Auto merge of rust-lang#11441 - Jarcho:issue_11365, r=xFrednet

`single_match`: fix checking of explicitly matched enums

fixes rust-lang#11365

This approach has false-negatives, but fixing them will require a significant amount of additional state tracking. The comment in `add_and_pats` has the explanation.

changelog: `single_match`: correct checking if the match explicitly matches all of an enum's variants.

clippy_lints/src/matches/match_wild_enum.rs

@@ -180,9 +180,8 @@ enum CommonPrefixSearcher<'a> {
 }
 impl<'a> CommonPrefixSearcher<'a> {
     fn with_path(&mut self, path: &'a [PathSegment<'a>]) {
-        match path {
-            [path @ .., _] => self.with_prefix(path),
-            [] => (),
+        if let [path @ .., _] = path {
+            self.with_prefix(path);
         }
     }
 

clippy_lints/src/matches/overlapping_arms.rs

@@ -33,19 +33,17 @@ fn all_ranges<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'_>], ty: Ty<'tcx>)
         .filter_map(|arm| {
             if let Arm { pat, guard: None, .. } = *arm {
                 if let PatKind::Range(ref lhs, ref rhs, range_end) = pat.kind {
-                    let lhs_const = match lhs {
-                        Some(lhs) => constant(cx, cx.typeck_results(), lhs)?,
-                        None => {
-                            let min_val_const = ty.numeric_min_val(cx.tcx)?;
-                            mir_to_const(cx, mir::Const::from_ty_const(min_val_const, ty, cx.tcx))?
-                        },
+                    let lhs_const = if let Some(lhs) = lhs {
+                        constant(cx, cx.typeck_results(), lhs)?
+                    } else {
+                        let min_val_const = ty.numeric_min_val(cx.tcx)?;
+                        mir_to_const(cx, mir::Const::from_ty_const(min_val_const, ty, cx.tcx))?
                     };
-                    let rhs_const = match rhs {
-                        Some(rhs) => constant(cx, cx.typeck_results(), rhs)?,
-                        None => {
-                            let max_val_const = ty.numeric_max_val(cx.tcx)?;
-                            mir_to_const(cx, mir::Const::from_ty_const(max_val_const, ty, cx.tcx))?
-                        },
+                    let rhs_const = if let Some(rhs) = rhs {
+                        constant(cx, cx.typeck_results(), rhs)?
+                    } else {
+                        let max_val_const = ty.numeric_max_val(cx.tcx)?;
+                        mir_to_const(cx, mir::Const::from_ty_const(max_val_const, ty, cx.tcx))?
                     };
                     let lhs_val = lhs_const.int_value(cx, ty)?;
                     let rhs_val = rhs_const.int_value(cx, ty)?;