Say which label occurs never or multiple times in error message

Cargo.lock

@@ -2888,6 +2888,7 @@ dependencies = [
  "comemo",
  "ecow",
  "if_chain",
+ "log",
  "serde",
  "typst",
  "unscanny",

crates/typst/src/model/introspect.rs

@@ -5,7 +5,7 @@ use std::hash::Hash;
 use std::num::NonZeroUsize;
 
 use comemo::{Prehashed, Track, Tracked, Validate};
-use ecow::{EcoString, EcoVec};
+use ecow::{eco_format, EcoString, EcoVec};
 use indexmap::IndexMap;
 
 use super::{Content, Selector};
@@ -388,11 +388,13 @@ impl Introspector {
         let mut found = None;
         for elem in self.all().filter(|elem| elem.label() == Some(label)) {
             if found.is_some() {
-                bail!("label occurs multiple times in the document");
+                bail!("label `{}` occurs multiple times in the document", label.repr());
             }
             found = Some(elem.clone());
         }
-        found.ok_or_else(|| "label does not exist in the document".into())
+        found.ok_or_else(|| {
+            eco_format!("label `{}` does not exist in the document", label.repr())
+        })
     }
 
     /// The total number pages.

tests/typ/meta/bibliography.typ

@@ -1,12 +1,5 @@
 // Test citations and bibliographies.
 
----
-// Test ambiguous reference.
-= Introduction <arrgh>
-// Error: 1-7 label occurs in the document and its bibliography
-@arrgh
-#bibliography("/files/works.bib")
-
 ---
 #set page(width: 200pt)
 = Details
@@ -41,3 +34,12 @@ And quark! @quark
 = Multiple Bibs
 Now we have multiple bibliographies containing #cite("glacier-melt", "keshav2007read")
 #bibliography(("/files/works.bib", "/files/works_too.bib"))
+
+---
+// Test ambiguous reference.
+= Introduction <arrgh>
+
+// Error: 1-7 label occurs in the document and its bibliography
+@arrgh
+#bibliography("/files/works.bib")
+

tests/typ/meta/link.typ

@@ -67,11 +67,11 @@ Text <hey>
 #link(<hey>)[Go to text.]
 
 ---
-// Error: 2-20 label does not exist in the document
+// Error: 2-20 label `<hey>` does not exist in the document
 #link(<hey>)[Nope.]
 
 ---
 Text <hey>
 Text <hey>
-// Error: 2-20 label occurs multiple times in the document
+// Error: 2-20 label `<hey>` occurs multiple times in the document
 #link(<hey>)[Nope.]

tests/typ/meta/ref.typ

@@ -10,14 +10,14 @@ See @setup.
 As seen in @intro, we proceed.
 
 ---
-// Error: 1-5 label does not exist in the document
+// Error: 1-5 label `<foo>` does not exist in the document
 @foo
 
 ---
 = First <foo>
 = Second <foo>
 
-// Error: 1-5 label occurs multiple times in the document
+// Error: 1-5 label `<foo>` occurs multiple times in the document
 @foo
 
 ---