1 files changed, 178 insertions, 0 deletions
diff --git a/dhall/src/semantics/error/mod.rs b/dhall/src/semantics/error/mod.rs
new file mode 100644
index 0000000..1288c12
--- /dev/null
+++ b/dhall/src/semantics/error/mod.rs
@@ -0,0 +1,178 @@
+use std::io::Error as IOError;
+
+use crate::semantics::core::context::TypecheckContext;
+use crate::semantics::core::value::Value;
+use crate::semantics::phase::resolve::ImportStack;
+use crate::semantics::phase::NormalizedExpr;
+use crate::syntax::{BinOp, Import, Label, ParseError, Span};
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum Error {
+    IO(IOError),
+    Parse(ParseError),
+    Decode(DecodeError),
+    Encode(EncodeError),
+    Resolve(ImportError),
+    Typecheck(TypeError),
+}
+
+#[derive(Debug)]
+pub enum ImportError {
+    Recursive(Import<NormalizedExpr>, Box<Error>),
+    UnexpectedImport(Import<NormalizedExpr>),
+    ImportCycle(ImportStack, Import<NormalizedExpr>),
+}
+
+#[derive(Debug)]
+pub enum DecodeError {
+    CBORError(serde_cbor::error::Error),
+    WrongFormatError(String),
+}
+
+#[derive(Debug)]
+pub enum EncodeError {
+    CBORError(serde_cbor::error::Error),
+}
+
+/// A structured type error that includes context
+#[derive(Debug)]
+pub struct TypeError {
+    message: TypeMessage,
+    context: TypecheckContext,
+}
+
+/// The specific type error
+#[derive(Debug)]
+pub(crate) enum TypeMessage {
+    UnboundVariable(Span),
+    InvalidInputType(Value),
+    InvalidOutputType(Value),
+    NotAFunction(Value),
+    TypeMismatch(Value, Value, Value),
+    AnnotMismatch(Value, Value),
+    InvalidListElement(usize, Value, Value),
+    InvalidListType(Value),
+    InvalidOptionalType(Value),
+    InvalidPredicate(Value),
+    IfBranchMismatch(Value, Value),
+    IfBranchMustBeTerm(bool, Value),
+    InvalidFieldType(Label, Value),
+    NotARecord(Label, Value),
+    MustCombineRecord(Value),
+    MissingRecordField(Label, Value),
+    MissingUnionField(Label, Value),
+    BinOpTypeMismatch(BinOp, Value),
+    InvalidTextInterpolation(Value),
+    Merge1ArgMustBeRecord(Value),
+    Merge2ArgMustBeUnion(Value),
+    MergeEmptyNeedsAnnotation,
+    MergeHandlerMissingVariant(Label),
+    MergeVariantMissingHandler(Label),
+    MergeAnnotMismatch,
+    MergeHandlerTypeMismatch,
+    MergeHandlerReturnTypeMustNotBeDependent,
+    ProjectionMustBeRecord,
+    ProjectionMissingEntry,
+    Sort,
+    RecordTypeDuplicateField,
+    RecordTypeMergeRequiresRecordType(Value),
+    UnionTypeDuplicateField,
+    EquivalenceArgumentMustBeTerm(bool, Value),
+    EquivalenceTypeMismatch(Value, Value),
+    AssertMismatch(Value, Value),
+    AssertMustTakeEquivalence,
+}
+
+impl TypeError {
+    pub(crate) fn new(
+        context: &TypecheckContext,
+        message: TypeMessage,
+    ) -> Self {
+        TypeError {
+            context: context.clone(),
+            message,
+        }
+    }
+}
+
+impl std::fmt::Display for TypeError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        use TypeMessage::*;
+        let msg = match &self.message {
+            UnboundVariable(span) => span.error("Type error: Unbound variable"),
+            InvalidInputType(v) => {
+                v.span().error("Type error: Invalid function input")
+            }
+            InvalidOutputType(v) => {
+                v.span().error("Type error: Invalid function output")
+            }
+            NotAFunction(v) => v.span().error("Type error: Not a function"),
+            TypeMismatch(x, y, z) => {
+                x.span()
+                    .error("Type error: Wrong type of function argument")
+                    + "\n"
+                    + &z.span().error(format!(
+                        "This argument has type {:?}",
+                        z.get_type().unwrap()
+                    ))
+                    + "\n"
+                    + &y.span().error(format!(
+                        "But the function expected an argument of type {:?}",
+                        y
+                    ))
+            }
+            _ => "Type error: Unhandled error".to_string(),
+        };
+        write!(f, "{}", msg)
+    }
+}
+
+impl std::error::Error for TypeError {}
+
+impl std::fmt::Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            Error::IO(err) => write!(f, "{}", err),
+            Error::Parse(err) => write!(f, "{}", err),
+            Error::Decode(err) => write!(f, "{:?}", err),
+            Error::Encode(err) => write!(f, "{:?}", err),
+            Error::Resolve(err) => write!(f, "{:?}", err),
+            Error::Typecheck(err) => write!(f, "{}", err),
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+impl From<IOError> for Error {
+    fn from(err: IOError) -> Error {
+        Error::IO(err)
+    }
+}
+impl From<ParseError> for Error {
+    fn from(err: ParseError) -> Error {
+        Error::Parse(err)
+    }
+}
+impl From<DecodeError> for Error {
+    fn from(err: DecodeError) -> Error {
+        Error::Decode(err)
+    }
+}
+impl From<EncodeError> for Error {
+    fn from(err: EncodeError) -> Error {
+        Error::Encode(err)
+    }
+}
+impl From<ImportError> for Error {
+    fn from(err: ImportError) -> Error {
+        Error::Resolve(err)
+    }
+}
+impl From<TypeError> for Error {
+    fn from(err: TypeError) -> Error {
+        Error::Typecheck(err)
+    }
+}