diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/loops/while_let_loop.rs')
-rw-r--r-- | src/tools/clippy/clippy_lints/src/loops/while_let_loop.rs | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/loops/while_let_loop.rs b/src/tools/clippy/clippy_lints/src/loops/while_let_loop.rs new file mode 100644 index 000000000..ca617859d --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/loops/while_let_loop.rs @@ -0,0 +1,96 @@ +use super::WHILE_LET_LOOP; +use clippy_utils::diagnostics::span_lint_and_sugg; +use clippy_utils::higher; +use clippy_utils::source::snippet_with_applicability; +use clippy_utils::ty::needs_ordered_drop; +use clippy_utils::visitors::any_temporaries_need_ordered_drop; +use rustc_errors::Applicability; +use rustc_hir::{Block, Expr, ExprKind, Local, MatchSource, Pat, StmtKind}; +use rustc_lint::LateContext; + +pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) { + let (init, has_trailing_exprs) = match (loop_block.stmts, loop_block.expr) { + ([stmt, stmts @ ..], expr) => { + if let StmtKind::Local(&Local { init: Some(e), els: None, .. }) | StmtKind::Semi(e) | StmtKind::Expr(e) = stmt.kind { + (e, !stmts.is_empty() || expr.is_some()) + } else { + return; + } + }, + ([], Some(e)) => (e, false), + _ => return, + }; + + if let Some(if_let) = higher::IfLet::hir(cx, init) + && let Some(else_expr) = if_let.if_else + && is_simple_break_expr(else_expr) + { + could_be_while_let(cx, expr, if_let.let_pat, if_let.let_expr, has_trailing_exprs); + } else if let ExprKind::Match(scrutinee, [arm1, arm2], MatchSource::Normal) = init.kind + && arm1.guard.is_none() + && arm2.guard.is_none() + && is_simple_break_expr(arm2.body) + { + could_be_while_let(cx, expr, arm1.pat, scrutinee, has_trailing_exprs); + } +} + +/// Returns `true` if expr contains a single break expression without a label or eub-expression. +fn is_simple_break_expr(e: &Expr<'_>) -> bool { + matches!(peel_blocks(e).kind, ExprKind::Break(dest, None) if dest.label.is_none()) +} + +/// Removes any blocks containing only a single expression. +fn peel_blocks<'tcx>(e: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> { + if let ExprKind::Block(b, _) = e.kind { + match (b.stmts, b.expr) { + ([s], None) => { + if let StmtKind::Expr(e) | StmtKind::Semi(e) = s.kind { + peel_blocks(e) + } else { + e + } + }, + ([], Some(e)) => peel_blocks(e), + _ => e, + } + } else { + e + } +} + +fn could_be_while_let<'tcx>( + cx: &LateContext<'tcx>, + expr: &'tcx Expr<'_>, + let_pat: &'tcx Pat<'_>, + let_expr: &'tcx Expr<'_>, + has_trailing_exprs: bool, +) { + if has_trailing_exprs + && (needs_ordered_drop(cx, cx.typeck_results().expr_ty(let_expr)) + || any_temporaries_need_ordered_drop(cx, let_expr)) + { + // Switching to a `while let` loop will extend the lifetime of some values. + return; + } + + // NOTE: we used to build a body here instead of using + // ellipsis, this was removed because: + // 1) it was ugly with big bodies; + // 2) it was not indented properly; + // 3) it wasn’t very smart (see #675). + let mut applicability = Applicability::HasPlaceholders; + span_lint_and_sugg( + cx, + WHILE_LET_LOOP, + expr.span, + "this loop could be written as a `while let` loop", + "try", + format!( + "while let {} = {} {{ .. }}", + snippet_with_applicability(cx, let_pat.span, "..", &mut applicability), + snippet_with_applicability(cx, let_expr.span, "..", &mut applicability), + ), + applicability, + ); +} |