Support setting fonts repeatedly with different covers (#6604)

crates/typst-layout/src/inline/shaping.rs

@@ -719,6 +719,10 @@ fn glyphs_width(glyphs: &[ShapedGlyph]) -> Abs {
 struct ShapingContext<'a, 'v> {
     engine: &'a Engine<'v>,
     glyphs: Vec<ShapedGlyph>,
+    /// Font families that have been used with unlimited coverage.
+    ///
+    /// These font families are considered exhausted and will not be used again,
+    /// even if they are declared again (e.g., during fallback after normal selection).
     used: Vec<Font>,
     styles: StyleChain<'a>,
     size: Abs,
@@ -777,7 +781,10 @@ fn shape_segment<'a>(
         return;
     };
 
-    ctx.used.push(font.clone());
+    // This font has been exhausted and will not be used again.
+    if covers.is_none() {
+        ctx.used.push(font.clone());
+    }
 
     // Fill the buffer with our text.
     let mut buffer = UnicodeBuffer::new();

tests/suite/text/font.typ

@@ -135,6 +135,34 @@ I
 
 The number 123.
 
+--- text-font-covers-repeat ---
+// Repeatedly use the same font.
+#set text(font: (
+  (name: "Libertinus Serif", covers: regex("[0-9]")),
+  "Libertinus Serif"
+))
+
+The number 123.
+
+--- text-font-covers-riffle ---
+// Repeatedly use two fonts alternately.
+#set text(font: (
+  (name: "Noto Color Emoji", covers: regex("[🔗⛓‍💥]")),
+  (name: "Twitter Color Emoji", covers: regex("[^🖥️]")),
+  "Noto Color Emoji",
+))
+
+🔗⛓‍💥🖥️🔑
+
+// The above should be the same as:
+#{
+  text(font: "Noto Color Emoji", "🔗⛓‍💥🖥️")
+  text(font: "Twitter Color Emoji", "🔑")
+}
+
+// but not:
+#text(font: "Twitter Color Emoji", "🔗⛓‍💥🖥️🔑")
+
 --- text-font-covers-bad-1 ---
 // Error: 17-59 coverage regex may only use dot, letters, and character classes
 // Hint: 17-59 the regex is applied to each letter individually