sort array trait implementation suggestions correctly

Author: cyrgani

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -27,8 +27,8 @@ use rustc_middle::ty::print::{
     with_forced_trimmed_paths,
 };
 use rustc_middle::ty::{
-    self, TraitRef, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
-    Upcast,
+    self, GenericArgKind, TraitRef, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
+    TypeVisitableExt, Upcast,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_span::{BytePos, DUMMY_SP, STDLIB_STABLE_CRATES, Span, Symbol, sym};
@@ -2316,7 +2316,19 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 cand
             })
             .collect();
-        impl_candidates.sort_by_key(|cand| (cand.similarity, cand.trait_ref.to_string()));
+        impl_candidates.sort_by_key(|cand| {
+            // When suggesting array types, sort them by the length of the array, not lexicographically (#135098)
+            let len = if let GenericArgKind::Type(ty) = cand.trait_ref.args[0].kind()
+                && let ty::Array(_, len) = ty.kind()
+            {
+                // Deprioritize suggestions for parameterized arrays.
+                len.try_to_target_usize(self.tcx).unwrap_or(u64::MAX)
+            } else {
+                0
+            };
+
+            (cand.similarity, len, cand.trait_ref.to_string())
+        });
         let mut impl_candidates: Vec<_> =
             impl_candidates.into_iter().map(|cand| cand.trait_ref).collect();
         impl_candidates.dedup();

tests/ui/consts/missing-larger-array-impl.stderr

@@ -8,11 +8,11 @@ LL |     <[X; 35] as Default>::default();
              &[T]
              &mut [T]
              [T; 0]
-             [T; 10]
-             [T; 11]
-             [T; 12]
-             [T; 13]
-             [T; 14]
+             [T; 1]
+             [T; 2]
+             [T; 3]
+             [T; 4]
+             [T; 5]
            and 27 others
 
 error: aborting due to 1 previous error

tests/ui/suggestions/issue-71394-no-from-impl.stderr

@@ -5,14 +5,14 @@ LL |     let _: &[i8] = data.into();
    |                         ^^^^ the trait `From<&[u8]>` is not implemented for `&[i8]`
    |
    = help: the following other types implement trait `From<T>`:
-             `[T; 10]` implements `From<(T, T, T, T, T, T, T, T, T, T)>`
-             `[T; 11]` implements `From<(T, T, T, T, T, T, T, T, T, T, T)>`
-             `[T; 12]` implements `From<(T, T, T, T, T, T, T, T, T, T, T, T)>`
              `[T; 1]` implements `From<(T,)>`
              `[T; 2]` implements `From<(T, T)>`
              `[T; 3]` implements `From<(T, T, T)>`
              `[T; 4]` implements `From<(T, T, T, T)>`
              `[T; 5]` implements `From<(T, T, T, T, T)>`
+             `[T; 6]` implements `From<(T, T, T, T, T, T)>`
+             `[T; 7]` implements `From<(T, T, T, T, T, T, T)>`
+             `[T; 8]` implements `From<(T, T, T, T, T, T, T, T)>`
            and 6 others
    = note: required for `&[u8]` to implement `Into<&[i8]>`