_cache.insert(au_size, core_text_font.clone());
-        Some(core_text_font)
+        Some(PlatformFont::new_with_ctfont(core_text_font))
     }
 }

components/fonts/platform/macos/font.rs

@@ -70,10 +70,43 @@ unsafe impl Sync for PlatformFont {}
 unsafe impl Send for PlatformFont {}
 
 impl PlatformFont {
+    pub(crate) fn new_with_ctfont(ctfont: CTFont) -> Self {
+        Self {
+            ctfont,
+            h_kern_subtable: None,
+        }
+    }
+
+    fn new(
+        font_identifier: FontIdentifier,
+        data: Option<&FontData>,
+        requested_size: Option<Au>,
+    ) -> Result<PlatformFont, &'static str> {
+        let size = match requested_size {
+            Some(s) => s.to_f64_px(),
+            None => 0.0,
+        };
+        let Some(mut platform_font) =
+            CoreTextFontCache::core_text_font(font_identifier, data, size)
+        else {
+            return Err("Could not generate CTFont for FontTemplateData");
+        };
+
+        platform_font.load_h_kern_subtable();
+        Ok(platform_font)
+    }
+
     /// Cache all the data needed for basic horizontal kerning. This is used only as a fallback or
     /// fast path (when the GPOS table is missing or unnecessary) so it needn't handle every case.
-    fn find_h_kern_subtable(&self) -> Option<CachedKernTable> {
+    fn load_h_kern_subtable(&mut self) {
-        let font_table = self.table_for_tag(KERN)?;
+        if self.h_kern_subtable.is_some() {
+            return;
+        }
+
+        let Some(font_table) = self.table_for_tag(KERN) else {
+            return;
+        };
+
         let mut result = CachedKernTable {
             font_table,
             pair_data_range: 0..0,
@@ -89,7 +122,7 @@ impl PlatformFont {
             let table = result.font_table.buffer();
             let version = BigEndian::read_u16(table);
             if version != 0 {
-                return None;
+                return;
             }
             let num_subtables = BigEndian::read_u16(&table[2..]);
             let mut start = 4;
@@ -102,7 +135,7 @@ impl PlatformFont {
                     // Found a matching subtable.
                     if !result.pair_data_range.is_empty() {
                         debug!("Found multiple horizontal kern tables. Disable fast path.");
-                        return None;
+                        return;
                     }
                     // Read the subtable header.
                     let subtable_start = start + SUBTABLE_HEADER_LEN;
@@ -112,7 +145,7 @@ impl PlatformFont {
                     result.pair_data_range = pair_data_start..end;
                     if result.pair_data_range.len() != n_pairs * KERN_PAIR_LEN {
                         debug!("Bad data in kern header. Disable fast path.");
-                        return None;
+                        return;
                     }
 
                     let pt_per_font_unit =
@@ -122,10 +155,9 @@ impl PlatformFont {
                 start = end;
             }
         }
+
         if !result.pair_data_range.is_empty() {
-            Some(result)
+            self.h_kern_subtable = Some(result);
-        } else {
-            None
         }
     }
 }
@@ -164,30 +196,6 @@ impl fmt::Debug for CachedKernTable {
     }
 }
 
-impl PlatformFont {
-    fn new(
-        font_identifier: FontIdentifier,
-        data: Option<&FontData>,
-        requested_size: Option<Au>,
-    ) -> Result<PlatformFont, &'static str> {
-        let size = match requested_size {
-            Some(s) => s.to_f64_px(),
-            None => 0.0,
-        };
-        let Some(core_text_font) = CoreTextFontCache::core_text_font(font_identifier, data, size)
-        else {
-            return Err("Could not generate CTFont for FontTemplateData");
-        };
-
-        let mut handle = PlatformFont {
-            ctfont: core_text_font.clone_with_font_size(size),
-            h_kern_subtable: None,
-        };
-        handle.h_kern_subtable = handle.find_h_kern_subtable();
-        Ok(handle)
-    }
-}
-
 impl PlatformFontMethods for PlatformFont {
     fn new_from_data(
         font_identifier: FontIdentifier,