1 files changed, 46 insertions, 0 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index 3e7f458cf..922256c03 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -160,4 +160,50 @@ impl_froms!(TokenTree: Leaf, Subtree);
          impl From < Subtree > for TokenTree {fn from (it : Subtree) -> TokenTree {TokenTree :: Subtree (it)}}"
     )
     }
+
+    fn assert_expansion(rules: &MacroRules, invocation: &str, expansion: &str) {
+        let source_file = ast::SourceFile::parse(invocation);
+        let macro_invocation = source_file
+            .syntax()
+            .descendants()
+            .find_map(ast::MacroCall::cast)
+            .unwrap();
+
+        let invocation_tt = ast_to_token_tree(macro_invocation.token_tree().unwrap()).unwrap();
+
+        let expaned = rules.expand(&invocation_tt).unwrap();
+        assert_eq!(expaned.to_string(), expansion);
+    }
+
+    #[test]
+    fn test_fail_match_pattern_by_token() {
+        let macro_definition = r#"
+        macro_rules! foo {
+            ($ i:ident) => (
+                mod $ i {}
+            );
+            (= $ i:ident) => (
+                fn $ i() {}
+            );
+            (+ $ i:ident) => (
+                struct $ i;
+            )
+        }
+"#;
+
+        let source_file = ast::SourceFile::parse(macro_definition);
+        let macro_definition = source_file
+            .syntax()
+            .descendants()
+            .find_map(ast::MacroCall::cast)
+            .unwrap();
+
+        let definition_tt = ast_to_token_tree(macro_definition.token_tree().unwrap()).unwrap();
+        let rules = crate::MacroRules::parse(&definition_tt).unwrap();
+
+        assert_expansion(&rules, "foo! { foo }", "mod foo {}");
+        assert_expansion(&rules, "foo! { = bar }", "fn bar () {}");
+        assert_expansion(&rules, "foo! { + Baz }", "struct Baz ;");
+    }
+
 }