Add #[heapsize]/#[derive(HeapSizeOf)] plugin to auto-derive HeapSizeOf impls

(fixes #5914)

components/plugins/heapsize.rs

@@ -0,0 +1,54 @@
+
+use syntax::ext::base::{Annotatable, ExtCtxt};
+use syntax::codemap::Span;
+use syntax::ptr::P;
+use syntax::ast::*;
+use syntax::attr::AttrMetaMethods;
+use syntax::ext::build::AstBuilder;
+use syntax::ext::deriving::generic::*;
+
+pub fn expand_heapsize(cx: &mut ExtCtxt, span: Span, mitem: &MetaItem, item: Annotatable, push: &mut FnMut(Annotatable)) {
+    let trait_def = TraitDef {
+        span: span,
+        attributes: Vec::new(),
+        path: ty::Path::new(vec!("util", "mem", "HeapSizeOf")),
+        additional_bounds: Vec::new(),
+        generics: ty::LifetimeBounds::empty(),
+        methods: vec![
+            MethodDef {
+                name: "heap_size_of_children",
+                generics: ty::LifetimeBounds::empty(),
+                explicit_self: ty::borrowed_explicit_self(),
+                args: vec!(),
+                ret_ty: ty::Literal(ty::Path::new_local("usize")),
+                attributes: vec!(),
+                is_unsafe: false,
+                combine_substructure: combine_substructure(Box::new(heapsize_substructure))
+            }
+        ],
+        associated_types: vec![],
+    };
+    trait_def.expand(cx, mitem, &item, push)
+}
+
+fn heapsize_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
+    let fields = match *substr.fields {
+        Struct(ref fs) | EnumMatching(_, _, ref fs) => fs,
+        _ => cx.span_bug(trait_span, "impossible substructure in `heapsize`")
+    };
+
+    fields.iter().fold(cx.expr_usize(trait_span, 0),
+                       |acc, ref item| {
+                        if item.attrs.iter()
+                               .find(|ref a| a.check_name("ignore_heapsize"))
+                               .is_some() {
+                            acc
+                        } else {
+                            cx.expr_binary(item.span, BiAdd, acc,
+                                           cx.expr_method_call(item.span,
+                                                               item.self_.clone(),
+                                                               substr.method_ident,
+                                                               Vec::new()))
+                        }
+                    })
+}