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new lint: unnecessary_indexing
#14058
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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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Note that you can generate even simplier expressions:
ais a slice ref, use:if let [b, ..] = aais an array, use:if let [b, ..] = &aaderefs to a slice, use:if let [b, ..] = &a[..]There was a problem hiding this comment.
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I can add it as an alternate suggestion, which one is more preferable though?