Warn about unknown font families during parsing (#3854)

crates/typst/src/text/font/book.rs

@@ -51,6 +51,11 @@ impl FontBook {
         self.infos.get(index)
     }
 
+    /// Returns true if the book contains a font family with the given name.
+    pub fn contains_family(&self, family: &str) -> bool {
+        self.families.contains_key(family)
+    }
+
     /// An ordered iterator over all font families this book knows and details
     /// about the fonts that are part of them.
     pub fn families(

crates/typst/src/text/mod.rs

@@ -35,7 +35,7 @@ use rustybuzz::{Feature, Tag};
 use smallvec::SmallVec;
 use ttf_parser::Rect;
 
-use crate::diag::{bail, SourceResult, StrResult};
+use crate::diag::{bail, warning, SourceResult, StrResult};
 use crate::engine::Engine;
 use crate::foundations::Packed;
 use crate::foundations::{
@@ -47,6 +47,7 @@ use crate::layout::{Abs, Axis, Dir, Length, Rel};
 use crate::model::ParElem;
 use crate::syntax::Spanned;
 use crate::visualize::{Color, Paint, RelativeTo, Stroke};
+use crate::World;
 
 /// Text styling.
 ///
@@ -122,6 +123,22 @@ pub struct TextElem {
     /// This is Latin. \
     /// هذا عربي.
     /// ```
+    #[parse({
+        let font_list: Option<Spanned<FontList>> = args.named("font")?;
+        if let Some(font_list) = &font_list {
+            let book = engine.world.book();
+            for family in &font_list.v {
+                if !book.contains_family(family.as_str()) {
+                    engine.tracer.warn(warning!(
+                        font_list.span,
+                        "unknown font family: {}",
+                        family.as_str(),
+                    ));
+                }
+            }
+        }
+        font_list.map(|font_list| font_list.v)
+    })]
     #[default(FontList(vec![FontFamily::new("Linux Libertine")]))]
     #[borrowed]
     #[ghost]

tests/suite/math/interactions.typ

@@ -17,6 +17,7 @@ $ x := #table(columns: 2)[x][y]/mat(1, 2, 3)
 
 --- math-font-switch ---
 // Test font switch.
+// Warning: 29-40 unknown font family: noto sans
 #let here = text.with(font: "Noto Sans")
 $#here[f] := #here[Hi there]$.
 

tests/suite/text/edge.typ

@@ -5,11 +5,13 @@
 #set text(size: 8pt)
 
 #let try(top, bottom) = rect(inset: 0pt, fill: conifer)[
+  // Warning: 19-34 unknown font family: ibm plex mono
   #set text(font: "IBM Plex Mono", top-edge: top, bottom-edge: bottom)
   From #top to #bottom
 ]
 
 #let try-bounds(top, bottom) = rect(inset: 0pt, fill: conifer)[
+  // Warning: 19-34 unknown font family: ibm plex mono
   #set text(font: "IBM Plex Mono", top-edge: top, bottom-edge: bottom)
   #top to #bottom: "yay, Typst"
 ]

tests/suite/text/font.typ

@@ -64,3 +64,15 @@ Emoji: 🐪, 🌋, 🏞
 --- text-bad-named-argument ---
 // Error: 11-31 unexpected argument: something
 #set text(something: "invalid")
+
+--- text-unknown-font-family-warning ---
+#text(font: "linux libertine", "I exist, ")
+// Warning: 13-27 unknown font family: non-existing
+#text(font: "non-existing", "but")
+// Warning: 17-36 unknown font family: also-non-existing
+#set text(font: "also-non-existing")
+I
+// Warning: 23-56 unknown font family: list-of
+// Warning: 23-56 unknown font family: non-existing-fonts
+#let var = text(font: ("list-of", "non-existing-fonts"))[don't]
+#var