1 files changed, 96 insertions, 0 deletions
diff --git a/third_party/rust/fluent-bundle/src/resolver/errors.rs b/third_party/rust/fluent-bundle/src/resolver/errors.rs
new file mode 100644
index 0000000000..831d8474a5
--- /dev/null
+++ b/third_party/rust/fluent-bundle/src/resolver/errors.rs
@@ -0,0 +1,96 @@
+use fluent_syntax::ast::InlineExpression;
+use std::error::Error;
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum ReferenceKind {
+    Function {
+        id: String,
+    },
+    Message {
+        id: String,
+        attribute: Option<String>,
+    },
+    Term {
+        id: String,
+        attribute: Option<String>,
+    },
+    Variable {
+        id: String,
+    },
+}
+
+impl<T> From<&InlineExpression<T>> for ReferenceKind
+where
+    T: ToString,
+{
+    fn from(exp: &InlineExpression<T>) -> Self {
+        match exp {
+            InlineExpression::FunctionReference { id, .. } => Self::Function {
+                id: id.name.to_string(),
+            },
+            InlineExpression::MessageReference { id, attribute } => Self::Message {
+                id: id.name.to_string(),
+                attribute: attribute.as_ref().map(|i| i.name.to_string()),
+            },
+            InlineExpression::TermReference { id, attribute, .. } => Self::Term {
+                id: id.name.to_string(),
+                attribute: attribute.as_ref().map(|i| i.name.to_string()),
+            },
+            InlineExpression::VariableReference { id, .. } => Self::Variable {
+                id: id.name.to_string(),
+            },
+            _ => unreachable!(),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum ResolverError {
+    Reference(ReferenceKind),
+    NoValue(String),
+    MissingDefault,
+    Cyclic,
+    TooManyPlaceables,
+}
+
+impl std::fmt::Display for ResolverError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Reference(exp) => match exp {
+                ReferenceKind::Function { id } => write!(f, "Unknown function: {}()", id),
+                ReferenceKind::Message {
+                    id,
+                    attribute: None,
+                } => write!(f, "Unknown message: {}", id),
+                ReferenceKind::Message {
+                    id,
+                    attribute: Some(attribute),
+                } => write!(f, "Unknown attribute: {}.{}", id, attribute),
+                ReferenceKind::Term {
+                    id,
+                    attribute: None,
+                } => write!(f, "Unknown term: -{}", id),
+                ReferenceKind::Term {
+                    id,
+                    attribute: Some(attribute),
+                } => write!(f, "Unknown attribute: -{}.{}", id, attribute),
+                ReferenceKind::Variable { id } => write!(f, "Unknown variable: ${}", id),
+            },
+            Self::NoValue(id) => write!(f, "No value: {}", id),
+            Self::MissingDefault => f.write_str("No default"),
+            Self::Cyclic => f.write_str("Cyclical dependency detected"),
+            Self::TooManyPlaceables => f.write_str("Too many placeables"),
+        }
+    }
+}
+
+impl<T> From<&InlineExpression<T>> for ResolverError
+where
+    T: ToString,
+{
+    fn from(exp: &InlineExpression<T>) -> Self {
+        Self::Reference(exp.into())
+    }
+}
+
+impl Error for ResolverError {}