Hint for label in both document and bibliography (#6457)

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

@@ -79,7 +79,12 @@ impl Label {
 
 impl Repr for Label {
     fn repr(&self) -> EcoString {
-        eco_format!("<{}>", self.resolve())
+        let resolved = self.resolve();
+        if typst_syntax::is_valid_label_literal_id(&resolved) {
+            eco_format!("<{resolved}>")
+        } else {
+            eco_format!("label({})", resolved.repr())
+        }
     }
 }
 

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

@@ -5,7 +5,7 @@ use crate::diag::{bail, At, Hint, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
     cast, elem, Cast, Content, Context, Func, IntoValue, Label, NativeElement, Packed,
-    Show, Smart, StyleChain, Synthesize,
+    Repr, Show, Smart, StyleChain, Synthesize,
 };
 use crate::introspection::{Counter, CounterKey, Locatable};
 use crate::math::EquationElem;
@@ -229,8 +229,15 @@ impl Show for Packed<RefElem> {
         // RefForm::Normal
 
         if BibliographyElem::has(engine, self.target) {
-            if elem.is_ok() {
-                bail!(span, "label occurs in the document and its bibliography");
+            if let Ok(elem) = elem {
+                bail!(
+                    span,
+                    "label `{}` occurs both in the document and its bibliography",
+                    self.target.repr();
+                    hint: "change either the {}'s label or the \
+                           bibliography key to resolve the ambiguity",
+                    elem.func().name(),
+                );
             }
 
             return Ok(to_citation(self, engine, styles)?.pack().spanned(span));

tests/suite/model/ref.typ

@@ -51,7 +51,8 @@ $ A = 1 $ <eq2>
 // Test ambiguous reference.
 = Introduction <arrgh>
 
-// Error: 1-7 label occurs in the document and its bibliography
+// Error: 1-7 label `<arrgh>` occurs both in the document and its bibliography
+// Hint: 1-7 change either the heading's label or the bibliography key to resolve the ambiguity
 @arrgh
 #bibliography("/assets/bib/works.bib")