376 lines
13 KiB
Rust
376 lines
13 KiB
Rust
use crate::utils::{get_item_name, snippet_with_applicability, span_lint, span_lint_and_sugg};
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use rustc_ast::ast::LitKind;
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use rustc_data_structures::fx::FxHashSet;
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use rustc_errors::Applicability;
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use rustc_hir::def_id::DefId;
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use rustc_hir::{AssocItemKind, BinOpKind, Expr, ExprKind, Impl, ImplItemRef, Item, ItemKind, TraitItemRef};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::{Span, Spanned, Symbol};
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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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match item.kind {
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ItemKind::Trait(_, _, _, _, ref trait_items) => check_trait_items(cx, item, trait_items),
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ItemKind::Impl(Impl {
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of_trait: None,
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items: ref impl_items,
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..
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}) => check_impl_items(cx, item, impl_items),
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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, .. }, ref left, ref 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 && {
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let did = cx.tcx.hir().local_def_id(item.id.hir_id);
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cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1
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}
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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 FxHashSet<DefId>, 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 = FxHashSet::default();
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let visited_trait_def_id = cx.tcx.hir().local_def_id(visited_trait.hir_id);
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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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fn check_impl_items(cx: &LateContext<'_>, item: &Item<'_>, impl_items: &[ImplItemRef<'_>]) {
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fn is_named_self(cx: &LateContext<'_>, item: &ImplItemRef<'_>, 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 && {
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let did = cx.tcx.hir().local_def_id(item.id.hir_id);
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cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1
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}
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} else {
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false
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}
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}
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let is_empty = if let Some(is_empty) = impl_items.iter().find(|i| is_named_self(cx, i, "is_empty")) {
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if cx.access_levels.is_exported(is_empty.id.hir_id) {
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return;
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}
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"a private"
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} else {
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"no corresponding"
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};
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if let Some(i) = impl_items.iter().find(|i| is_named_self(cx, i, "len")) {
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if cx.access_levels.is_exported(i.id.hir_id) {
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let def_id = cx.tcx.hir().local_def_id(item.hir_id);
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let ty = cx.tcx.type_of(def_id);
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span_lint(
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cx,
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LEN_WITHOUT_IS_EMPTY,
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item.span,
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&format!(
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"item `{}` has a public `len` method but {} `is_empty` method",
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ty, is_empty
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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_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>, op: &str, compare_to: u32) {
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if let (&ExprKind::MethodCall(ref method_path, _, ref args, _), &ExprKind::Lit(ref lit)) = (&method.kind, &lit.kind)
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{
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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(ref 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 {
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/// Gets an `AssocItem` and return true if it matches `is_empty(self)`.
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fn is_is_empty(cx: &LateContext<'_>, item: &ty::AssocItem) -> bool {
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if let ty::AssocKind::Fn = item.kind {
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if item.ident.name.as_str() == "is_empty" {
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let sig = cx.tcx.fn_sig(item.def_id);
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let ty = sig.skip_binder();
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ty.inputs().len() == 1
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} else {
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false
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}
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} else {
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false
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}
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}
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/// Checks the inherent impl's items for an `is_empty(self)` method.
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fn has_is_empty_impl(cx: &LateContext<'_>, id: DefId) -> bool {
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cx.tcx.inherent_impls(id).iter().any(|imp| {
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cx.tcx
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.associated_items(*imp)
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.in_definition_order()
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.any(|item| is_is_empty(cx, &item))
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})
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}
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let ty = &cx.typeck_results().expr_ty(expr).peel_refs();
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match ty.kind() {
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ty::Dynamic(ref tt, ..) => tt.principal().map_or(false, |principal| {
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cx.tcx
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.associated_items(principal.def_id())
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.in_definition_order()
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.any(|item| is_is_empty(cx, &item))
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}),
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ty::Projection(ref proj) => has_is_empty_impl(cx, proj.item_def_id),
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ty::Adt(id, _) => has_is_empty_impl(cx, id.did),
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ty::Array(..) | ty::Slice(..) | ty::Str => true,
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_ => false,
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}
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}
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