Warn when using variable fonts (#6425)

2 files changed, 18 insertions, 3 deletions

diff --git a/crates/typst-library/src/text/font/book.rs b/crates/typst-library/src/text/font/book.rs
index cd90a08f..d0c821b3 100644
--- a/crates/typst-library/src/text/font/book.rs
+++ b/crates/typst-library/src/text/font/book.rs
@@ -196,6 +196,8 @@ bitflags::bitflags! {
         const SERIF = 1 << 1;
         /// Font face has a MATH table
         const MATH = 1 << 2;
+        /// Font face has an fvar table
+        const VARIABLE = 1 << 3;
     }
 }
 
@@ -275,6 +277,7 @@ impl FontInfo {
         let mut flags = FontFlags::empty();
         flags.set(FontFlags::MONOSPACE, ttf.is_monospaced());
         flags.set(FontFlags::MATH, ttf.tables().math.is_some());
+        flags.set(FontFlags::VARIABLE, ttf.is_variable());
 
         // Determine whether this is a serif or sans-serif font.
         if let Some(panose) = ttf
diff --git a/crates/typst-library/src/text/mod.rs b/crates/typst-library/src/text/mod.rs
index 1c0696d1..563adbbd 100644
--- a/crates/typst-library/src/text/mod.rs
+++ b/crates/typst-library/src/text/mod.rs
@@ -1412,12 +1412,24 @@ pub fn is_default_ignorable(c: char) -> bool {
 fn check_font_list(engine: &mut Engine, list: &Spanned<FontList>) {
     let book = engine.world.book();
     for family in &list.v {
-        if !book.contains_family(family.as_str()) {
-            engine.sink.warn(warning!(
+        match book.select_family(family.as_str()).next() {
+            Some(index) => {
+                if book
+                    .info(index)
+                    .is_some_and(|x| x.flags.contains(FontFlags::VARIABLE))
+                {
+                    engine.sink.warn(warning!(
+                        list.span,
+                        "variable fonts are not currently supported and may render incorrectly";
+                        hint: "try installing a static version of \"{}\" instead", family.as_str()
+                    ))
+                }
+            }
+            None => engine.sink.warn(warning!(
                 list.span,
                 "unknown font family: {}",
                 family.as_str(),
-            ));
+            )),
         }
     }
 }