fix behavior for empty impls

Author: lcnr

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

@@ -282,11 +282,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // found when exploring `all_traits`, but we also need them to be acurate on
                     // our suggestions (#47759).
                     let found_assoc = |ty: Ty<'tcx>| {
-                        simplify_type(tcx, ty, TreatParams::AsPlaceholders).and_then(|simp| {
-                            tcx.incoherent_impls(simp)
-                            .iter()
-                            .find_map(|&id| self.associated_value(id, item_name))
-                        }).is_some()
+                        simplify_type(tcx, ty, TreatParams::AsPlaceholders)
+                            .and_then(|simp| {
+                                tcx.incoherent_impls(simp)
+                                    .iter()
+                                    .find_map(|&id| self.associated_value(id, item_name))
+                            })
+                            .is_some()
                     };
                     let found_candidate = candidates.next().is_some()
                         || found_assoc(tcx.types.i8)

compiler/rustc_typeck/src/coherence/inherent_impls.rs

@@ -7,7 +7,7 @@
 //! `tcx.inherent_impls(def_id)`). That value, however,
 //! is computed by selecting an idea from this table.
 
-use rustc_errors::{pluralize, struct_span_err};
+use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
@@ -151,24 +151,33 @@ impl<'tcx> InherentCollect<'tcx> {
         const ADD_ATTR: &str =
             "alternatively add `#[rustc_allow_incoherent_impl]` to the relevant impl items";
         if !self.tcx.hir().rustc_coherence_is_core() {
-            for item in items {
-                if !self.tcx.has_attr(item.id.def_id.to_def_id(), sym::rustc_allow_incoherent_impl)
-                {
-                    let mut err = struct_span_err!(
-                        self.tcx.sess,
-                        span,
-                        E0390,
-                        "cannot define inherent `impl` for primitive types",
-                    );
-
-                    if self.tcx.features().rustc_attrs {
-                        err.help(INTO_CORE).span_help(item.span, ADD_ATTR);
-                    } else {
-                        err.help("consider using a trait instead");
+            if self.tcx.features().rustc_attrs {
+                for item in items {
+                    if !self
+                        .tcx
+                        .has_attr(item.id.def_id.to_def_id(), sym::rustc_allow_incoherent_impl)
+                    {
+                        struct_span_err!(
+                            self.tcx.sess,
+                            span,
+                            E0390,
+                            "cannot define inherent `impl` for primitive types outside of `core`",
+                        )
+                        .help(INTO_CORE)
+                        .span_help(item.span, ADD_ATTR)
+                        .emit();
+                        return;
                     }
-                    err.emit();
-                    return;
                 }
+            } else {
+                struct_span_err!(
+                    self.tcx.sess,
+                    span,
+                    E0390,
+                    "cannot define inherent `impl` for primitive types",
+                )
+                .help("consider using an extension trait instead")
+                .emit();
             }
         }
 

src/test/ui/error-codes/E0390.stderr

@@ -4,7 +4,7 @@ error[E0390]: cannot define inherent `impl` for primitive types
 LL | impl *mut Foo {}
    |      ^^^^^^^^
    |
-   = help: consider using a trait instead
+   = help: consider using an extension trait instead
 
 error: aborting due to previous error
 

src/test/ui/kinds-of-primitive-impl.stderr

@@ -4,23 +4,23 @@ error[E0390]: cannot define inherent `impl` for primitive types
 LL | impl u8 {
    |      ^^
    |
-   = help: consider using a trait instead
+   = help: consider using an extension trait instead
 
 error[E0390]: cannot define inherent `impl` for primitive types
   --> $DIR/kinds-of-primitive-impl.rs:6:6
    |
 LL | impl str {
    |      ^^^
    |
-   = help: consider using a trait instead
+   = help: consider using an extension trait instead
 
 error[E0390]: cannot define inherent `impl` for primitive types
   --> $DIR/kinds-of-primitive-impl.rs:12:6
    |
 LL | impl char {
    |      ^^^^
    |
-   = help: consider using a trait instead
+   = help: consider using an extension trait instead
 
 error: aborting due to 3 previous errors