Restrict lint logic.

Restrict lint logic to apply on edition2018 only.

Author: xiongmao86

clippy_lints/src/single_component_use_path.rs

@@ -4,6 +4,7 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 use syntax::ast::{Item, ItemKind};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
+use rustc_span::edition::Edition;
 
 declare_clippy_lint! {
     /// **What it does:** Checking for imports with single component use path.
@@ -32,6 +33,7 @@ declare_lint_pass!(SingleComponentUsePath => [SINGLE_COMPONENT_USE_PATH]);
 impl EarlyLintPass for SingleComponentUsePath {
     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
         if_chain! {
+            if cx.sess.opts.edition == Edition::Edition2018;
             if let ItemKind::Use(use_tree) = &item.kind;
             if let segments = &use_tree.prefix.segments;
             if segments.len() == 1;