Implement get_last_with_len lint
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@ -936,6 +936,7 @@ All notable changes to this project will be documented in this file.
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[`for_loop_over_result`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_loop_over_result
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[`forget_copy`]: https://rust-lang.github.io/rust-clippy/master/index.html#forget_copy
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[`forget_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#forget_ref
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[`get_last_with_len`]: https://rust-lang.github.io/rust-clippy/master/index.html#get_last_with_len
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[`get_unwrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#get_unwrap
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[`identity_conversion`]: https://rust-lang.github.io/rust-clippy/master/index.html#identity_conversion
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[`identity_op`]: https://rust-lang.github.io/rust-clippy/master/index.html#identity_op
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@ -7,7 +7,7 @@
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A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
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[There are 303 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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[There are 304 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
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@ -0,0 +1,98 @@
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//! lint on using `x.get(x.len() - 1)` instead of `x.last()`
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use crate::utils::{match_type, paths, snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
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use if_chain::if_chain;
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use rustc::hir::{BinOpKind, Expr, ExprKind};
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::{declare_lint_pass, declare_tool_lint};
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use rustc_errors::Applicability;
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use syntax::ast::LitKind;
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use syntax::source_map::Spanned;
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use syntax::symbol::Symbol;
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declare_clippy_lint! {
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/// **What it does:** Checks for using `x.get(x.len() - 1)` instead of
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/// `x.last()`.
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///
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/// **Why is this bad?** Using `x.last()` is easier to read and has the same
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/// result.
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///
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/// Note that using `x[x.len() - 1]` is semantically different from
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/// `x.last()`. Indexing into the array will panic on out-of-bounds
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/// accesses, while `x.get()` and `x.last()` will return `None`.
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///
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/// There is another lint (get_unwrap) that covers the case of using
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/// `x.get(index).unwrap()` instead of `x[index]`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust
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/// // Bad
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/// let x = vec![2, 3, 5];
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/// let last_element = x.get(x.len() - 1);
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///
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/// // Good
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/// let x = vec![2, 3, 5];
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/// let last_element = x.last();
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/// ```
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pub GET_LAST_WITH_LEN,
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complexity,
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"Using `x.get(x.len() - 1)` when `x.last()` is correct and simpler"
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}
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declare_lint_pass!(GetLastWithLen => [GET_LAST_WITH_LEN]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for GetLastWithLen {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if_chain! {
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// Is a method call
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if let ExprKind::MethodCall(ref path, _, ref args) = expr.node;
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// Method name is "get"
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if path.ident.name == Symbol::intern("get");
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// Argument 0 (the struct we're calling the method on) is a vector
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if let Some(struct_calling_on) = args.get(0);
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let struct_ty = cx.tables.expr_ty(struct_calling_on);
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if match_type(cx, struct_ty, &paths::VEC);
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// Argument to "get" is a subtraction
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if let Some(get_index_arg) = args.get(1);
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if let ExprKind::Binary(Spanned{node: BinOpKind::Sub, ..},
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lhs, rhs) = &get_index_arg.node;
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// LHS of subtraction is "x.len()"
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if let ExprKind::MethodCall(arg_lhs_path, _, lhs_args) = &lhs.node;
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if arg_lhs_path.ident.name == Symbol::intern("len");
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if let Some(arg_lhs_struct) = lhs_args.get(0);
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// The two vectors referenced (x in x.get(...) and in x.len())
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if SpanlessEq::new(cx).eq_expr(struct_calling_on, arg_lhs_struct);
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// RHS of subtraction is 1
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if let ExprKind::Lit(rhs_lit) = &rhs.node;
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if let LitKind::Int(rhs_value, ..) = rhs_lit.node;
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if rhs_value == 1;
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then {
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let mut applicability = Applicability::MachineApplicable;
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let vec_name = snippet_with_applicability(
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cx,
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struct_calling_on.span, "vec",
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&mut applicability,
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);
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span_lint_and_sugg(
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cx,
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GET_LAST_WITH_LEN,
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expr.span,
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&format!("accessing last element with `{0}.get({0}.len() - 1)`", vec_name),
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"try",
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format!("{}.last()", vec_name),
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applicability);
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}
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}
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}
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}
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@ -186,6 +186,7 @@ pub mod fallible_impl_from;
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pub mod format;
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pub mod formatting;
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pub mod functions;
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pub mod get_last_with_len;
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pub mod identity_conversion;
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pub mod identity_op;
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pub mod if_not_else;
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@ -492,6 +493,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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reg.register_late_lint_pass(box types::CharLitAsU8);
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reg.register_late_lint_pass(box vec::UselessVec);
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reg.register_late_lint_pass(box drop_bounds::DropBounds);
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reg.register_late_lint_pass(box get_last_with_len::GetLastWithLen);
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reg.register_late_lint_pass(box drop_forget_ref::DropForgetRef);
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reg.register_late_lint_pass(box empty_enum::EmptyEnum);
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reg.register_late_lint_pass(box types::AbsurdExtremeComparisons);
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@ -710,6 +712,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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formatting::SUSPICIOUS_ELSE_FORMATTING,
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functions::NOT_UNSAFE_PTR_ARG_DEREF,
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functions::TOO_MANY_ARGUMENTS,
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get_last_with_len::GET_LAST_WITH_LEN,
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identity_conversion::IDENTITY_CONVERSION,
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identity_op::IDENTITY_OP,
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indexing_slicing::OUT_OF_BOUNDS_INDEXING,
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@ -981,6 +984,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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explicit_write::EXPLICIT_WRITE,
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format::USELESS_FORMAT,
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functions::TOO_MANY_ARGUMENTS,
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get_last_with_len::GET_LAST_WITH_LEN,
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identity_conversion::IDENTITY_CONVERSION,
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identity_op::IDENTITY_OP,
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int_plus_one::INT_PLUS_ONE,
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@ -0,0 +1,31 @@
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// run-rustfix
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#![warn(clippy::get_last_with_len)]
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fn dont_use_last() {
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let x = vec![2, 3, 5];
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let _ = x.last(); // ~ERROR Use x.last()
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}
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fn indexing_two_from_end() {
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let x = vec![2, 3, 5];
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let _ = x.get(x.len() - 2);
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}
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fn index_into_last() {
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let x = vec![2, 3, 5];
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let _ = x[x.len() - 1];
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}
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fn use_last_with_different_vec_length() {
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let x = vec![2, 3, 5];
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let y = vec!['a', 'b', 'c'];
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let _ = x.get(y.len() - 1);
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}
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fn main() {
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dont_use_last();
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indexing_two_from_end();
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index_into_last();
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use_last_with_different_vec_length();
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}
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@ -0,0 +1,31 @@
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// run-rustfix
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#![warn(clippy::get_last_with_len)]
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fn dont_use_last() {
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let x = vec![2, 3, 5];
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let _ = x.get(x.len() - 1); // ~ERROR Use x.last()
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}
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fn indexing_two_from_end() {
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let x = vec![2, 3, 5];
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let _ = x.get(x.len() - 2);
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}
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fn index_into_last() {
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let x = vec![2, 3, 5];
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let _ = x[x.len() - 1];
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}
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fn use_last_with_different_vec_length() {
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let x = vec![2, 3, 5];
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let y = vec!['a', 'b', 'c'];
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let _ = x.get(y.len() - 1);
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}
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fn main() {
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dont_use_last();
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indexing_two_from_end();
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index_into_last();
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use_last_with_different_vec_length();
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}
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@ -0,0 +1,10 @@
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error: accessing last element with `x.get(x.len() - 1)`
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--> $DIR/get_last_with_len.rs:7:13
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LL | let _ = x.get(x.len() - 1); // ~ERROR Use x.last()
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| ^^^^^^^^^^^^^^^^^^ help: try: `x.last()`
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= note: `-D clippy::get-last-with-len` implied by `-D warnings`
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error: aborting due to previous error
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