Display first pretty type error

7 files changed, 61 insertions, 9 deletions

diff --git a/dhall/src/error/mod.rs b/dhall/src/error/mod.rs
index 5338e2d..efbd578 100644
--- a/dhall/src/error/mod.rs
+++ b/dhall/src/error/mod.rs
@@ -1,6 +1,6 @@
 use std::io::Error as IOError;
 
-use dhall_syntax::{BinOp, Import, Label, ParseError, V};
+use dhall_syntax::{BinOp, Import, Label, ParseError, Span};
 
 use crate::core::context::TypecheckContext;
 use crate::core::value::Value;
@@ -48,7 +48,7 @@ pub struct TypeError {
 /// The specific type error
 #[derive(Debug)]
 pub(crate) enum TypeMessage {
-    UnboundVariable(V<Label>),
+    UnboundVariable(Span),
     InvalidInputType(Value),
     InvalidOutputType(Value),
     NotAFunction(Value),
@@ -102,8 +102,8 @@ impl TypeError {
 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(_) => "Unbound variable".to_string(),
+        let msg = match &self.message {
+            UnboundVariable(span) => span.error("Unbound variable"),
             InvalidInputType(_) => "Invalid function input".to_string(),
             InvalidOutputType(_) => "Invalid function output".to_string(),
             NotAFunction(_) => "Not a function".to_string(),
diff --git a/dhall/src/phase/typecheck.rs b/dhall/src/phase/typecheck.rs
index 63f5157..9d2c69b 100644
--- a/dhall/src/phase/typecheck.rs
+++ b/dhall/src/phase/typecheck.rs
@@ -339,7 +339,7 @@ fn type_with(
             None => {
                 return Err(TypeError::new(
                     ctx,
-                    TypeMessage::UnboundVariable(var.clone()),
+                    TypeMessage::UnboundVariable(span),
                 ))
             }
         },
diff --git a/dhall/src/tests.rs b/dhall/src/tests.rs
index 9790b95..cde3b03 100644
--- a/dhall/src/tests.rs
+++ b/dhall/src/tests.rs
@@ -20,6 +20,29 @@ right: `{}`"#,
     }};
 }
 
+/// Wrapper around string slice that makes debug output `{:?}` to print string same way as `{}`.
+/// Used in different `assert*!` macros in combination with `pretty_assertions` crate to make
+/// test failures to show nice diffs.
+#[derive(PartialEq, Eq)]
+#[doc(hidden)]
+pub struct PrettyString(String);
+
+/// Make diff to display string as multi-line string
+impl std::fmt::Debug for PrettyString {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        f.write_str(&self.0)
+    }
+}
+
+macro_rules! assert_eq_pretty_str {
+    ($left:expr, $right:expr) => {
+        assert_eq_pretty!(
+            PrettyString($left.to_string()),
+            PrettyString($right.to_string())
+        );
+    };
+}
+
 use std::fs::File;
 use std::io::{Read, Write};
 use std::path::PathBuf;
@@ -172,7 +195,7 @@ pub fn run_test(test: Test<'_>) -> Result<()> {
             if error_file_path.is_file() {
                 let expected_msg = std::fs::read_to_string(error_file_path)?;
                 let msg = format!("{}\n", err);
-                assert_eq_pretty!(msg, expected_msg);
+                assert_eq_pretty_str!(msg, expected_msg);
             } else {
                 std::fs::create_dir_all(error_file_path.parent().unwrap())?;
                 let mut file = File::create(error_file_path)?;
diff --git a/dhall/tests/type-errors/unit/AssertAlphaTrap.txt b/dhall/tests/type-errors/unit/AssertAlphaTrap.txt
index df2b6c1..f2fc8ce 100644
--- a/dhall/tests/type-errors/unit/AssertAlphaTrap.txt
+++ b/dhall/tests/type-errors/unit/AssertAlphaTrap.txt
@@ -1 +1,6 @@
-Type error: Unbound variable
+Type error:  --> 1:47
+  |
+1 | assert : (\(_: Bool) -> _) === (\(x: Bool) -> _)␊
+  |                                               ^
+  |
+  = Unbound variable
diff --git a/dhall/tests/type-errors/unit/UnionDeprecatedConstructorsKeyword.txt b/dhall/tests/type-errors/unit/UnionDeprecatedConstructorsKeyword.txt
index df2b6c1..f7903de 100644
--- a/dhall/tests/type-errors/unit/UnionDeprecatedConstructorsKeyword.txt
+++ b/dhall/tests/type-errors/unit/UnionDeprecatedConstructorsKeyword.txt
@@ -1 +1,6 @@
-Type error: Unbound variable
+Type error:  --> 1:1
+  |
+1 | constructors < Left : Natural | Right : Bool >␊
+  | ^----------^
+  |
+  = Unbound variable
diff --git a/dhall/tests/type-errors/unit/VariableFree.txt b/dhall/tests/type-errors/unit/VariableFree.txt
index df2b6c1..ef1d16e 100644
--- a/dhall/tests/type-errors/unit/VariableFree.txt
+++ b/dhall/tests/type-errors/unit/VariableFree.txt
@@ -1 +1,6 @@
-Type error: Unbound variable
+Type error:  --> 1:1
+  |
+1 | x␊
+  | ^
+  |
+  = Unbound variable
diff --git a/dhall_syntax/src/core/span.rs b/dhall_syntax/src/core/span.rs
index fa89c30..e2bf26d 100644
--- a/dhall_syntax/src/core/span.rs
+++ b/dhall_syntax/src/core/span.rs
@@ -53,4 +53,18 @@ impl Span {
             ),
         }
     }
+
+    pub fn error(&self, message: impl Into<String>) -> String {
+        use pest::error::{Error, ErrorVariant};
+        use pest::Span;
+        let message: String = message.into();
+        let span = match self {
+            self::Span::Parsed(span) => span,
+            _ => return format!("Unknown location: {}", message),
+        };
+        let span = Span::new(&*span.input, span.start, span.end).unwrap();
+        let err: ErrorVariant<!> = ErrorVariant::CustomError { message };
+        let err = Error::new_from_span(err, span);
+        format!("{}", err)
+    }
 }