Improve redundant_pattern_matching
Add a note when the drop order change may result in different behaviour.
This commit is contained in:
Jason Newcomb
parent
586a99348c
commit
b6581636bd
13 changed files with 579 additions and 89 deletions
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@ -423,7 +423,12 @@ declare_clippy_lint! {
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/// **Why is this bad?** It's more concise and clear to just use the proper
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/// utility function
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///
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/// **Known problems:** None.
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/// **Known problems:** This will change the drop order for the matched type. Both `if let` and
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/// `while let` will drop the value at the end of the block, both `if` and `while` will drop the
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/// value before entering the block. For most types this change will not matter, but for a few
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/// types this will not be an acceptable change (e.g. locks). See the
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/// [reference](https://doc.rust-lang.org/reference/destructors.html#drop-scopes) for more about
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/// drop order.
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///
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/// **Example:**
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///
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@ -1700,55 +1705,204 @@ where
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mod redundant_pattern_match {
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use super::REDUNDANT_PATTERN_MATCHING;
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use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet;
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use clippy_utils::source::{snippet, snippet_with_applicability};
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use clippy_utils::ty::{implements_trait, is_type_diagnostic_item, is_type_lang_item, match_type};
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use clippy_utils::{is_lang_ctor, is_qpath_def_path, is_trait_method, paths};
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use if_chain::if_chain;
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use rustc_ast::ast::LitKind;
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use rustc_errors::Applicability;
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use rustc_hir::LangItem::{OptionNone, OptionSome, PollPending, PollReady, ResultErr, ResultOk};
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use rustc_hir::{Arm, Expr, ExprKind, MatchSource, PatKind, QPath};
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use rustc_hir::{
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intravisit::{walk_expr, ErasedMap, NestedVisitorMap, Visitor},
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Arm, Block, Expr, ExprKind, LangItem, MatchSource, Node, PatKind, QPath,
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};
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use rustc_lint::LateContext;
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use rustc_middle::ty::{self, subst::GenericArgKind, Ty};
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use rustc_span::sym;
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pub fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let ExprKind::Match(op, arms, ref match_source) = &expr.kind {
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match match_source {
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MatchSource::Normal => find_sugg_for_match(cx, expr, op, arms),
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MatchSource::IfLetDesugar { .. } => find_sugg_for_if_let(cx, expr, op, arms, "if"),
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MatchSource::WhileLetDesugar => find_sugg_for_if_let(cx, expr, op, arms, "while"),
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MatchSource::IfLetDesugar { contains_else_clause } => {
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find_sugg_for_if_let(cx, expr, op, &arms[0], "if", *contains_else_clause)
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},
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MatchSource::WhileLetDesugar => find_sugg_for_if_let(cx, expr, op, &arms[0], "while", false),
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_ => {},
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}
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}
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}
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// Check if the drop order for a type matters
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fn type_needs_ordered_drop(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
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if !ty.needs_drop(cx.tcx, cx.param_env) {
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false
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} else if cx
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.tcx
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.lang_items()
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.drop_trait()
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.map_or(false, |id| !implements_trait(cx, ty, id, &[]))
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{
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// This type doesn't implement drop, so no side effects here.
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// Check if any component type has any.
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match ty.kind() {
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ty::Tuple(_) => ty.tuple_fields().any(|ty| type_needs_ordered_drop(cx, ty)),
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ty::Array(ty, _) => type_needs_ordered_drop(cx, ty),
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ty::Adt(adt, subs) => adt
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.all_fields()
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.map(|f| f.ty(cx.tcx, subs))
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.any(|ty| type_needs_ordered_drop(cx, ty)),
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_ => true,
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}
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}
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// Check for std types which implement drop, but only for memory allocation.
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else if is_type_diagnostic_item(cx, ty, sym::vec_type)
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|| is_type_lang_item(cx, ty, LangItem::OwnedBox)
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|| is_type_diagnostic_item(cx, ty, sym::Rc)
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|| is_type_diagnostic_item(cx, ty, sym::Arc)
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|| is_type_diagnostic_item(cx, ty, sym::cstring_type)
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|| match_type(cx, ty, &paths::BTREEMAP)
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|| match_type(cx, ty, &paths::LINKED_LIST)
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|| match_type(cx, ty, &paths::WEAK_RC)
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|| match_type(cx, ty, &paths::WEAK_ARC)
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{
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// Check all of the generic arguments.
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if let ty::Adt(_, subs) = ty.kind() {
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subs.types().any(|ty| type_needs_ordered_drop(cx, ty))
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} else {
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true
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}
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} else {
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true
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}
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}
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// Extract the generic arguments out of a type
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fn try_get_generic_ty(ty: Ty<'_>, index: usize) -> Option<Ty<'_>> {
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if_chain! {
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if let ty::Adt(_, subs) = ty.kind();
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if let Some(sub) = subs.get(index);
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if let GenericArgKind::Type(sub_ty) = sub.unpack();
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then {
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Some(sub_ty)
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} else {
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None
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}
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}
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}
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// Checks if there are any temporaries created in the given expression for which drop order
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// matters.
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fn temporaries_need_ordered_drop(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
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struct V<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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res: bool,
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}
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impl<'a, 'tcx> Visitor<'tcx> for V<'a, 'tcx> {
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type Map = ErasedMap<'tcx>;
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
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}
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fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
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match expr.kind {
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// Taking the reference of a value leaves a temporary
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// e.g. In `&String::new()` the string is a temporary value.
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// Remaining fields are temporary values
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// e.g. In `(String::new(), 0).1` the string is a temporary value.
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ExprKind::AddrOf(_, _, expr) | ExprKind::Field(expr, _) => {
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if !matches!(expr.kind, ExprKind::Path(_)) {
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if type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(expr)) {
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self.res = true;
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} else {
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self.visit_expr(expr);
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}
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}
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},
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// the base type is alway taken by reference.
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// e.g. In `(vec![0])[0]` the vector is a temporary value.
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ExprKind::Index(base, index) => {
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if !matches!(base.kind, ExprKind::Path(_)) {
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if type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(base)) {
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self.res = true;
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} else {
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self.visit_expr(base);
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}
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}
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self.visit_expr(index);
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},
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// Method calls can take self by reference.
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// e.g. In `String::new().len()` the string is a temporary value.
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ExprKind::MethodCall(_, _, [self_arg, args @ ..], _) => {
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if !matches!(self_arg.kind, ExprKind::Path(_)) {
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let self_by_ref = self
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.cx
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.typeck_results()
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.type_dependent_def_id(expr.hir_id)
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.map_or(false, |id| self.cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref());
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if self_by_ref
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&& type_needs_ordered_drop(self.cx, self.cx.typeck_results().expr_ty(self_arg))
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{
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self.res = true;
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} else {
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self.visit_expr(self_arg)
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}
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}
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args.iter().for_each(|arg| self.visit_expr(arg));
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},
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// Either explicitly drops values, or changes control flow.
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ExprKind::DropTemps(_)
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| ExprKind::Ret(_)
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| ExprKind::Break(..)
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| ExprKind::Yield(..)
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| ExprKind::Block(Block { expr: None, .. }, _)
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| ExprKind::Loop(..) => (),
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// Only consider the final expression.
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ExprKind::Block(Block { expr: Some(expr), .. }, _) => self.visit_expr(expr),
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_ => walk_expr(self, expr),
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}
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}
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}
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let mut v = V { cx, res: false };
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v.visit_expr(expr);
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v.res
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}
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fn find_sugg_for_if_let<'tcx>(
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cx: &LateContext<'tcx>,
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expr: &'tcx Expr<'_>,
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op: &Expr<'_>,
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arms: &[Arm<'_>],
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op: &'tcx Expr<'tcx>,
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arm: &Arm<'_>,
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keyword: &'static str,
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has_else: bool,
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) {
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// also look inside refs
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let mut kind = &arms[0].pat.kind;
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let mut kind = &arm.pat.kind;
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// if we have &None for example, peel it so we can detect "if let None = x"
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if let PatKind::Ref(inner, _mutability) = kind {
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kind = &inner.kind;
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}
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let good_method = match kind {
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let op_ty = cx.typeck_results().expr_ty(op);
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// Determine which function should be used, and the type contained by the corresponding
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// variant.
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let (good_method, inner_ty) = match kind {
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PatKind::TupleStruct(ref path, [sub_pat], _) => {
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if let PatKind::Wild = sub_pat.kind {
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if is_lang_ctor(cx, path, ResultOk) {
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"is_ok()"
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("is_ok()", try_get_generic_ty(op_ty, 0).unwrap_or(op_ty))
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} else if is_lang_ctor(cx, path, ResultErr) {
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"is_err()"
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("is_err()", try_get_generic_ty(op_ty, 1).unwrap_or(op_ty))
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} else if is_lang_ctor(cx, path, OptionSome) {
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"is_some()"
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("is_some()", op_ty)
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} else if is_lang_ctor(cx, path, PollReady) {
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"is_ready()"
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("is_ready()", op_ty)
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} else if is_qpath_def_path(cx, path, sub_pat.hir_id, &paths::IPADDR_V4) {
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"is_ipv4()"
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("is_ipv4()", op_ty)
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} else if is_qpath_def_path(cx, path, sub_pat.hir_id, &paths::IPADDR_V6) {
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"is_ipv6()"
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("is_ipv6()", op_ty)
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} else {
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return;
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}
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@ -1757,17 +1911,36 @@ mod redundant_pattern_match {
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}
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},
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PatKind::Path(ref path) => {
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if is_lang_ctor(cx, path, OptionNone) {
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let method = if is_lang_ctor(cx, path, OptionNone) {
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"is_none()"
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} else if is_lang_ctor(cx, path, PollPending) {
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"is_pending()"
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} else {
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return;
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}
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};
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// `None` and `Pending` don't have an inner type.
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(method, cx.tcx.types.unit)
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},
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_ => return,
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};
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// If this is the last expression in a block or there is an else clause then the whole
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// type needs to be considered, not just the inner type of the branch being matched on.
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// Note the last expression in a block is dropped after all local bindings.
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let check_ty = if has_else
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|| (keyword == "if" && matches!(cx.tcx.hir().parent_iter(expr.hir_id).next(), Some((_, Node::Block(..)))))
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{
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op_ty
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} else {
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inner_ty
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};
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// All temporaries created in the scrutinee expression are dropped at the same time as the
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// scrutinee would be, so they have to be considered as well.
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// e.g. in `if let Some(x) = foo.lock().unwrap().baz.as_ref() { .. }` the lock will be held
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// for the duration if body.
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let needs_drop = type_needs_ordered_drop(cx, check_ty) || temporaries_need_ordered_drop(cx, op);
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// check that `while_let_on_iterator` lint does not trigger
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if_chain! {
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if keyword == "while";
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@ -1786,7 +1959,7 @@ mod redundant_pattern_match {
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span_lint_and_then(
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cx,
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REDUNDANT_PATTERN_MATCHING,
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arms[0].pat.span,
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arm.pat.span,
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&format!("redundant pattern matching, consider using `{}`", good_method),
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|diag| {
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// while let ... = ... { ... }
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@ -1800,12 +1973,20 @@ mod redundant_pattern_match {
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// while let ... = ... { ... }
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// ^^^^^^^^^^^^^^^^^^^
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let span = expr_span.until(op_span.shrink_to_hi());
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diag.span_suggestion(
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span,
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"try this",
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format!("{} {}.{}", keyword, snippet(cx, op_span, "_"), good_method),
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Applicability::MachineApplicable, // snippet
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);
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let mut app = if needs_drop {
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Applicability::MaybeIncorrect
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} else {
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Applicability::MachineApplicable
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};
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let sugg = snippet_with_applicability(cx, op_span, "_", &mut app);
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diag.span_suggestion(span, "try this", format!("{} {}.{}", keyword, sugg, good_method), app);
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if needs_drop {
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diag.note("this will change drop order of the result, as well as all temporaries");
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diag.note("add `#[allow(clippy::redundant_pattern_matching)]` if this is important");
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}
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},
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);
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}
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