Filed a proper tracking issue.

Author: kennytm

src/librustc_lint/lib.rs

@@ -276,9 +276,8 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
         },
         FutureIncompatibleInfo {
             id: LintId::of(UNSTABLE_NAME_COLLISION),
-            reference: "pr #48552 <https://github.com/rust-lang/rust/pull/48552>",
+            reference: "issue #48919 <https://github.com/rust-lang/rust/issues/48919>",
             edition: None,
-            // FIXME: create a proper tracking issue.
             // Note: this item represents future incompatibility of all unstable functions in the
             //       standard library, and thus should never be removed or changed to an error.
         },

src/test/ui/inference_unstable.stderr

@@ -6,7 +6,7 @@ LL |     assert_eq!('x'.ipu_flatten(), 1);
    |
    = note: #[warn(unstable_name_collision)] on by default
    = warning: once this method is added to the standard library, there will be ambiguity here, which will cause a hard error!
-   = note: for more information, see pr #48552 <https://github.com/rust-lang/rust/pull/48552>
+   = note: for more information, see issue #48919 <https://github.com/rust-lang/rust/issues/48919>
    = help: call with fully qualified syntax `inference_unstable_itertools::IpuItertools::ipu_flatten(...)` to keep using the current method
    = note: add #![feature(ipu_flatten)] to the crate attributes to enable `inference_unstable_iterator::IpuIterator::ipu_flatten`