211 lines
7.1 KiB
Rust
211 lines
7.1 KiB
Rust
use rustc::lint::*;
|
||
use rustc::hir::def_id::DefId;
|
||
use rustc::ty::{self, MethodTraitItemId, ImplOrTraitItemId};
|
||
use rustc::hir::*;
|
||
use syntax::ast::{Lit, LitKind, Name};
|
||
use syntax::codemap::{Span, Spanned};
|
||
use syntax::ptr::P;
|
||
use utils::{get_item_name, in_macro, snippet, span_lint, span_lint_and_then, walk_ptrs_ty};
|
||
|
||
/// **What it does:** This lint 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 comparison.
|
||
///
|
||
/// **Known problems:** None
|
||
///
|
||
/// **Example:**
|
||
/// ```rust
|
||
/// if x.len() == 0 { .. }
|
||
/// ```
|
||
declare_lint! {
|
||
pub LEN_ZERO, Warn,
|
||
"checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` \
|
||
could be used instead"
|
||
}
|
||
|
||
/// **What it does:** This lint 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:**
|
||
/// ```rust
|
||
/// impl X {
|
||
/// fn len(&self) -> usize { .. }
|
||
/// }
|
||
/// ```
|
||
declare_lint! {
|
||
pub LEN_WITHOUT_IS_EMPTY, Warn,
|
||
"traits and impls that have `.len()` but not `.is_empty()`"
|
||
}
|
||
|
||
#[derive(Copy,Clone)]
|
||
pub struct LenZero;
|
||
|
||
impl LintPass for LenZero {
|
||
fn get_lints(&self) -> LintArray {
|
||
lint_array!(LEN_ZERO, LEN_WITHOUT_IS_EMPTY)
|
||
}
|
||
}
|
||
|
||
impl LateLintPass for LenZero {
|
||
fn check_item(&mut self, cx: &LateContext, item: &Item) {
|
||
if in_macro(cx, item.span) {
|
||
return;
|
||
}
|
||
|
||
match item.node {
|
||
ItemTrait(_, _, _, ref trait_items) => check_trait_items(cx, item, trait_items),
|
||
ItemImpl(_, _, _, None, _, ref impl_items) => check_impl_items(cx, item, impl_items),
|
||
_ => (),
|
||
}
|
||
}
|
||
|
||
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
|
||
if in_macro(cx, expr.span) {
|
||
return;
|
||
}
|
||
|
||
if let ExprBinary(Spanned { node: cmp, .. }, ref left, ref right) = expr.node {
|
||
match cmp {
|
||
BiEq => check_cmp(cx, expr.span, left, right, ""),
|
||
BiGt | BiNe => check_cmp(cx, expr.span, left, right, "!"),
|
||
_ => (),
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_trait_items(cx: &LateContext, item: &Item, trait_items: &[TraitItem]) {
|
||
fn is_named_self(item: &TraitItem, name: &str) -> bool {
|
||
item.name.as_str() == name &&
|
||
if let MethodTraitItem(ref sig, _) = item.node {
|
||
is_self_sig(sig)
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
if !trait_items.iter().any(|i| is_named_self(i, "is_empty")) {
|
||
for i in trait_items {
|
||
if is_named_self(i, "len") {
|
||
span_lint(cx,
|
||
LEN_WITHOUT_IS_EMPTY,
|
||
i.span,
|
||
&format!("trait `{}` has a `.len(_: &Self)` method, but no `.is_empty(_: &Self)` method. \
|
||
Consider adding one",
|
||
item.name));
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn check_impl_items(cx: &LateContext, item: &Item, impl_items: &[ImplItem]) {
|
||
fn is_named_self(item: &ImplItem, name: &str) -> bool {
|
||
item.name.as_str() == name &&
|
||
if let ImplItemKind::Method(ref sig, _) = item.node {
|
||
is_self_sig(sig)
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
if !impl_items.iter().any(|i| is_named_self(i, "is_empty")) {
|
||
for i in impl_items {
|
||
if is_named_self(i, "len") {
|
||
let ty = cx.tcx.node_id_to_type(item.id);
|
||
|
||
span_lint(cx,
|
||
LEN_WITHOUT_IS_EMPTY,
|
||
i.span,
|
||
&format!("item `{}` has a `.len(_: &Self)` method, but no `.is_empty(_: &Self)` method. \
|
||
Consider adding one",
|
||
ty));
|
||
return;
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn is_self_sig(sig: &MethodSig) -> bool {
|
||
if sig.decl.has_self() {
|
||
sig.decl.inputs.len() == 1
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
fn check_cmp(cx: &LateContext, span: Span, left: &Expr, right: &Expr, op: &str) {
|
||
// check if we are in an is_empty() method
|
||
if let Some(name) = get_item_name(cx, left) {
|
||
if name.as_str() == "is_empty" {
|
||
return;
|
||
}
|
||
}
|
||
match (&left.node, &right.node) {
|
||
(&ExprLit(ref lit), &ExprMethodCall(ref method, _, ref args)) |
|
||
(&ExprMethodCall(ref method, _, ref args), &ExprLit(ref lit)) => {
|
||
check_len_zero(cx, span, &method.node, args, lit, op)
|
||
}
|
||
_ => (),
|
||
}
|
||
}
|
||
|
||
fn check_len_zero(cx: &LateContext, span: Span, name: &Name, args: &[P<Expr>], lit: &Lit, op: &str) {
|
||
if let Spanned { node: LitKind::Int(0, _), .. } = *lit {
|
||
if name.as_str() == "len" && args.len() == 1 && has_is_empty(cx, &args[0]) {
|
||
span_lint_and_then(cx, LEN_ZERO, span, "length comparison to zero", |db| {
|
||
db.span_suggestion(span,
|
||
"consider using `is_empty`",
|
||
format!("{}{}.is_empty()", op, snippet(cx, args[0].span, "_")));
|
||
});
|
||
}
|
||
}
|
||
}
|
||
|
||
/// Check if this type has an `is_empty` method.
|
||
fn has_is_empty(cx: &LateContext, expr: &Expr) -> bool {
|
||
/// Get an `ImplOrTraitItem` and return true if it matches `is_empty(self)`.
|
||
fn is_is_empty(cx: &LateContext, id: &ImplOrTraitItemId) -> bool {
|
||
if let MethodTraitItemId(def_id) = *id {
|
||
if let ty::MethodTraitItem(ref method) = cx.tcx.impl_or_trait_item(def_id) {
|
||
method.name.as_str() == "is_empty" && method.fty.sig.skip_binder().inputs.len() == 1
|
||
} else {
|
||
false
|
||
}
|
||
} else {
|
||
false
|
||
}
|
||
}
|
||
|
||
/// Check the inherent impl's items for an `is_empty(self)` method.
|
||
fn has_is_empty_impl(cx: &LateContext, id: &DefId) -> bool {
|
||
let impl_items = cx.tcx.impl_items.borrow();
|
||
cx.tcx.inherent_impls.borrow().get(id).map_or(false, |ids| {
|
||
ids.iter().any(|iid| impl_items.get(iid).map_or(false, |iids| iids.iter().any(|i| is_is_empty(cx, i))))
|
||
})
|
||
}
|
||
|
||
let ty = &walk_ptrs_ty(cx.tcx.expr_ty(expr));
|
||
match ty.sty {
|
||
ty::TyTrait(_) => {
|
||
cx.tcx
|
||
.trait_item_def_ids
|
||
.borrow()
|
||
.get(&ty.ty_to_def_id().expect("trait impl not found"))
|
||
.map_or(false, |ids| ids.iter().any(|i| is_is_empty(cx, i)))
|
||
}
|
||
ty::TyProjection(_) => ty.ty_to_def_id().map_or(false, |id| has_is_empty_impl(cx, &id)),
|
||
ty::TyEnum(id, _) |
|
||
ty::TyStruct(id, _) => has_is_empty_impl(cx, &id.did),
|
||
ty::TyArray(..) | ty::TyStr => true,
|
||
_ => false,
|
||
}
|
||
}
|