Use Tag type from font-types crate to represent opentype tags (#38870)

The `font-types` crate is the tiny type-only base crate of `fontations`.
This uses a strongly typed representation of open type tags, and allows
us to remove our custom macro for creating them.

---------

Signed-off-by: Nico Burns <nico@nicoburns.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/fonts/font.rs

@@ -19,6 +19,7 @@ use log::debug;
 use malloc_size_of_derive::MallocSizeOf;
 use parking_lot::RwLock;
 use read_fonts::tables::os2::{Os2, SelectionFlags};
+use read_fonts::types::Tag;
 use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
 use style::computed_values::font_variant_caps;
@@ -38,22 +39,14 @@ use crate::{
     FontTemplateRefMethods, GlyphData, GlyphId, GlyphStore, LocalFontIdentifier, Shaper,
 };
 
-#[macro_export]
-macro_rules! ot_tag {
-    ($t1:expr, $t2:expr, $t3:expr, $t4:expr) => {
-        (($t1 as u32) << 24) | (($t2 as u32) << 16) | (($t3 as u32) << 8) | ($t4 as u32)
-    };
-}
-
-pub type OpenTypeTableTag = u32;
-pub const GPOS: OpenTypeTableTag = ot_tag!('G', 'P', 'O', 'S');
-pub const GSUB: OpenTypeTableTag = ot_tag!('G', 'S', 'U', 'B');
-pub const KERN: OpenTypeTableTag = ot_tag!('k', 'e', 'r', 'n');
-pub const SBIX: OpenTypeTableTag = ot_tag!('s', 'b', 'i', 'x');
-pub const CBDT: OpenTypeTableTag = ot_tag!('C', 'B', 'D', 'T');
-pub const COLR: OpenTypeTableTag = ot_tag!('C', 'O', 'L', 'R');
-pub const BASE: OpenTypeTableTag = ot_tag!('B', 'A', 'S', 'E');
-pub const LIGA: OpenTypeTableTag = ot_tag!('l', 'i', 'g', 'a');
+pub const GPOS: Tag = Tag::new(b"GPOS");
+pub const GSUB: Tag = Tag::new(b"GSUB");
+pub const KERN: Tag = Tag::new(b"kern");
+pub const SBIX: Tag = Tag::new(b"sbix");
+pub const CBDT: Tag = Tag::new(b"CBDT");
+pub const COLR: Tag = Tag::new(b"COLR");
+pub const BASE: Tag = Tag::new(b"BASE");
+pub const LIGA: Tag = Tag::new(b"liga");
 
 pub const LAST_RESORT_GLYPH_ADVANCE: FractionalPixel = 10.0;
 
@@ -112,7 +105,7 @@ pub trait PlatformFontMethods: Sized {
     fn glyph_h_kerning(&self, glyph0: GlyphId, glyph1: GlyphId) -> FractionalPixel;
 
     fn metrics(&self) -> FontMetrics;
-    fn table_for_tag(&self, _: FontTableTag) -> Option<FontTable>;
+    fn table_for_tag(&self, _: Tag) -> Option<FontTable>;
     fn typographic_bounds(&self, _: GlyphId) -> Rect<f32>;
 
     /// Get the necessary [`FontInstanceFlags`]` for this font.
@@ -148,24 +141,6 @@ pub trait PlatformFontMethods: Sized {
 // Used to abstract over the shaper's choice of fixed int representation.
 pub type FractionalPixel = f64;
 
-pub type FontTableTag = u32;
-
-trait FontTableTagConversions {
-    fn tag_to_str(&self) -> String;
-}
-
-impl FontTableTagConversions for FontTableTag {
-    fn tag_to_str(&self) -> String {
-        let bytes = [
-            (self >> 24) as u8,
-            (self >> 16) as u8,
-            (self >> 8) as u8,
-            *self as u8,
-        ];
-        str::from_utf8(&bytes).unwrap().to_owned()
-    }
-}
-
 pub trait FontTableMethods {
     fn buffer(&self) -> &[u8];
 }
@@ -533,7 +508,7 @@ impl Font {
         glyphs.finalize_changes();
     }
 
-    pub fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
+    pub fn table_for_tag(&self, tag: Tag) -> Option<FontTable> {
         let result = self.handle.table_for_tag(tag);
         let status = if result.is_some() {
             "Found"
@@ -544,7 +519,7 @@ impl Font {
         debug!(
             "{} font table[{}] in {:?},",
             status,
-            tag.tag_to_str(),
+            str::from_utf8(tag.as_ref()).unwrap(),
             self.identifier()
         );
         result

components/fonts/platform/freetype/font.rs

@@ -24,9 +24,7 @@ use webrender_api::{FontInstanceFlags, FontVariation};
 use super::LocalFontIdentifier;
 use super::library_handle::FreeTypeLibraryHandle;
 use crate::FontData;
-use crate::font::{
-    FontMetrics, FontTableMethods, FontTableTag, FractionalPixel, PlatformFontMethods,
-};
+use crate::font::{FontMetrics, FontTableMethods, FractionalPixel, PlatformFontMethods};
 use crate::font_template::FontTemplateDescriptor;
 use crate::glyph::GlyphId;
 use crate::platform::freetype::freetype_face::FreeTypeFace;
@@ -324,8 +322,7 @@ impl PlatformFontMethods for PlatformFont {
         }
     }
 
-    fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
-        let tag = Tag::from_u32(tag);
+    fn table_for_tag(&self, tag: Tag) -> Option<FontTable> {
         let font_ref = self.table_provider_data.font_ref().ok()?;
         let _table_data = font_ref.table_data(tag)?;
         Some(FontTable {

components/fonts/platform/macos/font.rs

@@ -18,15 +18,15 @@ use core_text::font_descriptor::{
 };
 use euclid::default::{Point2D, Rect, Size2D};
 use log::debug;
+use skrifa::Tag;
 use style::values::computed::font::{FontStretch, FontStyle, FontWeight};
 use webrender_api::{FontInstanceFlags, FontVariation};
 
 use super::core_text_font_cache::CoreTextFontCache;
 use super::font_list::LocalFontIdentifier;
 use crate::{
-    CBDT, COLR, FontData, FontIdentifier, FontMetrics, FontTableMethods, FontTableTag,
-    FontTemplateDescriptor, FractionalPixel, GlyphId, KERN, PlatformFontMethods, SBIX,
-    map_platform_values_to_style_values,
+    CBDT, COLR, FontData, FontIdentifier, FontMetrics, FontTableMethods, FontTemplateDescriptor,
+    FractionalPixel, GlyphId, KERN, PlatformFontMethods, SBIX, map_platform_values_to_style_values,
 };
 
 const KERN_PAIR_LEN: usize = 6;
@@ -346,8 +346,9 @@ impl PlatformFontMethods for PlatformFont {
         metrics
     }
 
-    fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
-        let result: Option<CFData> = self.ctfont.get_font_table(tag);
+    fn table_for_tag(&self, tag: Tag) -> Option<FontTable> {
+        let tag_u32 = u32::from_be_bytes(tag.to_be_bytes());
+        let result: Option<CFData> = self.ctfont.get_font_table(tag_u32);
         result.map(FontTable::wrap)
     }
 

components/fonts/platform/windows/font.rs

@@ -26,7 +26,7 @@ use winapi::shared::minwindef::{BOOL, FALSE};
 
 use super::font_list::LocalFontIdentifier;
 use crate::{
-    FontData, FontIdentifier, FontMetrics, FontTableMethods, FontTableTag, FontTemplateDescriptor,
+    FontData, FontIdentifier, FontMetrics, FontTableMethods, FontTemplateDescriptor,
     FractionalPixel, GlyphId, PlatformFontMethods,
 };
 
@@ -282,12 +282,12 @@ impl PlatformFontMethods for PlatformFont {
         metrics
     }
 
-    fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
+    fn table_for_tag(&self, tag: Tag) -> Option<FontTable> {
         // dwrote (and presumably the Windows APIs) accept a reversed version of the table
         // tag bytes, which means that `u32::swap_bytes` must be called here in order to
         // use a byte order compatible with the rest of Servo.
         self.face
-            .font_table(u32::swap_bytes(tag))
+            .font_table(u32::from_be_bytes(tag.to_be_bytes()).swap_bytes())
             .ok()
             .flatten()
             .map(|bytes| FontTable { data: bytes })

components/fonts/shapers/harfbuzz.rs

@@ -26,16 +26,17 @@ use harfbuzz_sys::{
     hb_variation_t,
 };
 use num_traits::Zero;
+use read_fonts::types::Tag;
 
 use super::{HarfBuzzShapedGlyphData, ShapedGlyphEntry, unicode_script_to_iso15924_tag};
 use crate::platform::font::FontTable;
 use crate::{
-    BASE, Font, FontBaseline, FontTableMethods, FontTableTag, GlyphId, GlyphStore, KERN, LIGA,
-    OpenTypeTableTag, ShapingFlags, ShapingOptions, fixed_to_float, float_to_fixed, ot_tag,
+    BASE, Font, FontBaseline, FontTableMethods, GlyphId, GlyphStore, KERN, LIGA, ShapingFlags,
+    ShapingOptions, fixed_to_float, float_to_fixed,
 };
 
-const HB_OT_TAG_DEFAULT_SCRIPT: OpenTypeTableTag = ot_tag!('D', 'F', 'L', 'T');
-const HB_OT_TAG_DEFAULT_LANGUAGE: OpenTypeTableTag = ot_tag!('d', 'f', 'l', 't');
+const HB_OT_TAG_DEFAULT_SCRIPT: hb_tag_t = u32::from_be_bytes(Tag::new(b"DFLT").to_be_bytes());
+const HB_OT_TAG_DEFAULT_LANGUAGE: hb_tag_t = u32::from_be_bytes(Tag::new(b"dflt").to_be_bytes());
 
 pub struct ShapedGlyphData {
     count: usize,
@@ -238,7 +239,7 @@ impl Shaper {
                 .contains(ShapingFlags::IGNORE_LIGATURES_SHAPING_FLAG)
             {
                 features.push(hb_feature_t {
-                    tag: LIGA,
+                    tag: u32::from_be_bytes(LIGA.to_be_bytes()),
                     value: 0,
                     start: 0,
                     end: hb_buffer_get_length(hb_buffer),
@@ -249,7 +250,7 @@ impl Shaper {
                 .contains(ShapingFlags::DISABLE_KERNING_SHAPING_FLAG)
             {
                 features.push(hb_feature_t {
-                    tag: KERN,
+                    tag: u32::from_be_bytes(KERN.to_be_bytes()),
                     value: 0,
                     start: 0,
                     end: hb_buffer_get_length(hb_buffer),
@@ -391,7 +392,7 @@ extern "C" fn font_table_func(
     assert!(!font.is_null());
 
     // TODO(Issue #197): reuse font table data, which will change the unsound trickery here.
-    let Some(font_table) = (unsafe { (*font).table_for_tag(tag as FontTableTag) }) else {
+    let Some(font_table) = (unsafe { (*font).table_for_tag(Tag::from_u32(tag)) }) else {
         return ptr::null_mut();
     };