Auto merge of #38313 - jseyfried:self_imports, r=nrc

resolve: clean up the semantics of `self` in an import list

Change `self` in an import list `use foo::bar::{self, ...};` to import `bar` only in the type namespace. Today, `bar` is imported in every namespace in which `foo::bar` is defined.

This is a [breaking-change], see #38293 (comment) for examples of code that would break.

Fixes #38293.
r? @nrc

src/librustc_resolve/build_reduced_graph.rs

@@ -168,6 +168,7 @@ impl<'a> Resolver<'a> {
                             target: binding,
                             source: source,
                             result: self.per_ns(|_, _| Cell::new(Err(Undetermined))),
+                            type_ns_only: false,
                         };
                         self.add_import_directive(
                             module_path, subclass, view_path.span, item.id, vis, expansion,
@@ -195,10 +196,10 @@ impl<'a> Resolver<'a> {
 
                         for source_item in source_items {
                             let node = source_item.node;
-                            let (module_path, ident, rename) = {
+                            let (module_path, ident, rename, type_ns_only) = {
                                 if node.name.name != keywords::SelfValue.name() {
                                     let rename = node.rename.unwrap_or(node.name);
-                                    (module_path.clone(), node.name, rename)
+                                    (module_path.clone(), node.name, rename, false)
                                 } else {
                                     let ident = *module_path.last().unwrap();
                                     if ident.name == keywords::CrateRoot.name() {
@@ -212,13 +213,14 @@ impl<'a> Resolver<'a> {
                                     }
                                     let module_path = module_path.split_last().unwrap().1;
                                     let rename = node.rename.unwrap_or(ident);
-                                    (module_path.to_vec(), ident, rename)
+                                    (module_path.to_vec(), ident, rename, true)
                                 }
                             };
                             let subclass = SingleImport {
                                 target: rename,
                                 source: ident,
                                 result: self.per_ns(|_, _| Cell::new(Err(Undetermined))),
+                                type_ns_only: type_ns_only,
                             };
                             let id = source_item.node.id;
                             self.add_import_directive(

src/librustc_resolve/lib.rs

@@ -894,6 +894,7 @@ enum NameBindingKind<'a> {
         binding: &'a NameBinding<'a>,
         directive: &'a ImportDirective<'a>,
         used: Cell<bool>,
+        legacy_self_import: bool,
     },
     Ambiguity {
         b1: &'a NameBinding<'a>,
@@ -1346,8 +1347,13 @@ impl<'a> Resolver<'a> {
         }
 
         match binding.kind {
-            NameBindingKind::Import { directive, binding, ref used } if !used.get() => {
+            NameBindingKind::Import { directive, binding, ref used, legacy_self_import }
+                    if !used.get() => {
                 used.set(true);
+                if legacy_self_import {
+                    self.warn_legacy_self_import(directive);
+                    return false;
+                }
                 self.used_imports.insert((directive.id, ns));
                 self.add_to_glob_map(directive.id, ident);
                 self.record_use(ident, ns, binding, span)
@@ -3112,6 +3118,12 @@ impl<'a> Resolver<'a> {
         err.emit();
         self.name_already_seen.insert(name, span);
     }
+
+    fn warn_legacy_self_import(&self, directive: &'a ImportDirective<'a>) {
+        let (id, span) = (directive.id, directive.span);
+        let msg = "`self` no longer imports values".to_string();
+        self.session.add_lint(lint::builtin::LEGACY_IMPORTS, id, span, msg);
+    }
 }
 
 fn is_struct_like(def: Def) -> bool {

src/librustc_resolve/resolve_imports.rs

@@ -41,6 +41,7 @@ pub enum ImportDirectiveSubclass<'a> {
         target: Ident,
         source: Ident,
         result: PerNS<Cell<Result<&'a NameBinding<'a>, Determinacy>>>,
+        type_ns_only: bool,
     },
     GlobImport {
         is_prelude: bool,
@@ -296,6 +297,7 @@ impl<'a> Resolver<'a> {
                 binding: binding,
                 directive: directive,
                 used: Cell::new(false),
+                legacy_self_import: false,
             },
             span: directive.span,
             vis: vis,
@@ -503,8 +505,9 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
         };
 
         directive.imported_module.set(Some(module));
-        let (source, target, result) = match directive.subclass {
-            SingleImport { source, target, ref result } => (source, target, result),
+        let (source, target, result, type_ns_only) = match directive.subclass {
+            SingleImport { source, target, ref result, type_ns_only } =>
+                (source, target, result, type_ns_only),
             GlobImport { .. } => {
                 self.resolve_glob_import(directive);
                 return true;
@@ -513,7 +516,7 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
         };
 
         let mut indeterminate = false;
-        self.per_ns(|this, ns| {
+        self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
             if let Err(Undetermined) = result[ns].get() {
                 result[ns].set(this.resolve_ident_in_module(module, source, ns, false, None));
             } else {
@@ -573,8 +576,8 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
             _ => return None,
         };
 
-        let (ident, result) = match directive.subclass {
-            SingleImport { source, ref result, .. } => (source, result),
+        let (ident, result, type_ns_only) = match directive.subclass {
+            SingleImport { source, ref result, type_ns_only, .. } => (source, result, type_ns_only),
             GlobImport { .. } if module.def_id() == directive.parent.def_id() => {
                 // Importing a module into itself is not allowed.
                 return Some("Cannot glob-import a module into itself.".to_string());
@@ -592,19 +595,36 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
         };
 
         let mut all_ns_err = true;
-        self.per_ns(|this, ns| {
+        let mut legacy_self_import = None;
+        self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
             if let Ok(binding) = result[ns].get() {
                 all_ns_err = false;
                 if this.record_use(ident, ns, binding, directive.span) {
                     this.resolution(module, ident, ns).borrow_mut().binding =
                         Some(this.dummy_binding);
                 }
             }
+        } else if let Ok(binding) = this.resolve_ident_in_module(module, ident, ns, false, None) {
+            legacy_self_import = Some(directive);
+            let binding = this.arenas.alloc_name_binding(NameBinding {
+                kind: NameBindingKind::Import {
+                    binding: binding,
+                    directive: directive,
+                    used: Cell::new(false),
+                    legacy_self_import: true,
+                },
+                ..*binding
+            });
+            let _ = this.try_define(directive.parent, ident, ns, binding);
         });
 
         if all_ns_err {
+            if let Some(directive) = legacy_self_import {
+                self.warn_legacy_self_import(directive);
+                return None;
+            }
             let mut all_ns_failed = true;
-            self.per_ns(|this, ns| {
+            self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
                 match this.resolve_ident_in_module(module, ident, ns, false, Some(span)) {
                     Ok(_) => all_ns_failed = false,
                     _ => {}

src/test/compile-fail/issue-28075.rs

@@ -18,7 +18,5 @@ extern crate lint_stability;
 
 use lint_stability::{unstable, deprecated}; //~ ERROR use of unstable library feature 'test_feature'
 
-use lint_stability::unstable::{self as u}; //~ ERROR use of unstable library feature 'test_feature'
-
 fn main() {
 }

src/test/compile-fail/issue-38293.rs

@@ -0,0 +1,33 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test that `fn foo::bar::{self}` only imports `bar` in the type namespace.
+
+#![allow(unused)]
+#![deny(legacy_imports)]
+
+mod foo {
+    pub fn f() { }
+}
+use foo::f::{self};
+//~^ ERROR `self` no longer imports values
+//~| WARN hard error
+
+mod bar {
+    pub fn baz() {}
+    pub mod baz {}
+}
+use bar::baz::{self};
+//~^ ERROR `self` no longer imports values
+//~| WARN hard error
+
+fn main() {
+    baz();
+}