Write a macro or syntax extension to generate OpenType tags

Fixes #4556

components/gfx/text/shaping/harfbuzz.rs

@@ -47,13 +47,17 @@ use std::mem;
 use std::cmp;
 use std::ptr;
 
+macro_rules! hb_tag {
+    ($t1:expr, $t2:expr, $t3:expr, $t4:expr) => (
+        (($t1 as u32) << 24) | (($t2 as u32) << 16) | (($t3 as u32) << 8) | ($t4 as u32)
+    );
+}
+
 static NO_GLYPH: i32 = -1;
 static CONTINUATION_BYTE: i32 = -2;
 
-static KERN: u32 = ((b'k' as u32) << 24) | ((b'e' as u32) << 16) | ((b'r' as u32) << 8) |
-    (b'n' as u32);
-static LIGA: u32 = ((b'l' as u32) << 24) | ((b'i' as u32) << 16) | ((b'g' as u32) << 8) |
-    (b'a' as u32);
+static KERN: u32 = hb_tag!('k', 'e', 'r', 'n');
+static LIGA: u32 = hb_tag!('l', 'i', 'g', 'a');
 
 pub struct ShapedGlyphData {
     count: int,

components/gfx/text/util.rs

@@ -128,20 +128,6 @@ pub fn fixed_to_rounded_int(before: int, f: i32) -> int {
     }
 }
 
-/* Generate a 32-bit TrueType tag from its 4 characters */
-pub fn true_type_tag(a: char, b: char, c: char, d: char) -> u32 {
-    let a = a as u32;
-    let b = b as u32;
-    let c = c as u32;
-    let d = d as u32;
-    (a << 24 | b << 16 | c << 8 | d) as u32
-}
-
-#[test]
-fn test_true_type_tag() {
-    assert_eq!(true_type_tag('c', 'm', 'a', 'p'), 0x_63_6D_61_70_u32);
-}
-
 #[test]
 fn test_transform_compress_none() {
     let test_strs = [