Fix type display on error. (#1631)

ast/src/parsed/display.rs

@@ -1019,17 +1019,13 @@ pub fn format_type_scheme_around_name<E: Display, N: Display>(
 
 impl Display for TypeBounds {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
-        fn format_var((var, bounds): (&String, &BTreeSet<String>)) -> String {
-            format!(
-                "{var}{}",
-                if bounds.is_empty() {
-                    String::new()
-                } else {
-                    format!(": {}", bounds.iter().join(" + "))
-                }
-            )
-        }
-        write!(f, "{}", self.bounds().map(format_var).format(", "))
+        write!(
+            f,
+            "{}",
+            self.bounds()
+                .map(|(var, bounds)| TypeBounds::format_var_bound(var, bounds))
+                .format(", ")
+        )
     }
 }
 

ast/src/parsed/types.rs

@@ -441,4 +441,20 @@ impl TypeBounds {
     pub fn bounds(&self) -> impl Iterator<Item = (&String, &BTreeSet<String>)> {
         self.0.iter().map(|(n, x)| (n, x))
     }
+
+    pub fn format_vars_with_nonempty_bounds(&self) -> String {
+        self.0
+            .iter()
+            .filter(|(_, b)| !b.is_empty())
+            .map(|(var, b)| Self::format_var_bound(var, b))
+            .join(", ")
+    }
+
+    pub fn format_var_bound(var: &String, bounds: &BTreeSet<String>) -> String {
+        if bounds.is_empty() {
+            var.clone()
+        } else {
+            format!("{var}: {}", bounds.iter().join(" + "))
+        }
+    }
 }

pil-analyzer/src/type_inference.rs

@@ -950,12 +950,13 @@ impl TypeChecker {
 
     fn format_type_with_bounds(&self, ty: Type) -> String {
         let scheme = self.to_type_scheme(ty);
-        if scheme.vars.is_empty() {
-            format!("{}", scheme.ty)
+        let bounds = scheme.vars.format_vars_with_nonempty_bounds();
+        if bounds.is_empty() {
+            scheme.ty.to_string()
         } else if let Type::TypeVar(_) = &scheme.ty {
-            format!("{}", scheme.vars)
+            bounds
         } else {
-            format!("{}, {}", scheme.ty, scheme.vars)
+            format!("{} with {bounds}", scheme.ty,)
         }
     }
 

pil-analyzer/tests/types.rs

@@ -588,7 +588,7 @@ fn type_vars_in_block_let() {
 }
 
 #[test]
-#[should_panic = "Expected type: int -> T, T\\nInferred type: int\\n"]
+#[should_panic = "Expected type: int -> T\\nInferred type: int\\n"]
 fn new_fixed_column_wrong_value_type() {
     let input = r#"namespace N(16);
         let f = constr |j| {