[pt::Builder] add error handling

macro/platformtree.rs

@@ -49,9 +49,9 @@ pub fn plugin_registrar(reg: &mut Registry) {
 pub fn macro_platformtree(cx: &mut ExtCtxt, _: Span, tts: &[ast::TokenTree])
     -> Box<MacResult> {
   let pt = Parser::new(cx, tts).parse_platformtree();
-  let builder = Builder::build(cx, pt.unwrap());
-
-  let items = builder.emit_items(cx);
+  let items = Builder::build(cx, pt.unwrap())
+    .expect(format!("Unexpected failure on {}", line!()).as_slice())
+    .emit_items(cx);
   MacItems::new(items)
 }
 

platformtree/builder/mod.rs

@@ -38,11 +38,11 @@ pub struct Builder {
 }
 
 impl Builder {
-  pub fn build(cx: &mut ExtCtxt, pt: Rc<node::PlatformTree>) -> Builder {
+  pub fn build(cx: &mut ExtCtxt, pt: Rc<node::PlatformTree>) -> Option<Builder> {
     let mut builder = Builder::new(pt.clone());
 
     if !pt.expect_subnodes(cx, ["mcu", "os", "drivers"]) {
-      return builder;  // TODO(farcaller): report error?
+      return None;
     }
 
     match pt.get_by_path("mcu") {
@@ -73,7 +73,7 @@ impl Builder {
       }
     }
 
-    builder
+    Some(builder)
   }
 
   fn walk_mutate(builder: &mut Builder, cx: &mut ExtCtxt, node: &Rc<node::Node>) {

src/hal/lpc17xx/platformtree.rs

@@ -114,8 +114,10 @@ mod test {
           }
         }
       }", |cx, failed, pt| {
-      let builder = Builder::build(cx, pt);
-      let items = builder.emit_items(cx);
+      let items = Builder::build(cx, pt)
+        .expect(format!("Unexpected failure on {}", line!()).as_slice())
+        .emit_items(cx);
+
       assert!(unsafe{*failed} == false);
       assert!(items.len() == 3);