use Void to ensure closure diverges

Cargo.toml

@@ -7,6 +7,9 @@ build = "build.rs"
 [build-dependencies]
 gcc = "0.3.3"
 
+[dependencies]
+void = "0.0.5"
+
 [features]
 default = ["os", "valgrind"]
 os = ["libc"]

examples/basic.rs

@@ -15,6 +15,7 @@ fn main() {
     let mut ctx = Context::new(stack, move || {
       println!("it's alive!");
       (*ctx_slot).swap();
+      panic!("Do not come back!")
     });
 
     ctx_slot = &mut ctx;

src/arch/common.rs

@@ -5,10 +5,13 @@ use core::mem::{size_of, align_of};
 use core::cmp::max;
 use core::ptr;
 
+use void::{self, Void};
+
 use super::imp::STACK_ALIGN;
 
-pub unsafe extern "C" fn rust_trampoline<F: FnOnce()>(f: *const F) {
+pub unsafe extern "C" fn rust_trampoline<F>(f: *const F) -> !
-  ptr::read(f)()
+  where F: FnOnce() -> Void {
+  void::unreachable(ptr::read(f)())
 }
 
 pub unsafe fn push<T>(spp: &mut *mut usize, value: T) -> *mut T {

src/arch/x86/mod.rs

@@ -3,6 +3,8 @@
 // See the LICENSE file included in this distribution.
 use core::prelude::*;
 
+use void::Void;
+
 use stack::Stack;
 use super::common::{push, rust_trampoline};
 
@@ -16,7 +18,8 @@ pub struct Registers {
 
 impl Registers {
   #[inline]
-  pub unsafe fn new<S, F>(stack: &mut S, f: F) -> Registers where S: Stack, F: FnOnce() {
+  pub unsafe fn new<S, F>(stack: &mut S, f: F) -> Registers
+    where S: Stack, F: FnOnce() -> Void {
     let sp_limit = stack.limit();
     let mut sp = stack.top() as *mut usize;
     let f_ptr = push(&mut sp, f);

src/arch/x86_64/mod.rs

@@ -2,6 +2,7 @@
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
 use stack::Stack;
+use void::Void;
 use super::common::{push, rust_trampoline};
 
 pub const STACK_ALIGN: usize = 16;
@@ -14,7 +15,8 @@ pub struct Registers {
 
 impl Registers {
   #[inline]
-  pub unsafe fn new<S, F>(stack: &mut S, f: F) -> Registers where S: Stack, F: FnOnce() {
+  pub unsafe fn new<S, F>(stack: &mut S, f: F) -> Registers
+    where S: Stack, F: FnOnce() -> Void {
     let sp_limit = stack.limit();
     let mut sp = stack.top() as *mut usize;
     let f_ptr = push(&mut sp, f);

src/context.rs

@@ -2,6 +2,9 @@
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
 use core::marker::PhantomData;
+
+use void::Void;
+
 use arch::Registers;
 use stack;
 use debug::StackId;
@@ -27,10 +30,9 @@ unsafe impl<'a, Stack> Send for Context<'a, Stack>
 impl<'a, Stack> Context<'a, Stack> where Stack: stack::Stack {
   /// Create a new Context. When it is swapped into,
   /// it will call the passed closure.
-  /// The closure shouldn't return - doing that will abort the process.
   #[inline]
   pub unsafe fn new<F>(mut stack: Stack, f: F) -> Context<'a, Stack>
-    where F: FnOnce() + Send + 'a {
+    where F: FnOnce() -> Void + Send + 'a {
     let stack_id = StackId::register(&mut stack);
     let regs = Registers::new(&mut stack, f);
     Context {

src/lib.rs

@@ -12,6 +12,8 @@
 #[macro_use]
 extern crate std;
 
+extern crate void;
+
 pub use context::Context;
 pub use stack::Stack;