5 files changed, 254 insertions, 124 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index 43afe24cc..6a9037bfc 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -150,7 +150,7 @@ impl MacroRules {
         Ok(MacroRules { rules, shift: Shift::new(tt) })
     }
 
-    pub fn expand(&self, tt: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
+    pub fn expand(&self, tt: &tt::Subtree) -> ExpandResult<tt::Subtree> {
         // apply shift
         let mut tt = tt.clone();
         self.shift.shift_all(&mut tt);
@@ -209,5 +209,35 @@ fn validate(pattern: &tt::Subtree) -> Result<(), ParseError> {
     Ok(())
 }
 
+pub struct ExpandResult<T>(pub T, pub Option<ExpandError>);
+
+impl<T> ExpandResult<T> {
+    pub fn ok(t: T) -> ExpandResult<T> {
+        ExpandResult(t, None)
+    }
+
+    pub fn only_err(err: ExpandError) -> ExpandResult<T>
+    where
+        T: Default,
+    {
+        ExpandResult(Default::default(), Some(err))
+    }
+
+    pub fn map<U>(self, f: impl FnOnce(T) -> U) -> ExpandResult<U> {
+        ExpandResult(f(self.0), self.1)
+    }
+
+    pub fn result(self) -> Result<T, ExpandError> {
+        self.1.map(Err).unwrap_or(Ok(self.0))
+    }
+}
+
+impl<T: Default> From<Result<T, ExpandError>> for ExpandResult<T> {
+    fn from(result: Result<T, ExpandError>) -> ExpandResult<T> {
+        result
+            .map_or_else(|e| ExpandResult(Default::default(), Some(e)), |it| ExpandResult(it, None))
+    }
+}
+
 #[cfg(test)]
 mod tests;
diff --git a/crates/ra_mbe/src/mbe_expander.rs b/crates/ra_mbe/src/mbe_expander.rs
index b455b7321..b1eacf124 100644
--- a/crates/ra_mbe/src/mbe_expander.rs
+++ b/crates/ra_mbe/src/mbe_expander.rs
@@ -8,19 +8,51 @@ mod transcriber;
 use ra_syntax::SmolStr;
 use rustc_hash::FxHashMap;
 
-use crate::ExpandError;
+use crate::{ExpandError, ExpandResult};
 
-pub(crate) fn expand(
-    rules: &crate::MacroRules,
-    input: &tt::Subtree,
-) -> Result<tt::Subtree, ExpandError> {
-    rules.rules.iter().find_map(|it| expand_rule(it, input).ok()).ok_or(ExpandError::NoMatchingRule)
+pub(crate) fn expand(rules: &crate::MacroRules, input: &tt::Subtree) -> ExpandResult<tt::Subtree> {
+    expand_rules(&rules.rules, input)
 }
 
-fn expand_rule(rule: &crate::Rule, input: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
-    let bindings = matcher::match_(&rule.lhs, input)?;
-    let res = transcriber::transcribe(&rule.rhs, &bindings)?;
-    Ok(res)
+fn expand_rules(rules: &[crate::Rule], input: &tt::Subtree) -> ExpandResult<tt::Subtree> {
+    let mut match_: Option<(matcher::Match, &crate::Rule)> = None;
+    for rule in rules {
+        let new_match = match matcher::match_(&rule.lhs, input) {
+            Ok(m) => m,
+            Err(_e) => {
+                // error in pattern parsing
+                continue;
+            }
+        };
+        if new_match.err.is_none() {
+            // If we find a rule that applies without errors, we're done.
+            // Unconditionally returning the transcription here makes the
+            // `test_repeat_bad_var` test fail.
+            let ExpandResult(res, transcribe_err) =
+                transcriber::transcribe(&rule.rhs, &new_match.bindings);
+            if transcribe_err.is_none() {
+                return ExpandResult::ok(res);
+            }
+        }
+        // Use the rule if we matched more tokens, or had fewer errors
+        if let Some((prev_match, _)) = &match_ {
+            if (new_match.unmatched_tts, new_match.err_count)
+                < (prev_match.unmatched_tts, prev_match.err_count)
+            {
+                match_ = Some((new_match, rule));
+            }
+        } else {
+            match_ = Some((new_match, rule));
+        }
+    }
+    if let Some((match_, rule)) = match_ {
+        // if we got here, there was no match without errors
+        let ExpandResult(result, transcribe_err) =
+            transcriber::transcribe(&rule.rhs, &match_.bindings);
+        ExpandResult(result, match_.err.or(transcribe_err))
+    } else {
+        ExpandResult(tt::Subtree::default(), Some(ExpandError::NoMatchingRule))
+    }
 }
 
 /// The actual algorithm for expansion is not too hard, but is pretty tricky.
@@ -111,7 +143,7 @@ mod tests {
     }
 
     fn assert_err(macro_body: &str, invocation: &str, err: ExpandError) {
-        assert_eq!(expand_first(&create_rules(&format_macro(macro_body)), invocation), Err(err));
+        assert_eq!(expand_first(&create_rules(&format_macro(macro_body)), invocation).1, Some(err));
     }
 
     fn format_macro(macro_body: &str) -> String {
@@ -135,10 +167,7 @@ mod tests {
         crate::MacroRules::parse(&definition_tt).unwrap()
     }
 
-    fn expand_first(
-        rules: &crate::MacroRules,
-        invocation: &str,
-    ) -> Result<tt::Subtree, ExpandError> {
+    fn expand_first(rules: &crate::MacroRules, invocation: &str) -> ExpandResult<tt::Subtree> {
         let source_file = ast::SourceFile::parse(invocation).ok().unwrap();
         let macro_invocation =
             source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
@@ -146,6 +175,6 @@ mod tests {
         let (invocation_tt, _) =
             ast_to_token_tree(&macro_invocation.token_tree().unwrap()).unwrap();
 
-        expand_rule(&rules.rules[0], &invocation_tt)
+        expand_rules(&rules.rules, &invocation_tt)
     }
 }
diff --git a/crates/ra_mbe/src/mbe_expander/matcher.rs b/crates/ra_mbe/src/mbe_expander/matcher.rs
index 49c53183a..2579382da 100644
--- a/crates/ra_mbe/src/mbe_expander/matcher.rs
+++ b/crates/ra_mbe/src/mbe_expander/matcher.rs
@@ -8,6 +8,7 @@ use crate::{
     ExpandError,
 };
 
+use super::ExpandResult;
 use ra_parser::{FragmentKind::*, TreeSink};
 use ra_syntax::{SmolStr, SyntaxKind};
 use tt::buffer::{Cursor, TokenBuffer};
@@ -58,36 +59,61 @@ macro_rules! err {
     };
 }
 
-macro_rules! bail {
-    ($($tt:tt)*) => {
-        return Err(err!($($tt)*))
-    };
+#[derive(Debug, Default)]
+pub(super) struct Match {
+    pub bindings: Bindings,
+    /// We currently just keep the first error and count the rest to compare matches.
+    pub err: Option<ExpandError>,
+    pub err_count: usize,
+    /// How many top-level token trees were left to match.
+    pub unmatched_tts: usize,
 }
 
-pub(super) fn match_(pattern: &tt::Subtree, src: &tt::Subtree) -> Result<Bindings, ExpandError> {
+impl Match {
+    pub fn add_err(&mut self, err: ExpandError) {
+        let prev_err = self.err.take();
+        self.err = prev_err.or(Some(err));
+        self.err_count += 1;
+    }
+}
+
+// General note: These functions have two channels to return errors, a `Result`
+// return value and the `&mut Match`. The returned Result is for pattern parsing
+// errors; if a branch of the macro definition doesn't parse, it doesn't make
+// sense to try using it. Matching errors are added to the `Match`. It might
+// make sense to make pattern parsing a separate step?
+
+pub(super) fn match_(pattern: &tt::Subtree, src: &tt::Subtree) -> Result<Match, ExpandError> {
     assert!(pattern.delimiter == None);
 
-    let mut res = Bindings::default();
+    let mut res = Match::default();
     let mut src = TtIter::new(src);
 
     match_subtree(&mut res, pattern, &mut src)?;
 
     if src.len() > 0 {
-        bail!("leftover tokens");
+        res.unmatched_tts += src.len();
+        res.add_err(err!("leftover tokens"));
     }
 
     Ok(res)
 }
 
 fn match_subtree(
-    bindings: &mut Bindings,
+    res: &mut Match,
     pattern: &tt::Subtree,
     src: &mut TtIter,
 ) -> Result<(), ExpandError> {
     for op in parse_pattern(pattern) {
         match op? {
             Op::TokenTree(tt::TokenTree::Leaf(lhs)) => {
-                let rhs = src.expect_leaf().map_err(|()| err!("expected leaf: `{}`", lhs))?;
+                let rhs = match src.expect_leaf() {
+                    Ok(l) => l,
+                    Err(()) => {
+                        res.add_err(err!("expected leaf: `{}`", lhs));
+                        continue;
+                    }
+                };
                 match (lhs, rhs) {
                     (
                         tt::Leaf::Punct(tt::Punct { char: lhs, .. }),
@@ -101,31 +127,51 @@ fn match_subtree(
                         tt::Leaf::Literal(tt::Literal { text: lhs, .. }),
                         tt::Leaf::Literal(tt::Literal { text: rhs, .. }),
                     ) if lhs == rhs => (),
-                    _ => return Err(ExpandError::UnexpectedToken),
+                    _ => {
+                        res.add_err(ExpandError::UnexpectedToken);
+                    }
                 }
             }
             Op::TokenTree(tt::TokenTree::Subtree(lhs)) => {
-                let rhs = src.expect_subtree().map_err(|()| err!("expected subtree"))?;
+                let rhs = match src.expect_subtree() {
+                    Ok(s) => s,
+                    Err(()) => {
+                        res.add_err(err!("expected subtree"));
+                        continue;
+                    }
+                };
                 if lhs.delimiter_kind() != rhs.delimiter_kind() {
-                    bail!("mismatched delimiter")
+                    res.add_err(err!("mismatched delimiter"));
+                    continue;
                 }
                 let mut src = TtIter::new(rhs);
-                match_subtree(bindings, lhs, &mut src)?;
+                match_subtree(res, lhs, &mut src)?;
                 if src.len() > 0 {
-                    bail!("leftover tokens");
+                    res.add_err(err!("leftover tokens"));
                 }
             }
             Op::Var { name, kind } => {
-                let kind = kind.as_ref().ok_or(ExpandError::UnexpectedToken)?;
-                match match_meta_var(kind.as_str(), src)? {
+                let kind = match kind {
+                    Some(k) => k,
+                    None => {
+                        res.add_err(ExpandError::UnexpectedToken);
+                        continue;
+                    }
+                };
+                let ExpandResult(matched, match_err) = match_meta_var(kind.as_str(), src);
+                match matched {
                     Some(fragment) => {
-                        bindings.inner.insert(name.clone(), Binding::Fragment(fragment));
+                        res.bindings.inner.insert(name.clone(), Binding::Fragment(fragment));
                     }
-                    None => bindings.push_optional(name),
+                    None if match_err.is_none() => res.bindings.push_optional(name),
+                    _ => {}
+                }
+                if let Some(err) = match_err {
+                    res.add_err(err);
                 }
             }
             Op::Repeat { subtree, kind, separator } => {
-                match_repeat(bindings, subtree, kind, separator, src)?
+                match_repeat(res, subtree, kind, separator, src)?;
             }
         }
     }
@@ -221,7 +267,7 @@ impl<'a> TtIter<'a> {
     pub(crate) fn expect_fragment(
         &mut self,
         fragment_kind: ra_parser::FragmentKind,
-    ) -> Result<tt::TokenTree, ()> {
+    ) -> ExpandResult<Option<tt::TokenTree>> {
         pub(crate) struct OffsetTokenSink<'a> {
             pub(crate) cursor: Cursor<'a>,
             pub(crate) error: bool,
@@ -246,45 +292,51 @@ impl<'a> TtIter<'a> {
 
         ra_parser::parse_fragment(&mut src, &mut sink, fragment_kind);
 
+        let mut err = None;
         if !sink.cursor.is_root() || sink.error {
-            // FIXME better recovery in this case would help completion inside macros immensely
-            return Err(());
+            err = Some(err!("expected {:?}", fragment_kind));
         }
 
         let mut curr = buffer.begin();
         let mut res = vec![];
 
-        while curr != sink.cursor {
-            if let Some(token) = curr.token_tree() {
-                res.push(token);
+        if sink.cursor.is_root() {
+            while curr != sink.cursor {
+                if let Some(token) = curr.token_tree() {
+                    res.push(token);
+                }
+                curr = curr.bump();
             }
-            curr = curr.bump();
         }
         self.inner = self.inner.as_slice()[res.len()..].iter();
-        match res.len() {
-            0 => Err(()),
-            1 => Ok(res[0].clone()),
-            _ => Ok(tt::TokenTree::Subtree(tt::Subtree {
+        if res.len() == 0 && err.is_none() {
+            err = Some(err!("no tokens consumed"));
+        }
+        let res = match res.len() {
+            1 => Some(res[0].clone()),
+            0 => None,
+            _ => Some(tt::TokenTree::Subtree(tt::Subtree {
                 delimiter: None,
                 token_trees: res.into_iter().cloned().collect(),
             })),
-        }
+        };
+        ExpandResult(res, err)
     }
 
     pub(crate) fn eat_vis(&mut self) -> Option<tt::TokenTree> {
         let mut fork = self.clone();
         match fork.expect_fragment(Visibility) {
-            Ok(tt) => {
+            ExpandResult(tt, None) => {
                 *self = fork;
-                Some(tt)
+                tt
             }
-            Err(()) => None,
+            ExpandResult(_, Some(_)) => None,
         }
     }
 }
 
 pub(super) fn match_repeat(
-    bindings: &mut Bindings,
+    res: &mut Match,
     pattern: &tt::Subtree,
     kind: RepeatKind,
     separator: Option<Separator>,
@@ -304,36 +356,46 @@ pub(super) fn match_repeat(
             }
         }
 
-        let mut nested = Bindings::default();
-        match match_subtree(&mut nested, pattern, &mut fork) {
-            Ok(()) => {
-                limit -= 1;
-                if limit == 0 {
-                    log::warn!("match_lhs excced in repeat pattern exceed limit => {:#?}\n{:#?}\n{:#?}\n{:#?}", pattern, src, kind, separator);
-                    break;
-                }
-                *src = fork;
+        let mut nested = Match::default();
+        match_subtree(&mut nested, pattern, &mut fork)?;
+        if nested.err.is_none() {
+            limit -= 1;
+            if limit == 0 {
+                log::warn!(
+                    "match_lhs exceeded repeat pattern limit => {:#?}\n{:#?}\n{:#?}\n{:#?}",
+                    pattern,
+                    src,
+                    kind,
+                    separator
+                );
+                break;
+            }
+            *src = fork;
 
-                bindings.push_nested(counter, nested)?;
-                counter += 1;
-                if counter == 1 {
-                    if let RepeatKind::ZeroOrOne = kind {
-                        break;
-                    }
+            if let Err(err) = res.bindings.push_nested(counter, nested.bindings) {
+                res.add_err(err);
+            }
+            counter += 1;
+            if counter == 1 {
+                if let RepeatKind::ZeroOrOne = kind {
+                    break;
                 }
             }
-            Err(_) => break,
+        } else {
+            break;
         }
     }
 
     match (kind, counter) {
-        (RepeatKind::OneOrMore, 0) => return Err(ExpandError::UnexpectedToken),
+        (RepeatKind::OneOrMore, 0) => {
+            res.add_err(ExpandError::UnexpectedToken);
+        }
         (_, 0) => {
             // Collect all empty variables in subtrees
             let mut vars = Vec::new();
             collect_vars(&mut vars, pattern)?;
             for var in vars {
-                bindings.push_empty(&var)
+                res.bindings.push_empty(&var)
             }
         }
         _ => (),
@@ -341,7 +403,7 @@ pub(super) fn match_repeat(
     Ok(())
 }
 
-fn match_meta_var(kind: &str, input: &mut TtIter) -> Result<Option<Fragment>, ExpandError> {
+fn match_meta_var(kind: &str, input: &mut TtIter) -> ExpandResult<Option<Fragment>> {
     let fragment = match kind {
         "path" => Path,
         "expr" => Expr,
@@ -352,34 +414,32 @@ fn match_meta_var(kind: &str, input: &mut TtIter) -> Result<Option<Fragment>, Ex
         "meta" => MetaItem,
         "item" => Item,
         _ => {
-            let tt = match kind {
-                "ident" => {
-                    let ident = input.expect_ident().map_err(|()| err!("expected ident"))?.clone();
-                    tt::Leaf::from(ident).into()
-                }
-                "tt" => input.expect_tt().map_err(|()| err!())?.clone(),
-                "lifetime" => {
-                    let ident = input.expect_lifetime().map_err(|()| err!())?;
-                    tt::Leaf::Ident(ident.clone()).into()
-                }
-                "literal" => {
-                    let literal = input.expect_literal().map_err(|()| err!())?.clone();
-                    tt::Leaf::from(literal).into()
-                }
+            let tt_result = match kind {
+                "ident" => input
+                    .expect_ident()
+                    .map(|ident| Some(tt::Leaf::from(ident.clone()).into()))
+                    .map_err(|()| err!("expected ident")),
+                "tt" => input.expect_tt().map(Some).map_err(|()| err!()),
+                "lifetime" => input
+                    .expect_lifetime()
+                    .map(|ident| Some(tt::Leaf::Ident(ident.clone()).into()))
+                    .map_err(|()| err!("expected lifetime")),
+                "literal" => input
+                    .expect_literal()
+                    .map(|literal| Some(tt::Leaf::from(literal.clone()).into()))
+                    .map_err(|()| err!()),
                 // `vis` is optional
                 "vis" => match input.eat_vis() {
-                    Some(vis) => vis,
-                    None => return Ok(None),
+                    Some(vis) => Ok(Some(vis)),
+                    None => Ok(None),
                 },
-                _ => return Err(ExpandError::UnexpectedToken),
+                _ => Err(ExpandError::UnexpectedToken),
             };
-            return Ok(Some(Fragment::Tokens(tt)));
+            return tt_result.map(|it| it.map(Fragment::Tokens)).into();
         }
     };
-    let tt =
-        input.expect_fragment(fragment).map_err(|()| err!("fragment did not parse as {}", kind))?;
-    let fragment = if kind == "expr" { Fragment::Ast(tt) } else { Fragment::Tokens(tt) };
-    Ok(Some(fragment))
+    let result = input.expect_fragment(fragment);
+    result.map(|tt| if kind == "expr" { tt.map(Fragment::Ast) } else { tt.map(Fragment::Tokens) })
 }
 
 fn collect_vars(buf: &mut Vec<SmolStr>, pattern: &tt::Subtree) -> Result<(), ExpandError> {
diff --git a/crates/ra_mbe/src/mbe_expander/transcriber.rs b/crates/ra_mbe/src/mbe_expander/transcriber.rs
index 7662020f3..4b173edd3 100644
--- a/crates/ra_mbe/src/mbe_expander/transcriber.rs
+++ b/crates/ra_mbe/src/mbe_expander/transcriber.rs
@@ -3,6 +3,7 @@
 
 use ra_syntax::SmolStr;
 
+use super::ExpandResult;
 use crate::{
     mbe_expander::{Binding, Bindings, Fragment},
     parser::{parse_template, Op, RepeatKind, Separator},
@@ -49,10 +50,7 @@ impl Bindings {
     }
 }
 
-pub(super) fn transcribe(
-    template: &tt::Subtree,
-    bindings: &Bindings,
-) -> Result<tt::Subtree, ExpandError> {
+pub(super) fn transcribe(template: &tt::Subtree, bindings: &Bindings) -> ExpandResult<tt::Subtree> {
     assert!(template.delimiter == None);
     let mut ctx = ExpandCtx { bindings: &bindings, nesting: Vec::new() };
     expand_subtree(&mut ctx, template)
@@ -75,35 +73,46 @@ struct ExpandCtx<'a> {
     nesting: Vec<NestingState>,
 }
 
-fn expand_subtree(ctx: &mut ExpandCtx, template: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
+fn expand_subtree(ctx: &mut ExpandCtx, template: &tt::Subtree) -> ExpandResult<tt::Subtree> {
     let mut buf: Vec<tt::TokenTree> = Vec::new();
+    let mut err = None;
     for op in parse_template(template) {
-        match op? {
+        let op = match op {
+            Ok(op) => op,
+            Err(e) => {
+                err = Some(e);
+                break;
+            }
+        };
+        match op {
             Op::TokenTree(tt @ tt::TokenTree::Leaf(..)) => buf.push(tt.clone()),
             Op::TokenTree(tt::TokenTree::Subtree(tt)) => {
-                let tt = expand_subtree(ctx, tt)?;
+                let ExpandResult(tt, e) = expand_subtree(ctx, tt);
+                err = err.or(e);
                 buf.push(tt.into());
             }
             Op::Var { name, kind: _ } => {
-                let fragment = expand_var(ctx, name)?;
+                let ExpandResult(fragment, e) = expand_var(ctx, name);
+                err = err.or(e);
                 push_fragment(&mut buf, fragment);
             }
             Op::Repeat { subtree, kind, separator } => {
-                let fragment = expand_repeat(ctx, subtree, kind, separator)?;
+                let ExpandResult(fragment, e) = expand_repeat(ctx, subtree, kind, separator);
+                err = err.or(e);
                 push_fragment(&mut buf, fragment)
             }
         }
     }
-    Ok(tt::Subtree { delimiter: template.delimiter, token_trees: buf })
+    ExpandResult(tt::Subtree { delimiter: template.delimiter, token_trees: buf }, err)
 }
 
-fn expand_var(ctx: &mut ExpandCtx, v: &SmolStr) -> Result<Fragment, ExpandError> {
-    let res = if v == "crate" {
+fn expand_var(ctx: &mut ExpandCtx, v: &SmolStr) -> ExpandResult<Fragment> {
+    if v == "crate" {
         // We simply produce identifier `$crate` here. And it will be resolved when lowering ast to Path.
         let tt =
             tt::Leaf::from(tt::Ident { text: "$crate".into(), id: tt::TokenId::unspecified() })
                 .into();
-        Fragment::Tokens(tt)
+        ExpandResult::ok(Fragment::Tokens(tt))
     } else if !ctx.bindings.contains(v) {
         // Note that it is possible to have a `$var` inside a macro which is not bound.
         // For example:
@@ -132,11 +141,13 @@ fn expand_var(ctx: &mut ExpandCtx, v: &SmolStr) -> Result<Fragment, ExpandError>
             ],
         }
         .into();
-        Fragment::Tokens(tt)
+        ExpandResult::ok(Fragment::Tokens(tt))
     } else {
-        ctx.bindings.get(&v, &mut ctx.nesting)?.clone()
-    };
-    Ok(res)
+        ctx.bindings.get(&v, &mut ctx.nesting).map_or_else(
+            |e| ExpandResult(Fragment::Tokens(tt::TokenTree::empty()), Some(e)),
+            |b| ExpandResult::ok(b.clone()),
+        )
+    }
 }
 
 fn expand_repeat(
@@ -144,17 +155,17 @@ fn expand_repeat(
     template: &tt::Subtree,
     kind: RepeatKind,
     separator: Option<Separator>,
-) -> Result<Fragment, ExpandError> {
+) -> ExpandResult<Fragment> {
     let mut buf: Vec<tt::TokenTree> = Vec::new();
     ctx.nesting.push(NestingState { idx: 0, at_end: false, hit: false });
     // Dirty hack to make macro-expansion terminate.
-    // This should be replaced by a propper macro-by-example implementation
+    // This should be replaced by a proper macro-by-example implementation
     let limit = 65536;
     let mut has_seps = 0;
     let mut counter = 0;
 
     loop {
-        let res = expand_subtree(ctx, template);
+        let ExpandResult(mut t, e) = expand_subtree(ctx, template);
         let nesting_state = ctx.nesting.last_mut().unwrap();
         if nesting_state.at_end || !nesting_state.hit {
             break;
@@ -172,10 +183,10 @@ fn expand_repeat(
             break;
         }
 
-        let mut t = match res {
-            Ok(t) => t,
-            Err(_) => continue,
-        };
+        if e.is_some() {
+            continue;
+        }
+
         t.delimiter = None;
         push_subtree(&mut buf, t);
 
@@ -209,14 +220,14 @@ fn expand_repeat(
         buf.pop();
     }
 
-    if RepeatKind::OneOrMore == kind && counter == 0 {
-        return Err(ExpandError::UnexpectedToken);
-    }
-
     // Check if it is a single token subtree without any delimiter
     // e.g {Delimiter:None> ['>'] /Delimiter:None>}
     let tt = tt::Subtree { delimiter: None, token_trees: buf }.into();
-    Ok(Fragment::Tokens(tt))
+
+    if RepeatKind::OneOrMore == kind && counter == 0 {
+        return ExpandResult(Fragment::Tokens(tt), Some(ExpandError::UnexpectedToken));
+    }
+    ExpandResult::ok(Fragment::Tokens(tt))
 }
 
 fn push_fragment(buf: &mut Vec<tt::TokenTree>, fragment: Fragment) {
diff --git a/crates/ra_mbe/src/tests.rs b/crates/ra_mbe/src/tests.rs
index 6d5d1e9e6..44f381938 100644
--- a/crates/ra_mbe/src/tests.rs
+++ b/crates/ra_mbe/src/tests.rs
@@ -1430,7 +1430,7 @@ impl MacroFixture {
         let (invocation_tt, _) =
             ast_to_token_tree(&macro_invocation.token_tree().unwrap()).unwrap();
 
-        self.rules.expand(&invocation_tt)
+        self.rules.expand(&invocation_tt).result()
     }
 
     fn assert_expand_err(&self, invocation: &str, err: &ExpandError) {
@@ -1662,5 +1662,5 @@ fn test_expand_bad_literal() {
         macro_rules! foo { ($i:literal) => {}; }
     "#,
     )
-    .assert_expand_err(r#"foo!(&k");"#, &ExpandError::NoMatchingRule);
+    .assert_expand_err(r#"foo!(&k");"#, &ExpandError::BindingError("".to_string()));
 }