new lint: unnecessary_path_exists #17331
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,211 @@ | ||
| use super::UNNECESSARY_PATH_EXISTS; | ||
| use clippy_utils::diagnostics::span_lint_and_then; | ||
| use clippy_utils::res::MaybeDef; | ||
| use clippy_utils::{SpanlessEq, get_enclosing_block, get_parent_expr, higher, path_to_local_with_projections, sym}; | ||
| use rustc_hir::{BinOpKind, Expr, ExprKind, MatchSource, Node, PatKind, StmtKind}; | ||
| use rustc_lint::LateContext; | ||
| use rustc_span::{Span, SyntaxContext}; | ||
|
|
||
| /// `expr` is a `.exists()` call on `recv`. Find out whether it's used either | ||
| /// directly (or through a chain of `&&`) as an `if` condition, or stored in a | ||
| /// `let` binding that's immediately checked by the following `if`, and if so | ||
| /// look for a redundant filesystem operation in the `then` branch. | ||
| pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, recv: &'tcx Expr<'tcx>) { | ||
| if is_path_method_call(cx, expr) | ||
| && let Some((then, ctxt)) = if_then_from_condition(cx, expr).or_else(|| if_then_from_stored_bool(cx, expr)) | ||
| && let Some(fs_call_span) = find_fs_call(cx, then, recv, ctxt) | ||
| { | ||
| span_lint_and_then( | ||
| cx, | ||
| UNNECESSARY_PATH_EXISTS, | ||
| expr.span, | ||
| "unnecessary `Path::exists` before a filesystem operation on the same path", | ||
| |diag| { | ||
| diag.span_note(fs_call_span, "the filesystem operation is here"); | ||
| diag.help( | ||
| "the `exists()` check is redundant and creates a TOCTOU race condition; \ | ||
| consider removing it and handling the error from the filesystem operation directly", | ||
| ); | ||
| }, | ||
| ); | ||
| } | ||
| } | ||
|
|
||
| /// If `current` is the operand of a `?` operator (i.e. `current?`), returns the | ||
| /// `Match` expression that the desugaring produces, so callers can keep | ||
| /// climbing from there. `EXPR?` lowers to | ||
| /// `Match(Call(<lang item Try::branch>, [EXPR]), _, TryDesugar(call_hir_id))`, | ||
| /// so this is recognized structurally via `MatchSource::TryDesugar`, not by | ||
| /// name/string matching on the call. | ||
| fn peel_try_desugar<'tcx>(cx: &LateContext<'tcx>, current: &'tcx Expr<'tcx>) -> Option<&'tcx Expr<'tcx>> { | ||
| let call_expr = get_parent_expr(cx, current)?; | ||
| let ExprKind::Call(_, [arg]) = call_expr.kind else { | ||
| return None; | ||
| }; | ||
| if arg.hir_id != current.hir_id { | ||
| return None; | ||
| } | ||
| let match_expr = get_parent_expr(cx, call_expr)?; | ||
| if let ExprKind::Match(_, _, MatchSource::TryDesugar(scrutinee_id)) = match_expr.kind | ||
| && scrutinee_id == call_expr.hir_id | ||
| { | ||
| Some(match_expr) | ||
| } else { | ||
| None | ||
| } | ||
| } | ||
|
|
||
| /// Repeatedly applies [`peel_try_desugar`], returning the outermost expression | ||
| /// once no more `?` layers can be peeled. | ||
| fn peel_try_desugars<'tcx>(cx: &LateContext<'tcx>, mut current: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> { | ||
| while let Some(match_expr) = peel_try_desugar(cx, current) { | ||
| current = match_expr; | ||
| } | ||
| current | ||
| } | ||
|
|
||
| /// Climbs through any enclosing `&&` chain (peeling a leading `?`, e.g. from | ||
| /// `path.try_exists()?`, first) looking for an enclosing `if` whose condition | ||
| /// is exactly the expression we climbed to. | ||
| fn if_then_from_condition<'tcx>( | ||
| cx: &LateContext<'tcx>, | ||
| exists_expr: &'tcx Expr<'tcx>, | ||
| ) -> Option<(&'tcx Expr<'tcx>, SyntaxContext)> { | ||
| let mut current = peel_try_desugars(cx, exists_expr); | ||
| loop { | ||
| let parent = get_parent_expr(cx, current)?; | ||
| match parent.kind { | ||
| ExprKind::Binary(op, lhs, rhs) | ||
| if op.node == BinOpKind::And && (lhs.hir_id == current.hir_id || rhs.hir_id == current.hir_id) => | ||
| { | ||
| current = parent; | ||
| }, | ||
| _ => { | ||
| let higher::If { cond, then, .. } = higher::If::hir(parent)?; | ||
| return (cond.hir_id == current.hir_id && !parent.span.from_expansion()) | ||
| .then(|| (then, parent.span.ctxt())); | ||
| }, | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Handles `let b = path.exists(); if b { ... }` (or the `try_exists()?` | ||
| /// equivalent), where the `if` immediately follows the `let` in the same | ||
| /// block. | ||
| fn if_then_from_stored_bool<'tcx>( | ||
| cx: &LateContext<'tcx>, | ||
| exists_expr: &'tcx Expr<'tcx>, | ||
| ) -> Option<(&'tcx Expr<'tcx>, SyntaxContext)> { | ||
| let outer = peel_try_desugars(cx, exists_expr); | ||
| let Node::LetStmt(local) = cx.tcx.parent_hir_node(outer.hir_id) else { | ||
| return None; | ||
| }; | ||
| let PatKind::Binding(_, binding_id, _, _) = local.pat.kind else { | ||
| return None; | ||
| }; | ||
|
|
||
| let block = get_enclosing_block(cx, local.hir_id)?; | ||
| if block.span.from_expansion() { | ||
| return None; | ||
| } | ||
| let idx = block | ||
| .stmts | ||
| .iter() | ||
| .position(|stmt| matches!(stmt.kind, StmtKind::Let(l) if l.hir_id == local.hir_id))?; | ||
| let next_expr = match block.stmts.get(idx + 1) { | ||
| Some(stmt) => match stmt.kind { | ||
| StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e), | ||
| StmtKind::Let(_) | StmtKind::Item(_) => None, | ||
| }, | ||
| None => block.expr, | ||
| }?; | ||
|
|
||
| let higher::If { cond, then, .. } = higher::If::hir(next_expr)?; | ||
| (path_to_local_with_projections(cond) == Some(binding_id)).then(|| (then, next_expr.span.ctxt())) | ||
| } | ||
|
|
||
| fn is_fs_method_name(name: rustc_span::Symbol) -> bool { | ||
| matches!( | ||
| name, | ||
| sym::canonicalize | ||
| | sym::is_dir | ||
| | sym::is_file | ||
| | sym::is_symlink | ||
| | sym::metadata | ||
| | sym::read_dir | ||
| | sym::read_link | ||
| | sym::symlink_metadata | ||
| ) | ||
| } | ||
|
|
||
| /// Returns `true` if `expr` is a method call that resolves to a method defined | ||
| /// on `std::path::Path` (handles any type that derefs to `Path`, e.g. `PathBuf`). | ||
| fn is_path_method_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool { | ||
| cx.typeck_results() | ||
| .type_dependent_def_id(expr.hir_id) | ||
| .is_some_and(|def_id| { | ||
| let parent = cx.tcx.parent(def_id); | ||
| cx.tcx | ||
| .type_of(parent) | ||
| .instantiate_identity() | ||
| .skip_norm_wip() | ||
| .is_diag_item(cx, sym::Path) | ||
| }) | ||
| } | ||
|
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Contributor
There was a problem hiding this comment. This can be shortened to |
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| /// Searches the `then` block of the `if` for the first filesystem method call | ||
| /// on the same receiver as the `exists()` check. | ||
| fn find_fs_call<'tcx>( | ||
| cx: &LateContext<'tcx>, | ||
| then: &'tcx Expr<'tcx>, | ||
| path_recv: &'tcx Expr<'tcx>, | ||
| ctxt: SyntaxContext, | ||
| ) -> Option<Span> { | ||
| let ExprKind::Block(block, _) = then.kind else { | ||
| return None; | ||
| }; | ||
| for stmt in block.stmts { | ||
| let candidate = match stmt.kind { | ||
| StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e), | ||
| StmtKind::Let(local) => local.init, | ||
| StmtKind::Item(_) => None, | ||
| }; | ||
| if let Some(span) = candidate.and_then(|e| find_fs_call_in_expr(cx, e, path_recv, ctxt)) { | ||
| return Some(span); | ||
| } | ||
| } | ||
| block.expr.and_then(|e| find_fs_call_in_expr(cx, e, path_recv, ctxt)) | ||
| } | ||
|
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Contributor
There was a problem hiding this comment. Why is this not just using |
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| /// Peels through method chains (e.g. `.metadata().unwrap()`) and the `?` operator | ||
| /// desugaring to find a filesystem method call on `path_recv`. | ||
| fn find_fs_call_in_expr<'tcx>( | ||
| cx: &LateContext<'tcx>, | ||
| expr: &'tcx Expr<'tcx>, | ||
| path_recv: &'tcx Expr<'tcx>, | ||
| ctxt: SyntaxContext, | ||
| ) -> Option<Span> { | ||
| match expr.kind { | ||
| ExprKind::MethodCall(method_seg, recv, _, _) => { | ||
| if is_fs_method_name(method_seg.ident.name) | ||
| && is_path_method_call(cx, expr) | ||
| && SpanlessEq::new(cx).eq_expr(ctxt, recv, path_recv) | ||
| { | ||
| return Some(expr.span); | ||
| } | ||
| // Peel through chains like `.metadata().unwrap()` or `.metadata().ok()` | ||
| find_fs_call_in_expr(cx, recv, path_recv, ctxt) | ||
| }, | ||
| // The `?` operator desugars to: | ||
| // Match(Call(TryTraitBranch, [inner_expr]), ..., TryDesugar) | ||
| // so we extract `inner_expr` and keep searching. | ||
| ExprKind::Match(scrutinee, _, MatchSource::TryDesugar(_)) => { | ||
| if let ExprKind::Call(_, [inner_expr]) = scrutinee.kind { | ||
| find_fs_call_in_expr(cx, inner_expr, path_recv, ctxt) | ||
| } else { | ||
| None | ||
| } | ||
| }, | ||
| _ => None, | ||
| } | ||
| } | ||
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You'll want to check if
recvis a projection first. As an unusual exampleif iter.next()?.exists() { iter.next()?.metadata() }shouldn't lint.