Handle ! as its own type, rather than incorrectly mapping it to void. (rust-lang#588)

Author: danielsn

compiler/cbmc/src/goto_program/typ.rs

@@ -576,9 +576,8 @@ impl Type {
     /// base_name: the local name of the parameter within the function `x`
     /// typ: The type of the parameter
     pub fn as_parameter(self, identifier: Option<String>, base_name: Option<String>) -> Parameter {
-        // FIXME: https://github.com/model-checking/rmc/issues/570
         assert!(
-            self.is_empty() || self.is_lvalue(),
+            self.is_lvalue(),
             "Expected lvalue from {:?} {:?} {:?}",
             self,
             identifier,

compiler/rustc_codegen_rmc/src/codegen/typ.rs

@@ -36,6 +36,10 @@ use ty::layout::HasParamEnv;
 const UNIT_TYPE_EMPTY_STRUCT_NAME: &str = "Unit";
 pub const FN_RETURN_VOID_VAR_NAME: &str = "VoidUnit";
 
+/// Map the never i.e. `!` type to an empty struct.
+/// The never type can appear as a function argument, e.g. in library/core/src/num/error.rs
+const NEVER_TYPE_EMPTY_STRUCT_NAME: &str = "Never";
+
 pub trait TypeExt {
     fn is_rust_fat_ptr(&self, st: &SymbolTable) -> bool;
     fn is_rust_slice_fat_ptr(&self, st: &SymbolTable) -> bool;
@@ -544,11 +548,7 @@ impl<'tcx> GotocCtx<'tcx> {
             ty::FnPtr(sig) => self.codegen_function_sig(*sig).to_pointer(),
             ty::Closure(_, subst) => self.codegen_ty_closure(ty, subst),
             ty::Generator(_, subst, _) => self.codegen_ty_generator(subst),
-            ty::Never =>
-            // unfortunately, there is no bottom in C. We must pick a type
-            {
-                Type::empty()
-            }
+            ty::Never => self.ensure_struct(NEVER_TYPE_EMPTY_STRUCT_NAME, None, |_, _| vec![]),
             ty::Tuple(ts) => {
                 if ts.is_empty() {
                     self.codegen_ty_unit()

src/test/rmc/Never/main.rs

@@ -0,0 +1,16 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+#![feature(never_type)]
+use std::convert::Infallible;
+
+/// Test using the never type
+pub fn foo(never: !) -> i32 {
+    return 1;
+}
+
+pub fn bar(infalliable: Infallible) -> i32 {
+    return 1;
+}
+
+// Give an empty main to make rustc happy.
+pub fn main() {}