Rollup merge of #34497 - oli-obk:double_negation, r=eddyb

Revert "skip double negation in const eval"

This reverts commit 735c018974.

fixes #34395

The original commit was based on a mis-understanding of the overflowing literal lint.

This needs to be ported to beta.

r? @eddyb

src/librustc_const_eval/eval.rs

@@ -543,8 +543,7 @@ pub fn eval_const_expr_partial<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let result = match e.node {
       hir::ExprUnary(hir::UnNeg, ref inner) => {
         // unary neg literals already got their sign during creation
-        match inner.node {
-            hir::ExprLit(ref lit) => {
+        if let hir::ExprLit(ref lit) = inner.node {
             use syntax::ast::*;
             use syntax::ast::LitIntType::*;
             const I8_OVERFLOW: u64 = ::std::i8::MAX as u64 + 1;
@@ -585,12 +584,6 @@ pub fn eval_const_expr_partial<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 },
                 _ => {},
             }
-            },
-            hir::ExprUnary(hir::UnNeg, ref inner) => {
-                // skip `--$expr`
-                return eval_const_expr_partial(tcx, inner, ty_hint, fn_args);
-            },
-            _ => {},
         }
         match eval_const_expr_partial(tcx, &inner, ty_hint, fn_args)? {
           Float(f) => Float(-f),

src/test/compile-fail/lint-type-overflow2.rs

@@ -15,6 +15,7 @@
 #[allow(unused_variables)]
 fn main() {
     let x2: i8 = --128; //~ error: literal out of range for i8
+    //~^ error: attempted to negate with overflow
 
     let x = -3.40282348e+38_f32; //~ error: literal out of range for f32
     let x =  3.40282348e+38_f32; //~ error: literal out of range for f32