Rollup merge of #145798 - compiler-errors:unnamed-lt-primary, r=lqd

Use unnamed lifetime spans as primary spans for `MISMATCHED_LIFETIME_SYNTAXES`

Fixes #145772

This PR changes the primary span(s) of the `MISMATCHED_LIFETIME_SYNTAXES` to point to the *unnamed* lifetime spans in both the inputs and *outputs* of the function signature. As reported in #145772, this should make it so that IDEs highlight the spans of the actionable part of this lint, rather than just the (possibly named) input spans like they do today.

This could be tweaked further perhaps, for example for `fn foo(_: T<'_>) -> T`, we don't need to highlight the elided lifetime if the actionable part is to change only the return type to `T<'_>`, but I think it's improvement on what's here today, so I think that should be follow-up since I think the logic might get a bit hairy.

cc ```@shepmaster```

Author: jhpratt

compiler/rustc_lint/src/lifetime_syntax.rs

@@ -214,9 +214,9 @@ impl<T> LifetimeSyntaxCategories<Vec<T>> {
         }
     }
 
-    pub fn flatten(&self) -> impl Iterator<Item = &T> {
-        let Self { hidden, elided, named } = self;
-        [hidden.iter(), elided.iter(), named.iter()].into_iter().flatten()
+    pub fn iter_unnamed(&self) -> impl Iterator<Item = &T> {
+        let Self { hidden, elided, named: _ } = self;
+        [hidden.iter(), elided.iter()].into_iter().flatten()
     }
 }
 
@@ -495,7 +495,7 @@ fn emit_mismatch_diagnostic<'tcx>(
 
     cx.emit_span_lint(
         MISMATCHED_LIFETIME_SYNTAXES,
-        inputs.flatten().copied().collect::<Vec<_>>(),
+        inputs.iter_unnamed().chain(outputs.iter_unnamed()).copied().collect::<Vec<_>>(),
         lints::MismatchedLifetimeSyntaxes { inputs, outputs, suggestions },
     );
 }

src/tools/clippy/tests/ui/ptr_arg.stderr

@@ -268,10 +268,10 @@ LL |     fn barbar(_x: &mut Vec<u32>, y: &mut String) {
    |                                     ^^^^^^^^^^^ help: change this to: `&mut str`
 
 error: eliding a lifetime that's named elsewhere is confusing
-  --> tests/ui/ptr_arg.rs:314:36
+  --> tests/ui/ptr_arg.rs:314:56
    |
 LL |     fn cow_good_ret_ty<'a>(input: &'a Cow<'a, str>) -> &str {
-   |                                    ^^     ^^           ---- the same lifetime is elided here
+   |                                    --     --           ^^^^ the same lifetime is elided here
    |                                    |      |
    |                                    |      the lifetime is named here
    |                                    the lifetime is named here

tests/ui/const-generics/type-dependent/issue-71348.full.stderr

@@ -1,8 +1,8 @@
 warning: hiding a lifetime that's named elsewhere is confusing
-  --> $DIR/issue-71348.rs:18:40
+  --> $DIR/issue-71348.rs:18:56
    |
 LL |     fn ask<'a, const N: &'static str>(&'a self) -> &'a <Self as Get<N>>::Target
-   |                                        ^^           -- ------------------------ the same lifetime is hidden here
+   |                                        --           -- ^^^^^^^^^^^^^^^^^^^^^^^^ the same lifetime is hidden here
    |                                        |            |
    |                                        |            the same lifetime is named here
    |                                        the lifetime is named here

tests/ui/impl-trait/rpit-assoc-pair-with-lifetime.stderr

@@ -1,8 +1,8 @@
 warning: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/rpit-assoc-pair-with-lifetime.rs:3:31
+  --> $DIR/rpit-assoc-pair-with-lifetime.rs:3:82
    |
 LL | pub fn iter<'a>(v: Vec<(u32, &'a u32)>) -> impl DoubleEndedIterator<Item = (u32, &u32)> {
-   |                               ^^ the lifetime is named here                      ---- the same lifetime is elided here
+   |                               -- the lifetime is named here                      ^^^^ the same lifetime is elided here
    |
    = help: the same lifetime is referred to in inconsistent ways, making the signature confusing
    = note: `#[warn(mismatched_lifetime_syntaxes)]` on by default

tests/ui/lifetimes/mismatched-lifetime-syntaxes-details/example-from-issue48686.stderr

@@ -1,8 +1,8 @@
 error: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/example-from-issue48686.rs:6:21
+  --> $DIR/example-from-issue48686.rs:6:50
    |
 LL |     pub fn get_mut(&'static self, x: &mut u8) -> &mut u8 {
-   |                     ^^^^^^^                      ------- the same lifetime is elided here
+   |                     -------                      ^^^^^^^ the same lifetime is elided here
    |                     |
    |                     the lifetime is named here
    |

tests/ui/lifetimes/mismatched-lifetime-syntaxes-details/missing-lifetime-kind.stderr

@@ -1,8 +1,8 @@
 error: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/missing-lifetime-kind.rs:3:22
+  --> $DIR/missing-lifetime-kind.rs:3:32
    |
 LL | fn ampersand<'a>(x: &'a u8) -> &u8 {
-   |                      ^^        --- the same lifetime is elided here
+   |                      --        ^^^ the same lifetime is elided here
    |                      |
    |                      the lifetime is named here
    |
@@ -18,10 +18,10 @@ LL | fn ampersand<'a>(x: &'a u8) -> &'a u8 {
    |                                 ++
 
 error: hiding a lifetime that's named elsewhere is confusing
-  --> $DIR/missing-lifetime-kind.rs:10:21
+  --> $DIR/missing-lifetime-kind.rs:10:31
    |
 LL | fn brackets<'a>(x: &'a u8) -> Brackets {
-   |                     ^^        -------- the same lifetime is hidden here
+   |                     --        ^^^^^^^^ the same lifetime is hidden here
    |                     |
    |                     the lifetime is named here
    |
@@ -32,10 +32,10 @@ LL | fn brackets<'a>(x: &'a u8) -> Brackets<'a> {
    |                                       ++++
 
 error: hiding a lifetime that's named elsewhere is confusing
-  --> $DIR/missing-lifetime-kind.rs:17:18
+  --> $DIR/missing-lifetime-kind.rs:17:28
    |
 LL | fn comma<'a>(x: &'a u8) -> Comma<u8> {
-   |                  ^^        --------- the same lifetime is hidden here
+   |                  --        ^^^^^^^^^ the same lifetime is hidden here
    |                  |
    |                  the lifetime is named here
    |
@@ -46,10 +46,10 @@ LL | fn comma<'a>(x: &'a u8) -> Comma<'a, u8> {
    |                                  +++
 
 error: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/missing-lifetime-kind.rs:22:23
+  --> $DIR/missing-lifetime-kind.rs:22:34
    |
 LL | fn underscore<'a>(x: &'a u8) -> &'_ u8 {
-   |                       ^^         -- the same lifetime is elided here
+   |                       --         ^^ the same lifetime is elided here
    |                       |
    |                       the lifetime is named here
    |

tests/ui/lifetimes/mismatched-lifetime-syntaxes-details/not-tied-to-crate.stderr

@@ -1,8 +1,8 @@
 warning: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/not-tied-to-crate.rs:8:16
+  --> $DIR/not-tied-to-crate.rs:8:31
    |
 LL |     fn bar(x: &'static u8) -> &u8 {
-   |                ^^^^^^^        --- the same lifetime is elided here
+   |                -------        ^^^ the same lifetime is elided here
    |                |
    |                the lifetime is named here
    |
@@ -18,10 +18,10 @@ LL |     fn bar(x: &'static u8) -> &'static u8 {
    |                                +++++++
 
 error: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/not-tied-to-crate.rs:14:16
+  --> $DIR/not-tied-to-crate.rs:14:31
    |
 LL |     fn baz(x: &'static u8) -> &u8 {
-   |                ^^^^^^^        --- the same lifetime is elided here
+   |                -------        ^^^ the same lifetime is elided here
    |                |
    |                the lifetime is named here
    |

tests/ui/lifetimes/mismatched-lifetime-syntaxes-details/static.stderr

@@ -1,8 +1,8 @@
 error: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/static.rs:16:18
+  --> $DIR/static.rs:16:33
    |
 LL | fn ampersand(x: &'static u8) -> &u8 {
-   |                  ^^^^^^^        --- the same lifetime is elided here
+   |                  -------        ^^^ the same lifetime is elided here
    |                  |
    |                  the lifetime is named here
    |
@@ -18,10 +18,10 @@ LL | fn ampersand(x: &'static u8) -> &'static u8 {
    |                                  +++++++
 
 error: hiding a lifetime that's named elsewhere is confusing
-  --> $DIR/static.rs:23:17
+  --> $DIR/static.rs:23:32
    |
 LL | fn brackets(x: &'static u8) -> Brackets {
-   |                 ^^^^^^^        -------- the same lifetime is hidden here
+   |                 -------        ^^^^^^^^ the same lifetime is hidden here
    |                 |
    |                 the lifetime is named here
    |
@@ -32,10 +32,10 @@ LL | fn brackets(x: &'static u8) -> Brackets<'static> {
    |                                        +++++++++
 
 error: hiding a lifetime that's named elsewhere is confusing
-  --> $DIR/static.rs:30:14
+  --> $DIR/static.rs:30:29
    |
 LL | fn comma(x: &'static u8) -> Comma<u8> {
-   |              ^^^^^^^        --------- the same lifetime is hidden here
+   |              -------        ^^^^^^^^^ the same lifetime is hidden here
    |              |
    |              the lifetime is named here
    |
@@ -46,10 +46,10 @@ LL | fn comma(x: &'static u8) -> Comma<'static, u8> {
    |                                   ++++++++
 
 error: eliding a lifetime that's named elsewhere is confusing
-  --> $DIR/static.rs:35:19
+  --> $DIR/static.rs:35:35
    |
 LL | fn underscore(x: &'static u8) -> &'_ u8 {
-   |                   ^^^^^^^         -- the same lifetime is elided here
+   |                   -------         ^^ the same lifetime is elided here
    |                   |
    |                   the lifetime is named here
    |

tests/ui/lifetimes/mismatched-lifetime-syntaxes.rs

@@ -36,8 +36,8 @@ fn explicit_bound_path_to_implicit_path<'a>(v: ContainsLifetime<'a>) -> Contains
 
 fn explicit_bound_path_to_explicit_anonymous_path<'a>(
     v: ContainsLifetime<'a>,
-    //~^ ERROR eliding a lifetime that's named elsewhere is confusing
 ) -> ContainsLifetime<'_> {
+    //~^ ERROR eliding a lifetime that's named elsewhere is confusing
     v
 }
 
@@ -188,8 +188,8 @@ mod impl_trait {
 
     fn explicit_bound_path_to_impl_trait_precise_capture<'a>(
         v: ContainsLifetime<'a>,
-        //~^ ERROR eliding a lifetime that's named elsewhere is confusing
     ) -> impl FnOnce() + use<'_> {
+        //~^ ERROR eliding a lifetime that's named elsewhere is confusing
         move || _ = v
     }
 }
@@ -208,8 +208,8 @@ mod dyn_trait {
 
     fn explicit_bound_path_to_dyn_trait_bound<'a>(
         v: ContainsLifetime<'a>,
-        //~^ ERROR hiding a lifetime that's named elsewhere is confusing
     ) -> Box<dyn Iterator<Item = ContainsLifetime> + '_> {
+        //~^ ERROR hiding a lifetime that's named elsewhere is confusing
         Box::new(iter::once(v))
     }
 }