feat(core): Infallible error types.

xmlity/src/types/infallible.rs

@@ -0,0 +1,51 @@
+use std::convert::Infallible;
+
+impl crate::de::Error for Infallible {
+    fn custom<T>(msg: T) -> Self
+    where
+        T: std::fmt::Display,
+    {
+        panic!("Infallible error: {msg}");
+    }
+
+    fn wrong_name(name: &crate::ExpandedName<'_>, expected: &crate::ExpandedName<'_>) -> Self {
+        panic!("Infallible error: wrong name \"{name}\", expected \"{expected}\"");
+    }
+
+    fn unexpected_visit<T>(unexpected: crate::de::Unexpected, _expected: &T) -> Self {
+        panic!("Infallible error: unexpected visit of {unexpected}");
+    }
+
+    fn missing_field(field: &str) -> Self {
+        panic!("Infallible error: missing field {field}");
+    }
+
+    fn no_possible_variant(ident: &str) -> Self {
+        panic!("Infallible error: no possible variant {ident}");
+    }
+
+    fn missing_data() -> Self {
+        panic!("Infallible error: missing data");
+    }
+
+    fn unknown_child() -> Self {
+        panic!("Infallible error: unknown child");
+    }
+
+    fn invalid_string() -> Self {
+        panic!("Infallible error: invalid string");
+    }
+}
+
+impl crate::ser::Error for Infallible {
+    fn custom<T>(msg: T) -> Self
+    where
+        T: std::fmt::Display,
+    {
+        panic!("Infallible error: {msg}");
+    }
+
+    fn unexpected_serialize(unexpected: crate::ser::Unexpected) -> Self {
+        panic!("Infallible error: unexpected serialize of {unexpected}");
+    }
+}

xmlity/src/types/mod.rs

@@ -3,6 +3,7 @@
 //! It also contains some visitors for the types which can be reused, including [`iterator::IteratorVisitor`].
 
 pub mod common;
+mod infallible;
 pub mod iterator;
 mod primitive;
 mod smart;