1 files changed, 64 insertions, 0 deletions

diff --git a/crates/ra_hir_expand/src/builtin_derive.rs b/crates/ra_hir_expand/src/builtin_derive.rs
new file mode 100644
index 000000000..0a70c63c0
--- /dev/null
+++ b/crates/ra_hir_expand/src/builtin_derive.rs
@@ -0,0 +1,64 @@
+//! Builtin derives.
+use crate::db::AstDatabase;
+use crate::{name, MacroCallId, MacroDefId, MacroDefKind};
+
+use crate::quote;
+
+macro_rules! register_builtin {
+    ( $(($name:ident, $kind: ident) => $expand:ident),* ) => {
+        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+        pub enum BuiltinDeriveExpander {
+            $($kind),*
+        }
+
+        impl BuiltinDeriveExpander {
+            pub fn expand(
+                &self,
+                db: &dyn AstDatabase,
+                id: MacroCallId,
+                tt: &tt::Subtree,
+            ) -> Result<tt::Subtree, mbe::ExpandError> {
+                let expander = match *self {
+                    $( BuiltinDeriveExpander::$kind => $expand, )*
+                };
+                expander(db, id, tt)
+            }
+        }
+
+        pub fn find_builtin_derive(ident: &name::Name) -> Option<MacroDefId> {
+            let kind = match ident {
+                 $( id if id == &name::$name => BuiltinDeriveExpander::$kind, )*
+                 _ => return None,
+            };
+
+            Some(MacroDefId { krate: None, ast_id: None, kind: MacroDefKind::BuiltInDerive(kind) })
+        }
+    };
+}
+
+register_builtin! {
+    (COPY_TRAIT, Copy) => copy_expand,
+    (CLONE_TRAIT, Clone) => clone_expand
+}
+
+fn copy_expand(
+    _db: &dyn AstDatabase,
+    _id: MacroCallId,
+    _tt: &tt::Subtree,
+) -> Result<tt::Subtree, mbe::ExpandError> {
+    let expanded = quote! {
+        impl Copy for Foo {}
+    };
+    Ok(expanded)
+}
+
+fn clone_expand(
+    _db: &dyn AstDatabase,
+    _id: MacroCallId,
+    _tt: &tt::Subtree,
+) -> Result<tt::Subtree, mbe::ExpandError> {
+    let expanded = quote! {
+        impl Clone for Foo {}
+    };
+    Ok(expanded)
+}