Taint resolution if there were multiple items of the same name

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -8,7 +8,7 @@
 use crate::def_collector::collect_definitions;
 use crate::imports::{ImportData, ImportKind};
 use crate::macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};
-use crate::Namespace::{self, MacroNS, TypeNS, ValueNS};
+use crate::Namespace::{MacroNS, TypeNS, ValueNS};
 use crate::{errors, BindingKey, MacroData, NameBindingData};
 use crate::{Determinacy, ExternPreludeEntry, Finalize, Module, ModuleKind, ModuleOrUniformRoot};
 use crate::{NameBinding, NameBindingKind, ParentScope, PathResult, PerNS, ResolutionError};
@@ -63,19 +63,6 @@ impl<'a, Id: Into<DefId>> ToNameBinding<'a> for (Res, ty::Visibility<Id>, Span,
 }
 
 impl<'a, 'tcx> Resolver<'a, 'tcx> {
-    /// Defines `name` in namespace `ns` of module `parent` to be `def` if it is not yet defined;
-    /// otherwise, reports an error.
-    pub(crate) fn define<T>(&mut self, parent: Module<'a>, ident: Ident, ns: Namespace, def: T)
-    where
-        T: ToNameBinding<'a>,
-    {
-        let binding = def.to_name_binding(self.arenas);
-        let key = self.new_disambiguated_key(ident, ns);
-        if let Err(old_binding) = self.try_define(parent, key, binding, false) {
-            self.report_conflict(parent, ident, ns, old_binding, binding);
-        }
-    }
-
     /// Walks up the tree of definitions starting at `def_id`,
     /// stopping at the first encountered module.
     /// Parent block modules for arbitrary def-ids are not recorded for the local crate,

compiler/rustc_resolve/src/imports.rs

@@ -8,17 +8,17 @@ use crate::errors::{
     ItemsInTraitsAreNotImportable,
 };
 use crate::Determinacy::{self, *};
-use crate::Namespace::*;
 use crate::{module_to_string, names_to_string, ImportSuggestion};
 use crate::{AmbiguityKind, BindingKey, ModuleKind, ResolutionError, Resolver, Segment};
 use crate::{Finalize, Module, ModuleOrUniformRoot, ParentScope, PerNS, ScopeSet};
 use crate::{NameBinding, NameBindingData, NameBindingKind, PathResult};
+use crate::{Namespace::*, ToNameBinding};
 
 use rustc_ast::NodeId;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::intern::Interned;
 use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, MultiSpan};
-use rustc_hir::def::{self, DefKind, PartialRes};
+use rustc_hir::def::{self, DefKind, Namespace, PartialRes};
 use rustc_middle::metadata::ModChild;
 use rustc_middle::metadata::Reexport;
 use rustc_middle::span_bug;
@@ -295,6 +295,27 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         })
     }
 
+    /// Defines `name` in namespace `ns` of module `parent` to be `def` if it is not yet defined;
+    /// otherwise, reports an error.
+    pub(crate) fn define<T>(&mut self, parent: Module<'a>, ident: Ident, ns: Namespace, def: T)
+    where
+        T: ToNameBinding<'a>,
+    {
+        let binding = def.to_name_binding(self.arenas);
+        let key = self.new_disambiguated_key(ident, ns);
+        if let Err(old_binding) = self.try_define(parent, key, binding, false) {
+            self.update_resolution(parent, key, false, |this, resolution| {
+                if let NameBindingKind::Res(_) = binding.kind {
+                    resolution.binding = Some(this.arenas.alloc_name_binding(NameBindingData {
+                        kind: NameBindingKind::Res(Res::Err),
+                        ..(*binding).clone()
+                    }));
+                }
+            });
+            self.report_conflict(parent, ident, ns, old_binding, binding);
+        }
+    }
+
     /// Define the name or return the existing binding if there is a collision.
     /// `update` indicates if the definition is a redefinition of an existing binding.
     pub(crate) fn try_define(

tests/ui/issues/issue-28472.stderr

@@ -13,9 +13,10 @@ LL | |   fn foo();
 error[E0428]: the name `foo` is defined multiple times
   --> $DIR/issue-28472.rs:9:3
    |
-LL |     fn foo();
-   |     --------- previous definition of the value `foo` here
-...
+LL | /   pub
+LL | |   fn foo();
+   | |___________- previous definition of the value `foo` here
+LL |
 LL | /   pub
 LL | |   static mut foo: u32;
    | |______________________^ `foo` redefined here

tests/ui/resolve/multiple_definitions_attribute_merging.rs

@@ -0,0 +1,13 @@
+//! This test used to ICE because the `repr(packed)` attributes
+//! ended up on the `Dealigned` struct's attribute list, but the
+//! derive didn't see that.
+
+#[repr(packed)]
+struct Dealigned<T>(u8, T);
+
+#[derive(PartialEq)]
+#[repr(C)]
+struct Dealigned<T>(u8, T);
+//~^ ERROR: `Dealigned` is defined multiple times
+
+fn main() {}

tests/ui/resolve/multiple_definitions_attribute_merging.stderr

@@ -0,0 +1,14 @@
+error[E0428]: the name `Dealigned` is defined multiple times
+  --> $DIR/multiple_definitions_attribute_merging.rs:10:1
+   |
+LL | struct Dealigned<T>(u8, T);
+   | --------------------------- previous definition of the type `Dealigned` here
+...
+LL | struct Dealigned<T>(u8, T);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Dealigned` redefined here
+   |
+   = note: `Dealigned` must be defined only once in the type namespace of this module
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0428`.

tests/ui/traits/issue-106072.rs

@@ -1,6 +1,4 @@
-#[derive(Clone)] //~  trait objects must include the `dyn` keyword
-//~^ ERROR: the size for values of type `(dyn Foo + 'static)` cannot be known
-//~| ERROR: return type cannot have an unboxed trait object
+#[derive(Clone)]
 struct Foo;
 trait Foo {} //~ the name `Foo` is defined multiple times
 fn main() {}

tests/ui/traits/issue-106072.stderr

@@ -1,5 +1,5 @@
 error[E0428]: the name `Foo` is defined multiple times
-  --> $DIR/issue-106072.rs:5:1
+  --> $DIR/issue-106072.rs:3:1
    |
 LL | struct Foo;
    | ----------- previous definition of the type `Foo` here
@@ -8,34 +8,6 @@ LL | trait Foo {}
    |
    = note: `Foo` must be defined only once in the type namespace of this module
 
-error[E0277]: the size for values of type `(dyn Foo + 'static)` cannot be known at compilation time
-  --> $DIR/issue-106072.rs:1:10
-   |
-LL | #[derive(Clone)]
-   |          ^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `(dyn Foo + 'static)`
-note: required by a bound in `Clone`
-  --> $SRC_DIR/core/src/clone.rs:LL:COL
-   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error[E0746]: return type cannot have an unboxed trait object
-  --> $DIR/issue-106072.rs:1:10
-   |
-LL | #[derive(Clone)]
-   |          ^^^^^ doesn't have a size known at compile-time
-   |
-   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error[E0782]: trait objects must include the `dyn` keyword
-  --> $DIR/issue-106072.rs:1:10
-   |
-LL | #[derive(Clone)]
-   |          ^^^^^
-   |
-   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: aborting due to 4 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0277, E0428, E0746, E0782.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0428`.