Fix an error of uncastable dict input (#3247)

crates/typst/src/foundations/cast.rs

@@ -43,11 +43,11 @@ 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.
+    /// Produce an error message for an inacceptable value type.
     ///
     /// ```
     /// assert_eq!(
-    ///   <Int as Reflect>::error(Value::None),
+    ///   <Int as Reflect>::error(&Value::None),
     ///   "expected integer, found none",
     /// );
     /// ```

crates/typst/src/foundations/dict.rs

@@ -113,15 +113,44 @@ impl Dict {
         self.0.iter()
     }
 
-    /// Return an "unexpected key" error if there is any remaining pair.
+    /// Check if there is any remaining pair, and if so return an
+    /// "unexpected key" error.
     pub fn finish(&self, expected: &[&str]) -> StrResult<()> {
-        if let Some((key, _)) = self.iter().next() {
+        let mut iter = self.iter().peekable();
-            let parts: Vec<_> = expected.iter().map(|s| eco_format!("\"{s}\"")).collect();
+        if iter.peek().is_none() {
-            let mut msg = format!("unexpected key {}, valid keys are ", key.repr());
+            return Ok(());
-            msg.push_str(&repr::separated_list(&parts, "and"));
-            return Err(msg.into());
         }
-        Ok(())
+        let unexpected: Vec<&str> = iter.map(|kv| kv.0.as_str()).collect();
+
+        Err(Self::unexpected_keys(unexpected, Some(expected)))
+    }
+
+    // Return an "unexpected key" error string.
+    pub fn unexpected_keys(
+        unexpected: Vec<&str>,
+        hint_expected: Option<&[&str]>,
+    ) -> EcoString {
+        let format_as_list = |arr: &[&str]| {
+            repr::separated_list(
+                &arr.iter().map(|s| eco_format!("\"{s}\"")).collect::<Vec<_>>(),
+                "and",
+            )
+        };
+
+        let mut msg = String::from(match unexpected.len() {
+            0 => unreachable!(),
+            1 => "unexpected key ",
+            _ => "unexpected keys ",
+        });
+
+        msg.push_str(&format_as_list(&unexpected[..]));
+
+        if let Some(expected) = hint_expected {
+            msg.push_str(", valid keys are ");
+            msg.push_str(&format_as_list(expected));
+        }
+
+        msg.into()
     }
 }
 

crates/typst/src/layout/corners.rs

@@ -164,7 +164,7 @@ where
     T: FromValue + Clone,
 {
     fn from_value(mut value: Value) -> StrResult<Self> {
-        let keys = [
+        let expected_keys = [
             "top-left",
             "top-right",
             "bottom-right",
@@ -177,7 +177,9 @@ where
         ];
 
         if let Value::Dict(dict) = &mut value {
-            if dict.iter().any(|(key, _)| keys.contains(&key.as_str())) {
+            if dict.is_empty() {
+                return Ok(Self::splat(None));
+            } else if dict.iter().any(|(key, _)| expected_keys.contains(&key.as_str())) {
                 let mut take = |key| dict.take(key).ok().map(T::from_value).transpose();
                 let rest = take("rest")?;
                 let left = take("left")?.or_else(|| rest.clone());
@@ -199,13 +201,18 @@ where
                         .or_else(|| left.clone()),
                 };
 
-                dict.finish(&keys)?;
+                dict.finish(&expected_keys)?;
                 return Ok(corners);
             }
         }
 
         if T::castable(&value) {
             Ok(Self::splat(Some(T::from_value(value)?)))
+        } else if let Value::Dict(dict) = &value {
+            let keys = dict.iter().map(|kv| kv.0.as_str()).collect();
+            // Do not hint at expected_keys, because T may be castable from Dict
+            // objects with other sets of expected keys.
+            Err(Dict::unexpected_keys(keys, None))
         } else {
             Err(Self::error(&value))
         }

crates/typst/src/layout/sides.rs

@@ -190,9 +190,11 @@ where
     T: Default + FromValue + Clone,
 {
     fn from_value(mut value: Value) -> StrResult<Self> {
-        let keys = ["left", "top", "right", "bottom", "x", "y", "rest"];
+        let expected_keys = ["left", "top", "right", "bottom", "x", "y", "rest"];
         if let Value::Dict(dict) = &mut value {
-            if dict.iter().any(|(key, _)| keys.contains(&key.as_str())) {
+            if dict.is_empty() {
+                return Ok(Self::splat(None));
+            } else if dict.iter().any(|(key, _)| expected_keys.contains(&key.as_str())) {
                 let mut take = |key| dict.take(key).ok().map(T::from_value).transpose();
                 let rest = take("rest")?;
                 let x = take("x")?.or_else(|| rest.clone());
@@ -204,13 +206,18 @@ where
                     bottom: take("bottom")?.or_else(|| y.clone()),
                 };
 
-                dict.finish(&keys)?;
+                dict.finish(&expected_keys)?;
                 return Ok(sides);
             }
         }
 
         if T::castable(&value) {
             Ok(Self::splat(Some(T::from_value(value)?)))
+        } else if let Value::Dict(dict) = &value {
+            let keys = dict.iter().map(|kv| kv.0.as_str()).collect();
+            // Do not hint at expected_keys, because T may be castable from Dict
+            // objects with other sets of expected keys.
+            Err(Dict::unexpected_keys(keys, None))
         } else {
             Err(Self::error(&value))
         }

tests/typ/bugs/3232-dict-wrong-keys.typ

@@ -0,0 +1,23 @@
+// Issue #3232: Confusing "expected relative length or dictionary, found dictionary"
+// https://github.com/typst/typst/issues/3232
+// Ref: false
+
+---
+// Error: 16-58 unexpected keys "unexpected" and "unexpected-too"
+#block(outset: (unexpected: 0.5em, unexpected-too: 0.2em), [Hi])
+
+---
+// Error: 14-56 unexpected keys "unexpected" and "unexpected-too"
+#box(radius: (unexpected: 0.5em, unexpected-too: 0.5em), [Hi])
+
+---
+// Error: 16-49 unexpected key "unexpected", valid keys are "left", "top", "right", "bottom", "x", "y", and "rest"
+#block(outset: (unexpected: 0.2em, right: 0.5em), [Hi]) // The 1st key is unexpected
+
+---
+// Error: 14-50 unexpected key "unexpected", valid keys are "top-left", "top-right", "bottom-right", "bottom-left", "left", "top", "right", "bottom", and "rest"
+#box(radius: (top-left: 0.5em, unexpected: 0.5em), [Hi]) // The 2nd key is unexpected
+
+---
+#block(outset: (:), [Hi]) // Ok
+#box(radius: (:), [Hi]) // Ok