4 files changed, 74 insertions, 72 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index 8a2d6ff63..34840dfa1 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -25,14 +25,17 @@ use ra_syntax::SmolStr;
 pub use tt::{Delimiter, Punct};
 
 #[derive(Debug, PartialEq, Eq)]
-pub enum MacroRulesError {
+pub enum ParseError {
+    ParseError,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum ExpandError {
     NoMatchingRule,
     UnexpectedToken,
     BindingError(String),
-    ParseError,
 }
 
-pub type Result<T> = ::std::result::Result<T, MacroRulesError>;
 pub use crate::syntax_bridge::{ast_to_token_tree, token_tree_to_ast_item_list};
 
 /// This struct contains AST for a single `macro_rules` definition. What might
@@ -45,10 +48,10 @@ pub struct MacroRules {
 }
 
 impl MacroRules {
-    pub fn parse(tt: &tt::Subtree) -> Result<MacroRules> {
+    pub fn parse(tt: &tt::Subtree) -> Result<MacroRules, ParseError> {
         mbe_parser::parse(tt)
     }
-    pub fn expand(&self, tt: &tt::Subtree) -> Result<tt::Subtree> {
+    pub fn expand(&self, tt: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
         mbe_expander::expand(self, tt)
     }
 }
diff --git a/crates/ra_mbe/src/mbe_expander.rs b/crates/ra_mbe/src/mbe_expander.rs
index 0a5bbf6b1..d4ce3bfe3 100644
--- a/crates/ra_mbe/src/mbe_expander.rs
+++ b/crates/ra_mbe/src/mbe_expander.rs
@@ -5,22 +5,21 @@ use rustc_hash::FxHashMap;
 use ra_syntax::SmolStr;
 use tt::TokenId;
 
-use crate::{MacroRulesError, Result};
+use crate::ExpandError;
 use crate::tt_cursor::TtCursor;
 
-pub(crate) fn expand(rules: &crate::MacroRules, input: &tt::Subtree) -> Result<tt::Subtree> {
-    rules
-        .rules
-        .iter()
-        .find_map(|it| expand_rule(it, input).ok())
-        .ok_or(MacroRulesError::NoMatchingRule)
+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)
 }
 
-fn expand_rule(rule: &crate::Rule, input: &tt::Subtree) -> Result<tt::Subtree> {
+fn expand_rule(rule: &crate::Rule, input: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
     let mut input = TtCursor::new(input);
     let bindings = match_lhs(&rule.lhs, &mut input)?;
     if !input.is_eof() {
-        return Err(MacroRulesError::UnexpectedToken);
+        return Err(ExpandError::UnexpectedToken);
     }
     expand_subtree(&rule.rhs, &bindings, &mut Vec::new())
 }
@@ -82,29 +81,30 @@ enum Binding {
 }
 
 impl Bindings {
-    fn get(&self, name: &SmolStr, nesting: &[usize]) -> Result<&tt::TokenTree> {
+    fn get(&self, name: &SmolStr, nesting: &[usize]) -> Result<&tt::TokenTree, ExpandError> {
         let mut b = self
             .inner
             .get(name)
-            .ok_or(MacroRulesError::BindingError(format!("could not find binding {}", name)))?;
+            .ok_or(ExpandError::BindingError(format!("could not find binding {}", name)))?;
         for &idx in nesting.iter() {
             b = match b {
                 Binding::Simple(_) => break,
-                Binding::Nested(bs) => bs.get(idx).ok_or(MacroRulesError::BindingError(
-                    format!("could not find nested binding {}", name),
-                ))?,
+                Binding::Nested(bs) => bs.get(idx).ok_or(ExpandError::BindingError(format!(
+                    "could not find nested binding {}",
+                    name
+                )))?,
             };
         }
         match b {
             Binding::Simple(it) => Ok(it),
-            Binding::Nested(_) => Err(MacroRulesError::BindingError(format!(
+            Binding::Nested(_) => Err(ExpandError::BindingError(format!(
                 "expected simple binding, found nested binding {}",
                 name
             ))),
         }
     }
 
-    fn push_nested(&mut self, nested: Bindings) -> Result<()> {
+    fn push_nested(&mut self, nested: Bindings) -> Result<(), ExpandError> {
         for (key, value) in nested.inner {
             if !self.inner.contains_key(&key) {
                 self.inner.insert(key.clone(), Binding::Nested(Vec::new()));
@@ -112,10 +112,10 @@ impl Bindings {
             match self.inner.get_mut(&key) {
                 Some(Binding::Nested(it)) => it.push(value),
                 _ => {
-                    return Err(MacroRulesError::BindingError(format!(
+                    return Err(ExpandError::BindingError(format!(
                         "nested binding for {} not found",
                         key
-                    )))
+                    )));
                 }
             }
         }
@@ -123,43 +123,44 @@ impl Bindings {
     }
 }
 
-fn match_lhs(pattern: &crate::Subtree, input: &mut TtCursor) -> Result<Bindings> {
+fn match_lhs(pattern: &crate::Subtree, input: &mut TtCursor) -> Result<Bindings, ExpandError> {
     let mut res = Bindings::default();
     for pat in pattern.token_trees.iter() {
         match pat {
             crate::TokenTree::Leaf(leaf) => match leaf {
                 crate::Leaf::Var(crate::Var { text, kind }) => {
-                    let kind = kind.clone().ok_or(MacroRulesError::ParseError)?;
+                    let kind = kind.clone().ok_or(ExpandError::UnexpectedToken)?;
                     match kind.as_str() {
                         "ident" => {
-                            let ident = input.eat_ident()?.clone();
+                            let ident =
+                                input.eat_ident().ok_or(ExpandError::UnexpectedToken)?.clone();
                             res.inner.insert(
                                 text.clone(),
                                 Binding::Simple(tt::Leaf::from(ident).into()),
                             );
                         }
-                        _ => return Err(MacroRulesError::UnexpectedToken),
+                        _ => return Err(ExpandError::UnexpectedToken),
                     }
                 }
                 crate::Leaf::Punct(punct) => {
-                    if input.eat_punct()? != punct {
-                        return Err(MacroRulesError::UnexpectedToken);
+                    if input.eat_punct() != Some(punct) {
+                        return Err(ExpandError::UnexpectedToken);
                     }
                 }
                 crate::Leaf::Ident(ident) => {
-                    if input.eat_ident()?.text != ident.text {
-                        return Err(MacroRulesError::UnexpectedToken);
+                    if input.eat_ident().map(|i| &i.text) != Some(&ident.text) {
+                        return Err(ExpandError::UnexpectedToken);
                     }
                 }
-                _ => return Err(MacroRulesError::UnexpectedToken),
+                _ => return Err(ExpandError::UnexpectedToken),
             },
             crate::TokenTree::Repeat(crate::Repeat { subtree, kind: _, separator }) => {
                 while let Ok(nested) = match_lhs(subtree, input) {
                     res.push_nested(nested)?;
                     if let Some(separator) = *separator {
                         if !input.is_eof() {
-                            if input.eat_punct()?.char != separator {
-                                return Err(MacroRulesError::UnexpectedToken);
+                            if input.eat_punct().map(|p| p.char) != Some(separator) {
+                                return Err(ExpandError::UnexpectedToken);
                             }
                         }
                     }
@@ -175,12 +176,12 @@ fn expand_subtree(
     template: &crate::Subtree,
     bindings: &Bindings,
     nesting: &mut Vec<usize>,
-) -> Result<tt::Subtree> {
+) -> Result<tt::Subtree, ExpandError> {
     let token_trees = template
         .token_trees
         .iter()
         .map(|it| expand_tt(it, bindings, nesting))
-        .collect::<Result<Vec<_>>>()?;
+        .collect::<Result<Vec<_>, ExpandError>>()?;
 
     Ok(tt::Subtree { token_trees, delimiter: template.delimiter })
 }
@@ -189,7 +190,7 @@ fn expand_tt(
     template: &crate::TokenTree,
     bindings: &Bindings,
     nesting: &mut Vec<usize>,
-) -> Result<tt::TokenTree> {
+) -> Result<tt::TokenTree, ExpandError> {
     let res: tt::TokenTree = match template {
         crate::TokenTree::Subtree(subtree) => expand_subtree(subtree, bindings, nesting)?.into(),
         crate::TokenTree::Repeat(repeat) => {
diff --git a/crates/ra_mbe/src/mbe_parser.rs b/crates/ra_mbe/src/mbe_parser.rs
index ee1b11091..d067e5248 100644
--- a/crates/ra_mbe/src/mbe_parser.rs
+++ b/crates/ra_mbe/src/mbe_parser.rs
@@ -1,10 +1,10 @@
 /// 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::{MacroRulesError, Result};
+use crate::ParseError;
 use crate::tt_cursor::TtCursor;
 
-pub(crate) fn parse(tt: &tt::Subtree) -> Result<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() {
@@ -19,7 +19,7 @@ pub(crate) fn parse(tt: &tt::Subtree) -> Result<crate::MacroRules> {
     Ok(crate::MacroRules { rules })
 }
 
-fn parse_rule(p: &mut TtCursor) -> Result<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('>')?;
@@ -28,14 +28,14 @@ fn parse_rule(p: &mut TtCursor) -> Result<crate::Rule> {
     Ok(crate::Rule { lhs, rhs })
 }
 
-fn parse_subtree(tt: &tt::Subtree) -> Result<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 Ok(tt) = p.eat() {
+    while let Some(tt) = p.eat() {
         let child: crate::TokenTree = match tt {
             tt::TokenTree::Leaf(leaf) => match leaf {
                 tt::Leaf::Punct(tt::Punct { char: '$', .. }) => {
-                    if p.at_ident().is_ok() {
+                    if p.at_ident().is_some() {
                         crate::Leaf::from(parse_var(&mut p)?).into()
                     } else {
                         parse_repeat(&mut p)?.into()
@@ -56,12 +56,12 @@ fn parse_subtree(tt: &tt::Subtree) -> Result<crate::Subtree> {
     Ok(crate::Subtree { token_trees, delimiter: tt.delimiter })
 }
 
-fn parse_var(p: &mut TtCursor) -> Result<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(':') {
         p.bump();
-        if let Ok(ident) = p.eat_ident() {
+        if let Some(ident) = p.eat_ident() {
             Some(ident.text.clone())
         } else {
             p.rev_bump();
@@ -73,21 +73,21 @@ fn parse_var(p: &mut TtCursor) -> Result<crate::Var> {
     Ok(crate::Var { text, kind })
 }
 
-fn parse_repeat(p: &mut TtCursor) -> Result<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::ParseError)?;
     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::ParseError)?.char),
     };
 
     let kind = match rep {
         '*' => crate::RepeatKind::ZeroOrMore,
         '+' => crate::RepeatKind::OneOrMore,
         '?' => crate::RepeatKind::ZeroOrOne,
-        _ => return Err(MacroRulesError::ParseError),
+        _ => return Err(ParseError::ParseError),
     };
     p.bump();
     Ok(crate::Repeat { subtree, kind, separator })
diff --git a/crates/ra_mbe/src/tt_cursor.rs b/crates/ra_mbe/src/tt_cursor.rs
index 117471841..d06bfbf9f 100644
--- a/crates/ra_mbe/src/tt_cursor.rs
+++ b/crates/ra_mbe/src/tt_cursor.rs
@@ -1,4 +1,4 @@
-use crate::{MacroRulesError, Result};
+use crate::ParseError;
 
 #[derive(Clone)]
 pub(crate) struct TtCursor<'a> {
@@ -19,24 +19,24 @@ impl<'a> TtCursor<'a> {
         self.subtree.token_trees.get(self.pos)
     }
 
-    pub(crate) fn at_punct(&self) -> Result<&'a tt::Punct> {
+    pub(crate) fn at_punct(&self) -> Option<&'a tt::Punct> {
         match self.current() {
-            Some(tt::TokenTree::Leaf(tt::Leaf::Punct(it))) => Ok(it),
-            _ => Err(MacroRulesError::ParseError),
+            Some(tt::TokenTree::Leaf(tt::Leaf::Punct(it))) => Some(it),
+            _ => None,
         }
     }
 
     pub(crate) fn at_char(&self, char: char) -> bool {
         match self.at_punct() {
-            Ok(tt::Punct { char: c, .. }) if *c == char => true,
+            Some(tt::Punct { char: c, .. }) if *c == char => true,
             _ => false,
         }
     }
 
-    pub(crate) fn at_ident(&mut self) -> Result<&'a tt::Ident> {
+    pub(crate) fn at_ident(&mut self) -> Option<&'a tt::Ident> {
         match self.current() {
-            Some(tt::TokenTree::Leaf(tt::Leaf::Ident(i))) => Ok(i),
-            _ => Err(MacroRulesError::ParseError),
+            Some(tt::TokenTree::Leaf(tt::Leaf::Ident(i))) => Some(i),
+            _ => None,
         }
     }
 
@@ -47,45 +47,43 @@ impl<'a> TtCursor<'a> {
         self.pos -= 1;
     }
 
-    pub(crate) fn eat(&mut self) -> Result<&'a tt::TokenTree> {
-        match self.current() {
-            Some(it) => {
-                self.bump();
-                Ok(it)
-            }
-            None => Err(MacroRulesError::ParseError),
-        }
+    pub(crate) fn eat(&mut self) -> Option<&'a tt::TokenTree> {
+        self.current().map(|it| {
+            self.bump();
+            it
+        })
     }
 
-    pub(crate) fn eat_subtree(&mut self) -> Result<&'a tt::Subtree> {
+    pub(crate) fn eat_subtree(&mut self) -> Result<&'a tt::Subtree, ParseError> {
         match self.current() {
             Some(tt::TokenTree::Subtree(sub)) => {
                 self.bump();
                 Ok(sub)
             }
-            _ => Err(MacroRulesError::ParseError),
+            _ => Err(ParseError::ParseError),
         }
     }
 
-    pub(crate) fn eat_punct(&mut self) -> Result<&'a tt::Punct> {
+    pub(crate) fn eat_punct(&mut self) -> Option<&'a tt::Punct> {
         self.at_punct().map(|it| {
             self.bump();
             it
         })
     }
 
-    pub(crate) fn eat_ident(&mut self) -> Result<&'a tt::Ident> {
+    pub(crate) fn eat_ident(&mut self) -> Option<&'a tt::Ident> {
         self.at_ident().map(|i| {
             self.bump();
             i
         })
     }
 
-    pub(crate) fn expect_char(&mut self, char: char) -> Result<()> {
+    pub(crate) fn expect_char(&mut self, char: char) -> Result<(), ParseError> {
         if self.at_char(char) {
             self.bump();
-            return Ok(());
+            Ok(())
+        } else {
+            Err(ParseError::ParseError)
         }
-        Err(MacroRulesError::ParseError)
     }
 }