Prohibit using macro-expanded macro_export macros through module-relative paths

src/librustc_resolve/build_reduced_graph.rs

@@ -789,7 +789,6 @@ impl<'a, 'b, 'cl> BuildReducedGraphVisitor<'a, 'b, 'cl> {
     fn visit_invoc(&mut self, id: ast::NodeId) -> &'b InvocationData<'b> {
         let mark = id.placeholder_to_mark();
         self.resolver.current_module.unresolved_invocations.borrow_mut().insert(mark);
-        self.resolver.unresolved_invocations_macro_export.insert(mark);
         let invocation = self.resolver.invocations[&mark];
         invocation.module.set(self.resolver.current_module);
         invocation.legacy_scope.set(self.legacy_scope);

src/librustc_resolve/lib.rs

@@ -1385,6 +1385,8 @@ pub struct Resolver<'a, 'b: 'a> {
     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)>,
 
     gated_errors: FxHashSet<Span>,
     disallowed_shadowing: Vec<&'a LegacyBinding<'a>>,
@@ -1432,9 +1434,6 @@ pub struct Resolver<'a, 'b: 'a> {
 
     /// Only supposed to be used by rustdoc, otherwise should be false.
     pub ignore_extern_prelude_feature: bool,
-
-    /// Macro invocations in the whole crate that can expand into a `#[macro_export] macro_rules`.
-    unresolved_invocations_macro_export: FxHashSet<Mark>,
 }
 
 /// Nothing really interesting here, it just provides memory for the rest of the crate.
@@ -1706,6 +1705,7 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             proc_mac_errors: Vec::new(),
             gated_errors: FxHashSet(),
             disallowed_shadowing: Vec::new(),
+            macro_expanded_macro_export_errors: BTreeSet::new(),
 
             arenas,
             dummy_binding: arenas.alloc_name_binding(NameBinding {
@@ -1737,7 +1737,6 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
             current_type_ascription: Vec::new(),
             injected_crate: None,
             ignore_extern_prelude_feature: false,
-            unresolved_invocations_macro_export: FxHashSet(),
         }
     }
 
@@ -4126,6 +4125,7 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
                                             ns: Namespace,
                                             module: Module<'a>,
                                             found_traits: &mut Vec<TraitCandidate>) {
+        assert!(ns == TypeNS || ns == ValueNS);
         let mut traits = module.traits.borrow_mut();
         if traits.is_none() {
             let mut collected_traits = Vec::new();
@@ -4371,6 +4371,14 @@ impl<'a, 'crateloader: 'a> Resolver<'a, 'crateloader> {
         self.report_proc_macro_import(krate);
         let mut reported_spans = FxHashSet();
 
+        for &(span_use, span_def) in &self.macro_expanded_macro_export_errors {
+            let msg = "macro-expanded `macro_export` macros from the current crate \
+                       cannot be referred to by absolute paths";
+            self.session.struct_span_err(span_use, msg)
+                        .span_note(span_def, "the macro is defined here")
+                        .emit();
+        }
+
         for &AmbiguityError { span, name, b1, b2, lexical } in &self.ambiguity_errors {
             if !reported_spans.insert(span) { continue }
             let participle = |binding: &NameBinding| {

src/librustc_resolve/macros.rs

@@ -196,9 +196,7 @@ impl<'a, 'crateloader: 'a> base::Resolver for Resolver<'a, 'crateloader> {
 
         self.current_module = invocation.module.get();
         self.current_module.unresolved_invocations.borrow_mut().remove(&mark);
-        self.unresolved_invocations_macro_export.remove(&mark);
         self.current_module.unresolved_invocations.borrow_mut().extend(derives);
-        self.unresolved_invocations_macro_export.extend(derives);
         for &derive in derives {
             self.invocations.insert(derive, invocation);
         }

src/librustc_resolve/resolve_imports.rs

@@ -146,6 +146,14 @@ impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
             .try_borrow_mut()
             .map_err(|_| Determined)?; // This happens when there is a cycle of imports
 
+        if let Some(binding) = resolution.binding {
+            if !restricted_shadowing && binding.expansion != Mark::root() {
+                if let NameBindingKind::Def(_, true) = binding.kind {
+                    self.macro_expanded_macro_export_errors.insert((path_span, binding.span));
+                }
+            }
+        }
+
         if record_used {
             if let Some(binding) = resolution.binding {
                 if let Some(shadowed_glob) = resolution.shadowed_glob {
@@ -211,9 +219,15 @@ impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
         // if it cannot be shadowed by some new item/import expanded from a macro.
         // This happens either if there are no unexpanded macros, or expanded names cannot
         // shadow globs (that happens in macro namespace or with restricted shadowing).
-        let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty() ||
-                                (ns == MacroNS && ptr::eq(module, self.graph_root) &&
-                                 !self.unresolved_invocations_macro_export.is_empty());
+        //
+        // Additionally, any macro in any module can plant names in the root module if it creates
+        // `macro_export` macros, so the root module effectively has unresolved invocations if any
+        // module has unresolved invocations.
+        // However, it causes resolution/expansion to stuck too often (#53144), so, to make
+        // progress, we have to ignore those potential unresolved invocations from other modules
+        // and prohibit access to macro-expanded `macro_export` macros instead (unless restricted
+        // shadowing is enabled, see `macro_expanded_macro_export_errors`).
+        let unexpanded_macros = !module.unresolved_invocations.borrow().is_empty();
         if let Some(binding) = resolution.binding {
             if !unexpanded_macros || ns == MacroNS || restricted_shadowing {
                 return check_usable(self, binding);

src/test/compile-fail-fulldeps/proc-macro/proc-macro-attributes.rs

@@ -21,7 +21,7 @@ extern crate derive_b;
 #[C] //~ ERROR: The attribute `C` is currently unknown to the compiler
 #[B(D)]
 #[B(E = "foo")]
-#[B arbitrary tokens] //~ expected one of `(` or `=`, found `arbitrary`
+#[B arbitrary tokens] //~ ERROR arbitrary tokens in non-macro attributes are unstable
 struct B;
 
 fn main() {}

src/test/ui/imports/local-modularized-tricky-fail-3.rs

@@ -0,0 +1,32 @@
+// Copyright 2018 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.
+
+// Crate-local macro expanded `macro_export` macros cannot be accessed with module-relative paths.
+
+#![feature(use_extern_macros)]
+
+macro_rules! define_exported { () => {
+    #[macro_export]
+    macro_rules! exported {
+        () => ()
+    }
+}}
+
+define_exported!();
+
+mod m {
+    use exported;
+    //~^ ERROR macro-expanded `macro_export` macros from the current crate cannot
+}
+
+fn main() {
+    ::exported!();
+    //~^ ERROR macro-expanded `macro_export` macros from the current crate cannot
+}

src/test/ui/imports/local-modularized-tricky-fail-3.stderr

@@ -0,0 +1,36 @@
+error: macro-expanded `macro_export` macros from the current crate cannot be referred to by absolute paths
+  --> $DIR/local-modularized-tricky-fail-3.rs:25:9
+   |
+LL |     use exported;
+   |         ^^^^^^^^
+   |
+note: the macro is defined here
+  --> $DIR/local-modularized-tricky-fail-3.rs:17:5
+   |
+LL | /     macro_rules! exported {
+LL | |         () => ()
+LL | |     }
+   | |_____^
+...
+LL |   define_exported!();
+   |   ------------------- in this macro invocation
+
+error: macro-expanded `macro_export` macros from the current crate cannot be referred to by absolute paths
+  --> $DIR/local-modularized-tricky-fail-3.rs:30:5
+   |
+LL |     ::exported!();
+   |     ^^^^^^^^^^
+   |
+note: the macro is defined here
+  --> $DIR/local-modularized-tricky-fail-3.rs:17:5
+   |
+LL | /     macro_rules! exported {
+LL | |         () => ()
+LL | |     }
+   | |_____^
+...
+LL |   define_exported!();
+   |   ------------------- in this macro invocation
+
+error: aborting due to 2 previous errors
+