Add std::error::Error impls to Error enums of parameter module (#413)

rclrs/src/parameter.rs

@@ -624,6 +624,18 @@ pub enum ParameterValueError {
     ReadOnly,
 }
 
+impl std::fmt::Display for ParameterValueError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ParameterValueError::OutOfRange => write!(f, "parameter value was out of the parameter's range"),
+            ParameterValueError::TypeMismatch => write!(f, "parameter was stored in a static type and an operation on a different type was attempted"),
+            ParameterValueError::ReadOnly => write!(f, "a write on a read-only parameter was attempted"),
+        }
+    }
+}
+
+impl std::error::Error for ParameterValueError {}
+
 /// Error that can be generated when doing operations on parameters.
 #[derive(Debug)]
 pub enum DeclarationError {
@@ -644,6 +656,27 @@ pub enum DeclarationError {
     InvalidRange,
 }
 
+impl std::fmt::Display for DeclarationError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            DeclarationError::AlreadyDeclared => write!(f, "parameter was already declared, but a new declaration was attempted"),
+            DeclarationError::NoValueAvailable => {
+                write!(f, "parameter was declared as non-optional but no value was available, either through a user specified default, a command-line override, or a previously set value")
+            },
+            DeclarationError::OverrideValueTypeMismatch => {
+                write!(f, "the override value that was provided has the wrong type")
+            },
+            DeclarationError::PriorValueTypeMismatch => {
+                write!(f, "the value that the parameter was already set to has the wrong type")
+            },
+            DeclarationError::InitialValueOutOfRange => write!(f, "the initial value that was selected is out of range"),
+            DeclarationError::InvalidRange => write!(f, "an invalid range was provided to a parameter declaration (i.e. lower bound > higher bound)"),
+        }
+    }
+}
+
+impl std::error::Error for DeclarationError {}
+
 impl<'a> Parameters<'a> {
     /// Tries to read a parameter of the requested type.
     ///

rclrs/src/parameter/value.rs

@@ -376,11 +376,24 @@ impl From<ParameterValue> for RmwParameterValue {
 
 /// An error that occured when trying to convert a parameter from an
 /// `rcl_interfaces::msg::ParameterValue`
+#[derive(Debug)]
 pub enum RmwParameterConversionError {
     /// The parameter type was not valid.
     InvalidParameterType,
 }
 
+impl std::fmt::Display for RmwParameterConversionError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            RmwParameterConversionError::InvalidParameterType => {
+                write!(f, "the parameter type was not valid")
+            }
+        }
+    }
+}
+
+impl std::error::Error for RmwParameterConversionError {}
+
 impl TryFrom<RmwParameterValue> for ParameterValue {
     type Error = RmwParameterConversionError;