1 files changed, 26 insertions, 1 deletions

diff --git a/crates/ra_hir_expand/src/proc_macro.rs b/crates/ra_hir_expand/src/proc_macro.rs
index 4d270e0de..97d1208ec 100644
--- a/crates/ra_hir_expand/src/proc_macro.rs
+++ b/crates/ra_hir_expand/src/proc_macro.rs
@@ -9,6 +9,15 @@ pub struct ProcMacroExpander {
     proc_macro_id: ProcMacroId,
 }
 
+macro_rules! err {
+    ($fmt:literal, $($tt:tt),*) => {
+        mbe::ExpandError::ProcMacroError(tt::ExpansionError::Unknown(format!($fmt, $($tt),*)))
+    };
+    ($fmt:literal) => {
+        mbe::ExpandError::ProcMacroError(tt::ExpansionError::Unknown($fmt.to_string()))
+    }
+}
+
 impl ProcMacroExpander {
     pub fn new(krate: CrateId, proc_macro_id: ProcMacroId) -> ProcMacroExpander {
         ProcMacroExpander { krate, proc_macro_id }
@@ -25,8 +34,24 @@ impl ProcMacroExpander {
             .proc_macro
             .get(self.proc_macro_id.0 as usize)
             .clone()
-            .ok_or_else(|| mbe::ExpandError::ConversionError)?;
+            .ok_or_else(|| err!("No derive macro found."))?;
+
+        let tt = remove_derive_atr(tt, &proc_macro.name)
+            .ok_or_else(|| err!("Fail to remove derive for custom derive"))?;
 
         proc_macro.expander.expand(&tt, None).map_err(mbe::ExpandError::from)
     }
 }
+
+fn remove_derive_atr(tt: &tt::Subtree, _name: &str) -> Option<tt::Subtree> {
+    // FIXME: proper handle the remove derive
+    // We assume the first 2 tokens are #[derive(name)]
+    if tt.token_trees.len() > 2 {
+        let mut tt = tt.clone();
+        tt.token_trees.remove(0);
+        tt.token_trees.remove(0);
+        return Some(tt);
+    }
+
+    None
+}