Fixing lint message and provide docs.

Author: xiongmao86

clippy_lints/src/single_component_use_path.rs

@@ -6,9 +6,25 @@ use if_chain::if_chain;
 use rustc_errors::Applicability;
 
 declare_clippy_lint! {
+    /// **What it does:** Checking for imports with single component use path.
+    ///
+    /// **Why is this bad?** Import with single component use path such as `use cratename;`
+    /// is not necessary in order to use the crate.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// 
+    /// ```rust, ignore
+    /// use bit_vec;
+    ///
+    /// fn main() {
+    ///     bit_vec::BitVec::new();
+    ///}
+    ///```
     pub SINGLE_COMPONENT_USE_PATH,
     style,
-    "use with single component path is redundant in 2018 edition"
+    "use with single component path is redundant"
 }
 
 declare_lint_pass!(SingleComponentUsePath => [SINGLE_COMPONENT_USE_PATH]);
@@ -24,7 +40,7 @@ impl EarlyLintPass for SingleComponentUsePath {
                     cx,
                     SINGLE_COMPONENT_USE_PATH,
                     item.span,
-                    "this import is redundant in 2018 edition",
+                    "this import is redundant",
                     "remove it entirely",
                     "".to_string(),
                     Applicability::MachineApplicable