1 files changed, 67 insertions, 0 deletions

diff --git a/crates/hir_expand/src/builtin_attr.rs b/crates/hir_expand/src/builtin_attr.rs
new file mode 100644
index 000000000..c8432005e
--- /dev/null
+++ b/crates/hir_expand/src/builtin_attr.rs
@@ -0,0 +1,67 @@
+//! Builtin derives.
+
+use syntax::ast;
+
+use crate::{db::AstDatabase, name, AstId, CrateId, MacroCallId, MacroDefId, MacroDefKind};
+
+macro_rules! register_builtin {
+    ( $(($name:ident, $variant:ident) => $expand:ident),* ) => {
+        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+        pub enum BuiltinAttrExpander {
+            $($variant),*
+        }
+
+        impl BuiltinAttrExpander {
+            pub fn expand(
+                &self,
+                db: &dyn AstDatabase,
+                id: MacroCallId,
+                tt: &tt::Subtree,
+            ) -> Result<tt::Subtree, mbe::ExpandError> {
+                let expander = match *self {
+                    $( BuiltinAttrExpander::$variant => $expand, )*
+                };
+                expander(db, id, tt)
+            }
+
+            fn find_by_name(name: &name::Name) -> Option<Self> {
+                match name {
+                    $( id if id == &name::name![$name] => Some(BuiltinAttrExpander::$variant), )*
+                     _ => None,
+                }
+            }
+        }
+
+    };
+}
+
+register_builtin! {
+    (bench, Bench) => dummy_attr_expand,
+    (cfg_accessible, CfgAccessible) => dummy_attr_expand,
+    (cfg_eval, CfgEval) => dummy_attr_expand,
+    (derive, Derive) => dummy_attr_expand,
+    (global_allocator, GlobalAllocator) => dummy_attr_expand,
+    (test, Test) => dummy_attr_expand,
+    (test_case, TestCase) => dummy_attr_expand
+}
+
+pub fn find_builtin_attr(
+    ident: &name::Name,
+    krate: CrateId,
+    ast_id: AstId<ast::Macro>,
+) -> Option<MacroDefId> {
+    let expander = BuiltinAttrExpander::find_by_name(ident)?;
+    Some(MacroDefId {
+        krate,
+        kind: MacroDefKind::BuiltInAttr(expander, ast_id),
+        local_inner: false,
+    })
+}
+
+fn dummy_attr_expand(
+    _db: &dyn AstDatabase,
+    _id: MacroCallId,
+    tt: &tt::Subtree,
+) -> Result<tt::Subtree, mbe::ExpandError> {
+    Ok(tt.clone())
+}