Add useful error message when an unsupported yaml hash key is found

Author: MartinHowarthFlexciton

src/file/format/yaml.rs

@@ -50,7 +50,7 @@ fn from_yaml_value(
                 match key {
                     yaml::Yaml::String(k) => m.insert(k.to_owned(), from_yaml_value(uri, value)?),
                     yaml::Yaml::Integer(k) => m.insert(k.to_string(), from_yaml_value(uri, value)?),
-                    _ => unreachable!(),
+                    other => Err(Box::new(UnsupportedHashKeyError(format!("{other:?}"))))?,
                 };
             }
             Ok(Value::new(uri, ValueKind::Table(m)))
@@ -103,3 +103,22 @@ impl Error for FloatParsingError {
         "Floating point number parsing failed"
     }
 }
+
+#[derive(Debug, Clone)]
+struct UnsupportedHashKeyError(String);
+
+impl fmt::Display for UnsupportedHashKeyError {
+    fn fmt(&self, format: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            format,
+            "Cannot parse {} because it is an unsupported hash key type",
+            self.0
+        )
+    }
+}
+
+impl Error for UnsupportedHashKeyError {
+    fn description(&self) -> &str {
+        "Unsupported yaml hash key found"
+    }
+}

tests/testsuite/file_yaml.rs

@@ -340,8 +340,9 @@ fn yaml() {
 }
 
 #[test]
-#[should_panic]
-fn test_yaml_parsing_unsupported_hash() {
+/// We only support certain types as keys to a yaml hash, this test ensures
+/// we communicate that to the user effectively.
+fn test_yaml_parsing_unsupported_hash_has_useful_error_message() {
     let result = Config::builder()
         .add_source(File::from_str(
             r#"
@@ -352,4 +353,8 @@ inner_vec:
         ))
         .build();
     assert!(result.is_err());
+    assert_data_eq!(
+        result.unwrap_err().to_string(),
+        str!["Cannot parse Array([Integer(1), Integer(2)]) because it is an unsupported hash key type"]
+    );
 }