Account for associated consts in the "unstable assoc item name colission" lint

Fix #81663.

Author: estebank

compiler/rustc_middle/src/lint.rs

@@ -345,12 +345,12 @@ pub fn struct_lint_level<'s, 'd>(
                  it will become a hard error";
 
             let explanation = if lint_id == LintId::of(builtin::UNSTABLE_NAME_COLLISIONS) {
-                "once this method is added to the standard library, \
-                 the ambiguity may cause an error or change in behavior!"
+                "once this associated item is added to the standard library, the ambiguity may \
+                 cause an error or change in behavior!"
                     .to_owned()
             } else if lint_id == LintId::of(builtin::MUTABLE_BORROW_RESERVATION_CONFLICT) {
-                "this borrowing pattern was not meant to be accepted, \
-                 and may become a hard error in the future"
+                "this borrowing pattern was not meant to be accepted, and may become a hard error \
+                 in the future"
                     .to_owned()
             } else if let Some(edition) = future_incompatible.edition {
                 format!("{} in the {} edition!", STANDARD_MESSAGE, edition)

compiler/rustc_typeck/src/check/method/probe.rs

@@ -10,6 +10,7 @@ use crate::hir::def_id::DefId;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lrc;
+use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::Namespace;
 use rustc_infer::infer::canonical::OriginalQueryValues;
@@ -1167,7 +1168,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         //
                         // We suppress warning if we're picking the method only because it is a
                         // suggestion.
-                        self.emit_unstable_name_collision_hint(p, &unstable_candidates);
+                        self.emit_unstable_name_collision_hint(p, &unstable_candidates, self_ty);
                     }
                 }
                 return Some(pick);
@@ -1246,24 +1247,46 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         &self,
         stable_pick: &Pick<'_>,
         unstable_candidates: &[(&Candidate<'tcx>, Symbol)],
+        self_ty: Ty<'tcx>,
     ) {
         self.tcx.struct_span_lint_hir(
             lint::builtin::UNSTABLE_NAME_COLLISIONS,
             self.fcx.body_id,
             self.span,
             |lint| {
-                let mut diag = lint.build(
-                    "a method with this name may be added to the standard library in the future",
-                );
-                // FIXME: This should be a `span_suggestion` instead of `help`
-                // However `self.span` only
-                // highlights the method name, so we can't use it. Also consider reusing the code from
-                // `report_method_error()`.
-                diag.help(&format!(
-                    "call with fully qualified syntax `{}(...)` to keep using the current method",
-                    self.tcx.def_path_str(stable_pick.item.def_id),
+                let def_kind = stable_pick.item.kind.as_def_kind();
+                let mut diag = lint.build(&format!(
+                    "{} {} with this name may be added to the standard library in the future",
+                    def_kind.article(),
+                    def_kind.descr(stable_pick.item.def_id),
                 ));
-
+                match (stable_pick.item.kind, stable_pick.item.container) {
+                    (ty::AssocKind::Fn, _) => {
+                        // FIXME: This should be a `span_suggestion` instead of `help`
+                        // However `self.span` only
+                        // highlights the method name, so we can't use it. Also consider reusing
+                        // the code from `report_method_error()`.
+                        diag.help(&format!(
+                            "call with fully qualified syntax `{}(...)` to keep using the current \
+                             method",
+                            self.tcx.def_path_str(stable_pick.item.def_id),
+                        ));
+                    }
+                    (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer(def_id)) => {
+                        diag.span_suggestion(
+                            self.span,
+                            "use the fully qualified path to the associated const",
+                            format!(
+                                "<{} as {}>::{}",
+                                self_ty,
+                                self.tcx.def_path_str(def_id),
+                                stable_pick.item.ident
+                            ),
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                    _ => {}
+                }
                 if self.tcx.sess.is_nightly_build() {
                     for (candidate, feature) in unstable_candidates {
                         diag.help(&format!(

src/test/ui/inference/auxiliary/inference_unstable_iterator.rs

@@ -8,7 +8,11 @@ pub trait IpuIterator {
     fn ipu_flatten(&self) -> u32 {
         0
     }
+    #[unstable(feature = "assoc_const_ipu_iter", issue = "99999")]
+    const C: i32;
 }
 
 #[stable(feature = "ipu_iterator", since = "1.0.0")]
-impl IpuIterator for char {}
+impl IpuIterator for char {
+    const C: i32 = 42;
+}

src/test/ui/inference/auxiliary/inference_unstable_itertools.rs

@@ -2,6 +2,10 @@ pub trait IpuItertools {
     fn ipu_flatten(&self) -> u32 {
         1
     }
+
+    const C: i32;
 }
 
-impl IpuItertools for char {}
+impl IpuItertools for char {
+    const C: i32 = 1;
+}

src/test/ui/inference/inference_unstable.rs

@@ -14,6 +14,9 @@ use inference_unstable_itertools::IpuItertools;
 
 fn main() {
     assert_eq!('x'.ipu_flatten(), 1);
-    //~^ WARN a method with this name may be added to the standard library in the future
-    //~^^ WARN once this method is added to the standard library, the ambiguity may cause an error
+//~^ WARN an associated function with this name may be added to the standard library in the future
+//~| WARN once this associated item is added to the standard library, the ambiguity may cause an
+    assert_eq!(char::C, 1);
+//~^ WARN an associated constant with this name may be added to the standard library in the future
+//~| WARN once this associated item is added to the standard library, the ambiguity may cause an
 }

src/test/ui/inference/inference_unstable.stderr

@@ -1,14 +1,24 @@
-warning: a method with this name may be added to the standard library in the future
+warning: an associated function with this name may be added to the standard library in the future
   --> $DIR/inference_unstable.rs:16:20
    |
 LL |     assert_eq!('x'.ipu_flatten(), 1);
    |                    ^^^^^^^^^^^
    |
    = note: `#[warn(unstable_name_collisions)]` on by default
-   = warning: once this method is added to the standard library, the ambiguity may cause an error or change in behavior!
+   = warning: once this associated item is added to the standard library, the ambiguity may cause an error or change in behavior!
    = 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
    = help: add `#![feature(ipu_flatten)]` to the crate attributes to enable `inference_unstable_iterator::IpuIterator::ipu_flatten`
 
-warning: 1 warning emitted
+warning: an associated constant with this name may be added to the standard library in the future
+  --> $DIR/inference_unstable.rs:19:16
+   |
+LL |     assert_eq!(char::C, 1);
+   |                ^^^^^^^ help: use the fully qualified path to the associated const: `<char as IpuItertools>::C`
+   |
+   = warning: once this associated item is added to the standard library, the ambiguity may cause an error or change in behavior!
+   = note: for more information, see issue #48919 <https://github.com/rust-lang/rust/issues/48919>
+   = help: add `#![feature(assoc_const_ipu_iter)]` to the crate attributes to enable `inference_unstable_iterator::IpuIterator::C`
+
+warning: 2 warnings emitted