Add guard for potential empty labels from bibliography (#5776)

crates/typst-library/src/foundations/label.rs

@@ -54,7 +54,9 @@ pub struct Label(PicoStr);
 
 impl Label {
     /// Creates a label from an interned string.
+    /// Callers need to ensure the given string is not empty.
     pub fn new(name: PicoStr) -> Self {
+        debug_assert!(name != PicoStr::EMPTY);
         Self(name)
     }
 

crates/typst-library/src/model/bibliography.rs

@@ -313,12 +313,17 @@ impl Bibliography {
         for (source, data) in sources.0.iter().zip(data) {
             let library = decode_library(source, data)?;
             for entry in library {
-                match map.entry(Label::new(PicoStr::intern(entry.key()))) {
+                let key = entry.key();
+                if key.is_empty() {
+                    bail!("empty bibliography key found");
+                }
+
+                match map.entry(Label::new(PicoStr::intern(key))) {
                     indexmap::map::Entry::Vacant(vacant) => {
                         vacant.insert(entry);
                     }
                     indexmap::map::Entry::Occupied(_) => {
-                        duplicates.push(entry.key().into());
+                        duplicates.push(key.into());
                     }
                 }
             }

crates/typst-utils/src/pico.rs

@@ -38,6 +38,9 @@ struct Interner {
 pub struct PicoStr(NonZeroU64);
 
 impl PicoStr {
+    /// Empty string as PicoStr
+    pub const EMPTY: PicoStr = PicoStr::constant("");
+
     /// Intern a string at runtime.
     pub fn intern(string: &str) -> PicoStr {
         // Try to use bitcode or exception representations.