[DEV-7087] TAMER: AsgError: Wrap TransitionError

See next commit.

tamer/src/ir/asg/base.rs

@@ -648,9 +648,8 @@ mod test {
         // Set up an object to fail redeclaration.
         let node = sut.declare(&sym, IdentKind::Meta, src.clone())?;
         let obj = sut.get(node).unwrap();
-        let msg = String::from("test fail");
-        obj.fail_redeclare
-            .replace(Some(TransitionError::Incompatible(msg.clone())));
+        let terr = TransitionError::Incompatible(String::from("test fail"));
+        obj.fail_redeclare.replace(Some(terr.clone()));
 
         // Should invoke StubIdentObject::redeclare on the above `obj`.
         let result = sut.declare(&sym, IdentKind::Meta, Source::default());
@@ -660,7 +659,7 @@ mod test {
             let obj = sut.get(node).unwrap();
             assert_eq!(src, obj.given_ident.as_ref().unwrap().2);
 
-            assert_eq!(AsgError::IncompatibleIdent(msg), err);
+            assert_eq!(AsgError::ObjectTransition(terr), err);
 
             Ok(())
         } else {

tamer/src/ir/asg/graph.rs

@@ -227,18 +227,12 @@ pub type Node<O> = Option<O>;
 /// The caller will know the problem values.
 #[derive(Debug, PartialEq)]
 pub enum AsgError<Ix: Debug> {
-    /// The provided identifier is not in a state that is permitted to
-    ///   receive a fragment.
+    /// An object could not change state in the manner requested.
     ///
-    /// See [`Asg::set_fragment`] for more information.
-    BadFragmentDest(String),
-
-    /// An attempt to redeclare an identifier with additional information
-    ///   has failed because the provided information was not compatible
-    ///   with the original declaration.
-    ///
-    /// See [`Asg::declare`] for more information.
-    IncompatibleIdent(String),
+    /// See [`Asg::declare`] and [`Asg::set_fragment`] for more
+    ///   information.
+    /// See also [`TransitionError`].
+    ObjectTransition(TransitionError),
 
     /// The node was not expected in the current context
     UnexpectedNode(String),
@@ -250,12 +244,7 @@ pub enum AsgError<Ix: Debug> {
 impl<Ix: Debug> std::fmt::Display for AsgError<Ix> {
     fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
         match self {
-            Self::BadFragmentDest(msg) => {
-                write!(fmt, "bad fragment destination: {}", msg)
-            }
-            Self::IncompatibleIdent(msg) => {
-                write!(fmt, "identifier redeclaration failed: {}", msg)
-            }
+            Self::ObjectTransition(err) => std::fmt::Display::fmt(&err, fmt),
             Self::UnexpectedNode(msg) => {
                 write!(fmt, "unexpected node: {}", msg)
             }
@@ -268,16 +257,16 @@ impl<Ix: Debug> std::fmt::Display for AsgError<Ix> {
 
 impl<Ix: Debug> std::error::Error for AsgError<Ix> {
     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        None
+        match self {
+            Self::ObjectTransition(err) => err.source(),
+            _ => None,
+        }
     }
 }
 
 impl<Ix: Debug> From<TransitionError> for AsgError<Ix> {
-    fn from(e: TransitionError) -> Self {
-        match e {
-            TransitionError::Incompatible(msg) => Self::IncompatibleIdent(msg),
-            TransitionError::BadFragmentDest(msg) => Self::BadFragmentDest(msg),
-        }
+    fn from(err: TransitionError) -> Self {
+        Self::ObjectTransition(err)
     }
 }
 

tamer/src/ir/asg/object.rs

@@ -340,7 +340,7 @@ impl<'i> IdentObjectState<'i, IdentObject<'i>> for IdentObject<'i> {
 ///   another.
 ///
 /// TODO: Provide enough information to construct a useful message.
-#[derive(Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum TransitionError {
     /// An attempt to redeclare an identifier with additional information
     ///   has failed because the provided information was not compatible
@@ -370,6 +370,12 @@ impl std::fmt::Display for TransitionError {
     }
 }
 
+impl std::error::Error for TransitionError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        None
+    }
+}
+
 /// Compiled fragment for identifier.
 ///
 /// This represents the text associated with an identifier.