Downgrade ambiguous_wide_pointer_comparisons suggestions to MaybeInco…

…rrect

It is possible to have more than one valid suggestion, which when
applied together via rustfix causes the code to no longer compile.

This is a temporary workaround; the real long term solution to these
issues is to solve <rust-lang#53934>.

compiler/rustc_lint/src/lints.rs

@@ -1543,7 +1543,7 @@ pub enum AmbiguousWidePointerComparisons<'a> {
 #[multipart_suggestion(
     lint_addr_metadata_suggestion,
     style = "verbose",
-    applicability = "machine-applicable"
+    applicability = "maybe-incorrect"
 )]
 pub struct AmbiguousWidePointerComparisonsAddrMetadataSuggestion<'a> {
     pub ne: &'a str,
@@ -1562,7 +1562,7 @@ pub enum AmbiguousWidePointerComparisonsAddrSuggestion<'a> {
     #[multipart_suggestion(
         lint_addr_suggestion,
         style = "verbose",
-        applicability = "machine-applicable"
+        applicability = "maybe-incorrect"
     )]
     AddrEq {
         ne: &'a str,
@@ -1578,7 +1578,7 @@ pub enum AmbiguousWidePointerComparisonsAddrSuggestion<'a> {
     #[multipart_suggestion(
         lint_addr_suggestion,
         style = "verbose",
-        applicability = "machine-applicable"
+        applicability = "maybe-incorrect"
     )]
     Cast {
         deref_left: &'a str,

tests/ui/lint/ambiguous_wide_pointer_comparisons_suggestions.fixed

@@ -0,0 +1,25 @@
+//@ run-rustfix
+//@ rustfix-only-machine-applicable
+//@ check-pass
+
+// See <https://github.com/rust-lang/rust/issues/121330>.
+
+use std::cmp::PartialEq;
+use std::rc::Rc;
+use std::sync::Arc;
+
+struct A;
+struct B;
+
+trait T {}
+impl T for A {}
+impl T for B {}
+
+fn main() {
+    fn cmp<T: ?Sized>(a: *mut T, b: *mut T) -> bool {
+        let _ = a == b;
+        //~^ WARN ambiguous wide pointer comparison
+
+        panic!();
+    }
+}

tests/ui/lint/ambiguous_wide_pointer_comparisons_suggestions.rs

@@ -0,0 +1,25 @@
+//@ run-rustfix
+//@ rustfix-only-machine-applicable
+//@ check-pass
+
+// See <https://github.com/rust-lang/rust/issues/121330>.
+
+use std::cmp::PartialEq;
+use std::rc::Rc;
+use std::sync::Arc;
+
+struct A;
+struct B;
+
+trait T {}
+impl T for A {}
+impl T for B {}
+
+fn main() {
+    fn cmp<T: ?Sized>(a: *mut T, b: *mut T) -> bool {
+        let _ = a == b;
+        //~^ WARN ambiguous wide pointer comparison
+
+        panic!();
+    }
+}

tests/ui/lint/ambiguous_wide_pointer_comparisons_suggestions.stderr

@@ -0,0 +1,18 @@
+warning: ambiguous wide pointer comparison, the comparison includes metadata which may not be expected
+  --> $DIR/ambiguous_wide_pointer_comparisons_suggestions.rs:20:17
+   |
+LL |         let _ = a == b;
+   |                 ^^^^^^
+   |
+   = note: `#[warn(ambiguous_wide_pointer_comparisons)]` on by default
+help: use `std::ptr::addr_eq` or untyped pointers to only compare their addresses
+   |
+LL |         let _ = std::ptr::addr_eq(a, b);
+   |                 ++++++++++++++++++ ~  +
+help: use explicit `std::ptr::eq` method to compare metadata and addresses
+   |
+LL |         let _ = std::ptr::eq(a, b);
+   |                 +++++++++++++ ~  +
+
+warning: 1 warning emitted
+