From 509743469035582d916e6a2f331fd5018c81447e Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Fri, 16 Aug 2019 11:11:28 +0200
Subject: Use `!` type instead of custom empty type

---
 dhall/src/phase/mod.rs           |  6 +++---
 dhall_syntax/src/core/expr.rs    | 14 ++------------
 dhall_syntax/src/core/visitor.rs |  2 +-
 dhall_syntax/src/lib.rs          |  1 +
 dhall_syntax/src/parser.rs       |  4 ++--
 5 files changed, 9 insertions(+), 18 deletions(-)

diff --git a/dhall/src/phase/mod.rs b/dhall/src/phase/mod.rs
index b73597c..2700e99 100644
--- a/dhall/src/phase/mod.rs
+++ b/dhall/src/phase/mod.rs
@@ -2,7 +2,7 @@ use std::borrow::Cow;
 use std::fmt::Display;
 use std::path::Path;
 
-use dhall_syntax::{Const, SubExpr, Void};
+use dhall_syntax::{Const, SubExpr};
 
 use crate::core::thunk::{Thunk, TypedThunk};
 use crate::core::value::Value;
@@ -17,8 +17,8 @@ pub(crate) mod parse;
 pub(crate) mod resolve;
 pub(crate) mod typecheck;
 
-pub type ParsedSubExpr = SubExpr<Void>;
-pub type DecodedSubExpr = SubExpr<Void>;
+pub type ParsedSubExpr = SubExpr<!>;
+pub type DecodedSubExpr = SubExpr<!>;
 pub type ResolvedSubExpr = SubExpr<Normalized>;
 pub type NormalizedSubExpr = SubExpr<Normalized>;
 
diff --git a/dhall_syntax/src/core/expr.rs b/dhall_syntax/src/core/expr.rs
index 30ac4eb..efbcee2 100644
--- a/dhall_syntax/src/core/expr.rs
+++ b/dhall_syntax/src/core/expr.rs
@@ -8,20 +8,10 @@ pub type Integer = isize;
 pub type Natural = usize;
 pub type Double = NaiveDouble;
 
-/// An empty type
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub enum Void {}
-
-impl std::fmt::Display for Void {
-    fn fmt(&self, _f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
-        match *self {}
-    }
-}
-
-pub fn trivial_result<T>(x: Result<T, Void>) -> T {
+pub fn trivial_result<T>(x: Result<T, !>) -> T {
     match x {
         Ok(x) => x,
-        Err(e) => match e {},
+        Err(e) => e,
     }
 }
 
diff --git a/dhall_syntax/src/core/visitor.rs b/dhall_syntax/src/core/visitor.rs
index 7b4ed4b..5a5fcc9 100644
--- a/dhall_syntax/src/core/visitor.rs
+++ b/dhall_syntax/src/core/visitor.rs
@@ -176,7 +176,7 @@ impl<'a, T, SE1, SE2, E1, E2> ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>
 where
     T: ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>,
 {
-    type Error = Void;
+    type Error = !;
 
     fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result<SE2, Self::Error> {
         Ok(self.0.visit_subexpr(subexpr))
diff --git a/dhall_syntax/src/lib.rs b/dhall_syntax/src/lib.rs
index 8406595..4566e64 100644
--- a/dhall_syntax/src/lib.rs
+++ b/dhall_syntax/src/lib.rs
@@ -1,6 +1,7 @@
 #![feature(trace_macros)]
 #![feature(slice_patterns)]
 #![feature(try_blocks)]
+#![feature(never_type)]
 #![allow(
     clippy::many_single_char_names,
     clippy::should_implement_trait,
diff --git a/dhall_syntax/src/parser.rs b/dhall_syntax/src/parser.rs
index d467970..bcaa00e 100644
--- a/dhall_syntax/src/parser.rs
+++ b/dhall_syntax/src/parser.rs
@@ -18,8 +18,8 @@ use crate::*;
 // their own crate because they are quite general and useful. For now they
 // are here and hopefully you can figure out how they work.
 
-pub(crate) type ParsedExpr = Expr<Void>;
-pub(crate) type ParsedSubExpr = SubExpr<Void>;
+pub(crate) type ParsedExpr = Expr<!>;
+pub(crate) type ParsedSubExpr = SubExpr<!>;
 type ParsedText = InterpolatedText<ParsedSubExpr>;
 type ParsedTextContents = InterpolatedTextContents<ParsedSubExpr>;
 
-- 
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