Conditionally skip two passes if their related attributes were not found

Cargo.lock

@@ -2722,6 +2722,7 @@ dependencies = [
  "rustc_errors 0.0.0",
  "rustc_mir 0.0.0",
  "syntax 0.0.0",
+ "syntax_ext 0.0.0",
  "syntax_pos 0.0.0",
 ]
 

src/librustc_driver/driver.rs

@@ -1017,6 +1017,10 @@ where
         krate = ReplaceBodyWithLoop::new(sess).fold_crate(krate);
     }
 
+    let (has_proc_macro_decls, has_global_allocator) = time(sess, "AST validation", || {
+        ast_validation::check_crate(sess, &krate)
+    });
+
     // If we're in rustdoc we're always compiling as an rlib, but that'll trip a
     // bunch of checks in the `modify` function below. For now just skip this
     // step entirely if we're rustdoc as it's not too useful anyway.
@@ -1031,6 +1035,7 @@ where
                 &mut resolver,
                 krate,
                 is_proc_macro_crate,
+                has_proc_macro_decls,
                 is_test_crate,
                 num_crate_types,
                 sess.diagnostic(),
@@ -1038,6 +1043,7 @@ where
         });
     }
 
+    if has_global_allocator {
         // Expand global allocators, which are treated as an in-tree proc macro
         krate = time(sess, "creating allocators", || {
             allocator::expand::modify(
@@ -1048,6 +1054,7 @@ where
                 sess.diagnostic(),
             )
         });
+    }
 
     // Done with macro expansion!
 
@@ -1065,10 +1072,6 @@ where
         println!("{}", json::as_json(&krate));
     }
 
-    time(sess, "AST validation", || {
-        ast_validation::check_crate(sess, &krate)
-    });
-
     time(sess, "name resolution", || {
         resolver.resolve_crate(&krate);
     });

src/librustc_passes/Cargo.toml

@@ -14,5 +14,6 @@ rustc = { path = "../librustc" }
 rustc_mir = { path = "../librustc_mir"}
 rustc_data_structures = { path = "../librustc_data_structures" }
 syntax = { path = "../libsyntax" }
+syntax_ext = { path = "../libsyntax_ext" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc_errors = { path = "../librustc_errors" }

src/librustc_passes/ast_validation.rs

@@ -15,12 +15,15 @@ use syntax::source_map::Spanned;
 use syntax::symbol::keywords;
 use syntax::ptr::P;
 use syntax::visit::{self, Visitor};
+use syntax_ext::proc_macro_decls::is_proc_macro_attr;
 use syntax_pos::Span;
 use errors;
 use errors::Applicability;
 
 struct AstValidator<'a> {
     session: &'a Session,
+    has_proc_macro_decls: bool,
+    has_global_allocator: bool,
 
     // Used to ban nested `impl Trait`, e.g., `impl Into<impl Debug>`.
     // Nested `impl Trait` _is_ allowed in associated type position,
@@ -367,6 +370,14 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
     }
 
     fn visit_item(&mut self, item: &'a Item) {
+        if item.attrs.iter().any(|attr| is_proc_macro_attr(attr)  ) {
+            self.has_proc_macro_decls = true;
+        }
+
+        if attr::contains_name(&item.attrs, "global_allocator") {
+            self.has_global_allocator = true;
+        }
+
         match item.node {
             ItemKind::Impl(unsafety, polarity, _, _, Some(..), ref ty, ref impl_items) => {
                 self.invalid_visibility(&item.vis, None);
@@ -590,10 +601,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
     }
 }
 
-pub fn check_crate(session: &Session, krate: &Crate) {
-    visit::walk_crate(&mut AstValidator {
+pub fn check_crate(session: &Session, krate: &Crate) -> (bool, bool) {
+    let mut validator = AstValidator {
         session,
+        has_proc_macro_decls: false,
+        has_global_allocator: false,
         outer_impl_trait: None,
         is_impl_trait_banned: false,
-    }, krate)
+    };
+    visit::walk_crate(&mut validator, krate);
+
+    (validator.has_proc_macro_decls, validator.has_global_allocator)
 }

src/librustc_passes/lib.rs

@@ -22,6 +22,7 @@ extern crate rustc_data_structures;
 extern crate log;
 #[macro_use]
 extern crate syntax;
+extern crate syntax_ext;
 extern crate syntax_pos;
 extern crate rustc_errors as errors;
 

src/libsyntax_ext/proc_macro_decls.rs

@@ -48,6 +48,7 @@ pub fn modify(sess: &ParseSess,
               resolver: &mut dyn (::syntax::ext::base::Resolver),
               mut krate: ast::Crate,
               is_proc_macro_crate: bool,
+              has_proc_macro_decls: bool,
               is_test_crate: bool,
               num_crate_types: usize,
               handler: &errors::Handler) -> ast::Crate {
@@ -64,7 +65,9 @@ pub fn modify(sess: &ParseSess,
             is_proc_macro_crate,
             is_test_crate,
         };
+        if has_proc_macro_decls || is_proc_macro_crate {
             visit::walk_crate(&mut collect, &krate);
+        }
         (collect.derives, collect.attr_macros, collect.bang_macros)
     };
 
@@ -85,7 +88,7 @@ pub fn modify(sess: &ParseSess,
     krate
 }
 
-fn is_proc_macro_attr(attr: &ast::Attribute) -> bool {
+pub fn is_proc_macro_attr(attr: &ast::Attribute) -> bool {
     PROC_MACRO_KINDS.iter().any(|kind| attr.check_name(kind))
 }