Auto merge of #56759 - petrochenkov:prestabuni, r=nikomatsakis

Stabilize `uniform_paths`

Address all the things described in #56417.

Assign visibilities to `macro_rules` items - `pub` to `macro_export`-ed macros and `pub(crate)` to non-exported macros, these visibilities determine how far these macros can be reexported with `use`.

Prohibit use of reexported inert attributes and "tool modules", after renaming (e.g. `use inline as imported_inline`) their respective tools and even compiler passes won't be able to recognize and properly check them.

Also turn use of uniform paths in 2015 macros into an error, I'd prefer to neither remove nor stabilize them right away because I still want to make some experiments in this area (uniform path fallback was added to 2015 macros used on 2018 edition in #56053 (comment)).

UPDATE: The last commit also stabilizes the feature `uniform_paths`.

Closes #53130
Closes #55618
Closes #56326
Closes #56398
Closes #56417
Closes #56821
Closes #57252
Closes #57422

src/librustc/hir/def.rs

@@ -240,7 +240,7 @@ impl CtorKind {
 }
 
 impl NonMacroAttrKind {
-    fn descr(self) -> &'static str {
+    pub fn descr(self) -> &'static str {
         match self {
             NonMacroAttrKind::Builtin => "built-in attribute",
             NonMacroAttrKind::Tool => "tool attribute",

src/librustc_resolve/lib.rs

@@ -67,7 +67,7 @@ use syntax_pos::{Span, DUMMY_SP, MultiSpan};
 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
 
 use std::cell::{Cell, RefCell};
-use std::{cmp, fmt, iter, ptr};
+use std::{cmp, fmt, iter, mem, ptr};
 use std::collections::BTreeSet;
 use std::mem::replace;
 use rustc_data_structures::ptr_key::PtrKey;
@@ -2375,11 +2375,27 @@ impl<'a> Resolver<'a> {
                 ast::UseTreeKind::Simple(..) if segments.len() == 1 => &[TypeNS, ValueNS][..],
                 _ => &[TypeNS],
             };
+            let report_error = |this: &Self, ns| {
+                let what = if ns == TypeNS { "type parameters" } else { "local variables" };
+                this.session.span_err(ident.span, &format!("imports cannot refer to {}", what));
+            };
+
             for &ns in nss {
-                if let Some(LexicalScopeBinding::Def(..)) =
-                        self.resolve_ident_in_lexical_scope(ident, ns, None, use_tree.prefix.span) {
-                    let what = if ns == TypeNS { "type parameters" } else { "local variables" };
-                    self.session.span_err(ident.span, &format!("imports cannot refer to {}", what));
+                match self.resolve_ident_in_lexical_scope(ident, ns, None, use_tree.prefix.span) {
+                    Some(LexicalScopeBinding::Def(..)) => {
+                        report_error(self, ns);
+                    }
+                    Some(LexicalScopeBinding::Item(binding)) => {
+                        let orig_blacklisted_binding =
+                            mem::replace(&mut self.blacklisted_binding, Some(binding));
+                        if let Some(LexicalScopeBinding::Def(..)) =
+                                self.resolve_ident_in_lexical_scope(ident, ns, None,
+                                                                    use_tree.prefix.span) {
+                            report_error(self, ns);
+                        }
+                        self.blacklisted_binding = orig_blacklisted_binding;
+                    }
+                    None => {}
                 }
             }
         } else if let ast::UseTreeKind::Nested(use_trees) = &use_tree.kind {
@@ -3874,6 +3890,13 @@ impl<'a> Resolver<'a> {
                         module = Some(ModuleOrUniformRoot::Module(next_module));
                         record_segment_def(self, def);
                     } else if def == Def::ToolMod && i + 1 != path.len() {
+                        if binding.is_import() {
+                            self.session.struct_span_err(
+                                ident.span, "cannot use a tool module through an import"
+                            ).span_note(
+                                binding.span, "the tool module imported here"
+                            ).emit();
+                        }
                         let def = Def::NonMacroAttr(NonMacroAttrKind::Tool);
                         return PathResult::NonModule(PathResolution::new(def));
                     } else if def == Def::Err {

src/librustc_resolve/macros.rs

@@ -376,6 +376,7 @@ impl<'a> Resolver<'a> {
                     .push((path, path_span, kind, parent_scope.clone(), def.ok()));
             }
 
+            self.prohibit_imported_non_macro_attrs(None, def.ok(), path_span);
             def
         } else {
             let binding = self.early_resolve_ident_in_lexical_scope(
@@ -390,7 +391,9 @@ impl<'a> Resolver<'a> {
                     .push((path[0].ident, kind, parent_scope.clone(), binding.ok()));
             }
 
-            binding.map(|binding| binding.def())
+            let def = binding.map(|binding| binding.def());
+            self.prohibit_imported_non_macro_attrs(binding.ok(), def.ok(), path_span);
+            def
         }
     }
 
@@ -828,27 +831,23 @@ impl<'a> Resolver<'a> {
             // but its `Def` should coincide with a crate passed with `--extern`
             // (otherwise there would be ambiguity) and we can skip feature error in this case.
             'ok: {
-                if !is_import || self.session.features_untracked().uniform_paths {
+                if !is_import || !rust_2015 {
                     break 'ok;
                 }
                 if ns == TypeNS && use_prelude && self.extern_prelude_get(ident, true).is_some() {
                     break 'ok;
                 }
-                if rust_2015 {
-                    let root_ident = Ident::new(keywords::PathRoot.name(), orig_ident.span);
-                    let root_module = self.resolve_crate_root(root_ident);
-                    if self.resolve_ident_in_module_ext(ModuleOrUniformRoot::Module(root_module),
-                                                        orig_ident, ns, None, false, path_span)
-                                                        .is_ok() {
-                        break 'ok;
-                    }
+                let root_ident = Ident::new(keywords::PathRoot.name(), orig_ident.span);
+                let root_module = self.resolve_crate_root(root_ident);
+                if self.resolve_ident_in_module_ext(ModuleOrUniformRoot::Module(root_module),
+                                                    orig_ident, ns, None, false, path_span)
+                                                    .is_ok() {
+                    break 'ok;
                 }
 
-                let msg = "imports can only refer to extern crate names \
-                           passed with `--extern` on stable channel";
-                let mut err = feature_err(&self.session.parse_sess, "uniform_paths",
-                                          ident.span, GateIssue::Language, msg);
-
+                let msg = "imports can only refer to extern crate names passed with \
+                           `--extern` in macros originating from 2015 edition";
+                let mut err = self.session.struct_span_err(ident.span, msg);
                 let what = self.binding_description(binding, ident,
                                                     flags.contains(Flags::MISC_FROM_PRELUDE));
                 let note_msg = format!("this import refers to {what}", what = what);
@@ -977,6 +976,20 @@ impl<'a> Resolver<'a> {
         }
     }
 
+    fn prohibit_imported_non_macro_attrs(&self, binding: Option<&'a NameBinding<'a>>,
+                                         def: Option<Def>, span: Span) {
+        if let Some(Def::NonMacroAttr(kind)) = def {
+            if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
+                let msg = format!("cannot use a {} through an import", kind.descr());
+                let mut err = self.session.struct_span_err(span, &msg);
+                if let Some(binding) = binding {
+                    err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
+                }
+                err.emit();
+            }
+        }
+    }
+
     fn suggest_macro_name(&mut self, name: &str, kind: MacroKind,
                           err: &mut DiagnosticBuilder<'a>, span: Span) {
         // First check if this is a locally-defined bang macro.
@@ -1073,17 +1086,21 @@ impl<'a> Resolver<'a> {
             let ident = ident.modern();
             self.macro_names.insert(ident);
             let def = Def::Macro(def_id, MacroKind::Bang);
-            let vis = ty::Visibility::Invisible; // Doesn't matter for legacy bindings
+            let is_macro_export = attr::contains_name(&item.attrs, "macro_export");
+            let vis = if is_macro_export {
+                ty::Visibility::Public
+            } else {
+                ty::Visibility::Restricted(DefId::local(CRATE_DEF_INDEX))
+            };
             let binding = (def, vis, item.span, expansion).to_name_binding(self.arenas);
             self.set_binding_parent_module(binding, self.current_module);
             let legacy_binding = self.arenas.alloc_legacy_binding(LegacyBinding {
                 parent_legacy_scope: *current_legacy_scope, binding, ident
             });
             *current_legacy_scope = LegacyScope::Binding(legacy_binding);
             self.all_macros.insert(ident.name, def);
-            if attr::contains_name(&item.attrs, "macro_export") {
+            if is_macro_export {
                 let module = self.graph_root;
-                let vis = ty::Visibility::Public;
                 self.define(module, ident, MacroNS,
                             (def, vis, item.span, expansion, IsMacroExport));
             } else {

src/librustc_resolve/resolve_imports.rs

@@ -223,6 +223,11 @@ impl<'a> Resolver<'a> {
         }
 
         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();

src/libsyntax/feature_gate.rs

@@ -434,9 +434,6 @@ declare_features! (
     // support for arbitrary delimited token streams in non-macro attributes
     (active, unrestricted_attribute_tokens, "1.30.0", Some(55208), None),
 
-    // Allows `use x::y;` to resolve through `self::x`, not just `::x`.
-    (active, uniform_paths, "1.30.0", Some(53130), None),
-
     // Allows unsized rvalues at arguments and parameters.
     (active, unsized_locals, "1.30.0", Some(48055), None),
 
@@ -687,6 +684,8 @@ declare_features! (
     (accepted, cfg_attr_multi, "1.33.0", Some(54881), None),
     // Top level or-patterns (`p | q`) in `if let` and `while let`.
     (accepted, if_while_or_patterns, "1.33.0", Some(48215), None),
+    // Allows `use x::y;` to search `x` in the current scope.
+    (accepted, uniform_paths, "1.32.0", Some(53130), None),
 );
 
 // If you change this, please modify `src/doc/unstable-book` as well. You must

src/test/run-pass/uniform-paths/auxiliary/issue-53691.rs

@@ -1,7 +1,5 @@
 // edition:2018
 
-#![feature(uniform_paths)]
-
 mod m { pub fn f() {} }
 mod n { pub fn g() {} }
 

src/test/run-pass/uniform-paths/basic-nested.rs

@@ -1,12 +1,12 @@
-// run-pass
-#![allow(unused_imports)]
-#![allow(non_camel_case_types)]
+// This test is similar to `basic.rs`, but nested in modules.
 
+// run-pass
 // edition:2018
 
-#![feature(decl_macro, uniform_paths)]
+#![feature(decl_macro)]
 
-// This test is similar to `basic.rs`, but nested in modules.
+#![allow(unused_imports)]
+#![allow(non_camel_case_types)]
 
 mod foo {
     // Test that ambiguity errors are not emitted between `self::test` and

src/test/run-pass/uniform-paths/basic.rs

@@ -1,10 +1,8 @@
 // run-pass
-#![allow(unused_imports)]
-#![allow(non_camel_case_types)]
-
 // edition:2018
 
-#![feature(uniform_paths)]
+#![allow(unused_imports)]
+#![allow(non_camel_case_types)]
 
 // Test that ambiguity errors are not emitted between `self::test` and
 // `::test`, assuming the latter (crate) is not in `extern_prelude`.

src/test/run-pass/uniform-paths/macros-nested.rs

@@ -1,11 +1,9 @@
-// run-pass
-#![allow(non_camel_case_types)]
+// This test is similar to `macros.rs`, but nested in modules.
 
+// run-pass
 // edition:2018
 
-#![feature(uniform_paths)]
-
-// This test is similar to `macros.rs`, but nested in modules.
+#![allow(non_camel_case_types)]
 
 mod foo {
     // Test that ambiguity errors are not emitted between `self::test` and

src/test/run-pass/uniform-paths/macros.rs

@@ -1,11 +1,9 @@
-// run-pass
-#![allow(non_camel_case_types)]
+// This test is similar to `basic.rs`, but with macros defining local items.
 
+// run-pass
 // edition:2018
 
-#![feature(uniform_paths)]
-
-// This test is similar to `basic.rs`, but with macros defining local items.
+#![allow(non_camel_case_types)]
 
 // Test that ambiguity errors are not emitted between `self::test` and
 // `::test`, assuming the latter (crate) is not in `extern_prelude`.

src/test/run-pass/uniform-paths/same-crate.rs

@@ -1,9 +1,6 @@
 // run-pass
-
 // edition:2018
 
-#![feature(uniform_paths)]
-
 pub const A: usize = 0;
 
 pub mod foo {

src/test/ui/editions/edition-imports-2015.rs

@@ -3,8 +3,6 @@
 // aux-build:edition-imports-2018.rs
 // aux-build:absolute.rs
 
-#![feature(uniform_paths)]
-
 #[macro_use]
 extern crate edition_imports_2018;
 

src/test/ui/editions/edition-imports-2015.stderr

@@ -1,5 +1,5 @@
 error: cannot glob-import all possible crates
-  --> $DIR/edition-imports-2015.rs:25:5
+  --> $DIR/edition-imports-2015.rs:23:5
    |
 LL |     gen_glob!(); //~ ERROR cannot glob-import all possible crates
    |     ^^^^^^^^^^^^

src/test/ui/editions/edition-imports-virtual-2015-gated.stderr

@@ -1,4 +1,4 @@
-error[E0658]: imports can only refer to extern crate names passed with `--extern` on stable channel (see issue #53130)
+error: imports can only refer to extern crate names passed with `--extern` in macros originating from 2015 edition
   --> <::edition_imports_2015::gen_gated macros>:1:50
    |
 LL | (  ) => { fn check_gated (  ) { enum E { A } use E :: * ; } }
@@ -9,7 +9,6 @@ LL | (  ) => { fn check_gated (  ) { enum E { A } use E :: * ; } }
 LL |     gen_gated!();
    |     ------------- not an extern crate passed with `--extern`
    |
-   = help: add #![feature(uniform_paths)] to the crate attributes to enable
 note: this import refers to the enum defined here
   --> $DIR/edition-imports-virtual-2015-gated.rs:9:5
    |
@@ -19,4 +18,3 @@ LL |     gen_gated!();
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0658`.

src/test/ui/imports/issue-56125.rs

@@ -2,8 +2,6 @@
 // compile-flags:--extern issue_56125
 // aux-build:issue-56125.rs
 
-#![feature(uniform_paths)]
-
 mod m1 {
     use issue_56125::last_segment::*;
     //~^ ERROR `issue_56125` is ambiguous