resolve: Avoid "self-confirming" resolutions in import validation

src/librustc_resolve/build_reduced_graph.rs

@@ -230,13 +230,18 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                 }
 
                 let subclass = SingleImport {
-                    target: ident,
                     source: source.ident,
-                    result: PerNS {
+                    target: ident,
+                    source_bindings: PerNS {
                         type_ns: Cell::new(Err(Undetermined)),
                         value_ns: Cell::new(Err(Undetermined)),
                         macro_ns: Cell::new(Err(Undetermined)),
                     },
+                    target_bindings: PerNS {
+                        type_ns: Cell::new(None),
+                        value_ns: Cell::new(None),
+                        macro_ns: Cell::new(None),
+                    },
                     type_ns_only,
                 };
                 self.add_import_directive(

src/librustc_resolve/lib.rs

@@ -1521,6 +1521,7 @@ pub struct Resolver<'a, 'b: 'a> {
 
     /// FIXME: Refactor things so that this is passed through arguments and not resolver.
     last_import_segment: bool,
+    blacklisted_binding: Option<&'a NameBinding<'a>>,
 
     /// The idents for the primitive types.
     primitive_type_table: PrimitiveTypeTable,
@@ -1871,6 +1872,7 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             current_self_type: None,
             current_self_item: None,
             last_import_segment: false,
+            blacklisted_binding: None,
 
             primitive_type_table: PrimitiveTypeTable::new(),
 

src/librustc_resolve/macros.rs

@@ -977,12 +977,14 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                 let what = self.binding_description(binding, ident,
                                                     flags.contains(Flags::MISC_FROM_PRELUDE));
                 let note_msg = format!("this import refers to {what}", what = what);
-                if binding.span.is_dummy() {
+                let label_span = if binding.span.is_dummy() {
                     err.note(&note_msg);
+                    ident.span
                 } else {
                     err.span_note(binding.span, &note_msg);
-                    err.span_label(binding.span, "not an extern crate passed with `--extern`");
-                }
+                    binding.span
+                };
+                err.span_label(label_span, "not an extern crate passed with `--extern`");
                 err.emit();
             }
 

src/librustc_resolve/resolve_imports.rs

@@ -42,9 +42,10 @@ use std::{mem, ptr};
 #[derive(Clone, Debug)]
 pub enum ImportDirectiveSubclass<'a> {
     SingleImport {
-        target: Ident,
         source: Ident,
-        result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
+        target: Ident,
+        source_bindings: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
+        target_bindings: PerNS<Cell<Option<&'a NameBinding<'a>>>>,
         type_ns_only: bool,
     },
     GlobImport {
@@ -227,6 +228,11 @@ impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
         }
 
         let check_usable = |this: &mut Self, binding: &'a NameBinding<'a>| {
+            if let Some(blacklisted_binding) = this.blacklisted_binding {
+                if ptr::eq(binding, blacklisted_binding) {
+                    return Err((Determined, Weak::No));
+                }
+            }
             // `extern crate` are always usable for backwards compatibility, see issue #37020,
             // remove this together with `PUB_USE_OF_PRIVATE_EXTERN_CRATE`.
             let usable = this.is_accessible(binding.vis) || binding.is_extern_crate();
@@ -642,10 +648,10 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
             if let Some((span, err, note)) = self.finalize_import(import) {
                 errors = true;
 
-                if let SingleImport { source, ref result, .. } = import.subclass {
+                if let SingleImport { source, ref source_bindings, .. } = import.subclass {
                     if source.name == "self" {
                         // Silence `unresolved import` error if E0429 is already emitted
-                        if let Err(Determined) = result.value_ns.get() {
+                        if let Err(Determined) = source_bindings.value_ns.get() {
                             continue;
                         }
                     }
@@ -765,9 +771,11 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         };
 
         directive.imported_module.set(Some(module));
-        let (source, target, result, type_ns_only) = match directive.subclass {
-            SingleImport { source, target, ref result, type_ns_only } =>
-                (source, target, result, type_ns_only),
+        let (source, target, source_bindings, target_bindings, type_ns_only) =
+                match directive.subclass {
+            SingleImport { source, target, ref source_bindings,
+                           ref target_bindings, type_ns_only } =>
+                (source, target, source_bindings, target_bindings, type_ns_only),
             GlobImport { .. } => {
                 self.resolve_glob_import(directive);
                 return true;
@@ -777,7 +785,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
 
         let mut indeterminate = false;
         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
-            if let Err(Undetermined) = result[ns].get() {
+            if let Err(Undetermined) = source_bindings[ns].get() {
                 // For better failure detection, pretend that the import will
                 // not define any names while resolving its module path.
                 let orig_vis = directive.vis.replace(ty::Visibility::Invisible);
@@ -786,13 +794,13 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
                 );
                 directive.vis.set(orig_vis);
 
-                result[ns].set(binding);
+                source_bindings[ns].set(binding);
             } else {
                 return
             };
 
             let parent = directive.parent_scope.module;
-            match result[ns].get() {
+            match source_bindings[ns].get() {
                 Err(Undetermined) => indeterminate = true,
                 Err(Determined) => {
                     this.update_resolution(parent, target, ns, |_, resolution| {
@@ -810,6 +818,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
                 }
                 Ok(binding) => {
                     let imported_binding = this.import(binding, directive);
+                    target_bindings[ns].set(Some(imported_binding));
                     let conflict = this.try_define(parent, target, ns, imported_binding);
                     if let Err(old_binding) = conflict {
                         this.report_conflict(parent, target, ns, imported_binding, old_binding);
@@ -879,8 +888,9 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
             PathResult::Indeterminate | PathResult::NonModule(..) => unreachable!(),
         };
 
-        let (ident, result, type_ns_only) = match directive.subclass {
-            SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
+        let (ident, source_bindings, target_bindings, type_ns_only) = match directive.subclass {
+            SingleImport { source, ref source_bindings, ref target_bindings, type_ns_only, .. } =>
+                (source, source_bindings, target_bindings, type_ns_only),
             GlobImport { is_prelude, ref max_vis } => {
                 if directive.module_path.len() <= 1 {
                     // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
@@ -919,17 +929,20 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         let mut all_ns_err = true;
         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
             let orig_vis = directive.vis.replace(ty::Visibility::Invisible);
+            let orig_blacklisted_binding =
+                mem::replace(&mut this.blacklisted_binding, target_bindings[ns].get());
             let orig_last_import_segment = mem::replace(&mut this.last_import_segment, true);
             let binding = this.resolve_ident_in_module(
                 module, ident, ns, Some(&directive.parent_scope), true, directive.span
             );
             this.last_import_segment = orig_last_import_segment;
+            this.blacklisted_binding = orig_blacklisted_binding;
             directive.vis.set(orig_vis);
 
             match binding {
                 Ok(binding) => {
                     // Consistency checks, analogous to `finalize_current_module_macro_resolutions`.
-                    let initial_def = result[ns].get().map(|initial_binding| {
+                    let initial_def = source_bindings[ns].get().map(|initial_binding| {
                         all_ns_err = false;
                         this.record_use(ident, ns, initial_binding,
                                         directive.module_path.is_empty());
@@ -1034,7 +1047,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         let mut reexport_error = None;
         let mut any_successful_reexport = false;
         self.per_ns(|this, ns| {
-            if let Ok(binding) = result[ns].get() {
+            if let Ok(binding) = source_bindings[ns].get() {
                 let vis = directive.vis.get();
                 if !binding.pseudo_vis().is_at_least(vis, &*this) {
                     reexport_error = Some((ns, binding));
@@ -1078,7 +1091,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
             let mut full_path = directive.module_path.clone();
             full_path.push(Segment::from_ident(ident));
             self.per_ns(|this, ns| {
-                if let Ok(binding) = result[ns].get() {
+                if let Ok(binding) = source_bindings[ns].get() {
                     this.lint_if_path_starts_with_module(
                         directive.crate_lint(),
                         &full_path,
@@ -1092,7 +1105,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
         // Record what this import resolves to for later uses in documentation,
         // this may resolve to either a value or a type, but for documentation
         // purposes it's good enough to just favor one over the other.
-        self.per_ns(|this, ns| if let Some(binding) = result[ns].get().ok() {
+        self.per_ns(|this, ns| if let Some(binding) = source_bindings[ns].get().ok() {
             let mut def = binding.def();
             if let Def::Macro(def_id, _) = def {
                 // `DefId`s from the "built-in macro crate" should not leak from resolve because

src/test/ui/feature-gates/feature-gate-uniform-paths.stderr

@@ -25,11 +25,7 @@ LL | use inline; //~ ERROR imports can only refer to extern crate names
    |     ^^^^^^ not an extern crate passed with `--extern`
    |
    = help: add #![feature(uniform_paths)] to the crate attributes to enable
-note: this import refers to the built-in attribute imported here
-  --> $DIR/feature-gate-uniform-paths.rs:21:5
-   |
-LL | use inline; //~ ERROR imports can only refer to extern crate names
-   |     ^^^^^^
+   = note: this import refers to a built-in attribute
 
 error[E0658]: imports can only refer to extern crate names passed with `--extern` on stable channel (see issue #53130)
   --> $DIR/feature-gate-uniform-paths.rs:23:5
@@ -38,11 +34,7 @@ LL | use Vec; //~ ERROR imports can only refer to extern crate names
    |     ^^^ not an extern crate passed with `--extern`
    |
    = help: add #![feature(uniform_paths)] to the crate attributes to enable
-note: this import refers to the struct imported here
-  --> $DIR/feature-gate-uniform-paths.rs:23:5
-   |
-LL | use Vec; //~ ERROR imports can only refer to extern crate names
-   |     ^^^
+   = note: this import refers to a struct from prelude
 
 error[E0658]: imports can only refer to extern crate names passed with `--extern` on stable channel (see issue #53130)
   --> $DIR/feature-gate-uniform-paths.rs:25:5
@@ -51,11 +43,7 @@ LL | use vec; //~ ERROR imports can only refer to extern crate names
    |     ^^^ not an extern crate passed with `--extern`
    |
    = help: add #![feature(uniform_paths)] to the crate attributes to enable
-note: this import refers to the macro imported here
-  --> $DIR/feature-gate-uniform-paths.rs:25:5
-   |
-LL | use vec; //~ ERROR imports can only refer to extern crate names
-   |     ^^^
+   = note: this import refers to a macro from prelude
 
 error: aborting due to 4 previous errors