4 files changed, 32 insertions, 9 deletions
diff --git a/clippy_lints/src/methods/iter_skip_next.rs b/clippy_lints/src/methods/iter_skip_next.rs
index e32594757d0..f5410c7fd7f 100644
--- a/clippy_lints/src/methods/iter_skip_next.rs
+++ b/clippy_lints/src/methods/iter_skip_next.rs
@@ -1,8 +1,10 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::is_trait_method;
+use clippy_utils::path_to_local;
 use clippy_utils::source::snippet;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
+use rustc_hir::{BindingAnnotation, Node, PatKind};
 use rustc_lint::LateContext;
 use rustc_span::sym;
 
@@ -11,14 +13,34 @@ use super::ITER_SKIP_NEXT;
 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, recv: &hir::Expr<'_>, arg: &hir::Expr<'_>) {
     // lint if caller of skip is an Iterator
     if is_trait_method(cx, expr, sym::Iterator) {
-        span_lint_and_sugg(
+        let mut application = Applicability::MachineApplicable;
+        span_lint_and_then(
             cx,
             ITER_SKIP_NEXT,
             expr.span.trim_start(recv.span).unwrap(),
             "called `skip(..).next()` on an iterator",
-            "use `nth` instead",
-            format!(".nth({})", snippet(cx, arg.span, "..")),
-            Applicability::MachineApplicable,
+            |diag| {
+                if_chain! {
+                    if let Some(id) = path_to_local(recv);
+                    if let Node::Binding(pat) = cx.tcx.hir().get(id);
+                    if let PatKind::Binding(ann, _, _, _)  = pat.kind;
+                    if ann != BindingAnnotation::Mutable;
+                    then {
+                        application = Applicability::Unspecified;
+                        diag.span_help(
+                            pat.span,
+                            &format!("for this change `{}` has to be mutable", snippet(cx, pat.span, "..")),
+                        );
+                    }
+                }
+
+                diag.span_suggestion(
+                    expr.span.trim_start(recv.span).unwrap(),
+                    "use `nth` instead",
+                    format!(".nth({})", snippet(cx, arg.span, "..")),
+                    application,
+                );
+            },
         );
     }
 }
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 4934240abfc..4e33b2ff14c 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -2112,7 +2112,7 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
                 {
                     wrong_self_convention::check(
                         cx,
-                        &name,
+                        name,
                         self_ty,
                         first_arg_ty,
                         first_arg.pat.span,
diff --git a/clippy_lints/src/methods/unwrap_or_else_default.rs b/clippy_lints/src/methods/unwrap_or_else_default.rs
index 276467b1dfd..f3af281d6ca 100644
--- a/clippy_lints/src/methods/unwrap_or_else_default.rs
+++ b/clippy_lints/src/methods/unwrap_or_else_default.rs
@@ -2,7 +2,8 @@
 
 use super::UNWRAP_OR_ELSE_DEFAULT;
 use clippy_utils::{
-    diagnostics::span_lint_and_sugg, is_trait_item, source::snippet_with_applicability, ty::is_type_diagnostic_item,
+    diagnostics::span_lint_and_sugg, is_default_equivalent_call, source::snippet_with_applicability,
+    ty::is_type_diagnostic_item,
 };
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -24,7 +25,7 @@ pub(super) fn check<'tcx>(
 
     if_chain! {
         if is_option || is_result;
-        if is_trait_item(cx, u_arg, sym::Default);
+        if is_default_equivalent_call(cx, u_arg);
         then {
             let mut applicability = Applicability::MachineApplicable;
 
diff --git a/clippy_lints/src/methods/utils.rs b/clippy_lints/src/methods/utils.rs
index 11ad881ee7b..24b44f819f4 100644
--- a/clippy_lints/src/methods/utils.rs
+++ b/clippy_lints/src/methods/utils.rs
@@ -57,7 +57,7 @@ pub(super) fn get_hint_if_single_char_arg(
         let string = r.as_str();
         if string.chars().count() == 1;
         then {
-            let snip = snippet_with_applicability(cx, arg.span, &string, applicability);
+            let snip = snippet_with_applicability(cx, arg.span, string, applicability);
             let ch = if let ast::StrStyle::Raw(nhash) = style {
                 let nhash = nhash as usize;
                 // for raw string: r##"a"##