diff --git a/clippy_lints/src/loops/never_loop.rs b/clippy_lints/src/loops/never_loop.rs index e97b7c941703..6d9f6215ed41 100644 --- a/clippy_lints/src/loops/never_loop.rs +++ b/clippy_lints/src/loops/never_loop.rs @@ -1,13 +1,36 @@ +use super::utils::make_iterator_snippet; use super::NEVER_LOOP; -use clippy_utils::diagnostics::span_lint; -use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, Stmt, StmtKind}; +use clippy_utils::diagnostics::span_lint_and_then; +use clippy_utils::higher; +use clippy_utils::source::snippet; +use rustc_errors::Applicability; +use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, LoopSource, Node, Pat, Stmt, StmtKind}; use rustc_lint::LateContext; use std::iter::{once, Iterator}; pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { - if let ExprKind::Loop(block, _, _, _) = expr.kind { + if let ExprKind::Loop(block, _, source, _) = expr.kind { match never_loop_block(block, expr.hir_id) { - NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"), + NeverLoopResult::AlwaysBreak => { + span_lint_and_then(cx, NEVER_LOOP, expr.span, "this loop never actually loops", |diag| { + if_chain! { + if let LoopSource::ForLoop = source; + if let Some((_, Node::Expr(parent_match))) = cx.tcx.hir().parent_iter(expr.hir_id).nth(1); + if let Some((pat, iterator, _, for_span)) = higher::for_loop(parent_match); + then { + // Suggests using an `if let` instead. This is `Unspecified` because the + // loop may (probably) contain `break` statements which would be invalid + // in an `if let`. + diag.span_suggestion_verbose( + for_span.with_hi(iterator.span.hi()), + "if you need the first element of the iterator, try writing", + for_to_if_let_sugg(cx, iterator, pat), + Applicability::Unspecified, + ); + } + }; + }); + }, NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (), } } @@ -170,3 +193,14 @@ fn never_loop_expr_branch<'a, T: Iterator>>(e: &mut T, main_ e.map(|e| never_loop_expr(e, main_loop_id)) .fold(NeverLoopResult::AlwaysBreak, combine_branches) } + +fn for_to_if_let_sugg(cx: &LateContext<'_>, iterator: &Expr<'_>, pat: &Pat<'_>) -> String { + let pat_snippet = snippet(cx, pat.span, "_"); + let iter_snippet = make_iterator_snippet(cx, iterator, &mut Applicability::Unspecified); + + format!( + "if let Some({pat}) = {iter}.next()", + pat = pat_snippet, + iter = iter_snippet + ) +} diff --git a/tests/ui/never_loop.stderr b/tests/ui/never_loop.stderr index c00b4c78cf28..9fbf3e9ce980 100644 --- a/tests/ui/never_loop.stderr +++ b/tests/ui/never_loop.stderr @@ -75,6 +75,11 @@ LL | | _ => return, LL | | } LL | | } | |_____^ + | +help: if you need the first element of the iterator, try writing + | +LL | if let Some(x) = (0..10).next() { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this loop never actually loops --> $DIR/never_loop.rs:157:5