Rollup merge of rust-lang#47862 - GuillaumeGomez:const-evaluation-ice, r=eddyb

Fix const evaluation ICE in rustdoc

Fixes rust-lang#47860.

r? @eddyb

Author: kennytm

src/librustdoc/clean/mod.rs

@@ -2447,7 +2447,12 @@ impl Clean<Type> for hir::Ty {
                 let def_id = cx.tcx.hir.body_owner_def_id(n);
                 let param_env = cx.tcx.param_env(def_id);
                 let substs = Substs::identity_for_item(cx.tcx, def_id);
-                let n = cx.tcx.const_eval(param_env.and((def_id, substs))).unwrap();
+                let n = cx.tcx.const_eval(param_env.and((def_id, substs))).unwrap_or_else(|_| {
+                    cx.tcx.mk_const(ty::Const {
+                        val: ConstVal::Unevaluated(def_id, substs),
+                        ty: cx.tcx.types.usize
+                    })
+                });
                 let n = if let ConstVal::Integral(ConstInt::Usize(n)) = n.val {
                     n.to_string()
                 } else if let ConstVal::Unevaluated(def_id, _) = n.val {
@@ -2577,7 +2582,9 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                 let mut n = cx.tcx.lift(&n).unwrap();
                 if let ConstVal::Unevaluated(def_id, substs) = n.val {
                     let param_env = cx.tcx.param_env(def_id);
-                    n = cx.tcx.const_eval(param_env.and((def_id, substs))).unwrap()
+                    if let Ok(new_n) = cx.tcx.const_eval(param_env.and((def_id, substs))) {
+                        n = new_n;
+                    }
                 };
                 let n = if let ConstVal::Integral(ConstInt::Usize(n)) = n.val {
                     n.to_string()

src/test/rustdoc/const-evalutation-ice.rs

@@ -0,0 +1,22 @@
+// Copyright 2018 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.
+
+// Just check if we don't get an ICE for the _S type.
+
+#![feature(const_size_of)]
+
+use std::cell::Cell;
+use std::mem;
+
+pub struct S {
+    s: Cell<usize>
+}
+
+pub type _S = [usize; 0 - (mem::size_of::<S>() != 4) as usize];