rust/clippy_lints/src/derive.rs

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use rustc::lint::*;
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use rustc::{declare_lint, lint_array};
use rustc::ty::{self, Ty};
use rustc::hir::*;
use syntax::codemap::Span;
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use crate::utils::paths;
use crate::utils::{is_automatically_derived, is_copy, match_path, span_lint_and_then};
/// **What it does:** Checks for deriving `Hash` but implementing `PartialEq`
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/// explicitly or vice versa.
///
/// **Why is this bad?** The implementation of these traits must agree (for
/// example for use with `HashMap`) so its probably a bad idea to use a
/// default-generated `Hash` implementation with an explicitly defined
/// `PartialEq`. In particular, the following must hold for any type:
///
/// ```rust
/// k1 == k2 ⇒ hash(k1) == hash(k2)
/// ```
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// #[derive(Hash)]
/// struct Foo;
///
/// impl PartialEq for Foo {
/// ...
/// }
/// ```
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declare_clippy_lint! {
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pub DERIVE_HASH_XOR_EQ,
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correctness,
"deriving `Hash` but implementing `PartialEq` explicitly"
}
/// **What it does:** Checks for explicit `Clone` implementations for `Copy`
/// types.
///
/// **Why is this bad?** To avoid surprising behaviour, these traits should
/// agree and the behaviour of `Copy` cannot be overridden. In almost all
/// situations a `Copy` type should have a `Clone` implementation that does
/// nothing more than copy the object, which is what `#[derive(Copy, Clone)]`
/// gets you.
///
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/// **Known problems:** Bounds of generic types are sometimes wrong: https://github.com/rust-lang/rust/issues/26925
///
/// **Example:**
/// ```rust
/// #[derive(Copy)]
/// struct Foo;
///
/// impl Clone for Foo {
/// ..
/// }
/// ```
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declare_clippy_lint! {
pub EXPL_IMPL_CLONE_ON_COPY,
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pedantic,
"implementing `Clone` explicitly on `Copy` types"
}
pub struct Derive;
impl LintPass for Derive {
fn get_lints(&self) -> LintArray {
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lint_array!(EXPL_IMPL_CLONE_ON_COPY, DERIVE_HASH_XOR_EQ)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Derive {
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
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if let ItemKind::Impl(_, _, _, _, Some(ref trait_ref), _, _) = item.node {
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let ty = cx.tcx.type_of(cx.tcx.hir.local_def_id(item.id));
let is_automatically_derived = is_automatically_derived(&*item.attrs);
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check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
if !is_automatically_derived {
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check_copy_clone(cx, item, trait_ref, ty);
}
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}
}
}
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/// Implementation of the `DERIVE_HASH_XOR_EQ` lint.
fn check_hash_peq<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
span: Span,
trait_ref: &TraitRef,
ty: Ty<'tcx>,
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hash_is_automatically_derived: bool,
) {
if_chain! {
if match_path(&trait_ref.path, &paths::HASH);
if let Some(peq_trait_def_id) = cx.tcx.lang_items().eq_trait();
then {
// Look for the PartialEq implementations for `ty`
cx.tcx.for_each_relevant_impl(peq_trait_def_id, ty, |impl_id| {
let peq_is_automatically_derived = is_automatically_derived(&cx.tcx.get_attrs(impl_id));
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if peq_is_automatically_derived == hash_is_automatically_derived {
return;
}
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let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
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// Only care about `impl PartialEq<Foo> for Foo`
// For `impl PartialEq<B> for A, input_types is [A, B]
if trait_ref.substs.type_at(1) == ty {
let mess = if peq_is_automatically_derived {
"you are implementing `Hash` explicitly but have derived `PartialEq`"
} else {
"you are deriving `Hash` but have implemented `PartialEq` explicitly"
};
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span_lint_and_then(
cx, DERIVE_HASH_XOR_EQ, span,
mess,
|db| {
if let Some(node_id) = cx.tcx.hir.as_local_node_id(impl_id) {
db.span_note(
cx.tcx.hir.span(node_id),
"`PartialEq` implemented here"
);
}
});
}
});
}
}
}
/// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
fn check_copy_clone<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, item: &Item, trait_ref: &TraitRef, ty: Ty<'tcx>) {
if match_path(&trait_ref.path, &paths::CLONE_TRAIT) {
if !is_copy(cx, ty) {
return;
}
match ty.sty {
ty::TyAdt(def, _) if def.is_union() => return,
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// Some types are not Clone by default but could be cloned “by hand” if necessary
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ty::TyAdt(def, substs) => for variant in &def.variants {
for field in &variant.fields {
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if let ty::TyFnDef(..) = field.ty(cx.tcx, substs).sty {
return;
}
}
for subst in substs {
if let ty::subst::UnpackedKind::Type(subst) = subst.unpack() {
if let ty::TyParam(_) = subst.sty {
return;
}
}
}
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},
_ => (),
}
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span_lint_and_then(
cx,
EXPL_IMPL_CLONE_ON_COPY,
item.span,
"you are implementing `Clone` explicitly on a `Copy` type",
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|db| {
db.span_note(item.span, "consider deriving `Clone` or removing `Copy`");
},
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);
}
}