Format and comment code

Author: b-NC

clippy_lints/src/methods/err_expect.rs

@@ -19,10 +19,14 @@ pub(super) fn check(
 ) {
     if_chain! {
         if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
+        // Test the version to make sure the lint can be showed (expect_err has been introduced in rust 1.17.0 : https://github.com/rust-lang/rust/pull/38982)
         if meets_msrv(msrv, &msrvs::EXPECT_ERR);
 
+        // Grabs the `Result<T, E>` type
         let result_type = cx.typeck_results().expr_ty(recv);
+        // Tests if the T type in a `Result<T, E>` is not None
         if let Some(data_type) = get_data_type(cx, result_type);
+        // Tests if the T type in a `Result<T, E>` implements debug
         if has_debug_impl(data_type, cx);
 
         then {
@@ -42,11 +46,12 @@ pub(super) fn check(
 /// Given a `Result<T, E>` type, return its data (`T`).
 fn get_data_type<'a>(cx: &LateContext<'_>, ty: Ty<'a>) -> Option<Ty<'a>> {
     match ty.kind() {
-        ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym::Result) => substs.types().nth(0),
+        ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym::Result) => substs.types().next(),
         _ => None,
     }
 }
 
+/// Givn a type, very if the Debug trait has been impl'd
 fn has_debug_impl<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
     cx.tcx
         .get_diagnostic_item(sym::Debug)

clippy_lints/src/methods/mod.rs

@@ -368,7 +368,7 @@ declare_clippy_lint! {
     /// Checks for `.err().expect()` calls on the `Result` type.
     ///
     /// ### Why is this bad?
-    /// Because .expect_err() can be called directly.
+    /// `.expect_err()` can be called directly to avoid the extra type conversion from `ok()`.
     ///
     /// ### Example
     /// ```should_panic