Enable len_zero for slices

clippy_lints/src/len_zero.rs

@@ -212,7 +212,7 @@ fn has_is_empty(cx: &LateContext, expr: &Expr) -> bool {
         },
         ty::TyProjection(_) => ty.ty_to_def_id().map_or(false, |id| has_is_empty_impl(cx, id)),
         ty::TyAdt(id, _) => has_is_empty_impl(cx, id.did),
-        ty::TyArray(..) | ty::TyStr => true,
+        ty::TyArray(..) | ty::TySlice(..) | ty::TyStr => true,
         _ => false,
     }
 }

clippy_lints/src/utils/mod.rs

@@ -238,7 +238,7 @@ pub fn match_path(path: &QPath, segments: &[&str]) -> bool {
         QPath::TypeRelative(ref ty, ref segment) => {
             match ty.node {
                 TyPath(ref inner_path) => {
-                    segments.len() > 0 && match_path(inner_path, &segments[..(segments.len() - 1)]) &&
+                    !segments.is_empty() && match_path(inner_path, &segments[..(segments.len() - 1)]) &&
                     segment.name == segments[segments.len() - 1]
                 },
                 _ => false,

tests/ui/len_zero.rs

@@ -185,3 +185,8 @@ fn main() {
         println!("Or this!");
     }
 }
+
+fn test_slice(b: &[u8]) {
+    if b.len() != 0 {
+    }
+}

tests/ui/len_zero.stderr

@@ -113,5 +113,14 @@ error: length comparison to zero
 help: consider using `is_empty`
     |     if with_is_empty.is_empty() {
 
-error: aborting due to 10 previous errors
+error: length comparison to zero
+   --> $DIR/len_zero.rs:190:8
+    |
+190 |     if b.len() != 0 {
+    |        ^^^^^^^^^^^^
+    |
+help: consider using `is_empty`
+    |     if !b.is_empty() {
+
+error: aborting due to 11 previous errors