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new lint: unnecessary_indexing
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,190 @@ | ||
use std::ops::ControlFlow; | ||
|
||
use clippy_utils::diagnostics::span_lint_and_then; | ||
use clippy_utils::source::snippet; | ||
use clippy_utils::ty::is_type_diagnostic_item; | ||
use clippy_utils::visitors::for_each_expr; | ||
use clippy_utils::{path_to_local, path_to_local_id}; | ||
use rustc_ast::{LitKind, Mutability}; | ||
use rustc_errors::Applicability; | ||
use rustc_hir::{Block, Expr, ExprKind, HirId, LetStmt, Node, UnOp}; | ||
use rustc_lint::{LateContext, LateLintPass}; | ||
use rustc_middle::ty::adjustment::{Adjust, AutoBorrow, AutoBorrowMutability}; | ||
use rustc_session::declare_lint_pass; | ||
use rustc_span::{Span, sym}; | ||
|
||
declare_clippy_lint! { | ||
/// ### What it does | ||
/// Checks for the use of `seq.is_empty()` in an if-conditional where `seq` is a slice, array, or Vec, | ||
/// and in which the first element of the sequence is indexed. | ||
/// | ||
/// ### Why is this bad? | ||
/// This code is unnecessarily complicated and can instead be simplified to the use of an | ||
/// if..let expression which accesses the first element of the sequence. | ||
/// | ||
/// ### Example | ||
/// ```no_run | ||
/// let a: &[i32] = &[1]; | ||
/// if !a.is_empty() { | ||
/// let b = a[0]; | ||
/// } | ||
/// ``` | ||
/// Use instead: | ||
/// ```no_run | ||
/// let a: &[i32] = &[1]; | ||
/// if let Some(b) = a.first() { | ||
/// | ||
/// } | ||
/// ``` | ||
#[clippy::version = "1.86.0"] | ||
pub UNNECESSARY_INDEXING, | ||
complexity, | ||
"unnecessary use of `seq.is_empty()` in a conditional when if..let is more appropriate" | ||
} | ||
|
||
declare_lint_pass!(UnnecessaryIndexing => [UNNECESSARY_INDEXING]); | ||
|
||
impl<'tcx> LateLintPass<'tcx> for UnnecessaryIndexing { | ||
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'_ Expr<'tcx>) { | ||
if let Some(if_expr) = clippy_utils::higher::If::hir(expr) | ||
&& !if_expr.cond.span.from_expansion() | ||
// check for negation | ||
&& let ExprKind::Unary(UnOp::Not, unary_inner) = if_expr.cond.kind | ||
// check for call of is_empty | ||
&& let ExprKind::MethodCall(method, conditional_receiver, _, _) = unary_inner.kind | ||
&& method.ident.as_str() == "is_empty" | ||
&& let expr_ty = cx.typeck_results().expr_ty(conditional_receiver) | ||
&& let peeled = expr_ty.peel_refs() | ||
&& (peeled.is_slice() || peeled.is_array() || is_type_diagnostic_item(cx, peeled, sym::Vec)) | ||
&& let ExprKind::Block(block, _) = if_expr.then.kind | ||
// do not lint if conditional receiver is mutable reference | ||
&& expr_ty.ref_mutability() != Some(Mutability::Mut) | ||
&& let Some(con_path) = path_to_local(conditional_receiver) | ||
&& let Some(r) = process_indexing(cx, block, con_path) | ||
&& let Some(receiver_span) = r.index_receiver_span | ||
{ | ||
let receiver = snippet(cx, receiver_span, ".."); | ||
let mut suggestions: Vec<(Span, String)> = vec![]; | ||
let mut message = "consider using `if..let` syntax instead of indexing".to_string(); | ||
span_lint_and_then( | ||
cx, | ||
UNNECESSARY_INDEXING, | ||
expr.span, | ||
"condition can be simplified with `if..let` syntax", | ||
|diag| { | ||
if let Some(first_local) = r.first_local | ||
&& let Some(name) = first_local.pat.simple_ident().map(|ident| ident.name) | ||
{ | ||
suggestions.push(( | ||
if_expr.cond.span, | ||
format!( | ||
"let Some({}{name}) = {receiver}.first()", | ||
// if we arent borrowing anything then we can pass a reference here for correctness | ||
if r.extra_exprs_borrow.is_empty() { "&" } else { "" }, | ||
), | ||
)); | ||
suggestions.push((first_local.span, String::new())); | ||
|
||
if !r.extra_exprs_borrow.is_empty() { | ||
suggestions.extend( | ||
r.extra_exprs_borrow | ||
.iter() | ||
.chain(r.extra_exprs_copy.iter()) | ||
.map(|x| (x.span, name.to_string())), | ||
); | ||
|
||
message.push_str(", and replacing indexing expression(s) with the value in `Some` variant"); | ||
} else if !r.extra_exprs_copy.is_empty() { | ||
suggestions.extend(r.extra_exprs_copy.iter().map(|x| (x.span, name.to_string()))); | ||
} | ||
} else if r.extra_exprs_borrow.is_empty() { | ||
suggestions.push((if_expr.cond.span, format!("let Some(&element) = {receiver}.first()"))); | ||
suggestions.extend(r.extra_exprs_copy.iter().map(|x| (x.span, "element".to_owned()))); | ||
} else { | ||
suggestions.push((if_expr.cond.span, format!("let Some(element) = {receiver}.first()"))); | ||
suggestions.extend( | ||
r.extra_exprs_borrow | ||
.iter() | ||
.chain(r.extra_exprs_copy.iter()) | ||
.map(|x| (x.span, "element".to_owned())), | ||
); | ||
} | ||
|
||
diag.multipart_suggestion(message, suggestions, Applicability::MaybeIncorrect); | ||
}, | ||
); | ||
} | ||
} | ||
} | ||
|
||
struct IndexCheckResult<'a> { | ||
// span of the receiver for the index operation, only Some in the event the indexing is via a direct primitive | ||
index_receiver_span: Option<Span>, | ||
// first local in the block - used as pattern for `Some(pat)` | ||
first_local: Option<&'a LetStmt<'a>>, | ||
// any other index expressions to replace with `pat` (or "element" if no local exists) | ||
extra_exprs_borrow: Vec<&'a Expr<'a>>, | ||
// copied extra index expressions: if we only have these and no borrows we can provide a correct suggestion of `let | ||
// Some(&a) = ...` | ||
extra_exprs_copy: Vec<&'a Expr<'a>>, | ||
} | ||
|
||
/// Checks the block for any indexing of the conditional receiver. Returns `None` if the block | ||
/// contains code that invalidates the lint, e.g., the receiver is accessed via a mutable reference. | ||
fn process_indexing<'a>( | ||
cx: &LateContext<'a>, | ||
block: &'a Block<'a>, | ||
conditional_receiver_hid: HirId, | ||
) -> Option<IndexCheckResult<'a>> { | ||
let mut index_receiver_span: Option<Span> = None; | ||
let mut first_local: Option<&LetStmt<'_>> = None; | ||
let mut extra_exprs_borrow: Vec<&Expr<'_>> = vec![]; | ||
let mut extra_exprs_copy: Vec<&Expr<'_>> = vec![]; | ||
|
||
// if res == Some(()), then mutation occurred | ||
// & therefore we should not lint on this | ||
let res = for_each_expr(cx, block, |x| { | ||
let adjustments = cx.typeck_results().expr_adjustments(x); | ||
if let ExprKind::Index(receiver, index, _) = x.kind | ||
&& let ExprKind::Lit(lit) = index.kind | ||
&& let LitKind::Int(val, _) = lit.node | ||
&& path_to_local_id(receiver, conditional_receiver_hid) | ||
&& val.0 == 0 | ||
{ | ||
index_receiver_span = Some(receiver.span); | ||
if let Node::LetStmt(local) = cx.tcx.parent_hir_node(x.hir_id) { | ||
if first_local.is_none() { | ||
first_local = Some(local); | ||
return ControlFlow::Continue::<()>(()); | ||
} | ||
} | ||
|
||
if let Node::Expr(x) = cx.tcx.parent_hir_node(x.hir_id) | ||
&& let ExprKind::AddrOf(_, _, _) = x.kind | ||
{ | ||
extra_exprs_borrow.push(x); | ||
} else { | ||
extra_exprs_copy.push(x); | ||
} | ||
} else if adjustments.iter().any(|adjustment| { | ||
matches!( | ||
adjustment.kind, | ||
Adjust::Borrow(AutoBorrow::Ref(AutoBorrowMutability::Mut { .. })) | ||
) | ||
}) { | ||
// do not lint on mutable auto borrows (https://github.com/rust-lang/rust-clippy/pull/12464#discussion_r1600352696) | ||
return ControlFlow::Break(()); | ||
} else if let ExprKind::AddrOf(_, Mutability::Mut, _) = x.kind { | ||
return ControlFlow::Break(()); | ||
} | ||
|
||
ControlFlow::Continue::<()>(()) | ||
}); | ||
|
||
res.is_none().then_some(IndexCheckResult { | ||
index_receiver_span, | ||
first_local, | ||
extra_exprs_borrow, | ||
extra_exprs_copy, | ||
}) | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,157 @@ | ||
#![allow(unused)] | ||
#![allow(dropping_copy_types)] | ||
#![allow(dropping_references)] | ||
#![warn(clippy::unnecessary_indexing)] | ||
|
||
macro_rules! not_empty { | ||
($seq:ident) => { | ||
!$seq.is_empty() | ||
}; | ||
} | ||
|
||
fn c(x: i32) -> i32 { | ||
println!("{x}"); | ||
10 | ||
} | ||
|
||
struct Struct; | ||
impl Struct { | ||
pub fn a(x: i32) -> i32 { | ||
println!("{x}"); | ||
10 | ||
} | ||
} | ||
|
||
fn main() { | ||
// lint on vecs with a call | ||
let a: Vec<i32> = vec![1]; | ||
if let Some(&element) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = c(element); | ||
} | ||
|
||
// lint on vecs with a method call | ||
let a: Vec<i32> = vec![1]; | ||
if let Some(&element) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = Struct::a(element); | ||
} | ||
|
||
// lint on arrays with a call | ||
let a: &[i32] = &[1]; | ||
if let Some(&element) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = c(element); | ||
} | ||
|
||
// lint on arrays with a method call | ||
let a: &[i32] = &[1]; | ||
if let Some(&element) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = Struct::a(element); | ||
} | ||
|
||
// lint on vecs with a local access | ||
let a: Vec<i32> = vec![1]; | ||
if let Some(&b) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
|
||
} | ||
|
||
// lint on arrays with a local access | ||
let a: &[i32] = &[1]; | ||
if let Some(&b) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
|
||
} | ||
|
||
// lint when access is not first line | ||
let a: &[i32] = &[1]; | ||
if let Some(&b) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
dbg!(a); | ||
|
||
} | ||
|
||
// lint on multiple accesses/locals | ||
let a: &[i32] = &[1]; | ||
if let Some(c) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
dbg!(a); | ||
let b = c; | ||
|
||
drop(c); | ||
} | ||
|
||
// lint on multiple accesses | ||
let a: &[i32] = &[1]; | ||
if let Some(&element) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
dbg!(a); | ||
drop(element); | ||
drop(element); | ||
} | ||
|
||
let _first = if let Some(&element) = a.first() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
element | ||
} else { | ||
1 | ||
}; | ||
|
||
// don't lint when the condition is from expansion | ||
if not_empty!(a) { | ||
let b = a[0]; | ||
} | ||
|
||
// dont lint when not accessing [0] | ||
let a: &[i32] = &[1, 2]; | ||
if !a.is_empty() { | ||
let b = a[1]; | ||
} | ||
|
||
// dont lint when access is dynamic | ||
const T: usize = 0; | ||
|
||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
let b = a[T]; | ||
} | ||
|
||
// dont lint without unary | ||
let a: &[i32] = &[1]; | ||
if a.is_empty() { | ||
let b = a[0]; | ||
} | ||
|
||
// dont lint if we have mutable reference | ||
let mut a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
drop(&mut a); | ||
let b = a[0]; | ||
} | ||
|
||
// dont lint if we have a mutable reference, even if the mutable reference occurs after what we are | ||
// linting against | ||
let mut a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
let b = a[0]; | ||
drop(&mut a); | ||
} | ||
|
||
// dont lint on mutable auto borrow | ||
let mut a = vec![1, 2, 3]; | ||
if !a.is_empty() { | ||
a.push(1); | ||
let b = a[0]; | ||
b; | ||
} | ||
|
||
// do not lint if conditional receiver is mutable reference | ||
let a = &mut vec![1, 2, 3]; | ||
if !a.is_empty() { | ||
let b = a[0]; | ||
a; | ||
b; | ||
} | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,157 @@ | ||
#![allow(unused)] | ||
#![allow(dropping_copy_types)] | ||
#![allow(dropping_references)] | ||
#![warn(clippy::unnecessary_indexing)] | ||
|
||
macro_rules! not_empty { | ||
($seq:ident) => { | ||
!$seq.is_empty() | ||
}; | ||
} | ||
|
||
fn c(x: i32) -> i32 { | ||
println!("{x}"); | ||
10 | ||
} | ||
|
||
struct Struct; | ||
impl Struct { | ||
pub fn a(x: i32) -> i32 { | ||
println!("{x}"); | ||
10 | ||
} | ||
} | ||
|
||
fn main() { | ||
// lint on vecs with a call | ||
let a: Vec<i32> = vec![1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = c(a[0]); | ||
} | ||
|
||
// lint on vecs with a method call | ||
let a: Vec<i32> = vec![1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = Struct::a(a[0]); | ||
} | ||
|
||
// lint on arrays with a call | ||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = c(a[0]); | ||
} | ||
|
||
// lint on arrays with a method call | ||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = Struct::a(a[0]); | ||
} | ||
|
||
// lint on vecs with a local access | ||
let a: Vec<i32> = vec![1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = a[0]; | ||
} | ||
|
||
// lint on arrays with a local access | ||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
let b = a[0]; | ||
} | ||
|
||
// lint when access is not first line | ||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
dbg!(a); | ||
let b = a[0]; | ||
} | ||
|
||
// lint on multiple accesses/locals | ||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
dbg!(a); | ||
let b = &a[0]; | ||
let c = a[0]; | ||
drop(a[0]); | ||
} | ||
|
||
// lint on multiple accesses | ||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
dbg!(a); | ||
drop(a[0]); | ||
drop(a[0]); | ||
} | ||
|
||
let _first = if !a.is_empty() { | ||
//~^ ERROR: condition can be simplified with `if..let` syntax | ||
a[0] | ||
} else { | ||
1 | ||
}; | ||
|
||
// don't lint when the condition is from expansion | ||
if not_empty!(a) { | ||
let b = a[0]; | ||
} | ||
|
||
// dont lint when not accessing [0] | ||
let a: &[i32] = &[1, 2]; | ||
if !a.is_empty() { | ||
let b = a[1]; | ||
} | ||
|
||
// dont lint when access is dynamic | ||
const T: usize = 0; | ||
|
||
let a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
let b = a[T]; | ||
} | ||
|
||
// dont lint without unary | ||
let a: &[i32] = &[1]; | ||
if a.is_empty() { | ||
let b = a[0]; | ||
} | ||
|
||
// dont lint if we have mutable reference | ||
let mut a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
drop(&mut a); | ||
let b = a[0]; | ||
} | ||
|
||
// dont lint if we have a mutable reference, even if the mutable reference occurs after what we are | ||
// linting against | ||
let mut a: &[i32] = &[1]; | ||
if !a.is_empty() { | ||
let b = a[0]; | ||
drop(&mut a); | ||
} | ||
|
||
// dont lint on mutable auto borrow | ||
let mut a = vec![1, 2, 3]; | ||
if !a.is_empty() { | ||
a.push(1); | ||
let b = a[0]; | ||
b; | ||
} | ||
|
||
// do not lint if conditional receiver is mutable reference | ||
let a = &mut vec![1, 2, 3]; | ||
if !a.is_empty() { | ||
let b = a[0]; | ||
a; | ||
b; | ||
} | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,179 @@ | ||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:28:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | let b = c(a[0]); | ||
LL | | } | ||
| |_____^ | ||
| | ||
= note: `-D clippy::unnecessary-indexing` implied by `-D warnings` | ||
= help: to override `-D warnings` add `#[allow(clippy::unnecessary_indexing)]` | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&element) = a.first() { | ||
LL | | ||
LL ~ let b = c(element); | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:35:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | let b = Struct::a(a[0]); | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&element) = a.first() { | ||
LL | | ||
LL ~ let b = Struct::a(element); | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:42:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | let b = c(a[0]); | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&element) = a.first() { | ||
LL | | ||
LL ~ let b = c(element); | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:49:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | let b = Struct::a(a[0]); | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&element) = a.first() { | ||
LL | | ||
LL ~ let b = Struct::a(element); | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:56:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | let b = a[0]; | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&b) = a.first() { | ||
LL | | ||
LL ~ | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:63:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | let b = a[0]; | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&b) = a.first() { | ||
LL | | ||
LL ~ | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:70:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | dbg!(a); | ||
LL | | let b = a[0]; | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&b) = a.first() { | ||
LL | | ||
LL | dbg!(a); | ||
LL ~ | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:78:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | dbg!(a); | ||
LL | | let b = &a[0]; | ||
LL | | let c = a[0]; | ||
LL | | drop(a[0]); | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing, and replacing indexing expression(s) with the value in `Some` variant | ||
| | ||
LL ~ if let Some(c) = a.first() { | ||
LL | | ||
LL | dbg!(a); | ||
LL ~ let b = c; | ||
LL ~ | ||
LL ~ drop(c); | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:88:5 | ||
| | ||
LL | / if !a.is_empty() { | ||
LL | | | ||
LL | | dbg!(a); | ||
LL | | drop(a[0]); | ||
LL | | drop(a[0]); | ||
LL | | } | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ if let Some(&element) = a.first() { | ||
LL | | ||
LL | dbg!(a); | ||
LL ~ drop(element); | ||
LL ~ drop(element); | ||
| | ||
|
||
error: condition can be simplified with `if..let` syntax | ||
--> tests/ui/unnecessary_indexing.rs:95:18 | ||
| | ||
LL | let _first = if !a.is_empty() { | ||
| __________________^ | ||
LL | | | ||
LL | | a[0] | ||
LL | | } else { | ||
LL | | 1 | ||
LL | | }; | ||
| |_____^ | ||
| | ||
help: consider using `if..let` syntax instead of indexing | ||
| | ||
LL ~ let _first = if let Some(&element) = a.first() { | ||
LL | | ||
LL ~ element | ||
| | ||
|
||
error: aborting due to 10 previous errors | ||
|
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Note that you can generate even simplier expressions:
a
is a slice ref, use:if let [b, ..] = a
a
is an array, use:if let [b, ..] = &a
a
derefs to a slice, use:if let [b, ..] = &a[..]
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I can add it as an alternate suggestion, which one is more preferable though?