1 files changed, 68 insertions, 15 deletions

diff --git a/crates/ra_mbe/src/mbe_parser.rs b/crates/ra_mbe/src/mbe_parser.rs
index 58e2533f1..e3669f66c 100644
--- a/crates/ra_mbe/src/mbe_parser.rs
+++ b/crates/ra_mbe/src/mbe_parser.rs
@@ -1,33 +1,34 @@
 /// This module parses a raw `tt::TokenStream` into macro-by-example token
 /// stream. This is a *mostly* identify function, expect for handling of
 /// `$var:tt_kind` and `$(repeat),*` constructs.
+use crate::ParseError;
 use crate::tt_cursor::TtCursor;
 
-pub(crate) fn parse(tt: &tt::Subtree) -> Option<crate::MacroRules> {
+pub(crate) fn parse(tt: &tt::Subtree) -> Result<crate::MacroRules, ParseError> {
     let mut parser = TtCursor::new(tt);
     let mut rules = Vec::new();
     while !parser.is_eof() {
         rules.push(parse_rule(&mut parser)?);
-        if parser.expect_char(';') == None {
+        if let Err(e) = parser.expect_char(';') {
             if !parser.is_eof() {
-                return None;
+                return Err(e);
             }
             break;
         }
     }
-    Some(crate::MacroRules { rules })
+    Ok(crate::MacroRules { rules })
 }
 
-fn parse_rule(p: &mut TtCursor) -> Option<crate::Rule> {
+fn parse_rule(p: &mut TtCursor) -> Result<crate::Rule, ParseError> {
     let lhs = parse_subtree(p.eat_subtree()?)?;
     p.expect_char('=')?;
     p.expect_char('>')?;
     let mut rhs = parse_subtree(p.eat_subtree()?)?;
     rhs.delimiter = crate::Delimiter::None;
-    Some(crate::Rule { lhs, rhs })
+    Ok(crate::Rule { lhs, rhs })
 }
 
-fn parse_subtree(tt: &tt::Subtree) -> Option<crate::Subtree> {
+fn parse_subtree(tt: &tt::Subtree) -> Result<crate::Subtree, ParseError> {
     let mut token_trees = Vec::new();
     let mut p = TtCursor::new(tt);
     while let Some(tt) = p.eat() {
@@ -52,10 +53,10 @@ fn parse_subtree(tt: &tt::Subtree) -> Option<crate::Subtree> {
         };
         token_trees.push(child);
     }
-    Some(crate::Subtree { token_trees, delimiter: tt.delimiter })
+    Ok(crate::Subtree { token_trees, delimiter: tt.delimiter })
 }
 
-fn parse_var(p: &mut TtCursor) -> Option<crate::Var> {
+fn parse_var(p: &mut TtCursor) -> Result<crate::Var, ParseError> {
     let ident = p.eat_ident().unwrap();
     let text = ident.text.clone();
     let kind = if p.at_char(':') {
@@ -69,25 +70,77 @@ fn parse_var(p: &mut TtCursor) -> Option<crate::Var> {
     } else {
         None
     };
-    Some(crate::Var { text, kind })
+    Ok(crate::Var { text, kind })
 }
 
-fn parse_repeat(p: &mut TtCursor) -> Option<crate::Repeat> {
+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()?;
+    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()?.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 None,
+        _ => return Err(ParseError::Expected(String::from("repeat"))),
     };
     p.bump();
-    Some(crate::Repeat { subtree, kind, separator })
+    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)
+    }
+
 }