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Add missing_trait_methods lint
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Alexendoo committed Oct 17, 2022
1 parent d917590 commit 56b8e19
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -4049,6 +4049,7 @@ Released 2018-09-13
[`missing_panics_doc`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_panics_doc
[`missing_safety_doc`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_safety_doc
[`missing_spin_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_spin_loop
[`missing_trait_methods`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_trait_methods
[`mistyped_literal_suffixes`]: https://rust-lang.github.io/rust-clippy/master/index.html#mistyped_literal_suffixes
[`mixed_case_hex_literals`]: https://rust-lang.github.io/rust-clippy/master/index.html#mixed_case_hex_literals
[`mixed_read_write_in_expression`]: https://rust-lang.github.io/rust-clippy/master/index.html#mixed_read_write_in_expression
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1 change: 1 addition & 0 deletions clippy_lints/src/lib.register_lints.rs
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Expand Up @@ -407,6 +407,7 @@ store.register_lints(&[
missing_doc::MISSING_DOCS_IN_PRIVATE_ITEMS,
missing_enforced_import_rename::MISSING_ENFORCED_IMPORT_RENAMES,
missing_inline::MISSING_INLINE_IN_PUBLIC_ITEMS,
missing_trait_methods::MISSING_TRAIT_METHODS,
mixed_read_write_in_expression::DIVERGING_SUB_EXPRESSION,
mixed_read_write_in_expression::MIXED_READ_WRITE_IN_EXPRESSION,
module_style::MOD_MODULE_FILES,
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1 change: 1 addition & 0 deletions clippy_lints/src/lib.register_restriction.rs
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Expand Up @@ -47,6 +47,7 @@ store.register_group(true, "clippy::restriction", Some("clippy_restriction"), ve
LintId::of(missing_doc::MISSING_DOCS_IN_PRIVATE_ITEMS),
LintId::of(missing_enforced_import_rename::MISSING_ENFORCED_IMPORT_RENAMES),
LintId::of(missing_inline::MISSING_INLINE_IN_PUBLIC_ITEMS),
LintId::of(missing_trait_methods::MISSING_TRAIT_METHODS),
LintId::of(mixed_read_write_in_expression::MIXED_READ_WRITE_IN_EXPRESSION),
LintId::of(module_style::MOD_MODULE_FILES),
LintId::of(module_style::SELF_NAMED_MODULE_FILES),
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2 changes: 2 additions & 0 deletions clippy_lints/src/lib.rs
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Expand Up @@ -289,6 +289,7 @@ mod missing_const_for_fn;
mod missing_doc;
mod missing_enforced_import_rename;
mod missing_inline;
mod missing_trait_methods;
mod mixed_read_write_in_expression;
mod module_style;
mod multi_assignments;
Expand Down Expand Up @@ -916,6 +917,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
store.register_late_pass(|_| Box::new(box_default::BoxDefault));
store.register_late_pass(|_| Box::new(implicit_saturating_add::ImplicitSaturatingAdd));
store.register_early_pass(|| Box::new(partial_pub_fields::PartialPubFields));
store.register_late_pass(|_| Box::new(missing_trait_methods::MissingTraitMethods));
// add lints here, do not remove this comment, it's used in `new_lint`
}

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96 changes: 96 additions & 0 deletions clippy_lints/src/missing_trait_methods.rs
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@@ -0,0 +1,96 @@
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::is_lint_allowed;
use rustc_hir::def_id::DefIdMap;
use rustc_hir::{Impl, Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::AssocItem;
use rustc_session::{declare_lint_pass, declare_tool_lint};

declare_clippy_lint! {
/// ### What it does
/// Checks if a provided method is used implicitly by a trait
/// implementation. A usage example would be a wrapper where every method
/// should perform some operation before delegating to the inner type's
/// implemenation.
///
/// This lint should typically be enabled on a specific trait `impl` item
/// rather than globally.
///
/// ### Why is this bad?
/// Indicates that a method is missing.
///
/// ### Example
/// ```rust
/// trait Trait {
/// fn required();
///
/// fn provided() {}
/// }
///
/// # struct Type;
/// #[warn(clippy::missing_trait_methods)]
/// impl Trait for Type {
/// fn required() { /* ... */ }
/// }
/// ```
/// Use instead:
/// ```rust
/// trait Trait {
/// fn required();
///
/// fn provided() {}
/// }
///
/// # struct Type;
/// #[warn(clippy::missing_trait_methods)]
/// impl Trait for Type {
/// fn required() { /* ... */ }
///
/// fn provided() { /* ... */ }
/// }
/// ```
#[clippy::version = "1.66.0"]
pub MISSING_TRAIT_METHODS,
restriction,
"trait implementation uses default provided method"
}
declare_lint_pass!(MissingTraitMethods => [MISSING_TRAIT_METHODS]);

impl<'tcx> LateLintPass<'tcx> for MissingTraitMethods {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
if !is_lint_allowed(cx, MISSING_TRAIT_METHODS, item.hir_id())
&& let ItemKind::Impl(Impl {
items,
of_trait: Some(trait_ref),
..
}) = item.kind
&& let Some(trait_id) = trait_ref.trait_def_id()
{
let mut provided: DefIdMap<&AssocItem> = cx
.tcx
.provided_trait_methods(trait_id)
.map(|assoc| (assoc.def_id, assoc))
.collect();

for impl_item in *items {
if let Some(def_id) = impl_item.trait_item_def_id {
provided.remove(&def_id);
}
}

for assoc in provided.values() {
let source_map = cx.tcx.sess.source_map();
let definition_span = source_map.guess_head_span(cx.tcx.def_span(assoc.def_id));

span_lint_and_help(
cx,
MISSING_TRAIT_METHODS,
source_map.guess_head_span(item.span),
&format!("missing trait method provided by default: `{}`", assoc.name),
Some(definition_span),
"implement the method",
);
}
}
}
}
1 change: 1 addition & 0 deletions src/docs.rs
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Expand Up @@ -317,6 +317,7 @@ docs! {
"missing_panics_doc",
"missing_safety_doc",
"missing_spin_loop",
"missing_trait_methods",
"mistyped_literal_suffixes",
"mixed_case_hex_literals",
"mixed_read_write_in_expression",
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40 changes: 40 additions & 0 deletions src/docs/missing_trait_methods.txt
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@@ -0,0 +1,40 @@
### What it does
Checks if a provided method is used implicitly by a trait
implementation. A usage example would be a wrapper where every method
should perform some operation before delegating to the inner type's
implemenation.

This lint should typically be enabled on a specific trait `impl` item
rather than globally.

### Why is this bad?
Indicates that a method is missing.

### Example
```
trait Trait {
fn required();

fn provided() {}
}

#[warn(clippy::missing_trait_methods)]
impl Trait for Type {
fn required() { /* ... */ }
}
```
Use instead:
```
trait Trait {
fn required();

fn provided() {}
}

#[warn(clippy::missing_trait_methods)]
impl Trait for Type {
fn required() { /* ... */ }

fn provided() { /* ... */ }
}
```
50 changes: 50 additions & 0 deletions tests/ui/missing_trait_methods.rs
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@@ -0,0 +1,50 @@
#![allow(unused, clippy::needless_lifetimes)]
#![warn(clippy::missing_trait_methods)]

trait A {
fn provided() {}
}

trait B {
fn required();

fn a(_: usize) -> usize {
1
}

fn b<'a, T: AsRef<[u8]>>(a: &'a T) -> &'a [u8] {
a.as_ref()
}
}

struct Partial;

impl A for Partial {}

impl B for Partial {
fn required() {}

fn a(_: usize) -> usize {
2
}
}

struct Complete;

impl A for Complete {
fn provided() {}
}

impl B for Complete {
fn required() {}

fn a(_: usize) -> usize {
2
}

fn b<T: AsRef<[u8]>>(a: &T) -> &[u8] {
a.as_ref()
}
}

fn main() {}
27 changes: 27 additions & 0 deletions tests/ui/missing_trait_methods.stderr
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@@ -0,0 +1,27 @@
error: missing trait method provided by default: `provided`
--> $DIR/missing_trait_methods.rs:22:1
|
LL | impl A for Partial {}
| ^^^^^^^^^^^^^^^^^^
|
help: implement the method
--> $DIR/missing_trait_methods.rs:5:5
|
LL | fn provided() {}
| ^^^^^^^^^^^^^
= note: `-D clippy::missing-trait-methods` implied by `-D warnings`

error: missing trait method provided by default: `b`
--> $DIR/missing_trait_methods.rs:24:1
|
LL | impl B for Partial {
| ^^^^^^^^^^^^^^^^^^
|
help: implement the method
--> $DIR/missing_trait_methods.rs:15:5
|
LL | fn b<'a, T: AsRef<[u8]>>(a: &'a T) -> &'a [u8] {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 2 previous errors

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