From 1ef32e4096bb813edee300a5fa89c355959ed878 Mon Sep 17 00:00:00 2001 From: Rotem Yaari Date: Mon, 8 Oct 2018 11:43:13 +0300 Subject: [PATCH] Improve diagnostics in case of lifetime elision (closes #3284) --- clippy_lints/src/lifetimes.rs | 2 +- tests/ui/lifetimes.rs | 6 ++++++ tests/ui/lifetimes.stderr | 36 ++++++++++++++++++++--------------- 3 files changed, 28 insertions(+), 16 deletions(-) diff --git a/clippy_lints/src/lifetimes.rs b/clippy_lints/src/lifetimes.rs index d1cf0da876b..81d37404d77 100644 --- a/clippy_lints/src/lifetimes.rs +++ b/clippy_lints/src/lifetimes.rs @@ -152,7 +152,7 @@ fn check_fn_inner<'a, 'tcx>( cx, NEEDLESS_LIFETIMES, span, - "explicit lifetimes given in parameter types where they could be elided", + "explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration)", ); } report_extra_lifetimes(cx, decl, generics); diff --git a/tests/ui/lifetimes.rs b/tests/ui/lifetimes.rs index cae18498779..c7ed303b43b 100644 --- a/tests/ui/lifetimes.rs +++ b/tests/ui/lifetimes.rs @@ -170,5 +170,11 @@ fn test<'a>(x: &'a [u8]) -> u8 { *y } +// #3284 - Give a hint regarding lifetime in return type + +struct Cow<'a> { x: &'a str, } +fn out_return_type_lts<'a>(e: &'a str) -> Cow<'a> { unimplemented!() } + + fn main() { } diff --git a/tests/ui/lifetimes.stderr b/tests/ui/lifetimes.stderr index 9e4fac1e4f2..46dbf6cce09 100644 --- a/tests/ui/lifetimes.stderr +++ b/tests/ui/lifetimes.stderr @@ -1,4 +1,4 @@ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:17:1 | 17 | fn distinct_lifetimes<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: u8) { } @@ -6,37 +6,37 @@ error: explicit lifetimes given in parameter types where they could be elided | = note: `-D clippy::needless-lifetimes` implied by `-D warnings` -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:19:1 | 19 | fn distinct_and_static<'a, 'b>(_x: &'a u8, _y: &'b u8, _z: &'static u8) { } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:27:1 | 27 | fn in_and_out<'a>(x: &'a u8, _y: u8) -> &'a u8 { x } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:39:1 | 39 | fn deep_reference_3<'a>(x: &'a u8, _y: u8) -> Result<&'a u8, ()> { Ok(x) } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:42:1 | 42 | fn where_clause_without_lt<'a, T>(x: &'a u8, _y: u8) -> Result<&'a u8, ()> where T: Copy { Ok(x) } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:48:1 | 48 | fn lifetime_param_2<'a, 'b>(_x: Ref<'a>, _y: &'b u8) { } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:62:1 | 62 | / fn fn_bound_2<'a, F, I>(_m: Lt<'a, I>, _f: F) -> Lt<'a, I> @@ -44,47 +44,53 @@ error: explicit lifetimes given in parameter types where they could be elided 64 | | { unreachable!() } | |__________________^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:87:5 | 87 | fn self_and_out<'s>(&'s self) -> &'s u8 { &self.x } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:91:5 | 91 | fn distinct_self_and_in<'s, 't>(&'s self, _x: &'t u8) { } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:107:1 | 107 | fn struct_with_lt<'a>(_foo: Foo<'a>) -> &'a str { unimplemented!() } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:127:1 | 127 | fn trait_obj_elided2<'a>(_arg: &'a Drop) -> &'a str { unimplemented!() } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:131:1 | 131 | fn alias_with_lt<'a>(_foo: FooAlias<'a>) -> &'a str { unimplemented!() } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:142:1 | 142 | fn named_input_elided_output<'a>(_arg: &'a str) -> &str { unimplemented!() } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: explicit lifetimes given in parameter types where they could be elided +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) --> $DIR/lifetimes.rs:146:1 | 146 | fn trait_bound_ok<'a, T: WithLifetime<'static>>(_: &'a u8, _: T) { unimplemented!() } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -error: aborting due to 14 previous errors +error: explicit lifetimes given in parameter types where they could be elided (or replaced with `'_` if needed by type declaration) + --> $DIR/lifetimes.rs:176:1 + | +176 | fn out_return_type_lts<'a>(e: &'a str) -> Cow<'a> { unimplemented!() } + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to 15 previous errors