Merge pull request #114 from Nadrieril/nice-type-errors

Ground work for pretty type errors

2 files changed, 25 insertions, 9 deletions

diff --git a/dhall/src/phase/binary.rs b/dhall/src/phase/binary.rs
index 8c98f77..b4f18da 100644
--- a/dhall/src/phase/binary.rs
+++ b/dhall/src/phase/binary.rs
@@ -5,8 +5,9 @@ use std::vec;
 
 use dhall_syntax::map::DupTreeMap;
 use dhall_syntax::{
-    rc, Expr, ExprF, FilePath, FilePrefix, Hash, Import, ImportLocation,
-    ImportMode, Integer, InterpolatedText, Label, Natural, Scheme, URL, V,
+    Expr, ExprF, FilePath, FilePrefix, Hash, Import, ImportLocation,
+    ImportMode, Integer, InterpolatedText, Label, Natural, RawExpr, Scheme,
+    Span, URL, V,
 };
 
 use crate::error::{DecodeError, EncodeError};
@@ -24,6 +25,11 @@ pub(crate) fn encode<E>(expr: &Expr<E>) -> Result<Vec<u8>, EncodeError> {
         .map_err(|e| EncodeError::CBORError(e))
 }
 
+// Should probably rename this
+pub fn rc<E>(x: RawExpr<E>) -> Expr<E> {
+    Expr::new(x, Span::Decoded)
+}
+
 fn cbor_value_to_dhall(data: &cbor::Value) -> Result<DecodedExpr, DecodeError> {
     use cbor::Value::*;
     use dhall_syntax::{BinOp, Builtin, Const};
diff --git a/dhall/src/phase/typecheck.rs b/dhall/src/phase/typecheck.rs
index 9013c1f..33919e4 100644
--- a/dhall/src/phase/typecheck.rs
+++ b/dhall/src/phase/typecheck.rs
@@ -2,7 +2,7 @@ use std::cmp::max;
 use std::collections::HashMap;
 
 use dhall_syntax::{
-    rc, Builtin, Const, Expr, ExprF, InterpolatedTextContents, Label,
+    Builtin, Const, Expr, ExprF, InterpolatedTextContents, Label, RawExpr, Span,
 };
 
 use crate::core::context::TypecheckContext;
@@ -142,6 +142,10 @@ pub(crate) fn const_to_value(c: Const) -> Value {
     }
 }
 
+pub fn rc<E>(x: RawExpr<E>) -> Expr<E> {
+    Expr::new(x, Span::Artificial)
+}
+
 // Ad-hoc macro to help construct the types of builtins
 macro_rules! make_type {
     (Type) => { ExprF::Const(Const::Type) };
@@ -300,6 +304,7 @@ fn type_with(
     e: Expr<Normalized>,
 ) -> Result<Value, TypeError> {
     use dhall_syntax::ExprF::{Annot, Embed, Lam, Let, Pi, Var};
+    let span = e.span();
 
     Ok(match e.as_ref() {
         Lam(var, annot, body) => {
@@ -334,7 +339,7 @@ fn type_with(
             None => {
                 return Err(TypeError::new(
                     ctx,
-                    TypeMessage::UnboundVariable(var.clone()),
+                    TypeMessage::UnboundVariable(span),
                 ))
             }
         },
@@ -344,7 +349,7 @@ fn type_with(
                 |e| type_with(ctx, e.clone()),
                 |_, _| unreachable!(),
             )?;
-            type_last_layer(ctx, expr)?
+            type_last_layer(ctx, expr, span)?
         }
     })
 }
@@ -354,6 +359,7 @@ fn type_with(
 fn type_last_layer(
     ctx: &TypecheckContext,
     e: ExprF<Value, Normalized>,
+    span: Span,
 ) -> Result<Value, TypeError> {
     use crate::error::TypeMessage::*;
     use dhall_syntax::BinOp::*;
@@ -580,6 +586,7 @@ fn type_last_layer(
                 l.get_type()?,
                 r.get_type()?,
             ),
+            Span::Artificial,
         )?),
         BinOp(RecursiveRecordTypeMerge, l, r) => {
             use crate::phase::normalize::merge_maps;
@@ -615,6 +622,7 @@ fn type_last_layer(
                             l.clone(),
                             r.clone(),
                         ),
+                        Span::Artificial,
                     )
                 },
             )?;
@@ -782,10 +790,12 @@ fn type_last_layer(
     };
 
     Ok(match ret {
-        RetTypeOnly(typ) => {
-            Value::from_valuef_and_type(ValueF::PartialExpr(e), typ)
-        }
-        RetWhole(v) => v,
+        RetTypeOnly(typ) => Value::from_valuef_and_type_and_span(
+            ValueF::PartialExpr(e),
+            typ,
+            span,
+        ),
+        RetWhole(v) => v.with_span(span),
     })
 }