rust-clippy/clippy_lints/src/len_zero.rs

277 lines
9.8 KiB
Rust
Raw Normal View History

use rustc::hir::def_id::DefId;
use rustc::hir::*;
2018-08-28 11:13:42 +00:00
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
2018-07-19 07:53:23 +00:00
use rustc::{declare_lint, lint_array};
use rustc::ty;
use std::collections::HashSet;
2016-02-24 16:38:57 +00:00
use syntax::ast::{Lit, LitKind, Name};
use syntax::source_map::{Span, Spanned};
2018-05-30 08:15:50 +00:00
use crate::utils::{get_item_name, in_macro, snippet, span_lint, span_lint_and_sugg, walk_ptrs_ty};
/// **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
2017-08-12 22:14:28 +00:00
/// than calculating their length. Notably, for slices, getting the length
/// requires a subtraction whereas `.is_empty()` is just a comparison. 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.
///
/// **Known problems:** None.
///
2016-07-15 22:25:44 +00:00
/// **Example:**
/// ```rust
/// if x.len() == 0 { .. }
/// if y.len() != 0 { .. }
/// ```
/// instead use
/// ```rust
/// if x.len().is_empty() { .. }
/// if !y.len().is_empty() { .. }
2016-07-15 22:25:44 +00:00
/// ```
2018-03-28 13:24:26 +00:00
declare_clippy_lint! {
pub LEN_ZERO,
2018-03-28 13:24:26 +00:00
style,
"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` \
could be used instead"
}
/// **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:**
2016-07-15 22:25:44 +00:00
/// ```rust
/// impl X {
/// pub fn len(&self) -> usize { .. }
/// }
/// ```
2018-03-28 13:24:26 +00:00
declare_clippy_lint! {
pub LEN_WITHOUT_IS_EMPTY,
2018-03-28 13:24:26 +00:00
style,
"traits or impls with a public `len` method but no corresponding `is_empty` method"
}
2017-08-09 07:30:56 +00:00
#[derive(Copy, Clone)]
pub struct LenZero;
impl LintPass for LenZero {
fn get_lints(&self) -> LintArray {
lint_array!(LEN_ZERO, LEN_WITHOUT_IS_EMPTY)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LenZero {
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
if in_macro(item.span) {
2016-02-24 19:53:15 +00:00
return;
}
2015-08-21 18:44:48 +00:00
match item.node {
2018-07-16 13:07:39 +00:00
ItemKind::Trait(_, _, _, _, ref trait_items) => check_trait_items(cx, item, trait_items),
ItemKind::Impl(_, _, _, _, None, _, ref impl_items) => check_impl_items(cx, item, impl_items),
2016-01-04 04:26:12 +00:00
_ => (),
}
}
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if in_macro(expr.span) {
2016-02-24 19:53:15 +00:00
return;
}
2018-07-12 07:30:57 +00:00
if let ExprKind::Binary(Spanned { node: cmp, .. }, ref left, ref right) = expr.node {
match cmp {
2018-07-12 07:50:09 +00:00
BinOpKind::Eq => {
check_cmp(cx, expr.span, left, right, "", 0); // len == 0
check_cmp(cx, expr.span, right, left, "", 0); // 0 == len
},
2018-07-12 07:50:09 +00:00
BinOpKind::Ne => {
check_cmp(cx, expr.span, left, right, "!", 0); // len != 0
check_cmp(cx, expr.span, right, left, "!", 0); // 0 != len
},
2018-07-12 07:50:09 +00:00
BinOpKind::Gt => {
check_cmp(cx, expr.span, left, right, "!", 0); // len > 0
check_cmp(cx, expr.span, right, left, "", 1); // 1 > len
},
2018-07-12 07:50:09 +00:00
BinOpKind::Lt => {
check_cmp(cx, expr.span, left, right, "", 1); // len < 1
check_cmp(cx, expr.span, right, left, "!", 0); // 0 < len
},
2018-07-12 07:50:09 +00:00
BinOpKind::Ge => check_cmp(cx, expr.span, left, right, "!", 1), // len <= 1
BinOpKind::Le => check_cmp(cx, expr.span, right, left, "!", 1), // 1 >= len
2016-01-04 04:26:12 +00:00
_ => (),
}
}
}
}
2018-07-23 11:01:12 +00:00
fn check_trait_items(cx: &LateContext<'_, '_>, visited_trait: &Item, trait_items: &[TraitItemRef]) {
fn is_named_self(cx: &LateContext<'_, '_>, item: &TraitItemRef, name: &str) -> bool {
2018-06-28 13:46:58 +00:00
item.ident.name == name && if let AssociatedItemKind::Method { has_self } = item.kind {
2017-09-05 09:33:04 +00:00
has_self && {
let did = cx.tcx.hir.local_def_id(item.id.node_id);
cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1
}
2017-09-05 09:33:04 +00:00
} else {
false
}
}
// fill the set with current and super traits
2018-07-23 11:01:12 +00:00
fn fill_trait_set(traitt: DefId, set: &mut HashSet<DefId>, cx: &LateContext<'_, '_>) {
if set.insert(traitt) {
2017-09-04 15:05:47 +00:00
for supertrait in ::rustc::traits::supertrait_def_ids(cx.tcx, traitt) {
fill_trait_set(supertrait, set, cx);
}
2016-01-04 04:26:12 +00:00
}
}
2017-09-03 21:15:15 +00:00
if cx.access_levels.is_exported(visited_trait.id) && trait_items.iter().any(|i| is_named_self(cx, i, "len")) {
let mut current_and_super_traits = HashSet::new();
2017-09-04 15:05:47 +00:00
let visited_trait_def_id = cx.tcx.hir.local_def_id(visited_trait.id);
fill_trait_set(visited_trait_def_id, &mut current_and_super_traits, cx);
let is_empty_method_found = current_and_super_traits
.iter()
2017-09-04 15:05:47 +00:00
.flat_map(|&i| cx.tcx.associated_items(i))
.any(|i| {
2018-06-28 13:46:58 +00:00
i.kind == ty::AssociatedKind::Method && i.method_has_self_argument && i.ident.name == "is_empty"
2017-11-04 19:55:56 +00:00
&& cx.tcx.fn_sig(i.def_id).inputs().skip_binder().len() == 1
2017-09-04 15:05:47 +00:00
});
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.name
),
);
}
}
}
2018-07-23 11:01:12 +00:00
fn check_impl_items(cx: &LateContext<'_, '_>, item: &Item, impl_items: &[ImplItemRef]) {
fn is_named_self(cx: &LateContext<'_, '_>, item: &ImplItemRef, name: &str) -> bool {
2018-06-28 13:46:58 +00:00
item.ident.name == name && if let AssociatedItemKind::Method { has_self } = item.kind {
2017-09-05 09:33:04 +00:00
has_self && {
let did = cx.tcx.hir.local_def_id(item.id.node_id);
cx.tcx.fn_sig(did).inputs().skip_binder().len() == 1
}
2017-09-05 09:33:04 +00:00
} 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.node_id) {
return;
} else {
"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.node_id) {
2017-02-02 16:53:28 +00:00
let def_id = cx.tcx.hir.local_def_id(item.id);
2017-04-27 12:00:35 +00:00
let ty = cx.tcx.type_of(def_id);
2017-08-09 07:30:56 +00:00
span_lint(
cx,
LEN_WITHOUT_IS_EMPTY,
item.span,
&format!(
"item `{}` has a public `len` method but {} `is_empty` method",
ty, is_empty
),
2017-08-09 07:30:56 +00:00
);
}
}
}
2018-07-23 11:01:12 +00:00
fn check_cmp(cx: &LateContext<'_, '_>, span: Span, method: &Expr, lit: &Expr, op: &str, compare_to: u32) {
2018-07-12 07:30:57 +00:00
if let (&ExprKind::MethodCall(ref method_path, _, ref args), &ExprKind::Lit(ref lit)) = (&method.node, &lit.node) {
// check if we are in an is_empty() method
if let Some(name) = get_item_name(cx, method) {
if name == "is_empty" {
return;
}
2016-01-04 04:26:12 +00:00
}
2018-06-28 13:46:58 +00:00
check_len(cx, span, method_path.ident.name, args, lit, op, compare_to)
}
}
2018-07-23 11:01:12 +00:00
fn check_len(cx: &LateContext<'_, '_>, span: Span, method_name: Name, args: &[Expr], lit: &Lit, op: &str, compare_to: u32) {
2017-09-05 09:33:04 +00:00
if let Spanned {
node: LitKind::Int(lit, _),
2017-09-05 09:33:04 +00:00
..
} = *lit
{
// check if length is compared to the specified number
if lit != u128::from(compare_to) {
return;
}
if method_name == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) {
2017-08-09 07:30:56 +00:00
span_lint_and_sugg(
cx,
LEN_ZERO,
span,
&format!("length comparison to {}", if compare_to == 0 { "zero" } else { "one" }),
2017-08-09 07:30:56 +00:00
"using `is_empty` is more concise",
format!("{}{}.is_empty()", op, snippet(cx, args[0].span, "_")),
);
2016-01-04 04:26:12 +00:00
}
}
}
2016-03-19 16:48:29 +00:00
/// Check if this type has an `is_empty` method.
2018-07-23 11:01:12 +00:00
fn has_is_empty(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
/// Get an `AssociatedItem` and return true if it matches `is_empty(self)`.
2018-07-23 11:01:12 +00:00
fn is_is_empty(cx: &LateContext<'_, '_>, item: &ty::AssociatedItem) -> bool {
if let ty::AssociatedKind::Method = item.kind {
2018-06-28 13:46:58 +00:00
if item.ident.name == "is_empty" {
let sig = cx.tcx.fn_sig(item.def_id);
let ty = sig.skip_binder();
ty.inputs().len() == 1
} else {
false
}
2016-01-04 04:26:12 +00:00
} else {
false
}
}
2016-03-19 16:48:29 +00:00
/// Check the inherent impl's items for an `is_empty(self)` method.
2018-07-23 11:01:12 +00:00
fn has_is_empty_impl(cx: &LateContext<'_, '_>, id: DefId) -> bool {
2017-08-09 07:30:56 +00:00
cx.tcx.inherent_impls(id).iter().any(|imp| {
2017-09-05 09:33:04 +00:00
cx.tcx
.associated_items(*imp)
.any(|item| is_is_empty(cx, &item))
2017-08-09 07:30:56 +00:00
})
}
2017-01-13 16:04:56 +00:00
let ty = &walk_ptrs_ty(cx.tables.expr_ty(expr));
match ty.sty {
ty::Dynamic(ref tt, ..) => cx.tcx
2018-07-15 00:04:23 +00:00
.associated_items(tt.principal().expect("trait impl not found").def_id())
2017-09-05 09:33:04 +00:00
.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,
}
}