Reimplemented lexer with vectors instead of iterators

8 files changed, 241 insertions, 187 deletions

diff --git a/crates/ra_syntax/src/lib.rs b/crates/ra_syntax/src/lib.rs
index 9931fec84..80b3a0b22 100644
--- a/crates/ra_syntax/src/lib.rs
+++ b/crates/ra_syntax/src/lib.rs
@@ -41,7 +41,7 @@ use crate::syntax_node::GreenNode;
 pub use crate::{
     algo::InsertPosition,
     ast::{AstNode, AstToken},
-    parsing::{classify_literal, tokenize, Token},
+    parsing::{first_token, single_token, tokenize, tokenize_append, Token, TokenizeError},
     ptr::{AstPtr, SyntaxNodePtr},
     syntax_error::{Location, SyntaxError, SyntaxErrorKind},
     syntax_node::{
diff --git a/crates/ra_syntax/src/parsing.rs b/crates/ra_syntax/src/parsing.rs
index 0387f0378..4e51f920b 100644
--- a/crates/ra_syntax/src/parsing.rs
+++ b/crates/ra_syntax/src/parsing.rs
@@ -7,15 +7,17 @@ mod text_tree_sink;
 mod reparsing;
 
 use crate::{syntax_node::GreenNode, SyntaxError};
+use text_token_source::TextTokenSource;
+use text_tree_sink::TextTreeSink;
 
-pub use self::lexer::{classify_literal, tokenize, Token};
+pub use lexer::*;
 
 pub(crate) use self::reparsing::incremental_reparse;
 
 pub(crate) fn parse_text(text: &str) -> (GreenNode, Vec<SyntaxError>) {
-    let tokens = tokenize(&text);
-    let mut token_source = text_token_source::TextTokenSource::new(text, &tokens);
-    let mut tree_sink = text_tree_sink::TextTreeSink::new(text, &tokens);
+    let ParsedTokens { tokens, errors } = tokenize(&text);
+    let mut token_source = TextTokenSource::new(text, &tokens);
+    let mut tree_sink = TextTreeSink::new(text, &tokens, errors);
     ra_parser::parse(&mut token_source, &mut tree_sink);
     tree_sink.finish()
 }
diff --git a/crates/ra_syntax/src/parsing/lexer.rs b/crates/ra_syntax/src/parsing/lexer.rs
index 9dca7d747..6d96f8400 100644
--- a/crates/ra_syntax/src/parsing/lexer.rs
+++ b/crates/ra_syntax/src/parsing/lexer.rs
@@ -1,10 +1,10 @@
 //! Lexer analyzes raw input string and produces lexemes (tokens).
-
-use std::iter::{FromIterator, IntoIterator};
+//! It is just a bridge to `rustc_lexer`.
 
 use crate::{
+    SyntaxError, SyntaxErrorKind,
     SyntaxKind::{self, *},
-    TextUnit,
+    TextRange, TextUnit,
 };
 
 /// A token of Rust source.
@@ -15,93 +15,96 @@ pub struct Token {
     /// The length of the token.
     pub len: TextUnit,
 }
-impl Token {
-    pub const fn new(kind: SyntaxKind, len: TextUnit) -> Self {
-        Self { kind, len }
-    }
-}
 
 #[derive(Debug)]
-/// Represents the result of parsing one token.
+/// Represents the result of parsing one token. Beware that the token may be malformed.
 pub struct ParsedToken {
     /// Parsed token.
     pub token: Token,
     /// If error is present then parsed token is malformed.
-    pub error: Option<TokenizeError>,
-}
-impl ParsedToken {
-    pub const fn new(token: Token, error: Option<TokenizeError>) -> Self {
-        Self { token, error }
-    }
+    pub error: Option<SyntaxError>,
 }
 
 #[derive(Debug, Default)]
-/// Represents the result of parsing one token.
+/// Represents the result of parsing source code of Rust language.
 pub struct ParsedTokens {
-    /// Parsed token.
+    /// Parsed tokens in order they appear in source code.
     pub tokens: Vec<Token>,
-    /// If error is present then parsed token is malformed.
-    pub errors: Vec<TokenizeError>,
+    /// Collection of all occured tokenization errors.
+    /// In general `self.errors.len() <= self.tokens.len()`
+    pub errors: Vec<SyntaxError>,
 }
-
-impl FromIterator<ParsedToken> for ParsedTokens {
-    fn from_iter<I: IntoIterator<Item = ParsedToken>>(iter: I) -> Self {
-        let res = Self::default();
-        for entry in iter {
-            res.tokens.push(entry.token);
-            if let Some(error) = entry.error {
-                res.errors.push(error);
-            }
+impl ParsedTokens {
+    /// Append `token` and `error` (if pressent) to the result.
+    pub fn push(&mut self, ParsedToken { token, error }: ParsedToken) {
+        self.tokens.push(token);
+        if let Some(error) = error {
+            self.errors.push(error)
         }
-        res
     }
 }
 
-/// Returns the first encountered token from the string.
-/// If the string contains zero or two or more tokens returns `None`.
-pub fn single_token(text: &str) -> Option<ParsedToken> {
-    // TODO: test whether this condition indeed checks for a single token
-    first_token(text).filter(|parsed| parsed.token.len.to_usize() == text.len())
+/// Same as `tokenize_append()`, just a shortcut for creating `ParsedTokens`
+/// and returning the result the usual way.
+pub fn tokenize(text: &str) -> ParsedTokens {
+    let mut parsed = ParsedTokens::default();
+    tokenize_append(text, &mut parsed);
+    parsed
 }
 
-/*
-/// Returns `ParsedTokens` which are basically a pair `(Vec<Token>, Vec<TokenizeError>)`
-/// This is just a shorthand for `tokenize(text).collect()`
-pub fn tokenize_to_vec_with_errors(text: &str) -> ParsedTokens {
-    tokenize(text).collect()
-}
+/// Break a string up into its component tokens.
+/// Returns `ParsedTokens` which are basically a pair `(Vec<Token>, Vec<SyntaxError>)`.
+/// Beware that it checks for shebang first and its length contributes to resulting
+/// tokens offsets.
+pub fn tokenize_append(text: &str, parsed: &mut ParsedTokens) {
+    // non-empty string is a precondtion of `rustc_lexer::strip_shebang()`.
+    if text.is_empty() {
+        return;
+    }
 
-/// The simplest version of tokenize, it just retunst a ready-made `Vec<Token>`.
-/// It discards all tokenization errors while parsing. If you need that infromation
-/// consider using `tokenize()` or `tokenize_to_vec_with_errors()`.
-pub fn tokenize_to_vec(text: &str) -> Vec<Token> {
-    tokenize(text).map(|parsed_token| parsed_token.token).collect()
-}
-*/
+    let mut offset: usize = rustc_lexer::strip_shebang(text)
+        .map(|shebang_len| {
+            parsed.tokens.push(Token { kind: SHEBANG, len: TextUnit::from_usize(shebang_len) });
+            shebang_len
+        })
+        .unwrap_or(0);
 
-/// Break a string up into its component tokens
-/// This is the core function, all other `tokenize*()` functions are simply
-/// handy shortcuts for this one.
-pub fn tokenize(text: &str) -> impl Iterator<Item = ParsedToken> + '_ {
-    let shebang = rustc_lexer::strip_shebang(text).map(|shebang_len| {
-        text = &text[shebang_len..];
-        ParsedToken::new(Token::new(SHEBANG, TextUnit::from_usize(shebang_len)), None)
-    });
+    let text_without_shebang = &text[offset..];
 
-    // Notice that we eagerly evaluate shebang since it may change text slice
-    // and we cannot simplify this into a single method call chain
-    shebang.into_iter().chain(tokenize_without_shebang(text))
+    for rustc_token in rustc_lexer::tokenize(text_without_shebang) {
+        parsed.push(rustc_token_to_parsed_token(&rustc_token, text, TextUnit::from_usize(offset)));
+        offset += rustc_token.len;
+    }
 }
 
-pub fn tokenize_without_shebang(text: &str) -> impl Iterator<Item = ParsedToken> + '_ {
-    rustc_lexer::tokenize(text).map(|rustc_token| {
-        let token_text = &text[..rustc_token.len];
-        text = &text[rustc_token.len..];
-        rustc_token_kind_to_parsed_token(&rustc_token.kind, token_text)
-    })
+/// Returns the first encountered token at the beginning of the string.
+/// If the string contains zero or *two or more tokens* returns `None`.
+///
+/// The main difference between `first_token()` and `single_token()` is that
+/// the latter returns `None` if the string contains more than one token.
+pub fn single_token(text: &str) -> Option<ParsedToken> {
+    first_token(text).filter(|parsed| parsed.token.len.to_usize() == text.len())
 }
 
-#[derive(Debug)]
+/// Returns the first encountered token at the beginning of the string.
+/// If the string contains zero tokens returns `None`.
+///
+/// The main difference between `first_token() and single_token()` is that
+/// the latter returns `None` if the string contains more than one token.
+pub fn first_token(text: &str) -> Option<ParsedToken> {
+    // non-empty string is a precondtion of `rustc_lexer::first_token()`.
+    if text.is_empty() {
+        None
+    } else {
+        let rustc_token = rustc_lexer::first_token(text);
+        Some(rustc_token_to_parsed_token(&rustc_token, text, TextUnit::from(0)))
+    }
+}
+
+/// Describes the values of `SyntaxErrorKind::TokenizeError` enum variant.
+/// It describes all the types of errors that may happen during the tokenization
+/// of Rust source.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum TokenizeError {
     /// Base prefix was provided, but there were no digits
     /// after it, e.g. `0x`.
@@ -124,94 +127,95 @@ pub enum TokenizeError {
     /// Raw byte string literal lacks trailing delimiter e.g. `"##`
     UnterminatedRawByteString,
 
-    /// Raw string lacks a quote after pound characters e.g. `r###`
+    /// Raw string lacks a quote after the pound characters e.g. `r###`
     UnstartedRawString,
-    /// Raw byte string lacks a quote after pound characters e.g. `br###`
+    /// Raw byte string lacks a quote after the pound characters e.g. `br###`
     UnstartedRawByteString,
 
     /// Lifetime starts with a number e.g. `'4ever`
     LifetimeStartsWithNumber,
 }
 
-fn rustc_token_kind_to_parsed_token(
-    rustc_token_kind: &rustc_lexer::TokenKind,
-    token_text: &str,
+/// Mapper function that converts `rustc_lexer::Token` with some additional context
+/// to `ParsedToken`
+fn rustc_token_to_parsed_token(
+    rustc_token: &rustc_lexer::Token,
+    text: &str,
+    token_start_offset: TextUnit,
 ) -> ParsedToken {
-    use rustc_lexer::TokenKind as TK;
-    use TokenizeError as TE;
-
     // We drop some useful infromation here (see patterns with double dots `..`)
     // Storing that info in `SyntaxKind` is not possible due to its layout requirements of
     // being `u16` that come from `rowan::SyntaxKind` type and changes to `rowan::SyntaxKind`
-    // would mean hell of a rewrite.
+    // would mean hell of a rewrite
 
-    let (syntax_kind, error) = match *rustc_token_kind {
-        TK::LineComment => ok(COMMENT),
-        TK::BlockComment { terminated } => ok_if(terminated, COMMENT, TE::UnterminatedBlockComment),
-        TK::Whitespace => ok(WHITESPACE),
-        TK::Ident => ok(if token_text == "_" {
-            UNDERSCORE
-        } else {
-            SyntaxKind::from_keyword(token_text).unwrap_or(IDENT)
-        }),
-        TK::RawIdent => ok(IDENT),
-        TK::Literal { kind, .. } => match_literal_kind(&kind),
-        TK::Lifetime { starts_with_number } => {
-            ok_if(!starts_with_number, LIFETIME, TE::LifetimeStartsWithNumber)
+    let token_range =
+        TextRange::offset_len(token_start_offset, TextUnit::from_usize(rustc_token.len));
+
+    let token_text = &text[token_range];
+
+    let (syntax_kind, error) = {
+        use rustc_lexer::TokenKind as TK;
+        use TokenizeError as TE;
+
+        match rustc_token.kind {
+            TK::LineComment => ok(COMMENT),
+            TK::BlockComment { terminated } => {
+                ok_if(terminated, COMMENT, TE::UnterminatedBlockComment)
+            }
+            TK::Whitespace => ok(WHITESPACE),
+            TK::Ident => ok(if token_text == "_" {
+                UNDERSCORE
+            } else {
+                SyntaxKind::from_keyword(token_text).unwrap_or(IDENT)
+            }),
+            TK::RawIdent => ok(IDENT),
+            TK::Literal { kind, .. } => match_literal_kind(&kind),
+            TK::Lifetime { starts_with_number } => {
+                ok_if(!starts_with_number, LIFETIME, TE::LifetimeStartsWithNumber)
+            }
+            TK::Semi => ok(SEMI),
+            TK::Comma => ok(COMMA),
+            TK::Dot => ok(DOT),
+            TK::OpenParen => ok(L_PAREN),
+            TK::CloseParen => ok(R_PAREN),
+            TK::OpenBrace => ok(L_CURLY),
+            TK::CloseBrace => ok(R_CURLY),
+            TK::OpenBracket => ok(L_BRACK),
+            TK::CloseBracket => ok(R_BRACK),
+            TK::At => ok(AT),
+            TK::Pound => ok(POUND),
+            TK::Tilde => ok(TILDE),
+            TK::Question => ok(QUESTION),
+            TK::Colon => ok(COLON),
+            TK::Dollar => ok(DOLLAR),
+            TK::Eq => ok(EQ),
+            TK::Not => ok(EXCL),
+            TK::Lt => ok(L_ANGLE),
+            TK::Gt => ok(R_ANGLE),
+            TK::Minus => ok(MINUS),
+            TK::And => ok(AMP),
+            TK::Or => ok(PIPE),
+            TK::Plus => ok(PLUS),
+            TK::Star => ok(STAR),
+            TK::Slash => ok(SLASH),
+            TK::Caret => ok(CARET),
+            TK::Percent => ok(PERCENT),
+            TK::Unknown => ok(ERROR),
         }
-        TK::Semi => ok(SEMI),
-        TK::Comma => ok(COMMA),
-        TK::Dot => ok(DOT),
-        TK::OpenParen => ok(L_PAREN),
-        TK::CloseParen => ok(R_PAREN),
-        TK::OpenBrace => ok(L_CURLY),
-        TK::CloseBrace => ok(R_CURLY),
-        TK::OpenBracket => ok(L_BRACK),
-        TK::CloseBracket => ok(R_BRACK),
-        TK::At => ok(AT),
-        TK::Pound => ok(POUND),
-        TK::Tilde => ok(TILDE),
-        TK::Question => ok(QUESTION),
-        TK::Colon => ok(COLON),
-        TK::Dollar => ok(DOLLAR),
-        TK::Eq => ok(EQ),
-        TK::Not => ok(EXCL),
-        TK::Lt => ok(L_ANGLE),
-        TK::Gt => ok(R_ANGLE),
-        TK::Minus => ok(MINUS),
-        TK::And => ok(AMP),
-        TK::Or => ok(PIPE),
-        TK::Plus => ok(PLUS),
-        TK::Star => ok(STAR),
-        TK::Slash => ok(SLASH),
-        TK::Caret => ok(CARET),
-        TK::Percent => ok(PERCENT),
-        TK::Unknown => ok(ERROR),
     };
 
-    return ParsedToken::new(
-        Token::new(syntax_kind, TextUnit::from_usize(token_text.len())),
-        error,
-    );
+    return ParsedToken {
+        token: Token { kind: syntax_kind, len: token_range.len() },
+        error: error
+            .map(|error| SyntaxError::new(SyntaxErrorKind::TokenizeError(error), token_range)),
+    };
 
     type ParsedSyntaxKind = (SyntaxKind, Option<TokenizeError>);
 
-    const fn ok(syntax_kind: SyntaxKind) -> ParsedSyntaxKind {
-        (syntax_kind, None)
-    }
-    const fn ok_if(cond: bool, syntax_kind: SyntaxKind, error: TokenizeError) -> ParsedSyntaxKind {
-        if cond {
-            ok(syntax_kind)
-        } else {
-            err(syntax_kind, error)
-        }
-    }
-    const fn err(syntax_kind: SyntaxKind, error: TokenizeError) -> ParsedSyntaxKind {
-        (syntax_kind, Some(error))
-    }
-
-    const fn match_literal_kind(kind: &rustc_lexer::LiteralKind) -> ParsedSyntaxKind {
+    fn match_literal_kind(kind: &rustc_lexer::LiteralKind) -> ParsedSyntaxKind {
         use rustc_lexer::LiteralKind as LK;
+        use TokenizeError as TE;
+
         match *kind {
             LK::Int { empty_int, .. } => ok_if(!empty_int, INT_NUMBER, TE::EmptyInt),
             LK::Float { empty_exponent, .. } => {
@@ -237,27 +241,17 @@ fn rustc_token_kind_to_parsed_token(
             }
         }
     }
-}
-
-pub fn first_token(text: &str) -> Option<ParsedToken> {
-    // Checking for emptyness because of `rustc_lexer::first_token()` invariant (see its body)
-    if text.is_empty() {
-        None
-    } else {
-        let rustc_token = rustc_lexer::first_token(text);
-        Some(rustc_token_kind_to_parsed_token(&rustc_token.kind, &text[..rustc_token.len]))
+    const fn ok(syntax_kind: SyntaxKind) -> ParsedSyntaxKind {
+        (syntax_kind, None)
     }
-}
-
-// TODO: think what to do with this ad hoc function
-pub fn classify_literal(text: &str) -> Option<ParsedToken> {
-    let t = rustc_lexer::first_token(text);
-    if t.len != text.len() {
-        return None;
+    const fn err(syntax_kind: SyntaxKind, error: TokenizeError) -> ParsedSyntaxKind {
+        (syntax_kind, Some(error))
+    }
+    fn ok_if(cond: bool, syntax_kind: SyntaxKind, error: TokenizeError) -> ParsedSyntaxKind {
+        if cond {
+            ok(syntax_kind)
+        } else {
+            err(syntax_kind, error)
+        }
     }
-    let kind = match t.kind {
-        rustc_lexer::TokenKind::Literal { kind, .. } => match_literal_kind(kind),
-        _ => return None,
-    };
-    Some(ParsedToken::new(Token::new(kind, TextUnit::from_usize(t.len))))
 }
diff --git a/crates/ra_syntax/src/parsing/reparsing.rs b/crates/ra_syntax/src/parsing/reparsing.rs
index 3abc09877..ad1a7c855 100644
--- a/crates/ra_syntax/src/parsing/reparsing.rs
+++ b/crates/ra_syntax/src/parsing/reparsing.rs
@@ -12,7 +12,7 @@ use ra_text_edit::AtomTextEdit;
 use crate::{
     algo,
     parsing::{
-        lexer::{tokenize, Token},
+        lexer::{single_token, tokenize, ParsedTokens, Token},
         text_token_source::TextTokenSource,
         text_tree_sink::TextTreeSink,
     },
@@ -41,36 +41,42 @@ fn reparse_token<'node>(
     root: &'node SyntaxNode,
     edit: &AtomTextEdit,
 ) -> Option<(GreenNode, TextRange)> {
-    let token = algo::find_covering_element(root, edit.delete).as_token()?.clone();
-    match token.kind() {
+    let prev_token = algo::find_covering_element(root, edit.delete).as_token()?.clone();
+    let prev_token_kind = prev_token.kind();
+    match prev_token_kind {
         WHITESPACE | COMMENT | IDENT | STRING | RAW_STRING => {
-            if token.kind() == WHITESPACE || token.kind() == COMMENT {
+            if prev_token_kind == WHITESPACE || prev_token_kind == COMMENT {
                 // removing a new line may extends previous token
-                if token.text()[edit.delete - token.text_range().start()].contains('\n') {
+                let deleted_range = edit.delete - prev_token.text_range().start();
+                if prev_token.text()[deleted_range].contains('\n') {
                     return None;
                 }
             }
 
-            let text = get_text_after_edit(token.clone().into(), &edit);
-            let lex_tokens = tokenize(&text);
-            let lex_token = match lex_tokens[..] {
-                [lex_token] if lex_token.kind == token.kind() => lex_token,
-                _ => return None,
-            };
+            let mut new_text = get_text_after_edit(prev_token.clone().into(), &edit);
+            let new_token_kind = single_token(&new_text)?.token.kind;
 
-            if lex_token.kind == IDENT && is_contextual_kw(&text) {
+            if new_token_kind != prev_token_kind
+                || (new_token_kind == IDENT && is_contextual_kw(&new_text))
+            {
                 return None;
             }
 
-            if let Some(next_char) = root.text().char_at(token.text_range().end()) {
-                let tokens_with_next_char = tokenize(&format!("{}{}", text, next_char));
-                if tokens_with_next_char.len() == 1 {
+            // Check that edited token is not a part of the bigger token.
+            // E.g. if for source code `bruh"str"` the user removed `ruh`, then
+            // `b` no longer remains an identifier, but becomes a part of byte string literal
+            if let Some(next_char) = root.text().char_at(prev_token.text_range().end()) {
+                new_text.push(next_char);
+                let token_with_next_char = single_token(&new_text);
+                if token_with_next_char.is_some() {
                     return None;
                 }
+                new_text.pop();
             }
 
-            let new_token = GreenToken::new(rowan::SyntaxKind(token.kind().into()), text.into());
-            Some((token.replace_with(new_token), token.text_range()))
+            let new_token =
+                GreenToken::new(rowan::SyntaxKind(prev_token_kind.into()), new_text.into());
+            Some((prev_token.replace_with(new_token), prev_token.text_range()))
         }
         _ => None,
     }
@@ -82,12 +88,12 @@ fn reparse_block<'node>(
 ) -> Option<(GreenNode, Vec<SyntaxError>, TextRange)> {
     let (node, reparser) = find_reparsable_node(root, edit.delete)?;
     let text = get_text_after_edit(node.clone().into(), &edit);
-    let tokens = tokenize(&text);
+    let ParsedTokens { tokens, errors } = tokenize(&text);
     if !is_balanced(&tokens) {
         return None;
     }
     let mut token_source = TextTokenSource::new(&text, &tokens);
-    let mut tree_sink = TextTreeSink::new(&text, &tokens);
+    let mut tree_sink = TextTreeSink::new(&text, &tokens, errors);
     reparser.parse(&mut token_source, &mut tree_sink);
     let (green, new_errors) = tree_sink.finish();
     Some((node.replace_with(green), new_errors, node.text_range()))
@@ -96,6 +102,9 @@ fn reparse_block<'node>(
 fn get_text_after_edit(element: SyntaxElement, edit: &AtomTextEdit) -> String {
     let edit =
         AtomTextEdit::replace(edit.delete - element.text_range().start(), edit.insert.clone());
+
+    // Note: we could move this match to a method or even further: use enum_dispatch crate
+    // https://crates.io/crates/enum_dispatch
     let text = match element {
         NodeOrToken::Token(token) => token.text().to_string(),
         NodeOrToken::Node(node) => node.text().to_string(),
@@ -112,6 +121,9 @@ fn is_contextual_kw(text: &str) -> bool {
 
 fn find_reparsable_node(node: &SyntaxNode, range: TextRange) -> Option<(SyntaxNode, Reparser)> {
     let node = algo::find_covering_element(node, range);
+
+    // Note: we could move this match to a method or even further: use enum_dispatch crate
+    // https://crates.io/crates/enum_dispatch
     let mut ancestors = match node {
         NodeOrToken::Token(it) => it.parent().ancestors(),
         NodeOrToken::Node(it) => it.ancestors(),
@@ -181,6 +193,8 @@ mod tests {
         let fully_reparsed = SourceFile::parse(&after);
         let incrementally_reparsed: Parse<SourceFile> = {
             let f = SourceFile::parse(&before);
+            // FIXME: it seems this initialization statement is unnecessary (see edit in outer scope)
+            // Investigate whether it should really be removed.
             let edit = AtomTextEdit { delete: range, insert: replace_with.to_string() };
             let (green, new_errors, range) =
                 incremental_reparse(f.tree().syntax(), &edit, f.errors.to_vec()).unwrap();
diff --git a/crates/ra_syntax/src/parsing/text_tree_sink.rs b/crates/ra_syntax/src/parsing/text_tree_sink.rs
index c36756d6c..5faac588b 100644
--- a/crates/ra_syntax/src/parsing/text_tree_sink.rs
+++ b/crates/ra_syntax/src/parsing/text_tree_sink.rs
@@ -92,14 +92,14 @@ impl<'a> TreeSink for TextTreeSink<'a> {
 }
 
 impl<'a> TextTreeSink<'a> {
-    pub(super) fn new(text: &'a str, tokens: &'a [Token]) -> TextTreeSink<'a> {
-        TextTreeSink {
+    pub(super) fn new(text: &'a str, tokens: &'a [Token], errors: Vec<SyntaxError>) -> Self {
+        Self {
             text,
             tokens,
             text_pos: 0.into(),
             token_pos: 0,
             state: State::PendingStart,
-            inner: SyntaxTreeBuilder::default(),
+            inner: SyntaxTreeBuilder::new(errors),
         }
     }
 
diff --git a/crates/ra_syntax/src/syntax_error.rs b/crates/ra_syntax/src/syntax_error.rs
index 9122dda29..af18a30f2 100644
--- a/crates/ra_syntax/src/syntax_error.rs
+++ b/crates/ra_syntax/src/syntax_error.rs
@@ -84,6 +84,9 @@ pub enum SyntaxErrorKind {
     ParseError(ParseError),
     EscapeError(EscapeError),
     TokenizeError(TokenizeError),
+    // FIXME: the obvious pattern of this enum dictates that the following enum variants
+    // should be wrapped into something like `SemmanticError(SemmanticError)`
+    // or `ValidateError(ValidateError)` or `SemmanticValidateError(...)`
     InvalidBlockAttr,
     InvalidMatchInnerAttr,
     InvalidTupleIndexFormat,
@@ -106,6 +109,7 @@ impl fmt::Display for SyntaxErrorKind {
             }
             ParseError(msg) => write!(f, "{}", msg.0),
             EscapeError(err) => write!(f, "{}", err),
+            TokenizeError(err) => write!(f, "{}", err),
             VisibilityNotAllowed => {
                 write!(f, "unnecessary visibility qualifier")
             }
@@ -116,6 +120,44 @@ impl fmt::Display for SyntaxErrorKind {
     }
 }
 
+impl fmt::Display for TokenizeError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let msg = match self {
+            TokenizeError::EmptyInt => "Missing digits after integer base prefix",
+            TokenizeError::EmptyExponent => "Missing digits after the exponent symbol",
+            TokenizeError::UnterminatedBlockComment => {
+                "Missing trailing `*/` symbols to terminate the block comment"
+            }
+            TokenizeError::UnterminatedChar => {
+                "Missing trailing `'` symbol to terminate the character literal"
+            }
+            TokenizeError::UnterminatedByte => {
+                "Missing trailing `'` symbol to terminate the byte literal"
+            }
+            TokenizeError::UnterminatedString => {
+                "Missing trailing `\"` symbol to terminate the string literal"
+            }
+            TokenizeError::UnterminatedByteString => {
+                "Missing trailing `\"` symbol to terminate the byte string literal"
+            }
+            TokenizeError::UnterminatedRawString => {
+                "Missing trailing `\"` with `#` symbols to terminate the raw string literal"
+            }
+            TokenizeError::UnterminatedRawByteString => {
+                "Missing trailing `\"` with `#` symbols to terminate the raw byte string literal"
+            }
+            TokenizeError::UnstartedRawString => {
+                "Missing `\"` symbol after `#` symbols to begin the raw string literal"
+            }
+            TokenizeError::UnstartedRawByteString => {
+                "Missing `\"` symbol after `#` symbols to begin the raw byte string literal"
+            }
+            TokenizeError::LifetimeStartsWithNumber => "Lifetime name cannot start with a number",
+        };
+        write!(f, "{}", msg)
+    }
+}
+
 impl fmt::Display for EscapeError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let msg = match self {
diff --git a/crates/ra_syntax/src/syntax_node.rs b/crates/ra_syntax/src/syntax_node.rs
index b3eb5da63..591855302 100644
--- a/crates/ra_syntax/src/syntax_node.rs
+++ b/crates/ra_syntax/src/syntax_node.rs
@@ -4,7 +4,7 @@
 //! `SyntaxNode`, and a basic traversal API (parent, children, siblings).
 //!
 //! The *real* implementation is in the (language-agnostic) `rowan` crate, this
-//! modules just wraps its API.
+//! module just wraps its API.
 
 use ra_parser::ParseError;
 use rowan::{GreenNodeBuilder, Language};
@@ -38,14 +38,15 @@ pub type SyntaxElementChildren = rowan::SyntaxElementChildren<RustLanguage>;
 
 pub use rowan::{Direction, NodeOrToken};
 
+#[derive(Default)]
 pub struct SyntaxTreeBuilder {
     errors: Vec<SyntaxError>,
     inner: GreenNodeBuilder<'static>,
 }
 
-impl Default for SyntaxTreeBuilder {
-    fn default() -> SyntaxTreeBuilder {
-        SyntaxTreeBuilder { errors: Vec::new(), inner: GreenNodeBuilder::new() }
+impl SyntaxTreeBuilder {
+    pub fn new(errors: Vec<SyntaxError>) -> Self {
+        Self { errors, inner: GreenNodeBuilder::default() }
     }
 }
 
diff --git a/crates/ra_syntax/src/tests.rs b/crates/ra_syntax/src/tests.rs
index 458920607..df21c957c 100644
--- a/crates/ra_syntax/src/tests.rs
+++ b/crates/ra_syntax/src/tests.rs
@@ -10,7 +10,8 @@ use crate::{fuzz, SourceFile};
 #[test]
 fn lexer_tests() {
     dir_tests(&test_data_dir(), &["lexer"], |text, _| {
-        let tokens = crate::tokenize(text);
+        // FIXME: add tests for errors (their format is up to discussion)
+        let tokens = crate::tokenize(text).tokens;
         dump_tokens(&tokens, text)
     })
 }