src/tools/clippy/tests/ui/elidable_lifetime_names.fixed

#![warn(clippy::elidable_lifetime_names)]
#![deny(clippy::needless_lifetimes)]

type Ref<'r> = &'r u8;

// No error; same lifetime on two params.
fn lifetime_param_1<'a>(_x: Ref<'a>, _y: &'a u8) {}

//~v ERROR: could be elided: 'a, 'b
fn lifetime_param_2(_x: Ref<'_>, _y: &u8) {}

// No error; bounded lifetime.
fn lifetime_param_3<'a, 'b: 'a>(_x: Ref<'a>, _y: &'b u8) {}

// No error; bounded lifetime.
fn lifetime_param_4<'a, 'b>(_x: Ref<'a>, _y: &'b u8)
where
    'b: 'a,
{
}

struct Lt<'a, I: 'static> {
    x: &'a I,
}

// No error; fn bound references `'a`.
fn fn_bound<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I>
where
    F: Fn(Lt<'a, I>) -> Lt<'a, I>,
{
    unreachable!()
}

//~v ERROR: could be elided: 'a
fn fn_bound_2<F, I>(_m: Lt<'_, I>, _f: F) -> Lt<'_, I>
where
    for<'x> F: Fn(Lt<'x, I>) -> Lt<'x, I>,
{
    unreachable!()
}

struct Foo<'a>(&'a u8);

//~v ERROR: could be elided: 'a
fn struct_with_lt(_foo: Foo<'_>) -> &str {
    unimplemented!()
}

// No warning; two input lifetimes (named on the reference, anonymous on `Foo`).
fn struct_with_lt2<'a>(_foo: &'a Foo) -> &'a str {
    unimplemented!()
}

// No warning; two input lifetimes (anonymous on the reference, named on `Foo`).
fn struct_with_lt3<'a>(_foo: &Foo<'a>) -> &'a str {
    unimplemented!()
}

//~v ERROR: could be elided: 'b
fn struct_with_lt4a<'a>(_foo: &'a Foo<'_>) -> &'a str {
    unimplemented!()
}

type FooAlias<'a> = Foo<'a>;

//~v ERROR: could be elided: 'a
fn alias_with_lt(_foo: FooAlias<'_>) -> &str {
    unimplemented!()
}

// No warning; two input lifetimes (named on the reference, anonymous on `FooAlias`).
fn alias_with_lt2<'a>(_foo: &'a FooAlias) -> &'a str {
    unimplemented!()
}

// No warning; two input lifetimes (anonymous on the reference, named on `FooAlias`).
fn alias_with_lt3<'a>(_foo: &FooAlias<'a>) -> &'a str {
    unimplemented!()
}

//~v ERROR: could be elided: 'b
fn alias_with_lt4a<'a>(_foo: &'a FooAlias<'_>) -> &'a str {
    unimplemented!()
}

// Issue #3284: give hint regarding lifetime in return type.
struct Cow<'a> {
    x: &'a str,
}

//~v ERROR: could be elided: 'a
fn out_return_type_lts(e: &str) -> Cow<'_> {
    unimplemented!()
}

mod issue2944 {
    trait Foo {}
    struct Bar;
    struct Baz<'a> {
        bar: &'a Bar,
    }

    //~v ERROR: could be elided: 'a
    impl Foo for Baz<'_> {}
    impl Bar {
        //~v ERROR: could be elided: 'a
        fn baz(&self) -> impl Foo + '_ {
            Baz { bar: self }
        }
    }
}

mod issue13923 {
    struct Py<'py> {
        data: &'py str,
    }

    enum Content<'t, 'py> {
        Py(Py<'py>),
        T1(&'t str),
        T2(&'t str),
    }

    enum ContentString<'t> {
        T1(&'t str),
        T2(&'t str),
    }

    impl<'t, 'py> ContentString<'t> {
        // `'py` cannot be elided
        fn map_content1(self, f: impl FnOnce(&'t str) -> &'t str) -> Content<'t, 'py> {
            match self {
                Self::T1(content) => Content::T1(f(content)),
                Self::T2(content) => Content::T2(f(content)),
            }
        }
    }

    //~v ERROR: could be elided: 'py
    impl<'t> ContentString<'t> {
        // `'py` can be elided because of `&self`
        fn map_content2(&self, f: impl FnOnce(&'t str) -> &'t str) -> Content<'t, '_> {
            match self {
                Self::T1(content) => Content::T1(f(content)),
                Self::T2(content) => Content::T2(f(content)),
            }
        }
    }

    //~v ERROR: could be elided: 'py
    impl<'t> ContentString<'t> {
        // `'py` can be elided because of `&'_ self`
        fn map_content3(&'_ self, f: impl FnOnce(&'t str) -> &'t str) -> Content<'t, '_> {
            match self {
                Self::T1(content) => Content::T1(f(content)),
                Self::T2(content) => Content::T2(f(content)),
            }
        }
    }

    impl<'t, 'py> ContentString<'t> {
        // `'py` should not be elided as the default lifetime, even if working, could be named as `'t`
        fn map_content4(self, f: impl FnOnce(&'t str) -> &'t str, o: &'t str) -> Content<'t, 'py> {
            match self {
                Self::T1(content) => Content::T1(f(content)),
                Self::T2(_) => Content::T2(o),
            }
        }
    }

    //~v ERROR: could be elided: 'py
    impl<'t> ContentString<'t> {
        // `'py` can be elided because of `&Self`
        fn map_content5(
            self: std::pin::Pin<&Self>,
            f: impl FnOnce(&'t str) -> &'t str,
            o: &'t str,
        ) -> Content<'t, '_> {
            match *self {
                Self::T1(content) => Content::T1(f(content)),
                Self::T2(_) => Content::T2(o),
            }
        }
    }

    struct Cx<'a, 'b> {
        a: &'a u32,
        b: &'b u32,
    }

    // `'c` cannot be elided because we have several input lifetimes
    fn one_explicit<'b>(x: Cx<'_, 'b>) -> &'b u32 {
        x.b
    }
}

fn issue15666_original() {
    struct UnitVariantAccess<'a, 'b, 's>(&'a &'b &'s ());

    trait Trait<'de> {}

    //~v elidable_lifetime_names
    impl<'de> Trait<'de> for UnitVariantAccess<'_, 'de, '_> {}
    //        ^^  ^^                                   ^^       ^^
}

#[allow(clippy::upper_case_acronyms)]
fn issue15666() {
    struct S1<'a>(&'a ());
    struct S2<'a, 'b>(&'a &'b ());
    struct S3<'a, 'b, 'c>(&'a &'b &'c ());

    trait T {}
    trait TA<'a> {}
    trait TB<'b> {}
    trait TC<'c> {}
    trait TAB<'a, 'b> {}
    trait TAC<'a, 'c> {}
    trait TBC<'b, 'c> {}
    trait TABC<'a, 'b, 'c> {}

    // 1 lifetime

    impl<'a> TA<'a> for S1<'a> {}

    //~v elidable_lifetime_names
    impl T for S1<'_> {}
    //   ^^

    // 2 lifetimes

    impl<'a, 'b> TAB<'a, 'b> for S2<'a, 'b> {}

    //~v elidable_lifetime_names
    impl<'a> TA<'a> for S2<'a, '_> {}
    //       ^^

    //~v elidable_lifetime_names
    impl<'b> TB<'b> for S2<'_, 'b> {}
    //   ^^

    //~v elidable_lifetime_names
    impl T for S2<'_, '_> {}
    //   ^^  ^^

    // 3 lifetimes

    impl<'a, 'b, 'c> TABC<'a, 'b, 'c> for S3<'a, 'b, 'c> {}

    //~v elidable_lifetime_names
    impl<'a, 'b> TAB<'a, 'b> for S3<'a, 'b, '_> {}
    //           ^^

    //~v elidable_lifetime_names
    impl<'a, 'c> TAC<'a, 'c> for S3<'a, '_, 'c> {}
    //       ^^

    //~v elidable_lifetime_names
    impl<'a> TA<'a> for S3<'a, '_, '_> {}
    //       ^^  ^^

    //~v elidable_lifetime_names
    impl<'b, 'c> TBC<'b, 'c> for S3<'_, 'b, 'c> {}
    //   ^^

    //~v elidable_lifetime_names
    impl<'b> TB<'b> for S3<'_, 'b, '_> {}
    //   ^^      ^^

    //~v elidable_lifetime_names
    impl<'c> TC<'c> for S3<'_, '_, 'c> {}
    //   ^^  ^^

    //~v elidable_lifetime_names
    impl T for S3<'_, '_, '_> {}
    //   ^^  ^^  ^^
}