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https://github.com/rust-lang/rust-clippy
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new lints len_zero and len_without_is_empty
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@ -23,6 +23,8 @@ Lints included in this crate:
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- `redundant_closure`: Warns on usage of eta-reducible closures like `|a| foo(a)` (which can be written as just `foo`)
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- `identity_op`: Warns on identity operations like `x + 0` or `y / 1` (which can be reduced to `x` and `y`, respectively)
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- `mut_mut`: Warns on `&mut &mut` which is either a copy'n'paste error, or shows a fundamental misunderstanding of references
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- `len_zero`: Warns on `_.len() == 0` and suggests using `_.is_empty()` (or similar comparisons with `>` or `!=`)
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- `len_without_is_empty`: Warns on traits or impls that have a `.len()` but no `.is_empty()` method
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To use, add the following lines to your Cargo.toml:
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101
src/len_zero.rs
Normal file
101
src/len_zero.rs
Normal file
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@ -0,0 +1,101 @@
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extern crate rustc_typeck as typeck;
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use syntax::ptr::P;
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use syntax::ast::*;
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use rustc::lint::{Context, LintPass, LintArray, Lint};
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use rustc::middle::ty::{self, node_id_to_type, sty, ty_ptr, ty_rptr, mt, MethodTraitItemId};
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use rustc::middle::def::{DefTy, DefStruct, DefTrait};
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use syntax::codemap::{Span, Spanned};
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declare_lint!(pub LEN_ZERO, Warn,
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"Warn on usage of double-mut refs, e.g. '&mut &mut ...'");
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declare_lint!(pub LEN_WITHOUT_IS_EMPTY, Warn,
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"Warn on traits and impls that have .len() but not .is_empty()");
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#[derive(Copy,Clone)]
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pub struct LenZero;
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impl LintPass for LenZero {
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fn get_lints(&self) -> LintArray {
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lint_array!(LEN_ZERO, LEN_WITHOUT_IS_EMPTY)
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}
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fn check_item(&mut self, cx: &Context, item: &Item) {
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match &item.node {
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&ItemTrait(_, _, _, ref trait_items) =>
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check_trait_items(cx, item, trait_items),
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&ItemImpl(_, _, _, None, _, ref impl_items) => // only non-trait
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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: &Context, expr: &Expr) {
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if let &ExprBinary(Spanned{node: cmp, ..}, ref left, ref right) =
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&expr.node {
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match cmp {
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BiEq => check_cmp(cx, expr.span, left, right, ""),
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BiGt | BiNe => check_cmp(cx, expr.span, left, right, "!"),
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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: &Context, item: &Item, trait_items: &[P<TraitItem>]) {
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fn is_named_self(item: &TraitItem, name: &str) -> bool {
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item.ident.as_str() == name && item.attrs.len() == 0
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}
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if !trait_items.iter().any(|i| is_named_self(i, "is_empty")) {
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//cx.span_lint(LEN_WITHOUT_IS_EMPTY, item.span, &format!("trait {}", item.ident.as_str()));
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for i in trait_items {
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if is_named_self(i, "len") {
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cx.span_lint(LEN_WITHOUT_IS_EMPTY, i.span,
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&format!("Trait '{}' has a '.len()' method, but no \
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'.is_empty()' method. Consider adding one.",
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item.ident.as_str()));
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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: &Context, item: &Item, impl_items: &[P<ImplItem>]) {
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fn is_named_self(item: &ImplItem, name: &str) -> bool {
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item.ident.as_str() == name && item.attrs.len() == 0
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}
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if !impl_items.iter().any(|i| is_named_self(i, "is_empty")) {
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for i in impl_items {
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if is_named_self(i, "len") {
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cx.span_lint(LEN_WITHOUT_IS_EMPTY, i.span,
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&format!("Item '{}' has a '.len()' method, but no \
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'.is_empty()' method. Consider adding one.",
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item.ident.as_str()));
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return;
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}
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}
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}
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}
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fn check_cmp(cx: &Context, span: Span, left: &Expr, right: &Expr, empty: &str) {
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match (&left.node, &right.node) {
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(&ExprLit(ref lit), &ExprMethodCall(ref method, _, ref args)) =>
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check_len_zero(cx, span, method, args, lit, empty),
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(&ExprMethodCall(ref method, _, ref args), &ExprLit(ref lit)) =>
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check_len_zero(cx, span, method, args, lit, empty),
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_ => ()
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}
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}
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fn check_len_zero(cx: &Context, span: Span, method: &SpannedIdent,
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args: &[P<Expr>], lit: &Lit, empty: &str) {
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if let &Spanned{node: LitInt(0, _), ..} = lit {
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if method.node.as_str() == "len" && args.len() == 1 {
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cx.span_lint(LEN_ZERO, span, &format!(
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"Consider replacing the len comparison with '{}_.is_empty()' if available",
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empty))
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}
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}
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}
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@ -24,6 +24,7 @@ pub mod approx_const;
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pub mod eta_reduction;
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pub mod identity_op;
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pub mod mut_mut;
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pub mod len_zero;
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#[plugin_registrar]
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pub fn plugin_registrar(reg: &mut Registry) {
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@ -42,6 +43,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
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reg.register_lint_pass(box eta_reduction::EtaPass as LintPassObject);
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reg.register_lint_pass(box identity_op::IdentityOp as LintPassObject);
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reg.register_lint_pass(box mut_mut::MutMut as LintPassObject);
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reg.register_lint_pass(box len_zero::LenZero as LintPassObject);
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reg.register_lint_group("clippy", vec![types::BOX_VEC, types::LINKEDLIST,
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misc::SINGLE_MATCH, misc::STR_TO_STRING,
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@ -56,5 +58,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
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eta_reduction::REDUNDANT_CLOSURE,
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identity_op::IDENTITY_OP,
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mut_mut::MUT_MUT,
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len_zero::LEN_ZERO,
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len_zero::LEN_WITHOUT_IS_EMPTY,
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]);
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}
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56
tests/compile-fail/len_zero.rs
Normal file
56
tests/compile-fail/len_zero.rs
Normal file
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@ -0,0 +1,56 @@
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#![feature(plugin)]
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#![plugin(clippy)]
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struct One;
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#[deny(len_without_is_empty)]
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impl One {
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fn len(self: &Self) -> isize { //~ERROR
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1
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}
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}
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#[deny(len_without_is_empty)]
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trait TraitsToo {
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fn len(self: &Self) -> isize; //~ERROR
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}
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impl TraitsToo for One {
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fn len(self: &Self) -> isize {
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0
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}
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}
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#[allow(dead_code)]
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struct HasIsEmpty;
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#[deny(len_without_is_empty)]
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#[allow(dead_code)]
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impl HasIsEmpty {
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fn len(self: &Self) -> isize {
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1
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}
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fn is_empty() -> bool {
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false
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}
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}
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#[deny(len_zero)]
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fn main() {
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let x = [1, 2];
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if x.len() == 0 { //~ERROR
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println!("This should not happen!");
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}
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let y = One;
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// false positives here
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if y.len() == 0 { //~ERROR
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println!("This should not happen either!");
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}
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let z : &TraitsToo = &y;
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if z.len() > 0 { //~ERROR
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println!("Nor should this!");
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}
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}
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