Merge pull request #146 from Nadrieril/never_never

Use stable toolchain  🎉

6 files changed, 21 insertions, 22 deletions

diff --git a/README.md b/README.md
index ba73b6d..19912e1 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,6 @@ official tooling instead; instructions can be found
 For now, the only supported way of integrating Dhall in your application is via
 the `serde_dhall` crate, and only parsing is supported.
 
-`serde_dhall` is a nightly crate, and only works with a nightly compiler.
 Add this to your `Cargo.toml`:
 
 ```toml
@@ -110,7 +109,7 @@ $ nix-shell -p rustup
 Once `rustup` is installed we can get it to manage our toolchain by running:
 
 ```bash
-$ rustup toolchain install nightly
+$ rustup toolchain install stable
 ```
 
 Then we can manage our building and testing with the [`cargo`](https://crates.io/) dependency manager:
diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index d7d7f05..058411c 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -1,5 +1,4 @@
 #![doc(html_root_url = "https://docs.rs/dhall/0.3.0")]
-#![feature(never_type)]
 #![allow(
     clippy::int_plus_one, // Comes from pest_consume macro
     clippy::module_inception,
diff --git a/dhall/src/semantics/nze/normalize.rs b/dhall/src/semantics/nze/normalize.rs
index 08e3e87..79d55e8 100644
--- a/dhall/src/semantics/nze/normalize.rs
+++ b/dhall/src/semantics/nze/normalize.rs
@@ -58,20 +58,21 @@ pub(crate) fn squash_textlit(
     ret
 }
 
-pub(crate) fn merge_maps<K, V, F, Err>(
+pub(crate) fn merge_maps<K, V, F>(
     map1: &HashMap<K, V>,
     map2: &HashMap<K, V>,
     mut f: F,
-) -> Result<HashMap<K, V>, Err>
+) -> HashMap<K, V>
 where
-    F: FnMut(&K, &V, &V) -> Result<V, Err>,
+    F: FnMut(&K, &V, &V) -> V,
     K: std::hash::Hash + Eq + Clone,
     V: Clone,
 {
     let mut kvs = HashMap::new();
     for (x, v2) in map2 {
         let newv = if let Some(v1) = map1.get(x) {
-            f(x, v1, v2)?
+            // Collision: the key is present in both maps
+            f(x, v1, v2)
         } else {
             v2.clone()
         };
@@ -81,7 +82,7 @@ where
         // Insert only if key not already present
         kvs.entry(x.clone()).or_insert_with(|| v1.clone());
     }
-    Ok(kvs)
+    kvs
 }
 
 // Small helper enum to avoid repetition
@@ -175,29 +176,29 @@ fn apply_binop<'a>(o: BinOp, x: &'a Nir, y: &'a Nir) -> Option<Ret<'a>> {
             Ret::NirRef(y)
         }
         (RecursiveRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
-            let kvs = merge_maps::<_, _, _, !>(kvs1, kvs2, |_, v1, v2| {
-                Ok(Nir::from_partial_expr(ExprKind::BinOp(
+            let kvs = merge_maps(kvs1, kvs2, |_, v1, v2| {
+                Nir::from_partial_expr(ExprKind::BinOp(
                     RecursiveRecordMerge,
                     v1.clone(),
                     v2.clone(),
-                )))
-            })?;
+                ))
+            });
             Ret::NirKind(RecordLit(kvs))
         }
 
         (RecursiveRecordTypeMerge, RecordType(kts_x), RecordType(kts_y)) => {
-            let kts = merge_maps::<_, _, _, !>(
+            let kts = merge_maps(
                 kts_x,
                 kts_y,
                 // If the Label exists for both records, then we hit the recursive case.
                 |_, l: &Nir, r: &Nir| {
-                    Ok(Nir::from_partial_expr(ExprKind::BinOp(
+                    Nir::from_partial_expr(ExprKind::BinOp(
                         RecursiveRecordTypeMerge,
                         l.clone(),
                         r.clone(),
-                    )))
+                    ))
                 },
-            )?;
+            );
             Ret::NirKind(RecordType(kts))
         }
 
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index 365df25..173b76d 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -346,9 +346,7 @@ fn type_one_layer(
 
             // Union the two records, prefering
             // the values found in the RHS.
-            let kts = merge_maps::<_, _, _, !>(kts_x, kts_y, |_, _, r_t| {
-                Ok(r_t.clone())
-            })?;
+            let kts = merge_maps(kts_x, kts_y, |_, _, r_t| r_t.clone());
 
             let u = max(x.ty().ty(), y.ty().ty());
             Nir::from_kind(NirKind::RecordType(kts)).to_type(u)
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index ce0a3d2..8023771 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -257,10 +257,12 @@ impl Expr {
     }
 }
 
-pub fn trivial_result<T>(x: Result<T, !>) -> T {
+// Empty enum to indicate that no error can occur
+enum X {}
+fn trivial_result<T>(x: Result<T, X>) -> T {
     match x {
         Ok(x) => x,
-        Err(e) => e,
+        Err(e) => match e {},
     }
 }
 
diff --git a/rust-toolchain b/rust-toolchain
index 7b70b33..a50908c 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-nightly-2020-03-12
+1.42.0