3 files changed, 98 insertions, 10 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 37455bc57..3738cfe8c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1012,6 +1012,7 @@ dependencies = [
  "ra_prof",
  "ra_syntax",
  "ra_tt",
+ "test_utils",
 ]
 
 [[package]]
diff --git a/crates/ra_hir_expand/Cargo.toml b/crates/ra_hir_expand/Cargo.toml
index d6e3c1f76..2cd522766 100644
--- a/crates/ra_hir_expand/Cargo.toml
+++ b/crates/ra_hir_expand/Cargo.toml
@@ -18,3 +18,4 @@ ra_parser = { path = "../ra_parser" }
 ra_prof = { path = "../ra_prof" }
 tt = { path = "../ra_tt", package = "ra_tt" }
 mbe = { path = "../ra_mbe", package = "ra_mbe" }
+test_utils = { path = "../test_utils"}
diff --git a/crates/ra_hir_expand/src/proc_macro.rs b/crates/ra_hir_expand/src/proc_macro.rs
index 97d1208ec..4e0e069c8 100644
--- a/crates/ra_hir_expand/src/proc_macro.rs
+++ b/crates/ra_hir_expand/src/proc_macro.rs
@@ -2,6 +2,7 @@
 
 use crate::{db::AstDatabase, LazyMacroId};
 use ra_db::{CrateId, ProcMacroId};
+use tt::buffer::{Cursor, TokenBuffer};
 
 #[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
 pub struct ProcMacroExpander {
@@ -36,22 +37,107 @@ impl ProcMacroExpander {
             .clone()
             .ok_or_else(|| err!("No derive macro found."))?;
 
-        let tt = remove_derive_atr(tt, &proc_macro.name)
+        let tt = remove_derive_attrs(tt)
             .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);
+fn eat_punct(cursor: &mut Cursor, c: char) -> bool {
+    if let Some(tt::TokenTree::Leaf(tt::Leaf::Punct(punct))) = cursor.token_tree() {
+        if punct.char == c {
+            *cursor = cursor.bump();
+            return true;
+        }
     }
+    false
+}
+
+fn eat_subtree(cursor: &mut Cursor, kind: tt::DelimiterKind) -> bool {
+    if let Some(tt::TokenTree::Subtree(subtree)) = cursor.token_tree() {
+        if Some(kind) == subtree.delimiter_kind() {
+            *cursor = cursor.bump_subtree();
+            return true;
+        }
+    }
+    false
+}
+
+fn eat_ident(cursor: &mut Cursor, t: &str) -> bool {
+    if let Some(tt::TokenTree::Leaf(tt::Leaf::Ident(ident))) = cursor.token_tree() {
+        if t == ident.text.as_str() {
+            *cursor = cursor.bump();
+            return true;
+        }
+    }
+    false
+}
+
+fn remove_derive_attrs(tt: &tt::Subtree) -> Option<tt::Subtree> {
+    let buffer = TokenBuffer::new(&tt.token_trees);
+    let mut p = buffer.begin();
+    let mut result = tt::Subtree::default();
+
+    while !p.eof() {
+        let curr = p;
 
-    None
+        if eat_punct(&mut p, '#') {
+            eat_punct(&mut p, '!');
+            let parent = p;
+            if eat_subtree(&mut p, tt::DelimiterKind::Bracket) {
+                if eat_ident(&mut p, "derive") {
+                    p = parent.bump();
+                    continue;
+                }
+            }
+        }
+
+        result.token_trees.push(curr.token_tree()?.clone());
+        p = curr.bump();
+    }
+
+    Some(result)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use test_utils::assert_eq_text;
+
+    #[test]
+    fn test_remove_derive_attrs() {
+        let tt = mbe::parse_to_token_tree(
+            r#"
+    #[allow(unused)]
+    #[derive(Copy)]
+    #[derive(Hello)]
+    struct A {
+        bar: u32
+    }
+"#,
+        )
+        .unwrap()
+        .0;
+        let result = format!("{:#?}", remove_derive_attrs(&tt).unwrap());
+
+        assert_eq_text!(
+            &result,
+            r#"
+SUBTREE $
+  PUNCH   # [alone] 0
+  SUBTREE [] 1
+    IDENT   allow 2
+    SUBTREE () 3
+      IDENT   unused 4
+  IDENT   struct 15
+  IDENT   A 16
+  SUBTREE {} 17
+    IDENT   bar 18
+    PUNCH   : [alone] 19
+    IDENT   u32 20
+"#
+            .trim()
+        );
+    }
 }