Warn on unused `#[macro_use]` imports.

src/libproc_macro_tokens/lib.rs

@@ -59,7 +59,7 @@
 
 extern crate syntax;
 extern crate syntax_pos;
-#[macro_use] extern crate log;
+extern crate log;
 
 pub mod build;
 pub mod parse;

src/librustc/lib.rs

@@ -57,7 +57,7 @@
 extern crate rustc_errors as errors;
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
-#[macro_use] extern crate syntax_pos;
+extern crate syntax_pos;
 #[macro_use] #[no_link] extern crate rustc_bitflags;
 
 extern crate serialize as rustc_serialize; // used by deriving

src/librustc_const_math/lib.rs

@@ -28,8 +28,8 @@
 #![feature(const_fn)]
 #![cfg_attr(not(stage0), feature(i128))]
 
-#[macro_use] extern crate log;
-#[macro_use] extern crate syntax;
+extern crate log;
+extern crate syntax;
 
 // SNAP: remove use of this crate
 extern crate rustc_i128;

src/librustc_driver/lib.rs

@@ -57,7 +57,6 @@
 extern crate rustc_llvm as llvm;
 #[macro_use]
 extern crate log;
-#[macro_use]
 extern crate syntax;
 extern crate syntax_ext;
 extern crate syntax_pos;

src/librustc_errors/lib.rs

@@ -27,9 +27,7 @@
 
 extern crate serialize;
 extern crate term;
-#[macro_use]
 extern crate log;
-#[macro_use]
 extern crate libc;
 extern crate std_unicode;
 extern crate serialize as rustc_serialize; // used by deriving

src/librustc_incremental/lib.rs

@@ -30,7 +30,7 @@
 extern crate serialize as rustc_serialize;
 
 #[macro_use] extern crate log;
-#[macro_use] extern crate syntax;
+extern crate syntax;
 extern crate syntax_pos;
 
 extern crate rustc_i128;

src/librustc_lint/lib.rs

@@ -37,7 +37,6 @@
 #![feature(slice_patterns)]
 #![feature(staged_api)]
 
-#[macro_use]
 extern crate syntax;
 #[macro_use]
 extern crate rustc;

src/librustc_plugin/Cargo.toml

@@ -13,7 +13,6 @@ crate-type = ["dylib"]
 log = { path = "../liblog" }
 rustc = { path = "../librustc" }
 rustc_back = { path = "../librustc_back" }
-rustc_bitflags = { path = "../librustc_bitflags" }
 rustc_metadata = { path = "../librustc_metadata" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }

src/librustc_plugin/lib.rs

@@ -63,9 +63,8 @@
 #![feature(rustc_diagnostic_macros)]
 #![feature(rustc_private)]
 
-#[macro_use] extern crate log;
+extern crate log;
 #[macro_use] extern crate syntax;
-#[macro_use] #[no_link] extern crate rustc_bitflags;
 
 extern crate rustc;
 extern crate rustc_back;

src/librustc_resolve/build_reduced_graph.rs

@@ -552,16 +552,35 @@ fn process_legacy_macro_imports(&mut self, item: &Item, module: Module<'a>, expa
             used = true; // Avoid the normal unused extern crate warning
         }
 
+        let (graph_root, arenas) = (self.graph_root, self.arenas);
+        let macro_use_directive = |span| arenas.alloc_import_directive(ImportDirective {
+            id: item.id,
+            parent: graph_root,
+            imported_module: Cell::new(Some(module)),
+            subclass: ImportDirectiveSubclass::MacroUse,
+            span: span,
+            module_path: Vec::new(),
+            vis: Cell::new(ty::Visibility::Restricted(DefId::local(CRATE_DEF_INDEX))),
+            expansion: expansion,
+            used: Cell::new(false),
+        });
+
         if let Some(span) = legacy_imports.import_all {
+            let directive = macro_use_directive(span);
+            self.potentially_unused_imports.push(directive);
             module.for_each_child(|ident, ns, binding| if ns == MacroNS {
-                self.legacy_import_macro(ident.name, binding, span, allow_shadowing);
+                let imported_binding = self.import(binding, directive);
+                self.legacy_import_macro(ident.name, imported_binding, span, allow_shadowing);
             });
         } else {
             for (name, span) in legacy_imports.imports {
                 let ident = Ident::with_empty_ctxt(name);
                 let result = self.resolve_ident_in_module(module, ident, MacroNS, false, None);
                 if let Ok(binding) = result {
-                    self.legacy_import_macro(name, binding, span, allow_shadowing);
+                    let directive = macro_use_directive(span);
+                    self.potentially_unused_imports.push(directive);
+                    let imported_binding = self.import(binding, directive);
+                    self.legacy_import_macro(name, imported_binding, span, allow_shadowing);
                 } else {
                     span_err!(self.session, span, E0469, "imported macro not found");
                 }

src/librustc_resolve/check_unused.rs

@@ -125,6 +125,11 @@ pub fn check_crate(resolver: &mut Resolver, krate: &ast::Crate) {
                 let msg = "unused extern crate".to_string();
                 resolver.session.add_lint(lint, directive.id, directive.span, msg);
             }
+            ImportDirectiveSubclass::MacroUse => {
+                let lint = lint::builtin::UNUSED_IMPORTS;
+                let msg = "unused `#[macro_use]` import".to_string();
+                resolver.session.add_lint(lint, directive.id, directive.span, msg);
+            }
             _ => {}
         }
     }

src/librustc_resolve/macros.rs

@@ -341,12 +341,15 @@ pub fn resolve_legacy_scope(&mut self,
             };
         }
 
-        let binding = match binding {
-            Some(binding) => MacroBinding::Legacy(binding),
-            None => match self.builtin_macros.get(&name).cloned() {
-                Some(binding) => MacroBinding::Modern(binding),
-                None => return None,
-            },
+        let binding = if let Some(binding) = binding {
+            MacroBinding::Legacy(binding)
+        } else if let Some(binding) = self.builtin_macros.get(&name).cloned() {
+            if !self.use_extern_macros {
+                self.record_use(Ident::with_empty_ctxt(name), MacroNS, binding, DUMMY_SP);
+            }
+            MacroBinding::Modern(binding)
+        } else {
+            return None;
         };
 
         if !self.use_extern_macros {
@@ -378,6 +381,7 @@ pub fn finalize_current_module_macro_resolutions(&mut self) {
             let (legacy_resolution, resolution) = match (legacy_resolution, resolution) {
                 (Some(legacy_resolution), Ok(resolution)) => (legacy_resolution, resolution),
                 (Some(MacroBinding::Modern(binding)), Err(_)) => {
+                    self.record_use(ident, MacroNS, binding, span);
                     self.err_if_macro_use_proc_macro(ident.name, span, binding);
                     continue
                 },

src/librustc_resolve/resolve_imports.rs

@@ -49,6 +49,7 @@ pub enum ImportDirectiveSubclass<'a> {
         // n.b. `max_vis` is only used in `finalize_import` to check for reexport errors.
     },
     ExternCrate,
+    MacroUse,
 }
 
 /// One import directive.
@@ -835,5 +836,6 @@ fn import_directive_subclass_to_string(subclass: &ImportDirectiveSubclass) -> St
         SingleImport { source, .. } => source.to_string(),
         GlobImport { .. } => "*".to_string(),
         ExternCrate => "<extern crate>".to_string(),
+        MacroUse => "#[macro_use]".to_string(),
     }
 }

src/libserialize/lib.rs

@@ -39,7 +39,7 @@
 
 // test harness access
 #[cfg(test)] extern crate test;
-#[macro_use] extern crate log;
+extern crate log;
 
 extern crate std_unicode;
 extern crate collections;

src/test/compile-fail/imports/unused-macro-use.rs

+// 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.
+
+#![deny(unused)]
+
+#[macro_use] //~ ERROR unused `#[macro_use]` import
+extern crate core;
+
+#[macro_use(
+    panic //~ ERROR unused `#[macro_use]` import
+)]
+extern crate core as core_2;
+
+fn main() {}

src/test/compile-fail/lint-unused-extern-crate.rs

@@ -26,8 +26,6 @@
 
 extern crate lint_unused_extern_crate as other; // no error, the use * marks it as used
 
-#[macro_use] extern crate core; // no error, the `#[macro_use]` marks it as used
-
 #[allow(unused_imports)]
 use rand::isaac::IsaacRng;
 

src/tools/cargotest/main.rs

@@ -25,7 +25,7 @@ struct Test {
     Test {
         name: "cargo",
         repo: "https://github.com/rust-lang/cargo",
-        sha: "b7be4f2ef2cf743492edc6dfb55d087ed88f2d76",
+        sha: "2324c2bbaf7fc6ea9cbdd77c034ef1af769cb617",
         lock: None,
     },
     Test {