Add hint when string is used in place of label (#4330)

6 files changed, 50 insertions, 16 deletions

diff --git a/crates/typst-syntax/src/lexer.rs b/crates/typst-syntax/src/lexer.rs
index 6719deaf..3f409b2d 100644
--- a/crates/typst-syntax/src/lexer.rs
+++ b/crates/typst-syntax/src/lexer.rs
@@ -408,7 +408,7 @@ impl Lexer<'_> {
     }
 
     fn ref_marker(&mut self) -> SyntaxKind {
-        self.s.eat_while(|c| is_id_continue(c) || matches!(c, ':' | '.'));
+        self.s.eat_while(is_valid_in_label_literal);
 
         // Don't include the trailing characters likely to be part of text.
         while matches!(self.s.scout(-1), Some('.' | ':')) {
@@ -419,7 +419,7 @@ impl Lexer<'_> {
     }
 
     fn label(&mut self) -> SyntaxKind {
-        let label = self.s.eat_while(|c| is_id_continue(c) || matches!(c, ':' | '.'));
+        let label = self.s.eat_while(is_valid_in_label_literal);
         if label.is_empty() {
             return self.error("label cannot be empty");
         }
@@ -918,3 +918,14 @@ fn is_math_id_start(c: char) -> bool {
 fn is_math_id_continue(c: char) -> bool {
     is_xid_continue(c) && c != '_'
 }
+
+/// Whether a character can be part of a label literal's name.
+#[inline]
+fn is_valid_in_label_literal(c: char) -> bool {
+    is_id_continue(c) || matches!(c, ':' | '.')
+}
+
+/// Returns true if this string is valid in a label literal.
+pub fn is_valid_label_literal_id(id: &str) -> bool {
+    !id.is_empty() && id.chars().all(is_valid_in_label_literal)
+}
diff --git a/crates/typst-syntax/src/lib.rs b/crates/typst-syntax/src/lib.rs
index 6a6063d2..5e7b710f 100644
--- a/crates/typst-syntax/src/lib.rs
+++ b/crates/typst-syntax/src/lib.rs
@@ -19,7 +19,8 @@ pub use self::file::FileId;
 pub use self::highlight::{highlight, highlight_html, Tag};
 pub use self::kind::SyntaxKind;
 pub use self::lexer::{
-    is_id_continue, is_id_start, is_ident, is_newline, link_prefix, split_newlines,
+    is_id_continue, is_id_start, is_ident, is_newline, is_valid_label_literal_id,
+    link_prefix, split_newlines,
 };
 pub use self::node::{LinkedChildren, LinkedNode, Side, SyntaxError, SyntaxNode};
 pub use self::parser::{parse, parse_code, parse_math};
diff --git a/crates/typst/src/foundations/cast.rs b/crates/typst/src/foundations/cast.rs
index b53576c2..51e36128 100644
--- a/crates/typst/src/foundations/cast.rs
+++ b/crates/typst/src/foundations/cast.rs
@@ -3,7 +3,7 @@ use std::fmt::Write;
 use std::hash::Hash;
 use std::ops::Add;
 
-use ecow::{eco_format, EcoString};
+use ecow::eco_format;
 use smallvec::SmallVec;
 use unicode_math_class::MathClass;
 
@@ -42,7 +42,7 @@ pub trait Reflect {
     /// dynamic checks instead of optimized machine code for each type).
     fn castable(value: &Value) -> bool;
 
-    /// Produce an error message for an inacceptable value type.
+    /// Produce an error message for an unacceptable value type.
     ///
     /// ```ignore
     /// assert_eq!(
@@ -51,7 +51,7 @@ pub trait Reflect {
     /// );
     /// ```
     fn error(found: &Value) -> HintedString {
-        Self::input().error(found).into()
+        Self::input().error(found)
     }
 }
 
@@ -300,7 +300,7 @@ pub enum CastInfo {
 impl CastInfo {
     /// Produce an error message describing what was expected and what was
     /// found.
-    pub fn error(&self, found: &Value) -> EcoString {
+    pub fn error(&self, found: &Value) -> HintedString {
         let mut matching_type = false;
         let mut parts = vec![];
 
@@ -328,13 +328,26 @@ impl CastInfo {
             write!(msg, "{}", found.ty()).unwrap();
         }
 
+        let mut msg: HintedString = msg.into();
+
         if let Value::Int(i) = found {
-            if parts.iter().any(|p| p == "length") && !matching_type {
-                write!(msg, ": a length needs a unit - did you mean {i}pt?").unwrap();
+            if !matching_type && parts.iter().any(|p| p == "length") {
+                msg.hint(eco_format!("a length needs a unit - did you mean {i}pt?"));
+            }
+        } else if let Value::Str(s) = found {
+            if !matching_type && parts.iter().any(|p| p == "label") {
+                if typst_syntax::is_valid_label_literal_id(s) {
+                    msg.hint(eco_format!(
+                        "use `<{s}>` or `label({})` to create a label",
+                        s.repr()
+                    ));
+                } else {
+                    msg.hint(eco_format!("use `label({})` to create a label", s.repr()));
+                }
             }
         }
 
-        msg.into()
+        msg
     }
 
     /// Walk all contained non-union infos.
diff --git a/crates/typst/src/foundations/value.rs b/crates/typst/src/foundations/value.rs
index d2190ae7..47ce5d5d 100644
--- a/crates/typst/src/foundations/value.rs
+++ b/crates/typst/src/foundations/value.rs
@@ -610,11 +610,7 @@ macro_rules! primitive {
                 match value {
                     Value::$variant(v) => Ok(v),
                     $(Value::$other$(($binding))? => Ok($out),)*
-                    v => Err(eco_format!(
-                        "expected {}, found {}",
-                        Type::of::<Self>(),
-                        v.ty(),
-                    ).into()),
+                    v => Err(<Self as Reflect>::error(&v)),
                 }
             }
         }
diff --git a/tests/suite/layout/length.typ b/tests/suite/layout/length.typ
index 68755619..34a4b939 100644
--- a/tests/suite/layout/length.typ
+++ b/tests/suite/layout/length.typ
@@ -45,7 +45,8 @@
 }
 
 --- length-unit-hint ---
-// Error: 1:17-1:19 expected length, found integer: a length needs a unit - did you mean 12pt?
+// Error: 17-19 expected length, found integer
+// Hint: 17-19 a length needs a unit - did you mean 12pt?
 #set text(size: 12)
 
 --- length-ignore-em-pt-hint ---
diff --git a/tests/suite/model/cite.typ b/tests/suite/model/cite.typ
index 24d6ad04..750db38b 100644
--- a/tests/suite/model/cite.typ
+++ b/tests/suite/model/cite.typ
@@ -114,3 +114,15 @@ B #cite(<netwok>) #cite(<arrgh>).
 @mcintosh_anxiety
 #show bibliography: none
 #bibliography("/assets/bib/works.bib", style: "chicago-author-date")
+
+--- cite-type-error-hint ---
+// Test hint for cast error from str to label
+// Error: 7-15 expected label, found string
+// Hint: 7-15 use `<netwok>` or `label("netwok")` to create a label
+#cite("netwok")
+
+--- cite-type-error-hint-invalid-literal ---
+// Test hint for cast error from str to label
+// Error: 7-17 expected label, found string
+// Hint: 7-17 use `label("%@&#*!\\")` to create a label
+#cite("%@&#*!\\")