Switch to Ignore output mode for () blocks

Closes #11709
Closes #11865

src/librustc/middle/trans/base.rs

@@ -1510,16 +1510,19 @@ pub fn trans_closure<'a>(ccx: @CrateContext,
     // emitting should be enabled.
     debuginfo::start_emitting_source_locations(&fcx);
 
+    let dest = match fcx.llretptr.get() {
+        Some(e) => {expr::SaveIn(e)}
+        None => {
+            assert!(type_is_zero_size(bcx.ccx(), block_ty))
+            expr::Ignore
+        }
+    };
+
     // This call to trans_block is the place where we bridge between
     // translation calls that don't have a return value (trans_crate,
     // trans_mod, trans_item, et cetera) and those that do
     // (trans_block, trans_expr, et cetera).
-    if body.expr.is_none() || type_is_zero_size(bcx.ccx(), block_ty) {
-        bcx = controlflow::trans_block(bcx, body, expr::Ignore);
-    } else {
-        let dest = expr::SaveIn(fcx.llretptr.get().unwrap());
-        bcx = controlflow::trans_block(bcx, body, dest);
-    }
+    bcx = controlflow::trans_block(bcx, body, dest);
 
     match fcx.llreturn.get() {
         Some(_) => {

src/librustc/middle/trans/controlflow.rs

@@ -74,7 +74,7 @@ pub fn trans_stmt<'a>(cx: &'a Block<'a>,
 
 pub fn trans_block<'a>(bcx: &'a Block<'a>,
                        b: &ast::Block,
-                       dest: expr::Dest)
+                       mut dest: expr::Dest)
                        -> &'a Block<'a> {
     let _icx = push_ctxt("trans_block");
     let fcx = bcx.fcx;
@@ -85,6 +85,14 @@ pub fn trans_block<'a>(bcx: &'a Block<'a>,
     for s in b.stmts.iter() {
         bcx = trans_stmt(bcx, *s);
     }
+
+    if dest != expr::Ignore {
+        let block_ty = node_id_type(bcx, b.id);
+        if b.expr.is_none() || type_is_zero_size(bcx.ccx(), block_ty) {
+            dest = expr::Ignore;
+        }
+    }
+
     match b.expr {
         Some(e) => {
             bcx = expr::trans_into(bcx, e, dest);

src/test/run-pass/issue-11709.rs

@@ -0,0 +1,47 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-pretty
+
+// Don't fail on blocks without results
+// There are several tests in this run-pass that raised
+// when this bug was oppened. The cases where the compiler
+// failed before the fix have a comment.
+
+struct S {x:()}
+
+
+fn test(slot: &mut Option<proc() -> proc()>, _: proc()) -> () {
+  let a = slot.take();
+  let _a = match a {
+    // `{let .. a(); }` would break
+    Some(a) => { let _a = a(); },
+    None => (),
+  };
+}
+
+fn not(b: bool) -> bool {
+    if b {
+        !b
+    } else {
+        // `fail!(...)` would break
+        fail!("Break the compiler");
+    }
+}
+
+pub fn main() {
+    // {} would break
+    let _r = {};
+    let mut slot = None;
+    // `{ test(...); }` would break
+    let _s : S  = S{ x: { test(&mut slot, proc() {}); } };
+
+    let _b = not(true);
+}