feat: support mods inside cfg_if macro

Author: calebcartwright

src/modules.rs

@@ -105,7 +105,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
         visitor.visit_item(&item);
         for module_item in visitor.mods() {
             if let ast::ItemKind::Mod(ref sub_mod) = module_item.item.node {
-                self.visit_sub_mod(&item, Cow::Owned(sub_mod.clone()))?;
+                self.visit_sub_mod(&module_item.item, Cow::Owned(sub_mod.clone()))?;
             }
         }
         Ok(())
@@ -477,7 +477,14 @@ fn parse_mod_items<'a>(parser: &mut parser::Parser<'a>, inner_lo: Span) -> PResu
 
 fn is_cfg_if(item: &ast::Item) -> bool {
     match item.node {
-        ast::ItemKind::Mac(..) if item.ident.name == Symbol::intern("cfg_if") => true,
+        ast::ItemKind::Mac(ref mac) => {
+            if let Some(first_segment) = mac.node.path.segments.first() {
+                if first_segment.ident.name == Symbol::intern("cfg_if") {
+                    return true;
+                }
+            }
+            false
+        }
         _ => false,
     }
 }

src/modules/visitor.rs

@@ -43,8 +43,21 @@ impl<'a, 'ast: 'a> Visitor<'ast> for CfgIfVisitor<'a> {
 
 impl<'a, 'ast: 'a> CfgIfVisitor<'a> {
     fn visit_mac_inner(&mut self, mac: &'ast ast::Mac) -> Result<(), &'static str> {
-        if mac.node.path != Symbol::intern("cfg_if") {
-            return Err("Expected cfg_if");
+        // Support both:
+        // ```
+        // extern crate cfg_if;
+        // cfg_if::cfg_if! {..}
+        // ```
+        // And:
+        // ```
+        // #[macro_use]
+        // extern crate cfg_if;
+        // cfg_if! {..}
+        // ```
+        if let Some(first_segment) = mac.node.path.segments.first() {
+            if first_segment.ident.name != Symbol::intern("cfg_if") {
+                return Err("Expected cfg_if");
+            }
         }
 
         let mut parser = stream_to_parser_with_base_dir(