Add #[jstraceable] syntax extension

1 files changed, 76 insertions, 0 deletions

diff --git a/components/plugins/jstraceable.rs b/components/plugins/jstraceable.rs
new file mode 100644
index 00000000000..5a113ab1691
--- /dev/null
+++ b/components/plugins/jstraceable.rs
@@ -0,0 +1,76 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use syntax::ext::base::ExtCtxt;
+use syntax::codemap::Span;
+use syntax::ptr::P;
+use syntax::ast::{Item, MetaItem, Expr};
+use syntax::ast;
+use syntax::ext::build::AstBuilder;
+use syntax::ext::deriving::generic::{combine_substructure, EnumMatching, FieldInfo, MethodDef, Struct, Substructure, TraitDef, ty};
+
+ pub fn expand_jstraceable(cx: &mut ExtCtxt, span: Span, mitem: &MetaItem, item: &Item, push: |P<Item>|) {
+    let trait_def = TraitDef {
+        span: span,
+        attributes: Vec::new(),
+        path: ty::Path::new(vec!("dom","bindings","trace","JSTraceable")),
+        additional_bounds: Vec::new(),
+        generics: ty::LifetimeBounds::empty(),
+        methods: vec!(
+            MethodDef {
+                name: "trace",
+                generics: ty::LifetimeBounds::empty(),
+                explicit_self: ty::borrowed_explicit_self(),
+                args: vec!(ty::Ptr(box ty::Literal(ty::Path::new(vec!("js","jsapi","JSTracer"))), ty::Raw(ast::MutMutable))),
+                ret_ty: ty::nil_ty(),
+                attributes: vec!(),
+                combine_substructure: combine_substructure(|a, b, c| {
+                    jstraceable_substructure(a, b, c)
+                })
+            }
+        )
+    };
+    trait_def.expand(cx, mitem, item, push)    
+}
+
+// Mostly copied from syntax::ext::deriving::hash
+fn jstraceable_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
+    let state_expr = match substr.nonself_args {
+        [ref state_expr] => state_expr,
+        _ => cx.span_bug(trait_span, "incorrect number of arguments in `jstraceable`")
+    };
+    let hash_ident = substr.method_ident;
+    let call_hash = |span, thing_expr| {
+        let expr = cx.expr_method_call(span, thing_expr, hash_ident, vec!(state_expr.clone()));
+        cx.stmt_expr(expr)
+    };
+    let mut stmts = Vec::new();
+
+    let fields = match *substr.fields {
+        Struct(ref fs) => fs,
+        EnumMatching(index, variant, ref fs) => {
+            // Determine the discriminant. We will feed this value to the byte
+            // iteration function.
+            let discriminant = match variant.node.disr_expr {
+                Some(ref d) => d.clone(),
+                None => cx.expr_uint(trait_span, index)
+            };
+
+            stmts.push(call_hash(trait_span, discriminant));
+
+            fs
+        }
+        _ => cx.span_bug(trait_span, "impossible substructure in `jstraceable`")
+    };
+
+    for &FieldInfo { ref self_, span, .. } in fields.iter() {
+        stmts.push(call_hash(span, self_.clone()));
+    }
+
+    if stmts.len() == 0 {
+        cx.span_bug(trait_span, "#[jstraceable] needs at least one field");
+    }
+
+    cx.expr_block(cx.block(trait_span, stmts, None))
+}