rustc: Process #[cfg]/#[cfg_attr] on crates

This commit implements processing these two attributes at the crate level as
well as at the item level. When #[cfg] is applied at the crate level, then the
entire crate will be omitted if the cfg doesn't match. The #[cfg_attr] attribute
is processed as usual in that the attribute is included or not depending on
whether the cfg matches.

This was spurred on by motivations of #18585 where #[cfg_attr] annotations will
be applied at the crate-level.

cc #18585

3 files changed, 56 insertions, 13 deletions

diff --git a/src/libsyntax/config.rs b/src/libsyntax/config.rs
index 72c62a173fc..257bfd69f43 100644
--- a/src/libsyntax/config.rs
+++ b/src/libsyntax/config.rs
@@ -15,6 +15,8 @@ use {ast, fold, attr};
 use codemap::Spanned;
 use ptr::P;
 
+use util::small_vector::SmallVector;
+
 /// A folder that strips out items that do not belong in the current
 /// configuration.
 struct Context<'a> {
@@ -47,6 +49,9 @@ impl<'a> fold::Folder for Context<'a> {
     fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
         fold::noop_fold_mac(mac, self)
     }
+    fn fold_item(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
+        fold_item(self, item)
+    }
 }
 
 pub fn strip_items(krate: ast::Crate,
@@ -72,13 +77,9 @@ fn fold_mod(cx: &mut Context, ast::Mod {inner, view_items, items}: ast::Mod) ->
         view_items: view_items.into_iter().filter_map(|a| {
             filter_view_item(cx, a).map(|x| cx.fold_view_item(x))
         }).collect(),
-        items: items.into_iter().filter_map(|a| {
-            if item_in_cfg(cx, &*a) {
-                Some(cx.fold_item(a))
-            } else {
-                None
-            }
-        }).flat_map(|x| x.into_iter()).collect()
+        items: items.into_iter().flat_map(|a| {
+            cx.fold_item(a).into_iter()
+        }).collect()
     }
 }
 
@@ -104,6 +105,14 @@ fn fold_foreign_mod(cx: &mut Context, ast::ForeignMod {abi, view_items, items}:
     }
 }
 
+fn fold_item(cx: &mut Context, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
+    if item_in_cfg(cx, &*item) {
+        SmallVector::one(item.map(|i| cx.fold_item_simple(i)))
+    } else {
+        SmallVector::zero()
+    }
+}
+
 fn fold_item_underscore(cx: &mut Context, item: ast::Item_) -> ast::Item_ {
     let item = match item {
         ast::ItemImpl(a, b, c, impl_items) => {
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index cd4a3d10c48..1132ea372b7 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -1057,12 +1057,41 @@ pub fn noop_fold_mod<T: Folder>(Mod {inner, view_items, items}: Mod, folder: &mu
 
 pub fn noop_fold_crate<T: Folder>(Crate {module, attrs, config, exported_macros, span}: Crate,
                                   folder: &mut T) -> Crate {
+    let config = folder.fold_meta_items(config);
+
+    let mut items = folder.fold_item(P(ast::Item {
+        ident: token::special_idents::invalid,
+        attrs: attrs,
+        id: ast::DUMMY_NODE_ID,
+        vis: ast::Public,
+        span: span,
+        node: ast::ItemMod(module),
+    })).into_iter();
+
+    let (module, attrs, span) = match items.next() {
+        Some(item) => {
+            assert!(items.next().is_none(),
+                    "a crate cannot expand to more than one item");
+            item.and_then(|ast::Item { attrs, span, node, .. }| {
+                match node {
+                    ast::ItemMod(m) => (m, attrs, span),
+                    _ => panic!("fold converted a module to not a module"),
+                }
+            })
+        }
+        None => (ast::Mod {
+            inner: span,
+            view_items: Vec::new(),
+            items: Vec::new(),
+        }, Vec::new(), span)
+    };
+
     Crate {
-        module: folder.fold_mod(module),
-        attrs: attrs.move_map(|x| folder.fold_attribute(x)),
-        config: folder.fold_meta_items(config),
+        module: module,
+        attrs: attrs,
+        config: config,
         exported_macros: exported_macros,
-        span: folder.new_span(span)
+        span: span,
     }
 }
 
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index a7db8e800a9..29637e88dd5 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -108,7 +108,10 @@ impl<'a> fold::Folder for TestHarnessGenerator<'a> {
     }
 
     fn fold_item(&mut self, i: P<ast::Item>) -> SmallVector<P<ast::Item>> {
-        self.cx.path.push(i.ident);
+        let ident = i.ident;
+        if ident.name != token::special_idents::invalid.name {
+            self.cx.path.push(ident);
+        }
         debug!("current path: {}",
                ast_util::path_name_i(self.cx.path.as_slice()));
 
@@ -143,7 +146,9 @@ impl<'a> fold::Folder for TestHarnessGenerator<'a> {
             ast::ItemMod(..) => fold::noop_fold_item(i, self),
             _ => SmallVector::one(i),
         };
-        self.cx.path.pop();
+        if ident.name != token::special_idents::invalid.name {
+            self.cx.path.pop();
+        }
         res
     }