-use crate::utils::{get_item_name, snippet_with_applicability, span_lint, span_lint_and_sugg, walk_ptrs_ty};
-use rustc::ty;
+use crate::utils::{
+ get_item_name, get_parent_as_impl, is_allowed, snippet_with_applicability, span_lint, span_lint_and_sugg,
+ span_lint_and_then,
+};
+use if_chain::if_chain;
+use rustc_ast::ast::LitKind;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::Applicability;
-use rustc_hir::def_id::DefId;
-use rustc_hir::*;
+use rustc_hir::{
+ def_id::DefId, AssocItemKind, BinOpKind, Expr, ExprKind, FnRetTy, ImplItem, ImplItemKind, ImplicitSelfKind, Item,
+ ItemKind, Mutability, Node, TraitItemRef, TyKind,
+};
use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty::{self, AssocKind, FnSig};
use rustc_session::{declare_lint_pass, declare_tool_lint};
-use rustc_span::source_map::{Span, Spanned};
-use syntax::ast::{LitKind, Name};
+use rustc_span::source_map::{Span, Spanned, Symbol};
declare_clippy_lint! {
/// **What it does:** Checks for getting the length of something via `.len()`
"traits or impls with a public `len` method but no corresponding `is_empty` method"
}
-declare_lint_pass!(LenZero => [LEN_ZERO, LEN_WITHOUT_IS_EMPTY]);
+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"
+}
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LenZero {
- fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item<'_>) {
+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 {
- of_trait: None,
- items: ref impl_items,
- ..
- } => check_impl_items(cx, item, impl_items),
- _ => (),
+ if let ItemKind::Trait(_, _, _, _, ref trait_items) = item.kind {
+ check_trait_items(cx, item, trait_items);
+ }
+ }
+
+ fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
+ if_chain! {
+ if item.ident.as_str() == "len";
+ if let ImplItemKind::Fn(sig, _) = &item.kind;
+ if sig.decl.implicit_self.has_implicit_self();
+ if cx.access_levels.is_exported(item.hir_id());
+ if matches!(sig.decl.output, FnRetTy::Return(_));
+ if let Some(imp) = get_parent_as_impl(cx.tcx, item.hir_id());
+ if imp.of_trait.is_none();
+ if let TyKind::Path(ty_path) = &imp.self_ty.kind;
+ if let Some(ty_id) = cx.qpath_res(ty_path, imp.self_ty.hir_id).opt_def_id();
+ if let Some(local_id) = ty_id.as_local();
+ let ty_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_id);
+ if !is_allowed(cx, LEN_WITHOUT_IS_EMPTY, ty_hir_id);
+ then {
+ let (name, kind) = match cx.tcx.hir().find(ty_hir_id) {
+ Some(Node::ForeignItem(x)) => (x.ident.name, "extern type"),
+ Some(Node::Item(x)) => match x.kind {
+ ItemKind::Struct(..) => (x.ident.name, "struct"),
+ ItemKind::Enum(..) => (x.ident.name, "enum"),
+ ItemKind::Union(..) => (x.ident.name, "union"),
+ _ => (x.ident.name, "type"),
+ }
+ _ => return,
+ };
+ check_for_is_empty(cx, sig.span, sig.decl.implicit_self, ty_id, name, kind)
+ }
}
}
- fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if expr.span.from_expansion() {
return;
}
}
}
-fn check_trait_items(cx: &LateContext<'_, '_>, visited_trait: &Item<'_>, trait_items: &[TraitItemRef]) {
- fn is_named_self(cx: &LateContext<'_, '_>, item: &TraitItemRef, name: &str) -> bool {
+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::Method { 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
- }
+ && if let AssocItemKind::Fn { has_self } = item.kind {
+ has_self && { cx.tcx.fn_sig(item.id.def_id).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<'_, '_>) {
+ fn fill_trait_set(traitt: DefId, set: &mut FxHashSet<DefId>, cx: &LateContext<'_>) {
if set.insert(traitt) {
- for supertrait in rustc_infer::traits::supertrait_def_ids(cx.tcx, 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")) {
+ 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();
- let visited_trait_def_id = cx.tcx.hir().local_def_id(visited_trait.hir_id);
- fill_trait_set(visited_trait_def_id, &mut current_and_super_traits, cx);
+ 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::Method
- && i.method_has_self_argument
+ 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
});
}
}
-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::Method { 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
- }
+/// Checks if the given signature matches the expectations for `is_empty`
+fn check_is_empty_sig(cx: &LateContext<'_>, sig: FnSig<'_>, self_kind: ImplicitSelfKind) -> bool {
+ match &**sig.inputs_and_output {
+ [arg, res] if *res == cx.tcx.types.bool => {
+ matches!(
+ (arg.kind(), self_kind),
+ (ty::Ref(_, _, Mutability::Not), ImplicitSelfKind::ImmRef)
+ | (ty::Ref(_, _, Mutability::Mut), ImplicitSelfKind::MutRef)
+ ) || (!arg.is_ref() && matches!(self_kind, ImplicitSelfKind::Imm | ImplicitSelfKind::Mut))
+ },
+ _ => 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;
- } 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.hir_id) {
- let def_id = cx.tcx.hir().local_def_id(item.hir_id);
- let ty = cx.tcx.type_of(def_id);
+/// Checks if the given type has an `is_empty` method with the appropriate signature.
+fn check_for_is_empty(
+ cx: &LateContext<'_>,
+ span: Span,
+ self_kind: ImplicitSelfKind,
+ impl_ty: DefId,
+ item_name: Symbol,
+ item_kind: &str,
+) {
+ let is_empty = Symbol::intern("is_empty");
+ let is_empty = cx
+ .tcx
+ .inherent_impls(impl_ty)
+ .iter()
+ .flat_map(|&id| cx.tcx.associated_items(id).filter_by_name_unhygienic(is_empty))
+ .find(|item| item.kind == AssocKind::Fn);
- span_lint(
- cx,
- LEN_WITHOUT_IS_EMPTY,
- item.span,
- &format!(
- "item `{}` has a public `len` method but {} `is_empty` method",
- ty, is_empty
+ let (msg, is_empty_span, self_kind) = match is_empty {
+ None => (
+ format!(
+ "{} `{}` has a public `len` method, but no `is_empty` method",
+ item_kind,
+ item_name.as_str(),
+ ),
+ None,
+ None,
+ ),
+ Some(is_empty)
+ if !cx
+ .access_levels
+ .is_exported(cx.tcx.hir().local_def_id_to_hir_id(is_empty.def_id.expect_local())) =>
+ {
+ (
+ format!(
+ "{} `{}` has a public `len` method, but a private `is_empty` method",
+ item_kind,
+ item_name.as_str(),
),
- );
+ Some(cx.tcx.def_span(is_empty.def_id)),
+ None,
+ )
+ },
+ Some(is_empty)
+ if !(is_empty.fn_has_self_parameter
+ && check_is_empty_sig(cx, cx.tcx.fn_sig(is_empty.def_id).skip_binder(), self_kind)) =>
+ {
+ (
+ format!(
+ "{} `{}` has a public `len` method, but the `is_empty` method has an unexpected signature",
+ item_kind,
+ item_name.as_str(),
+ ),
+ Some(cx.tcx.def_span(is_empty.def_id)),
+ Some(self_kind),
+ )
+ },
+ Some(_) => return,
+ };
+
+ span_lint_and_then(cx, LEN_WITHOUT_IS_EMPTY, span, &msg, |db| {
+ if let Some(span) = is_empty_span {
+ db.span_note(span, "`is_empty` defined here");
}
- }
+ if let Some(self_kind) = self_kind {
+ db.note(&format!(
+ "expected signature: `({}self) -> bool`",
+ match self_kind {
+ ImplicitSelfKind::ImmRef => "&",
+ ImplicitSelfKind::MutRef => "&mut ",
+ _ => "",
+ }
+ ));
+ }
+ });
}
-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) {
+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" {
}
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<'_, '_>,
+ cx: &LateContext<'_>,
span: Span,
- method_name: Name,
+ method_name: Symbol,
args: &[Expr<'_>],
lit: &LitKind,
op: &str,
}
}
+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 {
+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::Method = item.kind {
+ 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();
}
/// Checks the inherent impl's items for an `is_empty(self)` method.
- fn has_is_empty_impl(cx: &LateContext<'_, '_>, id: DefId) -> bool {
+ fn has_is_empty_impl(cx: &LateContext<'_>, id: DefId) -> bool {
cx.tcx.inherent_impls(id).iter().any(|imp| {
cx.tcx
.associated_items(*imp)
})
}
- let ty = &walk_ptrs_ty(cx.tables.expr_ty(expr));
- match ty.kind {
- ty::Dynamic(ref tt, ..) => {
- if let Some(principal) = tt.principal() {
- cx.tcx
- .associated_items(principal.def_id())
- .in_definition_order()
- .any(|item| is_is_empty(cx, &item))
- } else {
- false
- }
- },
+ 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,
projects / rust.git / blobdiff