Fix ICE comparing ExprRange

`eq_expr` on hir::utils was throwing an ICE due to an invalid
LateContext being used. Due to this missusage, it was generating an ICE
with the code on the following issue:
https://github.com/rust-lang-nursery/rust-clippy/issues/2423

clippy_lints/src/consts.rs

@@ -229,7 +229,18 @@ pub fn constant_simple(lcx: &LateContext, e: &Expr) -> Option<Constant> {
     constant(lcx, e).and_then(|(cst, res)| if res { None } else { Some(cst) })
 }
 
-struct ConstEvalLateContext<'a, 'tcx: 'a> {
+/// Creates a ConstEvalLateContext from the given LateContext and TypeckTables
+pub fn constant_context<'c, 'cc>(lcx: &LateContext<'c, 'cc>, tables: &'cc ty::TypeckTables<'cc>) -> ConstEvalLateContext<'c, 'cc> {
+    ConstEvalLateContext {
+        tcx: lcx.tcx,
+        tables,
+        param_env: lcx.param_env,
+        needed_resolution: false,
+        substs: lcx.tcx.intern_substs(&[]),
+    }
+}
+
+pub struct ConstEvalLateContext<'a, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     tables: &'a ty::TypeckTables<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
@@ -239,7 +250,7 @@ struct ConstEvalLateContext<'a, 'tcx: 'a> {
 
 impl<'c, 'cc> ConstEvalLateContext<'c, 'cc> {
     /// simple constant folding: Insert an expression, get a constant or none.
-    fn expr(&mut self, e: &Expr) -> Option<Constant> {
+    pub fn expr(&mut self, e: &Expr) -> Option<Constant> {
         match e.node {
             ExprPath(ref qpath) => self.fetch_path(qpath, e.hir_id),
             ExprBlock(ref block) => self.block(block),

clippy_lints/src/utils/hir_utils.rs

@@ -1,4 +1,4 @@
-use consts::constant;
+use consts::{constant, constant_context};
 use rustc::lint::*;
 use rustc::hir::*;
 use std::hash::{Hash, Hasher};
@@ -117,8 +117,12 @@ impl<'a, 'tcx: 'a> SpanlessEq<'a, 'tcx> {
                 !self.ignore_fn && l_path == r_path && self.eq_exprs(l_args, r_args)
             },
             (&ExprRepeat(ref le, ll_id), &ExprRepeat(ref re, rl_id)) => {
-                self.eq_expr(le, re)
-                    && self.eq_expr(&self.cx.tcx.hir.body(ll_id).value, &self.cx.tcx.hir.body(rl_id).value)
+                let mut celcx = constant_context(self.cx, self.cx.tcx.body_tables(ll_id));
+                let ll = celcx.expr(&self.cx.tcx.hir.body(ll_id).value);
+                let mut celcx = constant_context(self.cx, self.cx.tcx.body_tables(rl_id));
+                let rl = celcx.expr(&self.cx.tcx.hir.body(rl_id).value);
+
+                self.eq_expr(le, re) && ll == rl
             },
             (&ExprRet(ref l), &ExprRet(ref r)) => both(l, r, |l, r| self.eq_expr(l, r)),
             (&ExprPath(ref l), &ExprPath(ref r)) => self.eq_qpath(l, r),

tests/ui/copies.rs

@@ -396,3 +396,18 @@ fn ifs_same_cond() {
 }
 
 fn main() {}
+
+// Issue #2423. This was causing an ICE
+fn func() {
+    if true {
+        f(&[0; 62]);
+        f(&[0; 4]);
+        f(&[0; 3]);
+    } else {
+        f(&[0; 62]);
+        f(&[0; 6]);
+        f(&[0; 6]);
+    }
+}
+
+fn f(val: &[u8]) {}