Make font fallback disableable

src/eval/state.rs

@@ -119,13 +119,6 @@ impl Default for ParState {
 /// Defines font properties.
 #[derive(Debug, Clone, Eq, PartialEq, Hash)]
 pub struct FontState {
-    /// Whether 300 extra font weight should be added to what is defined by the
-    /// `variant`.
-    pub strong: bool,
-    /// Whether the the font style defined by the `variant` should be inverted.
-    pub emph: bool,
-    /// Whether a monospace font should be preferred.
-    pub monospace: bool,
     /// The font size.
     pub size: Length,
     /// The selected font variant (the final variant also depends on `strong`
@@ -140,6 +133,15 @@ pub struct FontState {
     /// A list of font families with generic class definitions (the final
     /// family list also depends on `monospace`).
     pub families: Rc<FamilyState>,
+    /// Whether 300 extra font weight should be added to what is defined by the
+    /// `variant`.
+    pub strong: bool,
+    /// Whether the the font style defined by the `variant` should be inverted.
+    pub emph: bool,
+    /// Whether a monospace font should be preferred.
+    pub monospace: bool,
+    /// Whether font fallback to a base list should occur.
+    pub fallback: bool,
 }
 
 impl FontState {
@@ -164,10 +166,11 @@ impl FontState {
 
     /// The resolved family iterator.
     pub fn families(&self) -> impl Iterator<Item = &str> + Clone {
-        let head = self
-            .monospace
-            .then(|| self.families.monospace.as_slice())
-            .unwrap_or_default();
+        let head = if self.monospace {
+            self.families.monospace.as_slice()
+        } else {
+            &[]
+        };
 
         let core = self.families.list.iter().flat_map(move |family| {
             match family {
@@ -178,10 +181,13 @@ impl FontState {
             }
         });
 
-        head.iter()
-            .chain(core)
-            .chain(self.families.base.iter())
-            .map(String::as_str)
+        let tail = if self.fallback {
+            self.families.base.as_slice()
+        } else {
+            &[]
+        };
+
+        head.iter().chain(core).chain(tail).map(String::as_str)
     }
 
     /// Access the `families` state mutably.
@@ -193,19 +199,20 @@ impl FontState {
 impl Default for FontState {
     fn default() -> Self {
         Self {
-            families: Rc::new(FamilyState::default()),
+            size: Length::pt(11.0),
             variant: FontVariant {
                 style: FontStyle::Normal,
                 weight: FontWeight::REGULAR,
                 stretch: FontStretch::NORMAL,
             },
-            strong: false,
-            emph: false,
-            monospace: false,
-            size: Length::pt(11.0),
             top_edge: VerticalFontMetric::CapHeight,
             bottom_edge: VerticalFontMetric::Baseline,
             fill: Paint::Color(Color::Rgba(RgbaColor::BLACK)),
+            families: Rc::new(FamilyState::default()),
+            strong: false,
+            emph: false,
+            monospace: false,
+            fallback: true,
         }
     }
 }

src/library/text.rs

@@ -19,6 +19,7 @@ pub fn font(ctx: &mut EvalContext, args: &mut Arguments) -> TypResult<Value> {
     let serif = args.named("serif")?;
     let sans_serif = args.named("sans-serif")?;
     let monospace = args.named("monospace")?;
+    let fallback = args.named("fallback")?;
 
     ctx.template.modify(move |state| {
         let font = state.font_mut();
@@ -66,6 +67,10 @@ pub fn font(ctx: &mut EvalContext, args: &mut Arguments) -> TypResult<Value> {
         if let Some(FamilyDef(monospace)) = &monospace {
             font.families_mut().monospace = monospace.clone();
         }
+
+        if let Some(fallback) = fallback {
+            font.fallback = fallback;
+        }
     });
 
     Ok(Value::None)

tests/typ/text/font.typ

@@ -33,6 +33,18 @@ Emoji: 🐪, 🌋, 🏞
   This is [#font(fill: rgb("FA644B")) way more] colorful.
 ]
 
+// Disable font fallback beyond the user-specified list.
+// Without disabling, Latin Modern Math would come to the rescue.
+#font("PT Sans", "Twitter Color Emoji", fallback: false)
+2π = 𝛼 + 𝛽. ✅
+
+---
+// Test class definitions.
+#font(sans-serif: "PT Sans")
+[#font(family: sans-serif) Sans-serif.] \
+[#font(monospace) Monospace.] \
+[#font(monospace, monospace: ("Nope", "Latin Modern Math")) Math.]
+
 ---
 // Test top and bottom edge.
 
@@ -47,13 +59,6 @@ Emoji: 🐪, 🌋, 🏞
 #try(cap-height, baseline)
 #try(x-height, baseline)
 
----
-// Test class definitions.
-#font(sans-serif: "PT Sans")
-[#font(family: sans-serif) Sans-serif.] \
-[#font(monospace) Monospace.] \
-[#font(monospace, monospace: ("Nope", "Latin Modern Math")) Math.]
-
 ---
 // Error: 7-12 unexpected argument
 #font(false)