---

yaml
---
r: 273121
b: refs/heads/beta
c: 54b15c7
h: refs/heads/master
i:
  273119: 574c651

Author: oli-obk

[refs]

@@ -23,7 +23,7 @@ refs/tags/0.9: 36870b185fc5f5486636d4515f0e22677493f225
 refs/tags/0.10: ac33f2b15782272ae348dbd7b14b8257b2148b5a
 refs/tags/0.11.0: e1247cb1d0d681be034adb4b558b5a0c0d5720f9
 refs/tags/0.12.0: f0c419429ef30723ceaf6b42f9b5a2aeb5d2e2d1
-refs/heads/beta: 6ee60037f9cee27d9de70195d7e63d4946465a2f
+refs/heads/beta: 54b15c7160e165621f0a7ae6a71db30dded254df
 refs/tags/1.0.0-alpha: e42bd6d93a1d3433c486200587f8f9e12590a4d7
 refs/heads/tmp: e06d2ad9fcd5027bcaac5b08fc9aa39a49d0ecd3
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f

branches/beta/src/librustc/middle/const_eval.rs

@@ -743,7 +743,21 @@ pub fn eval_const_expr_partial<'tcx>(tcx: &TyCtxt<'tcx>,
             }
         };
 
-        let val = try!(eval_const_expr_partial(tcx, &base, base_hint, fn_args));
+        let val = match eval_const_expr_partial(tcx, &base, base_hint, fn_args) {
+            Ok(val) => val,
+            Err(ConstEvalErr { kind: InferredWrongType(val), .. }) => {
+                // Something like `5i8 as usize` doesn't need a type hint for the base
+                // instead take the type hint from the inner value
+                let hint = match val.int_type() {
+                    Some(IntType::UnsignedInt(ty)) => ty_hint.checked_or(tcx.mk_mach_uint(ty)),
+                    Some(IntType::SignedInt(ty)) => ty_hint.checked_or(tcx.mk_mach_int(ty)),
+                    // we had a type hint, so we can't have an unknown type
+                    None => unreachable!(),
+                };
+                try!(eval_const_expr_partial(tcx, &base, hint, fn_args))
+            },
+            Err(e) => return Err(e),
+        };
         match cast_const(tcx, val, ety) {
             Ok(val) => val,
             Err(kind) => return Err(ConstEvalErr { span: e.span, kind: kind }),

branches/beta/src/librustc_const_eval/int.rs

@@ -9,6 +9,8 @@
 // except according to those terms.
 
 use std::cmp::Ordering;
+use syntax::attr::IntType;
+use syntax::ast::{IntTy, UintTy};
 
 use super::is::*;
 use super::us::*;
@@ -258,6 +260,22 @@ impl ConstInt {
             ConstInt::Infer(_) | ConstInt::InferSigned(_) => panic!("no type info for const int"),
         }
     }
+
+    pub fn int_type(self) -> Option<IntType> {
+        match self {
+            ConstInt::I8(_) => Some(IntType::SignedInt(IntTy::I8)),
+            ConstInt::I16(_) => Some(IntType::SignedInt(IntTy::I16)),
+            ConstInt::I32(_) => Some(IntType::SignedInt(IntTy::I32)),
+            ConstInt::I64(_) => Some(IntType::SignedInt(IntTy::I64)),
+            ConstInt::Isize(_) => Some(IntType::SignedInt(IntTy::Is)),
+            ConstInt::U8(_) => Some(IntType::UnsignedInt(UintTy::U8)),
+            ConstInt::U16(_) => Some(IntType::UnsignedInt(UintTy::U16)),
+            ConstInt::U32(_) => Some(IntType::UnsignedInt(UintTy::U32)),
+            ConstInt::U64(_) => Some(IntType::UnsignedInt(UintTy::U64)),
+            ConstInt::Usize(_) => Some(IntType::UnsignedInt(UintTy::Us)),
+            _ => None,
+        }
+    }
 }
 
 impl ::std::cmp::PartialOrd for ConstInt {