fonts: Use skrifa to get raw font table data on Linux (servo#38690)

Use skrifa instead of freetype for extracting raw table data. Allows us
to replace unsafe Freetype code with safe Skrifa code. Also allows us to
avoid copying the table data. Instead we return Arc'd data.

---------

Signed-off-by: Nico Burns <nico@nicoburns.com>

Author: nicoburns

Cargo.lock

@@ -138,6 +138,7 @@ servo-media-dummy = { git = "https://github.com/servo/media" }
 servo-media-gstreamer = { git = "https://github.com/servo/media" }
 servo-tracing = { path = "components/servo_tracing" }
 servo_arc = { git = "https://github.com/servo/stylo", branch = "2025-08-01" }
+skrifa = "0.31.3"
 smallbitvec = "2.6.0"
 smallvec = { version = "1.15", features = ["serde", "union"] }
 string_cache = "0.8"

Cargo.toml

@@ -45,6 +45,7 @@ serde = { workspace = true }
 servo_arc = { workspace = true }
 servo_config = { path = "../config" }
 servo_url = { path = "../url" }
+skrifa = { workspace = true }
 smallvec = { workspace = true }
 stylo = { workspace = true }
 stylo_atoms = { workspace = true }

components/fonts/Cargo.toml

@@ -10,17 +10,19 @@ use std::{mem, ptr};
 use app_units::Au;
 use euclid::default::{Point2D, Rect, Size2D};
 use freetype_sys::{
-    FT_Byte, FT_Done_Face, FT_Error, FT_F26Dot6, FT_FACE_FLAG_COLOR, FT_FACE_FLAG_FIXED_SIZES,
-    FT_FACE_FLAG_SCALABLE, FT_Face, FT_Get_Char_Index, FT_Get_Kerning, FT_GlyphSlot, FT_Int32,
-    FT_KERNING_DEFAULT, FT_LOAD_COLOR, FT_LOAD_DEFAULT, FT_LOAD_NO_HINTING, FT_Load_Glyph, FT_Long,
-    FT_New_Face, FT_New_Memory_Face, FT_Pos, FT_Select_Size, FT_Set_Char_Size, FT_Size_Metrics,
-    FT_SizeRec, FT_UInt, FT_ULong, FT_Vector,
+    FT_Done_Face, FT_F26Dot6, FT_FACE_FLAG_COLOR, FT_FACE_FLAG_FIXED_SIZES, FT_FACE_FLAG_SCALABLE,
+    FT_Face, FT_Get_Char_Index, FT_Get_Kerning, FT_GlyphSlot, FT_Int32, FT_KERNING_DEFAULT,
+    FT_LOAD_COLOR, FT_LOAD_DEFAULT, FT_LOAD_NO_HINTING, FT_Load_Glyph, FT_Long, FT_New_Face,
+    FT_New_Memory_Face, FT_Pos, FT_Select_Size, FT_Set_Char_Size, FT_Size_Metrics, FT_SizeRec,
+    FT_UInt, FT_ULong, FT_Vector,
 };
 use log::debug;
 use memmap2::Mmap;
 use parking_lot::ReentrantMutex;
 use read_fonts::tables::os2::SelectionFlags;
+use read_fonts::types::Tag;
 use read_fonts::{FontRef, ReadError, TableProvider};
+use servo_arc::Arc;
 use style::Zero;
 use style::computed_values::font_stretch::T as FontStretch;
 use style::computed_values::font_weight::T as FontWeight;
@@ -49,12 +51,17 @@ fn fixed_26_dot_6_to_float(fixed: FT_F26Dot6) -> f64 {
 
 #[derive(Debug)]
 pub struct FontTable {
-    buffer: Vec<u8>,
+    data: FreeTypeFaceTableProviderData,
+    tag: Tag,
 }
 
 impl FontTableMethods for FontTable {
     fn buffer(&self) -> &[u8] {
-        &self.buffer
+        let font_ref = self.data.font_ref().expect("Font checked before creating");
+        let table_data = font_ref
+            .table_data(self.tag)
+            .expect("Table existence checked before creating");
+        table_data.as_bytes()
     }
 }
 
@@ -164,7 +171,7 @@ impl PlatformFontMethods for PlatformFont {
             requested_face_size,
             actual_face_size,
             table_provider_data: FreeTypeFaceTableProviderData::Local(
-                memory_mapped_font_data,
+                Arc::new(memory_mapped_font_data),
                 font_identifier.index(),
             ),
         })
@@ -393,22 +400,13 @@ impl PlatformFontMethods for PlatformFont {
     }
 
     fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
-        let face = self.face.lock();
-        let tag = tag as FT_ULong;
-
-        unsafe {
-            // Get the length
-            let mut len = 0;
-            if 0 != FT_Load_Sfnt_Table(*face, tag, 0, ptr::null_mut(), &mut len) {
-                return None;
-            }
-            // Get the bytes
-            let mut buf = vec![0u8; len as usize];
-            if 0 != FT_Load_Sfnt_Table(*face, tag, 0, buf.as_mut_ptr(), &mut len) {
-                return None;
-            }
-            Some(FontTable { buffer: buf })
-        }
+        let tag = Tag::from_u32(tag);
+        let font_ref = self.table_provider_data.font_ref().ok()?;
+        let _table_data = font_ref.table_data(tag)?;
+        Some(FontTable {
+            data: self.table_provider_data.clone(),
+            tag,
+        })
     }
 
     fn typographic_bounds(&self, glyph_id: GlyphId) -> Rect<f32> {
@@ -529,19 +527,10 @@ impl FreeTypeFaceHelpers for FT_Face {
     }
 }
 
-unsafe extern "C" {
-    fn FT_Load_Sfnt_Table(
-        face: FT_Face,
-        tag: FT_ULong,
-        offset: FT_Long,
-        buffer: *mut FT_Byte,
-        length: *mut FT_ULong,
-    ) -> FT_Error;
-}
-
+#[derive(Clone)]
 enum FreeTypeFaceTableProviderData {
     Web(FontData),
-    Local(Mmap, u32),
+    Local(Arc<Mmap>, u32),
 }
 
 impl FreeTypeFaceTableProviderData {