mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-11 22:02:55 +00:00
373 lines
12 KiB
Rust
373 lines
12 KiB
Rust
use crate::utils::{get_item_name, snippet_with_applicability, span_lint, span_lint_and_sugg};
|
||
use rustc_ast::ast::LitKind;
|
||
use rustc_data_structures::fx::FxHashSet;
|
||
use rustc_errors::Applicability;
|
||
use rustc_hir::def_id::DefId;
|
||
use rustc_hir::{AssocItemKind, BinOpKind, Expr, ExprKind, Impl, ImplItemRef, Item, ItemKind, TraitItemRef};
|
||
use rustc_lint::{LateContext, LateLintPass};
|
||
use rustc_middle::ty;
|
||
use rustc_session::{declare_lint_pass, declare_tool_lint};
|
||
use rustc_span::source_map::{Span, Spanned, Symbol};
|
||
|
||
declare_clippy_lint! {
|
||
/// **What it does:** Checks for getting the length of something via `.len()`
|
||
/// just to compare to zero, and suggests using `.is_empty()` where applicable.
|
||
///
|
||
/// **Why is this bad?** Some structures can answer `.is_empty()` much faster
|
||
/// than calculating their length. So it is good to get into the habit of using
|
||
/// `.is_empty()`, and having it is cheap.
|
||
/// Besides, it makes the intent clearer than a manual comparison in some contexts.
|
||
///
|
||
/// **Known problems:** None.
|
||
///
|
||
/// **Example:**
|
||
/// ```ignore
|
||
/// if x.len() == 0 {
|
||
/// ..
|
||
/// }
|
||
/// if y.len() != 0 {
|
||
/// ..
|
||
/// }
|
||
/// ```
|
||
/// instead use
|
||
/// ```ignore
|
||
/// if x.is_empty() {
|
||
/// ..
|
||
/// }
|
||
/// if !y.is_empty() {
|
||
/// ..
|
||
/// }
|
||
/// ```
|
||
pub LEN_ZERO,
|
||
style,
|
||
"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead"
|
||
}
|
||
|
||
declare_clippy_lint! {
|
||
/// **What it does:** Checks for items that implement `.len()` but not
|
||
/// `.is_empty()`.
|
||
///
|
||
/// **Why is this bad?** It is good custom to have both methods, because for
|
||
/// some data structures, asking about the length will be a costly operation,
|
||
/// whereas `.is_empty()` can usually answer in constant time. Also it used to
|
||
/// lead to false positives on the [`len_zero`](#len_zero) lint – currently that
|
||
/// lint will ignore such entities.
|
||
///
|
||
/// **Known problems:** None.
|
||
///
|
||
/// **Example:**
|
||
/// ```ignore
|
||
/// impl X {
|
||
/// pub fn len(&self) -> usize {
|
||
/// ..
|
||
/// }
|
||
/// }
|
||
/// ```
|
||
pub LEN_WITHOUT_IS_EMPTY,
|
||
style,
|
||
"traits or impls with a public `len` method but no corresponding `is_empty` method"
|
||
}
|
||
|
||
declare_clippy_lint! {
|
||
/// **What it does:** Checks for comparing to an empty slice such as `""` or `[]`,
|
||
/// and suggests using `.is_empty()` where applicable.
|
||
///
|
||
/// **Why is this bad?** Some structures can answer `.is_empty()` much faster
|
||
/// than checking for equality. So it is good to get into the habit of using
|
||
/// `.is_empty()`, and having it is cheap.
|
||
/// Besides, it makes the intent clearer than a manual comparison in some contexts.
|
||
///
|
||
/// **Known problems:** None.
|
||
///
|
||
/// **Example:**
|
||
///
|
||
/// ```ignore
|
||
/// if s == "" {
|
||
/// ..
|
||
/// }
|
||
///
|
||
/// if arr == [] {
|
||
/// ..
|
||
/// }
|
||
/// ```
|
||
/// Use instead:
|
||
/// ```ignore
|
||
/// if s.is_empty() {
|
||
/// ..
|
||
/// }
|
||
///
|
||
/// if arr.is_empty() {
|
||
/// ..
|
||
/// }
|
||
/// ```
|
||
pub COMPARISON_TO_EMPTY,
|
||
style,
|
||
"checking `x == \"\"` or `x == []` (or similar) when `.is_empty()` could be used instead"
|
||
}
|
||
|
||
declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY, COMPARISON_TO_EMPTY]);
|
||
|
||
impl<'tcx> LateLintPass<'tcx> for LenZero {
|
||
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
|
||
if item.span.from_expansion() {
|
||
return;
|
||
}
|
||
|
||
match item.kind {
|
||
ItemKind::Trait(_, _, _, _, ref trait_items) => check_trait_items(cx, item, trait_items),
|
||
ItemKind::Impl(Impl {
|
||
of_trait: None,
|
||
items: ref impl_items,
|
||
..
|
||
}) => check_impl_items(cx, item, impl_items),
|
||
_ => (),
|
||
}
|
||
}
|
||
|
||
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
|
||
if expr.span.from_expansion() {
|
||
return;
|
||
}
|
||
|
||
if let ExprKind::Binary(Spanned { node: cmp, .. }, ref left, ref right) = expr.kind {
|
||
match cmp {
|
||
BinOpKind::Eq => {
|
||
check_cmp(cx, expr.span, left, right, "", 0); // len == 0
|
||
check_cmp(cx, expr.span, right, left, "", 0); // 0 == len
|
||
},
|
||
BinOpKind::Ne => {
|
||
check_cmp(cx, expr.span, left, right, "!", 0); // len != 0
|
||
check_cmp(cx, expr.span, right, left, "!", 0); // 0 != len
|
||
},
|
||
BinOpKind::Gt => {
|
||
check_cmp(cx, expr.span, left, right, "!", 0); // len > 0
|
||
check_cmp(cx, expr.span, right, left, "", 1); // 1 > len
|
||
},
|
||
BinOpKind::Lt => {
|
||
check_cmp(cx, expr.span, left, right, "", 1); // len < 1
|
||
check_cmp(cx, expr.span, right, left, "!", 0); // 0 < len
|
||
},
|
||
BinOpKind::Ge => check_cmp(cx, expr.span, left, right, "!", 1), // len >= 1
|
||
BinOpKind::Le => check_cmp(cx, expr.span, right, left, "!", 1), // 1 <= len
|
||
_ => (),
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_trait_items(cx: &LateContext<'_>, visited_trait: &Item<'_>, trait_items: &[TraitItemRef]) {
|
||
fn is_named_self(cx: &LateContext<'_>, item: &TraitItemRef, name: &str) -> bool {
|
||
item.ident.name.as_str() == name
|
||
&& if let AssocItemKind::Fn { has_self } = item.kind {
|
||
has_self && {
|
||
let did = cx.tcx.hir().local_def_id(item.id.hir_id);
|
||
cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1
|
||
}
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
// fill the set with current and super traits
|
||
fn fill_trait_set(traitt: DefId, set: &mut FxHashSet<DefId>, cx: &LateContext<'_>) {
|
||
if set.insert(traitt) {
|
||
for supertrait in rustc_trait_selection::traits::supertrait_def_ids(cx.tcx, traitt) {
|
||
fill_trait_set(supertrait, set, cx);
|
||
}
|
||
}
|
||
}
|
||
|
||
if cx.access_levels.is_exported(visited_trait.hir_id()) && trait_items.iter().any(|i| is_named_self(cx, i, "len")) {
|
||
let mut current_and_super_traits = FxHashSet::default();
|
||
fill_trait_set(visited_trait.def_id.to_def_id(), &mut current_and_super_traits, cx);
|
||
|
||
let is_empty_method_found = current_and_super_traits
|
||
.iter()
|
||
.flat_map(|&i| cx.tcx.associated_items(i).in_definition_order())
|
||
.any(|i| {
|
||
i.kind == ty::AssocKind::Fn
|
||
&& i.fn_has_self_parameter
|
||
&& i.ident.name == sym!(is_empty)
|
||
&& cx.tcx.fn_sig(i.def_id).inputs().skip_binder().len() == 1
|
||
});
|
||
|
||
if !is_empty_method_found {
|
||
span_lint(
|
||
cx,
|
||
LEN_WITHOUT_IS_EMPTY,
|
||
visited_trait.span,
|
||
&format!(
|
||
"trait `{}` has a `len` method but no (possibly inherited) `is_empty` method",
|
||
visited_trait.ident.name
|
||
),
|
||
);
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_impl_items(cx: &LateContext<'_>, item: &Item<'_>, impl_items: &[ImplItemRef<'_>]) {
|
||
fn is_named_self(cx: &LateContext<'_>, item: &ImplItemRef<'_>, name: &str) -> bool {
|
||
item.ident.name.as_str() == name
|
||
&& if let AssocItemKind::Fn { has_self } = item.kind {
|
||
has_self && {
|
||
let did = cx.tcx.hir().local_def_id(item.id.hir_id);
|
||
cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1
|
||
}
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
let is_empty = if let Some(is_empty) = impl_items.iter().find(|i| is_named_self(cx, i, "is_empty")) {
|
||
if cx.access_levels.is_exported(is_empty.id.hir_id) {
|
||
return;
|
||
}
|
||
"a private"
|
||
} else {
|
||
"no corresponding"
|
||
};
|
||
|
||
if let Some(i) = impl_items.iter().find(|i| is_named_self(cx, i, "len")) {
|
||
if cx.access_levels.is_exported(i.id.hir_id) {
|
||
let ty = cx.tcx.type_of(item.def_id);
|
||
|
||
span_lint(
|
||
cx,
|
||
LEN_WITHOUT_IS_EMPTY,
|
||
item.span,
|
||
&format!(
|
||
"item `{}` has a public `len` method but {} `is_empty` method",
|
||
ty, is_empty
|
||
),
|
||
);
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>, op: &str, compare_to: u32) {
|
||
if let (&ExprKind::MethodCall(ref method_path, _, ref args, _), &ExprKind::Lit(ref lit)) = (&method.kind, &lit.kind)
|
||
{
|
||
// check if we are in an is_empty() method
|
||
if let Some(name) = get_item_name(cx, method) {
|
||
if name.as_str() == "is_empty" {
|
||
return;
|
||
}
|
||
}
|
||
|
||
check_len(cx, span, method_path.ident.name, args, &lit.node, op, compare_to)
|
||
} else {
|
||
check_empty_expr(cx, span, method, lit, op)
|
||
}
|
||
}
|
||
|
||
fn check_len(
|
||
cx: &LateContext<'_>,
|
||
span: Span,
|
||
method_name: Symbol,
|
||
args: &[Expr<'_>],
|
||
lit: &LitKind,
|
||
op: &str,
|
||
compare_to: u32,
|
||
) {
|
||
if let LitKind::Int(lit, _) = *lit {
|
||
// check if length is compared to the specified number
|
||
if lit != u128::from(compare_to) {
|
||
return;
|
||
}
|
||
|
||
if method_name.as_str() == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) {
|
||
let mut applicability = Applicability::MachineApplicable;
|
||
span_lint_and_sugg(
|
||
cx,
|
||
LEN_ZERO,
|
||
span,
|
||
&format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }),
|
||
&format!("using `{}is_empty` is clearer and more explicit", op),
|
||
format!(
|
||
"{}{}.is_empty()",
|
||
op,
|
||
snippet_with_applicability(cx, args[0].span, "_", &mut applicability)
|
||
),
|
||
applicability,
|
||
);
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_empty_expr(cx: &LateContext<'_>, span: Span, lit1: &Expr<'_>, lit2: &Expr<'_>, op: &str) {
|
||
if (is_empty_array(lit2) || is_empty_string(lit2)) && has_is_empty(cx, lit1) {
|
||
let mut applicability = Applicability::MachineApplicable;
|
||
span_lint_and_sugg(
|
||
cx,
|
||
COMPARISON_TO_EMPTY,
|
||
span,
|
||
"comparison to empty slice",
|
||
&format!("using `{}is_empty` is clearer and more explicit", op),
|
||
format!(
|
||
"{}{}.is_empty()",
|
||
op,
|
||
snippet_with_applicability(cx, lit1.span, "_", &mut applicability)
|
||
),
|
||
applicability,
|
||
);
|
||
}
|
||
}
|
||
|
||
fn is_empty_string(expr: &Expr<'_>) -> bool {
|
||
if let ExprKind::Lit(ref lit) = expr.kind {
|
||
if let LitKind::Str(lit, _) = lit.node {
|
||
let lit = lit.as_str();
|
||
return lit == "";
|
||
}
|
||
}
|
||
false
|
||
}
|
||
|
||
fn is_empty_array(expr: &Expr<'_>) -> bool {
|
||
if let ExprKind::Array(ref arr) = expr.kind {
|
||
return arr.is_empty();
|
||
}
|
||
false
|
||
}
|
||
|
||
/// Checks if this type has an `is_empty` method.
|
||
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(ref 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,
|
||
}
|
||
}
|