500 lines
17 KiB
Rust
500 lines
17 KiB
Rust
use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then};
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::{get_item_name, get_parent_as_impl, is_allowed};
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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::def_id::DefIdSet;
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use rustc_hir::{
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def_id::DefId, AssocItemKind, BinOpKind, Expr, ExprKind, FnRetTy, ImplItem, ImplItemKind, ImplicitSelfKind, Item,
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ItemKind, Mutability, Node, TraitItemRef, TyKind,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, AssocKind, FnSig, Ty, TyS};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::{
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source_map::{Span, Spanned, Symbol},
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symbol::sym,
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};
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declare_clippy_lint! {
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/// **What it does:** Checks for getting the length of something via `.len()`
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/// just to compare to zero, and suggests using `.is_empty()` where applicable.
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///
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/// **Why is this bad?** Some structures can answer `.is_empty()` much faster
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/// than calculating their length. So it is good to get into the habit of using
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/// `.is_empty()`, and having it is cheap.
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/// Besides, it makes the intent clearer than a manual comparison in some contexts.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```ignore
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/// if x.len() == 0 {
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/// ..
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/// }
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/// if y.len() != 0 {
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/// ..
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/// }
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/// ```
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/// instead use
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/// ```ignore
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/// if x.is_empty() {
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/// ..
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/// }
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/// if !y.is_empty() {
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/// ..
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/// }
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/// ```
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pub LEN_ZERO,
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style,
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"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for items that implement `.len()` but not
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/// `.is_empty()`.
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///
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/// **Why is this bad?** It is good custom to have both methods, because for
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/// some data structures, asking about the length will be a costly operation,
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/// whereas `.is_empty()` can usually answer in constant time. Also it used to
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/// lead to false positives on the [`len_zero`](#len_zero) lint – currently that
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/// lint will ignore such entities.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```ignore
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/// impl X {
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/// pub fn len(&self) -> usize {
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/// ..
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/// }
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/// }
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/// ```
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pub LEN_WITHOUT_IS_EMPTY,
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style,
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"traits or impls with a public `len` method but no corresponding `is_empty` method"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for comparing to an empty slice such as `""` or `[]`,
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/// and suggests using `.is_empty()` where applicable.
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///
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/// **Why is this bad?** Some structures can answer `.is_empty()` much faster
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/// than checking for equality. So it is good to get into the habit of using
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/// `.is_empty()`, and having it is cheap.
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/// Besides, it makes the intent clearer than a manual comparison in some contexts.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```ignore
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/// if s == "" {
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/// ..
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/// }
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///
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/// if arr == [] {
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/// ..
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/// }
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/// ```
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/// Use instead:
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/// ```ignore
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/// if s.is_empty() {
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/// ..
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/// }
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///
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/// if arr.is_empty() {
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/// ..
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/// }
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/// ```
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pub COMPARISON_TO_EMPTY,
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style,
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"checking `x == \"\"` or `x == []` (or similar) when `.is_empty()` could be used instead"
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}
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declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY, COMPARISON_TO_EMPTY]);
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impl<'tcx> LateLintPass<'tcx> for LenZero {
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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if item.span.from_expansion() {
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return;
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}
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if let ItemKind::Trait(_, _, _, _, trait_items) = item.kind {
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check_trait_items(cx, item, trait_items);
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
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if_chain! {
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if item.ident.as_str() == "len";
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if let ImplItemKind::Fn(sig, _) = &item.kind;
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if sig.decl.implicit_self.has_implicit_self();
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if cx.access_levels.is_exported(item.hir_id());
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if matches!(sig.decl.output, FnRetTy::Return(_));
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if let Some(imp) = get_parent_as_impl(cx.tcx, item.hir_id());
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if imp.of_trait.is_none();
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if let TyKind::Path(ty_path) = &imp.self_ty.kind;
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if let Some(ty_id) = cx.qpath_res(ty_path, imp.self_ty.hir_id).opt_def_id();
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if let Some(local_id) = ty_id.as_local();
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let ty_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_id);
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if !is_allowed(cx, LEN_WITHOUT_IS_EMPTY, ty_hir_id);
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if let Some(output) = parse_len_output(cx, cx.tcx.fn_sig(item.def_id).skip_binder());
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then {
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let (name, kind) = match cx.tcx.hir().find(ty_hir_id) {
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Some(Node::ForeignItem(x)) => (x.ident.name, "extern type"),
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Some(Node::Item(x)) => match x.kind {
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ItemKind::Struct(..) => (x.ident.name, "struct"),
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ItemKind::Enum(..) => (x.ident.name, "enum"),
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ItemKind::Union(..) => (x.ident.name, "union"),
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_ => (x.ident.name, "type"),
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}
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_ => return,
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};
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check_for_is_empty(cx, sig.span, sig.decl.implicit_self, output, ty_id, name, kind)
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}
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}
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}
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if expr.span.from_expansion() {
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return;
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}
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if let ExprKind::Binary(Spanned { node: cmp, .. }, left, right) = expr.kind {
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match cmp {
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BinOpKind::Eq => {
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check_cmp(cx, expr.span, left, right, "", 0); // len == 0
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check_cmp(cx, expr.span, right, left, "", 0); // 0 == len
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},
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BinOpKind::Ne => {
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check_cmp(cx, expr.span, left, right, "!", 0); // len != 0
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check_cmp(cx, expr.span, right, left, "!", 0); // 0 != len
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},
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BinOpKind::Gt => {
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check_cmp(cx, expr.span, left, right, "!", 0); // len > 0
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check_cmp(cx, expr.span, right, left, "", 1); // 1 > len
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},
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BinOpKind::Lt => {
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check_cmp(cx, expr.span, left, right, "", 1); // len < 1
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check_cmp(cx, expr.span, right, left, "!", 0); // 0 < len
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},
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BinOpKind::Ge => check_cmp(cx, expr.span, left, right, "!", 1), // len >= 1
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BinOpKind::Le => check_cmp(cx, expr.span, right, left, "!", 1), // 1 <= len
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_ => (),
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}
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}
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}
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}
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fn check_trait_items(cx: &LateContext<'_>, visited_trait: &Item<'_>, trait_items: &[TraitItemRef]) {
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fn is_named_self(cx: &LateContext<'_>, item: &TraitItemRef, name: &str) -> bool {
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item.ident.name.as_str() == name
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&& if let AssocItemKind::Fn { has_self } = item.kind {
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has_self && { cx.tcx.fn_sig(item.id.def_id).inputs().skip_binder().len() == 1 }
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} else {
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false
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}
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}
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// fill the set with current and super traits
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fn fill_trait_set(traitt: DefId, set: &mut DefIdSet, cx: &LateContext<'_>) {
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if set.insert(traitt) {
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for supertrait in rustc_trait_selection::traits::supertrait_def_ids(cx.tcx, traitt) {
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fill_trait_set(supertrait, set, cx);
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}
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}
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}
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if cx.access_levels.is_exported(visited_trait.hir_id()) && trait_items.iter().any(|i| is_named_self(cx, i, "len")) {
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let mut current_and_super_traits = DefIdSet::default();
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fill_trait_set(visited_trait.def_id.to_def_id(), &mut current_and_super_traits, cx);
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let is_empty_method_found = current_and_super_traits
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.iter()
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.flat_map(|&i| cx.tcx.associated_items(i).in_definition_order())
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.any(|i| {
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i.kind == ty::AssocKind::Fn
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&& i.fn_has_self_parameter
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&& i.ident.name == sym!(is_empty)
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&& cx.tcx.fn_sig(i.def_id).inputs().skip_binder().len() == 1
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});
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if !is_empty_method_found {
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span_lint(
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cx,
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LEN_WITHOUT_IS_EMPTY,
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visited_trait.span,
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&format!(
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"trait `{}` has a `len` method but no (possibly inherited) `is_empty` method",
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visited_trait.ident.name
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),
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);
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}
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}
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}
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#[derive(Debug, Clone, Copy)]
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enum LenOutput<'tcx> {
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Integral,
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Option(DefId),
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Result(DefId, Ty<'tcx>),
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}
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fn parse_len_output(cx: &LateContext<'_>, sig: FnSig<'tcx>) -> Option<LenOutput<'tcx>> {
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match *sig.output().kind() {
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ty::Int(_) | ty::Uint(_) => Some(LenOutput::Integral),
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ty::Adt(adt, subs) if cx.tcx.is_diagnostic_item(sym::option_type, adt.did) => {
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subs.type_at(0).is_integral().then(|| LenOutput::Option(adt.did))
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},
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ty::Adt(adt, subs) if cx.tcx.is_diagnostic_item(sym::result_type, adt.did) => subs
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.type_at(0)
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.is_integral()
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.then(|| LenOutput::Result(adt.did, subs.type_at(1))),
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_ => None,
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}
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}
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impl LenOutput<'_> {
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fn matches_is_empty_output(self, ty: Ty<'_>) -> bool {
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match (self, ty.kind()) {
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(_, &ty::Bool) => true,
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(Self::Option(id), &ty::Adt(adt, subs)) if id == adt.did => subs.type_at(0).is_bool(),
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(Self::Result(id, err_ty), &ty::Adt(adt, subs)) if id == adt.did => {
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subs.type_at(0).is_bool() && TyS::same_type(subs.type_at(1), err_ty)
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},
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_ => false,
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}
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}
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fn expected_sig(self, self_kind: ImplicitSelfKind) -> String {
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let self_ref = match self_kind {
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ImplicitSelfKind::ImmRef => "&",
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ImplicitSelfKind::MutRef => "&mut ",
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_ => "",
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};
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match self {
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Self::Integral => format!("expected signature: `({}self) -> bool`", self_ref),
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Self::Option(_) => format!(
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"expected signature: `({}self) -> bool` or `({}self) -> Option<bool>",
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self_ref, self_ref
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),
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Self::Result(..) => format!(
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"expected signature: `({}self) -> bool` or `({}self) -> Result<bool>",
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self_ref, self_ref
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),
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}
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}
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}
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/// Checks if the given signature matches the expectations for `is_empty`
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fn check_is_empty_sig(sig: FnSig<'_>, self_kind: ImplicitSelfKind, len_output: LenOutput<'_>) -> bool {
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match &**sig.inputs_and_output {
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[arg, res] if len_output.matches_is_empty_output(res) => {
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matches!(
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(arg.kind(), self_kind),
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(ty::Ref(_, _, Mutability::Not), ImplicitSelfKind::ImmRef)
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| (ty::Ref(_, _, Mutability::Mut), ImplicitSelfKind::MutRef)
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) || (!arg.is_ref() && matches!(self_kind, ImplicitSelfKind::Imm | ImplicitSelfKind::Mut))
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},
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_ => false,
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}
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}
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/// Checks if the given type has an `is_empty` method with the appropriate signature.
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fn check_for_is_empty(
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cx: &LateContext<'_>,
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span: Span,
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self_kind: ImplicitSelfKind,
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output: LenOutput<'_>,
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impl_ty: DefId,
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item_name: Symbol,
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item_kind: &str,
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) {
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let is_empty = Symbol::intern("is_empty");
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let is_empty = cx
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.tcx
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.inherent_impls(impl_ty)
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.iter()
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.flat_map(|&id| cx.tcx.associated_items(id).filter_by_name_unhygienic(is_empty))
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.find(|item| item.kind == AssocKind::Fn);
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let (msg, is_empty_span, self_kind) = match is_empty {
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None => (
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format!(
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"{} `{}` has a public `len` method, but no `is_empty` method",
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item_kind,
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item_name.as_str(),
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),
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None,
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None,
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),
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Some(is_empty)
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if !cx
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.access_levels
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.is_exported(cx.tcx.hir().local_def_id_to_hir_id(is_empty.def_id.expect_local())) =>
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{
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(
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format!(
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"{} `{}` has a public `len` method, but a private `is_empty` method",
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item_kind,
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item_name.as_str(),
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),
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Some(cx.tcx.def_span(is_empty.def_id)),
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None,
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)
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},
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Some(is_empty)
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if !(is_empty.fn_has_self_parameter
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&& check_is_empty_sig(cx.tcx.fn_sig(is_empty.def_id).skip_binder(), self_kind, output)) =>
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{
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(
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format!(
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"{} `{}` has a public `len` method, but the `is_empty` method has an unexpected signature",
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item_kind,
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item_name.as_str(),
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),
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Some(cx.tcx.def_span(is_empty.def_id)),
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Some(self_kind),
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)
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},
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Some(_) => return,
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};
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span_lint_and_then(cx, LEN_WITHOUT_IS_EMPTY, span, &msg, |db| {
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if let Some(span) = is_empty_span {
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db.span_note(span, "`is_empty` defined here");
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}
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if let Some(self_kind) = self_kind {
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db.note(&output.expected_sig(self_kind));
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}
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});
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}
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fn check_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>, op: &str, compare_to: u32) {
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if let (&ExprKind::MethodCall(method_path, _, args, _), &ExprKind::Lit(ref lit)) = (&method.kind, &lit.kind) {
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// check if we are in an is_empty() method
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if let Some(name) = get_item_name(cx, method) {
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if name.as_str() == "is_empty" {
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return;
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}
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}
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check_len(cx, span, method_path.ident.name, args, &lit.node, op, compare_to)
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} else {
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check_empty_expr(cx, span, method, lit, op)
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}
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}
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fn check_len(
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cx: &LateContext<'_>,
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span: Span,
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method_name: Symbol,
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args: &[Expr<'_>],
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lit: &LitKind,
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op: &str,
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compare_to: u32,
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) {
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if let LitKind::Int(lit, _) = *lit {
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// check if length is compared to the specified number
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if lit != u128::from(compare_to) {
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return;
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}
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if method_name.as_str() == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) {
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
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cx,
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LEN_ZERO,
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span,
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&format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }),
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&format!("using `{}is_empty` is clearer and more explicit", op),
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format!(
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"{}{}.is_empty()",
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op,
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snippet_with_applicability(cx, args[0].span, "_", &mut applicability)
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),
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applicability,
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);
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}
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}
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}
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fn check_empty_expr(cx: &LateContext<'_>, span: Span, lit1: &Expr<'_>, lit2: &Expr<'_>, op: &str) {
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if (is_empty_array(lit2) || is_empty_string(lit2)) && has_is_empty(cx, lit1) {
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
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cx,
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COMPARISON_TO_EMPTY,
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span,
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"comparison to empty slice",
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&format!("using `{}is_empty` is clearer and more explicit", op),
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format!(
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"{}{}.is_empty()",
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op,
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snippet_with_applicability(cx, lit1.span, "_", &mut applicability)
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),
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applicability,
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);
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}
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}
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fn is_empty_string(expr: &Expr<'_>) -> bool {
|
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if let ExprKind::Lit(ref lit) = expr.kind {
|
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if let LitKind::Str(lit, _) = lit.node {
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let lit = lit.as_str();
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return lit == "";
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}
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}
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false
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}
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fn is_empty_array(expr: &Expr<'_>) -> bool {
|
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if let ExprKind::Array(arr) = expr.kind {
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return arr.is_empty();
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}
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false
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}
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/// Checks if this type has an `is_empty` method.
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fn has_is_empty(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
|
||
/// Gets an `AssocItem` and return true if it matches `is_empty(self)`.
|
||
fn is_is_empty(cx: &LateContext<'_>, item: &ty::AssocItem) -> bool {
|
||
if let ty::AssocKind::Fn = item.kind {
|
||
if item.ident.name.as_str() == "is_empty" {
|
||
let sig = cx.tcx.fn_sig(item.def_id);
|
||
let ty = sig.skip_binder();
|
||
ty.inputs().len() == 1
|
||
} else {
|
||
false
|
||
}
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
/// Checks the inherent impl's items for an `is_empty(self)` method.
|
||
fn has_is_empty_impl(cx: &LateContext<'_>, id: DefId) -> bool {
|
||
cx.tcx.inherent_impls(id).iter().any(|imp| {
|
||
cx.tcx
|
||
.associated_items(*imp)
|
||
.in_definition_order()
|
||
.any(|item| is_is_empty(cx, item))
|
||
})
|
||
}
|
||
|
||
let ty = &cx.typeck_results().expr_ty(expr).peel_refs();
|
||
match ty.kind() {
|
||
ty::Dynamic(tt, ..) => tt.principal().map_or(false, |principal| {
|
||
cx.tcx
|
||
.associated_items(principal.def_id())
|
||
.in_definition_order()
|
||
.any(|item| is_is_empty(cx, item))
|
||
}),
|
||
ty::Projection(ref proj) => has_is_empty_impl(cx, proj.item_def_id),
|
||
ty::Adt(id, _) => has_is_empty_impl(cx, id.did),
|
||
ty::Array(..) | ty::Slice(..) | ty::Str => true,
|
||
_ => false,
|
||
}
|
||
}
|