Rollup merge of #98184 - compiler-errors:elided-lifetime-in-impl-nll, r=cjgillot

Give name if anonymous region appears in impl signature

Fixes #98170

We probably should remove the two unwraps in [`report_general_error`](https://doc.rust-lang.org/nightly/nightly-rustc/src/rustc_borrowck/diagnostics/region_errors.rs.html#683-685), but I have no idea what to provide if those regions are missing, so I've kept those in. Let me know if I should try harder to remove those.

2 files changed, 69 insertions, 0 deletions

diff --git a/src/test/ui/nll/issue-98170.rs b/src/test/ui/nll/issue-98170.rs
new file mode 100644
index 00000000000..6bb12f52d3f
--- /dev/null
+++ b/src/test/ui/nll/issue-98170.rs
@@ -0,0 +1,25 @@
+pub struct MyStruct<'a> {
+    field: &'a [u32],
+}
+
+impl MyStruct<'_> {
+    pub fn new<'a>(field: &'a [u32]) -> MyStruct<'a> {
+        Self { field }
+        //~^ ERROR lifetime may not live long enough
+        //~| ERROR lifetime may not live long enough
+    }
+}
+
+trait Trait<'a> {
+    fn new(field: &'a [u32]) -> MyStruct<'a>;
+}
+
+impl<'a> Trait<'a> for MyStruct<'_> {
+    fn new(field: &'a [u32]) -> MyStruct<'a> {
+        Self { field }
+        //~^ ERROR lifetime may not live long enough
+        //~| ERROR lifetime may not live long enough
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/nll/issue-98170.stderr b/src/test/ui/nll/issue-98170.stderr
new file mode 100644
index 00000000000..0d17365e71b
--- /dev/null
+++ b/src/test/ui/nll/issue-98170.stderr
@@ -0,0 +1,44 @@
+error: lifetime may not live long enough
+  --> $DIR/issue-98170.rs:7:9
+   |
+LL | impl MyStruct<'_> {
+   |               -- lifetime `'1` appears in the `impl`'s self type
+LL |     pub fn new<'a>(field: &'a [u32]) -> MyStruct<'a> {
+   |                -- lifetime `'a` defined here
+LL |         Self { field }
+   |         ^^^^^^^^^^^^^^ associated function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
+
+error: lifetime may not live long enough
+  --> $DIR/issue-98170.rs:7:16
+   |
+LL | impl MyStruct<'_> {
+   |               -- lifetime `'1` appears in the `impl`'s self type
+LL |     pub fn new<'a>(field: &'a [u32]) -> MyStruct<'a> {
+   |                -- lifetime `'a` defined here
+LL |         Self { field }
+   |                ^^^^^ this usage requires that `'a` must outlive `'1`
+
+error: lifetime may not live long enough
+  --> $DIR/issue-98170.rs:19:9
+   |
+LL | impl<'a> Trait<'a> for MyStruct<'_> {
+   |      --                         -- lifetime `'1` appears in the `impl`'s self type
+   |      |
+   |      lifetime `'a` defined here
+LL |     fn new(field: &'a [u32]) -> MyStruct<'a> {
+LL |         Self { field }
+   |         ^^^^^^^^^^^^^^ associated function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
+
+error: lifetime may not live long enough
+  --> $DIR/issue-98170.rs:19:16
+   |
+LL | impl<'a> Trait<'a> for MyStruct<'_> {
+   |      --                         -- lifetime `'1` appears in the `impl`'s self type
+   |      |
+   |      lifetime `'a` defined here
+LL |     fn new(field: &'a [u32]) -> MyStruct<'a> {
+LL |         Self { field }
+   |                ^^^^^ this usage requires that `'a` must outlive `'1`
+
+error: aborting due to 4 previous errors
+