3 files changed, 58 insertions, 6 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index 34840dfa1..2c75b7b4f 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -26,7 +26,7 @@ pub use tt::{Delimiter, Punct};
 
 #[derive(Debug, PartialEq, Eq)]
 pub enum ParseError {
-    ParseError,
+    Expected(String),
 }
 
 #[derive(Debug, PartialEq, Eq)]
diff --git a/crates/ra_mbe/src/mbe_parser.rs b/crates/ra_mbe/src/mbe_parser.rs
index d067e5248..e3669f66c 100644
--- a/crates/ra_mbe/src/mbe_parser.rs
+++ b/crates/ra_mbe/src/mbe_parser.rs
@@ -77,18 +77,70 @@ fn parse_repeat(p: &mut TtCursor) -> Result<crate::Repeat, ParseError> {
     let subtree = p.eat_subtree().unwrap();
     let mut subtree = parse_subtree(subtree)?;
     subtree.delimiter = crate::Delimiter::None;
-    let sep = p.eat_punct().ok_or(ParseError::ParseError)?;
+    let sep = p.eat_punct().ok_or(ParseError::Expected(String::from("separator")))?;
     let (separator, rep) = match sep.char {
         '*' | '+' | '?' => (None, sep.char),
-        char => (Some(char), p.eat_punct().ok_or(ParseError::ParseError)?.char),
+        char => {
+            (Some(char), p.eat_punct().ok_or(ParseError::Expected(String::from("separator")))?.char)
+        }
     };
 
     let kind = match rep {
         '*' => crate::RepeatKind::ZeroOrMore,
         '+' => crate::RepeatKind::OneOrMore,
         '?' => crate::RepeatKind::ZeroOrOne,
-        _ => return Err(ParseError::ParseError),
+        _ => return Err(ParseError::Expected(String::from("repeat"))),
     };
     p.bump();
     Ok(crate::Repeat { subtree, kind, separator })
 }
+
+#[cfg(test)]
+mod tests {
+    use ra_syntax::{ast, AstNode};
+
+    use super::*;
+    use crate::ast_to_token_tree;
+
+    #[test]
+    fn test_invalid_parse() {
+        expect_err("invalid", "subtree");
+
+        is_valid("($i:ident) => ()");
+        expect_err("$i:ident => ()", "subtree");
+        expect_err("($i:ident) ()", "`=`");
+        expect_err("($($i:ident)_) => ()", "separator");
+    }
+
+    fn expect_err(macro_body: &str, expected: &str) {
+        assert_eq!(
+            create_rules(&format_macro(macro_body)),
+            Err(ParseError::Expected(String::from(expected)))
+        );
+    }
+
+    fn is_valid(macro_body: &str) {
+        assert!(create_rules(&format_macro(macro_body)).is_ok());
+    }
+
+    fn format_macro(macro_body: &str) -> String {
+        format!(
+            "
+        macro_rules! foo {{
+            {}
+        }}
+",
+            macro_body
+        )
+    }
+
+    fn create_rules(macro_definition: &str) -> Result<crate::MacroRules, ParseError> {
+        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();
+        parse(&definition_tt)
+    }
+
+}
diff --git a/crates/ra_mbe/src/tt_cursor.rs b/crates/ra_mbe/src/tt_cursor.rs
index d06bfbf9f..3128cb9ae 100644
--- a/crates/ra_mbe/src/tt_cursor.rs
+++ b/crates/ra_mbe/src/tt_cursor.rs
@@ -60,7 +60,7 @@ impl<'a> TtCursor<'a> {
                 self.bump();
                 Ok(sub)
             }
-            _ => Err(ParseError::ParseError),
+            _ => Err(ParseError::Expected(String::from("subtree"))),
         }
     }
 
@@ -83,7 +83,7 @@ impl<'a> TtCursor<'a> {
             self.bump();
             Ok(())
         } else {
-            Err(ParseError::ParseError)
+            Err(ParseError::Expected(format!("`{}`", char)))
         }
     }
 }