Auto merge of #53461 - petrochenkov:pmu, r=alexcrichton

resolve: Do not error on access to proc macros imported with `#[macro_use]`

This error is artificial, but previously, when `#[macro_use] extern crate x;` was stable, but non-derive proc macros were not, it worked like kind of a feature gate. Now both features are stable, so the error is no longer necessary.

This PR simplifies how `#[macro_use] extern crate x;` works - it takes all items from macro namespace of `x`'s root and puts them into macro prelude from which they all can now be accessed.

src/librustc_resolve/lib.rs

@@ -1429,8 +1429,6 @@ pub struct Resolver<'a, 'b: 'a> {
     ambiguity_errors: Vec<AmbiguityError<'a>>,
     /// `use` injections are delayed for better placement and deduplication
     use_injections: Vec<UseError<'a>>,
-    /// `use` injections for proc macros wrongly imported with #[macro_use]
-    proc_mac_errors: Vec<macros::ProcMacError>,
     /// crate-local macro expanded `macro_export` referred to by a module-relative path
     macro_expanded_macro_export_errors: BTreeSet<(Span, Span)>,
 
@@ -1458,9 +1456,6 @@ pub struct Resolver<'a, 'b: 'a> {
     /// Avoid duplicated errors for "name already defined".
     name_already_seen: FxHashMap<Name, Span>,
 
-    /// A set of procedural macros imported by `#[macro_use]` that have already been warned about
-    warned_proc_macros: FxHashSet<Name>,
-
     potentially_unused_imports: Vec<&'a ImportDirective<'a>>,
 
     /// This table maps struct IDs into struct constructor IDs,
@@ -1744,7 +1739,6 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             privacy_errors: Vec::new(),
             ambiguity_errors: Vec::new(),
             use_injections: Vec::new(),
-            proc_mac_errors: Vec::new(),
             macro_expanded_macro_export_errors: BTreeSet::new(),
 
             arenas,
@@ -1766,7 +1760,6 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             local_macro_def_scopes: FxHashMap(),
             name_already_seen: FxHashMap(),
             whitelisted_legacy_custom_derives: Vec::new(),
-            warned_proc_macros: FxHashSet(),
             potentially_unused_imports: Vec::new(),
             struct_constructors: DefIdMap(),
             found_unresolved_macro: false,
@@ -4602,7 +4595,6 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
 
     fn report_errors(&mut self, krate: &Crate) {
         self.report_with_use_injections(krate);
-        self.report_proc_macro_import(krate);
         let mut reported_spans = FxHashSet();
 
         for &(span_use, span_def) in &self.macro_expanded_macro_export_errors {

src/librustc_resolve/macros.rs

@@ -19,7 +19,6 @@ use rustc::hir::def_id::{DefId, CRATE_DEF_INDEX, DefIndex,
 use rustc::hir::def::{Def, NonMacroAttrKind};
 use rustc::hir::map::{self, DefCollector};
 use rustc::{ty, lint};
-use rustc::middle::cstore::CrateStore;
 use syntax::ast::{self, Name, Ident};
 use syntax::attr;
 use syntax::errors::DiagnosticBuilder;
@@ -110,14 +109,6 @@ pub struct ParentScope<'a> {
     crate derives: Vec<ast::Path>,
 }
 
-pub struct ProcMacError {
-    crate_name: Symbol,
-    name: Symbol,
-    module: ast::NodeId,
-    use_span: Span,
-    warn_msg: &'static str,
-}
-
 // Macro namespace is separated into two sub-namespaces, one for bang macros and
 // one for attribute-like macros (attributes, derives).
 // We ignore resolutions from one sub-namespace when searching names in scope for another.
@@ -980,7 +971,6 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                     check_consistency(self, binding.def_ignoring_ambiguity());
                     if from_prelude {
                         self.record_use(ident, MacroNS, binding);
-                        self.err_if_macro_use_proc_macro(ident.name, span, binding);
                     }
                 }
             };
@@ -1132,69 +1122,6 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
         }
     }
 
-    /// Error if `ext` is a Macros 1.1 procedural macro being imported by `#[macro_use]`
-    fn err_if_macro_use_proc_macro(&mut self, name: Name, use_span: Span,
-                                   binding: &NameBinding<'a>) {
-        let krate = match binding.def() {
-            Def::NonMacroAttr(..) | Def::Err => return,
-            Def::Macro(def_id, _) => def_id.krate,
-            _ => unreachable!(),
-        };
-
-        // Plugin-based syntax extensions are exempt from this check
-        if krate == CrateNum::BuiltinMacros { return; }
-
-        let ext = binding.get_macro(self);
-
-        match *ext {
-            // If `ext` is a procedural macro, check if we've already warned about it
-            SyntaxExtension::AttrProcMacro(..) | SyntaxExtension::ProcMacro { .. } =>
-                if !self.warned_proc_macros.insert(name) { return; },
-            _ => return,
-        }
-
-        let warn_msg = match *ext {
-            SyntaxExtension::AttrProcMacro(..) =>
-                "attribute procedural macros cannot be imported with `#[macro_use]`",
-            SyntaxExtension::ProcMacro { .. } =>
-                "procedural macros cannot be imported with `#[macro_use]`",
-            _ => return,
-        };
-
-        let def_id = self.current_module.normal_ancestor_id;
-        let node_id = self.definitions.as_local_node_id(def_id).unwrap();
-
-        self.proc_mac_errors.push(ProcMacError {
-            crate_name: self.cstore.crate_name_untracked(krate),
-            name,
-            module: node_id,
-            use_span,
-            warn_msg,
-        });
-    }
-
-    pub fn report_proc_macro_import(&mut self, krate: &ast::Crate) {
-        for err in self.proc_mac_errors.drain(..) {
-            let (span, found_use) = ::UsePlacementFinder::check(krate, err.module);
-
-            if let Some(span) = span {
-                let found_use = if found_use { "" } else { "\n" };
-                self.session.struct_span_err(err.use_span, err.warn_msg)
-                    .span_suggestion_with_applicability(
-                        span,
-                        "instead, import the procedural macro like any other item",
-                        format!("use {}::{};{}", err.crate_name, err.name, found_use),
-                        Applicability::MachineApplicable
-                    ).emit();
-            } else {
-                self.session.struct_span_err(err.use_span, err.warn_msg)
-                    .help(&format!("instead, import the procedural macro like any other item: \
-                                    `use {}::{};`", err.crate_name, err.name))
-                    .emit();
-            }
-        }
-    }
-
     fn gate_legacy_custom_derive(&mut self, name: Symbol, span: Span) {
         if !self.session.features_untracked().custom_derive {
             let sess = &self.session.parse_sess;

src/test/ui-fulldeps/proc-macro/macro-use-attr.rs

@@ -8,12 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-pass
 // aux-build:attr_proc_macro.rs
 
 #[macro_use] extern crate attr_proc_macro;
 
 #[attr_proc_macro]
-//~^ ERROR: attribute procedural macros cannot be imported with `#[macro_use]`
 struct Foo;
 
 fn main() {

src/test/ui-fulldeps/proc-macro/macro-use-bang.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-pass
 // aux-build:bang_proc_macro.rs
 
 #![feature(proc_macro_non_items)]
@@ -17,5 +18,4 @@ extern crate bang_proc_macro;
 
 fn main() {
     bang_proc_macro!(println!("Hello, world!"));
-    //~^ ERROR: procedural macros cannot be imported with `#[macro_use]`
 }