From b33e1fc80bb0e7191c1ea3378569ed8c0fe4af6d Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Mon, 11 Nov 2019 18:20:52 +0000
Subject: Add more detail to TypeMismatch error

---
 dhall/src/error/mod.rs                                  | 17 ++++++++++++++---
 dhall/tests/type-errors/hurkensParadox.txt              |  7 +++++++
 .../unit/FunctionApplicationArgumentNotMatch.txt        | 12 ++++++++++++
 .../tests/type-errors/unit/ListLiteralEmptyNotType.txt  |  7 +++++++
 .../unit/MergeHandlerNotMatchAlternativeType.txt        | 12 ++++++++++++
 .../type-errors/unit/NaturalSubtractNotNatural.txt      |  7 +++++++
 6 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/dhall/src/error/mod.rs b/dhall/src/error/mod.rs
index 4d59cbb..e4baea0 100644
--- a/dhall/src/error/mod.rs
+++ b/dhall/src/error/mod.rs
@@ -111,9 +111,20 @@ impl std::fmt::Display for TypeError {
                 v.span().error("Type error: Invalid function output")
             }
             NotAFunction(v) => v.span().error("Type error: Not a function"),
-            TypeMismatch(v, _, _) => v
-                .span()
-                .error("Type error: Wrong type of function argument"),
+            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)
diff --git a/dhall/tests/type-errors/hurkensParadox.txt b/dhall/tests/type-errors/hurkensParadox.txt
index 69428b8..870388d 100644
--- a/dhall/tests/type-errors/hurkensParadox.txt
+++ b/dhall/tests/type-errors/hurkensParadox.txt
@@ -1 +1,8 @@
 [unknown location] Type error: Wrong type of function argument
+[unknown location] This argument has type Sort
+ --> 5:21
+  |
+5 | in  let pow = λ(X : Kind) → X → Type␊
+  |                     ^--^
+  |
+  = But the function expected an argument of type Kind
diff --git a/dhall/tests/type-errors/unit/FunctionApplicationArgumentNotMatch.txt b/dhall/tests/type-errors/unit/FunctionApplicationArgumentNotMatch.txt
index 69428b8..d3b1f50 100644
--- a/dhall/tests/type-errors/unit/FunctionApplicationArgumentNotMatch.txt
+++ b/dhall/tests/type-errors/unit/FunctionApplicationArgumentNotMatch.txt
@@ -1 +1,13 @@
 [unknown location] Type error: Wrong type of function argument
+ --> 1:22
+  |
+1 | (λ(_ : Natural) → _) True␊
+  |                      ^--^
+  |
+  = This argument has type Value@WHNF { value: AppliedBuiltin(Bool, []), type: Type }
+ --> 1:8
+  |
+1 | (λ(_ : Natural) → _) True␊
+  |        ^-----^
+  |
+  = But the function expected an argument of type Value@WHNF { value: AppliedBuiltin(Natural, []), type: Type }
diff --git a/dhall/tests/type-errors/unit/ListLiteralEmptyNotType.txt b/dhall/tests/type-errors/unit/ListLiteralEmptyNotType.txt
index bc5cc40..e075521 100644
--- a/dhall/tests/type-errors/unit/ListLiteralEmptyNotType.txt
+++ b/dhall/tests/type-errors/unit/ListLiteralEmptyNotType.txt
@@ -4,3 +4,10 @@
   |      ^--^
   |
   = Type error: Wrong type of function argument
+ --> 1:11
+  |
+1 | [] : List Type␊
+  |           ^--^
+  |
+  = This argument has type Kind
+[unknown location] But the function expected an argument of type Type
diff --git a/dhall/tests/type-errors/unit/MergeHandlerNotMatchAlternativeType.txt b/dhall/tests/type-errors/unit/MergeHandlerNotMatchAlternativeType.txt
index 69428b8..3f6c6a6 100644
--- a/dhall/tests/type-errors/unit/MergeHandlerNotMatchAlternativeType.txt
+++ b/dhall/tests/type-errors/unit/MergeHandlerNotMatchAlternativeType.txt
@@ -1 +1,13 @@
 [unknown location] Type error: Wrong type of function argument
+ --> 1:38
+  |
+1 | merge { x = λ(_ : Bool) → _ } (< x : Natural >.x 1)␊
+  |                                      ^-----^
+  |
+  = This argument has type Type
+ --> 1:19
+  |
+1 | merge { x = λ(_ : Bool) → _ } (< x : Natural >.x 1)␊
+  |                   ^--^
+  |
+  = But the function expected an argument of type Value@WHNF { value: AppliedBuiltin(Bool, []), type: Type }
diff --git a/dhall/tests/type-errors/unit/NaturalSubtractNotNatural.txt b/dhall/tests/type-errors/unit/NaturalSubtractNotNatural.txt
index fd906bf..02a9c45 100644
--- a/dhall/tests/type-errors/unit/NaturalSubtractNotNatural.txt
+++ b/dhall/tests/type-errors/unit/NaturalSubtractNotNatural.txt
@@ -4,3 +4,10 @@
   | ^--------------^
   |
   = Type error: Wrong type of function argument
+ --> 1:18
+  |
+1 | Natural/subtract True True␊
+  |                  ^--^
+  |
+  = This argument has type Value@WHNF { value: AppliedBuiltin(Bool, []), type: Type }
+[unknown location] But the function expected an argument of type Value@WHNF { value: AppliedBuiltin(Natural, []), type: Type }
-- 
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