organizize

353 files changed, 13650 insertions, 0 deletions

diff --git a/crates/libsyntax2/Cargo.toml b/crates/libsyntax2/Cargo.toml
new file mode 100644
index 000000000..f67735540
--- /dev/null
+++ b/crates/libsyntax2/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "libsyntax2"
+version = "0.1.0"
+authors = ["Aleksey Kladov <[email protected]>"]
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+unicode-xid = "0.1.0"
+text_unit = "0.1.2"
+itertools = "0.7.5"
+drop_bomb = "0.1.4"
+parking_lot = "0.6.0"
+
+[dev-dependencies]
+testutils = { path = "./tests/testutils" }
diff --git a/crates/libsyntax2/src/algo/mod.rs b/crates/libsyntax2/src/algo/mod.rs
new file mode 100644
index 000000000..d2de70fd4
--- /dev/null
+++ b/crates/libsyntax2/src/algo/mod.rs
@@ -0,0 +1,123 @@
+pub mod walk;
+
+use {SyntaxNodeRef, TextUnit, TextRange};
+
+pub fn find_leaf_at_offset(node: SyntaxNodeRef, offset: TextUnit) -> LeafAtOffset {
+    let range = node.range();
+    assert!(
+        contains_offset_nonstrict(range, offset),
+        "Bad offset: range {:?} offset {:?}", range, offset
+    );
+    if range.is_empty() {
+        return LeafAtOffset::None;
+    }
+
+    if node.is_leaf() {
+        return LeafAtOffset::Single(node);
+    }
+
+    let mut children = node.children()
+        .filter(|child| {
+            let child_range = child.range();
+            !child_range.is_empty() && contains_offset_nonstrict(child_range, offset)
+        });
+
+    let left = children.next().unwrap();
+    let right = children.next();
+    assert!(children.next().is_none());
+    return if let Some(right) = right {
+        match (find_leaf_at_offset(left, offset), find_leaf_at_offset(right, offset)) {
+            (LeafAtOffset::Single(left), LeafAtOffset::Single(right)) =>
+                LeafAtOffset::Between(left, right),
+            _ => unreachable!()
+        }
+    } else {
+        find_leaf_at_offset(left, offset)
+    };
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum LeafAtOffset<'a> {
+    None,
+    Single(SyntaxNodeRef<'a>),
+    Between(SyntaxNodeRef<'a>, SyntaxNodeRef<'a>)
+}
+
+impl<'a> LeafAtOffset<'a> {
+    pub fn right_biased(self) -> Option<SyntaxNodeRef<'a>> {
+        match self {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => Some(node),
+            LeafAtOffset::Between(_, right) => Some(right)
+        }
+    }
+
+    pub fn left_biased(self) -> Option<SyntaxNodeRef<'a>> {
+        match self {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => Some(node),
+            LeafAtOffset::Between(left, _) => Some(left)
+        }
+    }
+}
+
+impl<'f> Iterator for LeafAtOffset<'f> {
+    type Item = SyntaxNodeRef<'f>;
+
+    fn next(&mut self) -> Option<SyntaxNodeRef<'f>> {
+        match *self {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => { *self = LeafAtOffset::None; Some(node) }
+            LeafAtOffset::Between(left, right) => { *self = LeafAtOffset::Single(right); Some(left) }
+        }
+    }
+}
+
+
+pub fn find_covering_node(root: SyntaxNodeRef, range: TextRange) -> SyntaxNodeRef {
+    assert!(is_subrange(root.range(), range));
+    let (left, right) = match (
+        find_leaf_at_offset(root, range.start()).right_biased(),
+        find_leaf_at_offset(root, range.end()).left_biased()
+    ) {
+        (Some(l), Some(r)) => (l, r),
+        _ => return root
+    };
+
+    common_ancestor(left, right)
+}
+
+fn common_ancestor<'a>(n1: SyntaxNodeRef<'a>, n2: SyntaxNodeRef<'a>) -> SyntaxNodeRef<'a> {
+    for p in ancestors(n1) {
+        if ancestors(n2).any(|a| a == p) {
+            return p;
+        }
+    }
+    panic!("Can't find common ancestor of {:?} and {:?}", n1, n2)
+}
+
+pub fn ancestors<'a>(node: SyntaxNodeRef<'a>) -> impl Iterator<Item=SyntaxNodeRef<'a>> {
+    Ancestors(Some(node))
+}
+
+#[derive(Debug)]
+struct Ancestors<'a>(Option<SyntaxNodeRef<'a>>);
+
+impl<'a> Iterator for Ancestors<'a> {
+    type Item = SyntaxNodeRef<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.take().map(|n| {
+            self.0 = n.parent();
+            n
+        })
+    }
+}
+
+fn contains_offset_nonstrict(range: TextRange, offset: TextUnit) -> bool {
+    range.start() <= offset && offset <= range.end()
+}
+
+fn is_subrange(range: TextRange, subrange: TextRange) -> bool {
+    range.start() <= subrange.start() && subrange.end() <= range.end()
+}
diff --git a/crates/libsyntax2/src/algo/search.rs b/crates/libsyntax2/src/algo/search.rs
new file mode 100644
index 000000000..46404f537
--- /dev/null
+++ b/crates/libsyntax2/src/algo/search.rs
@@ -0,0 +1,136 @@
+use {Node, NodeType, TextUnit, TextRange};
+use ::visitor::{visitor, process_subtree_bottom_up};
+
+pub fn child_of_type(node: Node, ty: NodeType) -> Option<Node> {
+    node.children().find(|n| n.ty() == ty)
+}
+
+pub fn children_of_type<'f>(node: Node<'f>, ty: NodeType) -> Box<Iterator<Item=Node<'f>> + 'f> {
+    Box::new(node.children().filter(move |n| n.ty() == ty))
+}
+
+pub fn subtree<'f>(node: Node<'f>) -> Box<Iterator<Item=Node<'f>> + 'f> {
+    Box::new(node.children().flat_map(subtree).chain(::std::iter::once(node)))
+}
+
+pub fn descendants_of_type<'f>(node: Node<'f>, ty: NodeType) -> Vec<Node<'f>> {
+    process_subtree_bottom_up(
+        node,
+        visitor(Vec::new())
+            .visit_nodes(&[ty], |node, nodes| nodes.push(node))
+    )
+}
+
+pub fn child_of_type_exn(node: Node, ty: NodeType) -> Node {
+    child_of_type(node, ty).unwrap_or_else(|| {
+        panic!("No child of type {:?} for {:?}\
+                ----\
+                {}\
+                ----", ty, node.ty(), node.text())
+    })
+}
+
+
+pub fn ancestors(node: Node) -> Ancestors {
+    Ancestors(Some(node))
+}
+
+pub struct Ancestors<'f>(Option<Node<'f>>);
+
+impl<'f> Iterator for Ancestors<'f> {
+    type Item = Node<'f>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let current = self.0;
+        self.0 = current.and_then(|n| n.parent());
+        current
+    }
+}
+
+pub fn is_leaf(node: Node) -> bool {
+    node.children().next().is_none() && !node.range().is_empty()
+}
+
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum Direction {
+    Left, Right
+}
+
+pub fn sibling(node: Node, dir: Direction) -> Option<Node> {
+    let (parent, idx) = child_position(node)?;
+    let idx = match dir {
+        Direction::Left => idx.checked_sub(1)?,
+        Direction::Right => idx + 1,
+    };
+    parent.children().nth(idx)
+}
+
+pub mod ast {
+    use {Node, AstNode, TextUnit, AstChildren};
+    use visitor::{visitor, process_subtree_bottom_up};
+    use super::{ancestors, find_leaf_at_offset, LeafAtOffset};
+
+    pub fn ancestor<'f, T: AstNode<'f>>(node: Node<'f>) -> Option<T> {
+        ancestors(node)
+            .filter_map(T::wrap)
+            .next()
+    }
+
+    pub fn ancestor_exn<'f, T: AstNode<'f>>(node: Node<'f>) -> T {
+        ancestor(node).unwrap()
+    }
+
+    pub fn children_of_type<'f, N: AstNode<'f>>(node: Node<'f>) -> AstChildren<N> {
+        AstChildren::new(node.children())
+    }
+
+    pub fn descendants_of_type<'f, N: AstNode<'f>>(node: Node<'f>) -> Vec<N> {
+        process_subtree_bottom_up(
+            node,
+            visitor(Vec::new())
+                .visit::<N, _>(|node, acc| acc.push(node))
+        )
+    }
+
+    pub fn node_at_offset<'f, T: AstNode<'f>>(node: Node<'f>, offset: TextUnit) -> Option<T> {
+        match find_leaf_at_offset(node, offset) {
+            LeafAtOffset::None => None,
+            LeafAtOffset::Single(node) => ancestor(node),
+            LeafAtOffset::Between(left, right) => ancestor(left).or_else(|| ancestor(right)),
+        }
+    }
+}
+
+pub mod traversal {
+    use {Node};
+
+    pub fn bottom_up<'f, F: FnMut(Node<'f>)>(node: Node<'f>, mut f: F)
+    {
+        go(node, &mut f);
+
+        fn go<'f, F: FnMut(Node<'f>)>(node: Node<'f>, f: &mut F) {
+            for child in node.children() {
+                go(child, f)
+            }
+            f(node);
+        }
+    }
+}
+
+fn child_position(child: Node) -> Option<(Node, usize)> {
+    child.parent()
+        .map(|parent| {
+            (parent, parent.children().position(|n| n == child).unwrap())
+        })
+}
+
+fn common_ancestor<'f>(n1: Node<'f>, n2: Node<'f>) -> Node<'f> {
+    for p in ancestors(n1) {
+        if ancestors(n2).any(|a| a == p) {
+            return p;
+        }
+    }
+    panic!("Can't find common ancestor of {:?} and {:?}", n1, n2)
+}
+
diff --git a/crates/libsyntax2/src/algo/walk.rs b/crates/libsyntax2/src/algo/walk.rs
new file mode 100644
index 000000000..a50ec2a09
--- /dev/null
+++ b/crates/libsyntax2/src/algo/walk.rs
@@ -0,0 +1,45 @@
+use SyntaxNodeRef;
+
+pub fn preorder<'a>(root: SyntaxNodeRef<'a>) -> impl Iterator<Item = SyntaxNodeRef<'a>> {
+    walk(root).filter_map(|event| match event {
+        WalkEvent::Enter(node) => Some(node),
+        WalkEvent::Exit(_) => None,
+    })
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum WalkEvent<'a> {
+    Enter(SyntaxNodeRef<'a>),
+    Exit(SyntaxNodeRef<'a>),
+}
+
+pub fn walk<'a>(root: SyntaxNodeRef<'a>) -> impl Iterator<Item = WalkEvent<'a>> {
+    let mut done = false;
+    ::itertools::unfold(WalkEvent::Enter(root), move |pos| {
+        if done {
+            return None;
+        }
+        let res = *pos;
+        *pos = match *pos {
+            WalkEvent::Enter(node) => match node.first_child() {
+                Some(child) => WalkEvent::Enter(child),
+                None => WalkEvent::Exit(node),
+            },
+            WalkEvent::Exit(node) => {
+                if node == root {
+                    done = true;
+                    WalkEvent::Exit(node)
+                } else {
+                    match node.next_sibling() {
+                        Some(sibling) => WalkEvent::Enter(sibling),
+                        None => match node.parent() {
+                            Some(node) => WalkEvent::Exit(node),
+                            None => WalkEvent::Exit(node),
+                        },
+                    }
+                }
+            }
+        };
+        Some(res)
+    })
+}
diff --git a/crates/libsyntax2/src/ast/generated.rs b/crates/libsyntax2/src/ast/generated.rs
new file mode 100644
index 000000000..2f813050a
--- /dev/null
+++ b/crates/libsyntax2/src/ast/generated.rs
@@ -0,0 +1,54 @@
+use std::sync::Arc;
+use {
+    SyntaxNode, SyntaxRoot, TreeRoot, AstNode,
+    SyntaxKind::*,
+};
+
+
+#[derive(Debug, Clone, Copy)]
+pub struct File<R: TreeRoot = Arc<SyntaxRoot>> {
+    syntax: SyntaxNode<R>,
+}
+
+impl<R: TreeRoot> AstNode<R> for File<R> {
+    fn cast(syntax: SyntaxNode<R>) -> Option<Self> {
+        match syntax.kind() {
+            FILE => Some(File { syntax }),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode<R> { &self.syntax }
+}
+
+
+#[derive(Debug, Clone, Copy)]
+pub struct Function<R: TreeRoot = Arc<SyntaxRoot>> {
+    syntax: SyntaxNode<R>,
+}
+
+impl<R: TreeRoot> AstNode<R> for Function<R> {
+    fn cast(syntax: SyntaxNode<R>) -> Option<Self> {
+        match syntax.kind() {
+            FUNCTION => Some(Function { syntax }),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode<R> { &self.syntax }
+}
+
+
+#[derive(Debug, Clone, Copy)]
+pub struct Name<R: TreeRoot = Arc<SyntaxRoot>> {
+    syntax: SyntaxNode<R>,
+}
+
+impl<R: TreeRoot> AstNode<R> for Name<R> {
+    fn cast(syntax: SyntaxNode<R>) -> Option<Self> {
+        match syntax.kind() {
+            NAME => Some(Name { syntax }),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode<R> { &self.syntax }
+}
+
diff --git a/crates/libsyntax2/src/ast/generated.rs.tera b/crates/libsyntax2/src/ast/generated.rs.tera
new file mode 100644
index 000000000..242837801
--- /dev/null
+++ b/crates/libsyntax2/src/ast/generated.rs.tera
@@ -0,0 +1,22 @@
+use std::sync::Arc;
+use {
+    SyntaxNode, SyntaxRoot, TreeRoot, AstNode,
+    SyntaxKind::*,
+};
+{% for node in ast %}
+{% set Name = node.kind | camel  %}
+#[derive(Debug, Clone, Copy)]
+pub struct {{ Name }}<R: TreeRoot = Arc<SyntaxRoot>> {
+    syntax: SyntaxNode<R>,
+}
+
+impl<R: TreeRoot> AstNode<R> for {{ Name }}<R> {
+    fn cast(syntax: SyntaxNode<R>) -> Option<Self> {
+        match syntax.kind() {
+            {{ node.kind }} => Some({{ Name }} { syntax }),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode<R> { &self.syntax }
+}
+{% endfor %}
diff --git a/crates/libsyntax2/src/ast/mod.rs b/crates/libsyntax2/src/ast/mod.rs
new file mode 100644
index 000000000..eeb7ae6f6
--- /dev/null
+++ b/crates/libsyntax2/src/ast/mod.rs
@@ -0,0 +1,74 @@
+mod generated;
+
+use std::sync::Arc;
+use {
+    SyntaxNode, SyntaxRoot, TreeRoot, SyntaxError,
+    SyntaxKind::*,
+};
+pub use self::generated::*;
+
+pub trait AstNode<R: TreeRoot>: Sized {
+    fn cast(syntax: SyntaxNode<R>) -> Option<Self>;
+    fn syntax(&self) -> &SyntaxNode<R>;
+}
+
+impl File<Arc<SyntaxRoot>> {
+    pub fn parse(text: &str) -> Self {
+        File::cast(::parse(text)).unwrap()
+    }
+}
+
+impl<R: TreeRoot> File<R> {
+    pub fn errors(&self) -> Vec<SyntaxError> {
+        self.syntax().root.errors.clone()
+    }
+
+    pub fn functions<'a>(&'a self) -> impl Iterator<Item = Function<R>> + 'a {
+        self.syntax()
+            .children()
+            .filter_map(Function::cast)
+    }
+}
+
+impl<R: TreeRoot> Function<R> {
+    pub fn name(&self) -> Option<Name<R>> {
+        self.syntax()
+            .children()
+            .filter_map(Name::cast)
+            .next()
+    }
+
+    pub fn has_atom_attr(&self, atom: &str) -> bool {
+        self.syntax()
+            .children()
+            .filter(|node| node.kind() == ATTR)
+            .any(|attr| {
+                let mut metas = attr.children().filter(|node| node.kind() == META_ITEM);
+                let meta = match metas.next() {
+                    None => return false,
+                    Some(meta) => {
+                        if metas.next().is_some() {
+                            return false;
+                        }
+                        meta
+                    }
+                };
+                let mut children = meta.children();
+                match children.next() {
+                    None => false,
+                    Some(child) => {
+                        if children.next().is_some() {
+                            return false;
+                        }
+                        child.kind() == IDENT && child.text() == atom
+                    }
+                }
+            })
+    }
+}
+
+impl<R: TreeRoot> Name<R> {
+    pub fn text(&self) -> String {
+        self.syntax().text()
+    }
+}
diff --git a/crates/libsyntax2/src/grammar.ron b/crates/libsyntax2/src/grammar.ron
new file mode 100644
index 000000000..bcc79843a
--- /dev/null
+++ b/crates/libsyntax2/src/grammar.ron
@@ -0,0 +1,227 @@
+Grammar(
+    single_byte_tokens: [
+        [";", "SEMI"],
+        [",", "COMMA"],
+        ["(", "L_PAREN"],
+        [")", "R_PAREN"],
+        ["{", "L_CURLY"],
+        ["}", "R_CURLY"],
+        ["[", "L_BRACK"],
+        ["]", "R_BRACK"],
+        ["<", "L_ANGLE"],
+        [">", "R_ANGLE"],
+        ["@", "AT"],
+        ["#", "POUND"],
+        ["~", "TILDE"],
+        ["?", "QUESTION"],
+        ["$", "DOLLAR"],
+        ["&", "AMP"],
+        ["|", "PIPE"],
+        ["+", "PLUS"],
+        ["*", "STAR"],
+        ["/", "SLASH"],
+        ["^", "CARET"],
+        ["%", "PERCENT"],
+    ],
+    multi_byte_tokens: [
+        [".", "DOT"],
+        ["..", "DOTDOT"],
+        ["...", "DOTDOTDOT"],
+        ["..=", "DOTDOTEQ"],
+        [":", "COLON"],
+        ["::", "COLONCOLON"],
+        ["=", "EQ"],
+        ["==", "EQEQ"],
+        ["=>", "FAT_ARROW"],
+        ["!", "EXCL"],
+        ["!=", "NEQ"],
+        ["-", "MINUS"],
+        ["->", "THIN_ARROW"],
+        ["<=", "LTEQ"],
+        [">=", "GTEQ"],
+        ["+=", "PLUSEQ"],
+        ["-=", "MINUSEQ"],
+        ["&&", "AMPAMP"],
+        ["||", "PIPEPIPE"],
+        ["<<", "SHL"],
+        [">>", "SHR"],
+        ["<<=", "SHLEQ"],
+        [">>=", "SHREQ"],
+    ],
+    keywords: [
+        "use",
+        "fn",
+        "struct",
+        "enum",
+        "trait",
+        "impl",
+        "true",
+        "false",
+        "as",
+        "extern",
+        "crate",
+        "mod",
+        "pub",
+        "self",
+        "super",
+        "in",
+        "where",
+        "for",
+        "loop",
+        "while",
+        "if",
+        "else",
+        "match",
+        "const",
+        "static",
+        "mut",
+        "unsafe",
+        "type",
+        "ref",
+        "let",
+        "move",
+        "return",
+    ],
+    contextual_keywords: [
+        "auto",
+        "default",
+        "union",
+    ],
+    tokens: [
+        "ERROR",
+        "IDENT",
+        "UNDERSCORE",
+        "WHITESPACE",
+        "INT_NUMBER",
+        "FLOAT_NUMBER",
+        "LIFETIME",
+        "CHAR",
+        "BYTE",
+        "STRING",
+        "RAW_STRING",
+        "BYTE_STRING",
+        "RAW_BYTE_STRING",
+        "COMMENT",
+        "DOC_COMMENT",
+        "SHEBANG",
+    ],
+    nodes: [
+        "FILE",
+
+        "STRUCT_ITEM",
+        "ENUM_ITEM",
+        "FUNCTION",
+        "EXTERN_CRATE_ITEM",
+        "MOD_ITEM",
+        "USE_ITEM",
+        "STATIC_ITEM",
+        "CONST_ITEM",
+        "TRAIT_ITEM",
+        "IMPL_ITEM",
+        "TYPE_ITEM",
+        "MACRO_CALL",
+        "TOKEN_TREE",
+
+        "PAREN_TYPE",
+        "TUPLE_TYPE",
+        "NEVER_TYPE",
+        "PATH_TYPE",
+        "POINTER_TYPE",
+        "ARRAY_TYPE",
+        "SLICE_TYPE",
+        "REFERENCE_TYPE",
+        "PLACEHOLDER_TYPE",
+        "FN_POINTER_TYPE",
+        "FOR_TYPE",
+        "IMPL_TRAIT_TYPE",
+
+        "REF_PAT",
+        "BIND_PAT",
+        "PLACEHOLDER_PAT",
+        "PATH_PAT",
+        "STRUCT_PAT",
+        "TUPLE_STRUCT_PAT",
+        "TUPLE_PAT",
+        "SLICE_PAT",
+        "RANGE_PAT",
+
+        // atoms
+        "TUPLE_EXPR",
+        "ARRAY_EXPR",
+        "PAREN_EXPR",
+        "PATH_EXPR",
+        "LAMBDA_EXPR",
+        "IF_EXPR",
+        "WHILE_EXPR",
+        "LOOP_EXPR",
+        "FOR_EXPR",
+        "BLOCK_EXPR",
+        "RETURN_EXPR",
+        "MATCH_EXPR",
+        "MATCH_ARM",
+        "MATCH_GUARD",
+        "STRUCT_LIT",
+        "STRUCT_LIT_FIELD",
+
+        // postfix
+        "CALL_EXPR",
+        "INDEX_EXPR",
+        "METHOD_CALL_EXPR",
+        "FIELD_EXPR",
+        "TRY_EXPR",
+        "CAST_EXPR",
+
+        // unary
+        "REF_EXPR",
+        "PREFIX_EXPR",
+
+        "RANGE_EXPR", // just weird
+        "BIN_EXPR",
+
+
+        "EXTERN_BLOCK_EXPR",
+        "ENUM_VARIANT",
+        "NAMED_FIELD",
+        "POS_FIELD",
+        "ATTR",
+        "META_ITEM", // not an item actually
+        "USE_TREE",
+        "PATH",
+        "PATH_SEGMENT",
+        "LITERAL",
+        "ALIAS",
+        "VISIBILITY",
+        "WHERE_CLAUSE",
+        "WHERE_PRED",
+        "ABI",
+        "NAME",
+        "NAME_REF",
+
+        "LET_STMT",
+        "EXPR_STMT",
+
+        "TYPE_PARAM_LIST",
+        "LIFETIME_PARAM",
+        "TYPE_PARAM",
+        "TYPE_ARG_LIST",
+        "LIFETIME_ARG",
+        "TYPE_ARG",
+        "ASSOC_TYPE_ARG",
+
+        "PARAM_LIST",
+        "PARAM",
+        "SELF_PARAM",
+        "ARG_LIST",
+    ],
+    ast: [
+        (
+            kind: "FILE"
+        ),
+        (
+            kind: "FUNCTION"
+        ),
+        (
+            kind: "NAME"
+        ),
+    ]
+)
diff --git a/crates/libsyntax2/src/grammar/attributes.rs b/crates/libsyntax2/src/grammar/attributes.rs
new file mode 100644
index 000000000..c411d4d7f
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/attributes.rs
@@ -0,0 +1,79 @@
+use super::*;
+
+pub(super) fn inner_attributes(p: &mut Parser) {
+    while p.current() == POUND && p.nth(1) == EXCL {
+        attribute(p, true)
+    }
+}
+
+pub(super) fn outer_attributes(p: &mut Parser) {
+    while p.at(POUND) {
+        attribute(p, false)
+    }
+}
+
+fn attribute(p: &mut Parser, inner: bool) {
+    let attr = p.start();
+    assert!(p.at(POUND));
+    p.bump();
+
+    if inner {
+        assert!(p.at(EXCL));
+        p.bump();
+    }
+
+    if p.expect(L_BRACK) {
+        meta_item(p);
+        p.expect(R_BRACK);
+    }
+    attr.complete(p, ATTR);
+}
+
+fn meta_item(p: &mut Parser) {
+    if p.at(IDENT) {
+        let meta_item = p.start();
+        p.bump();
+        match p.current() {
+            EQ => {
+                p.bump();
+                if expressions::literal(p).is_none() {
+                    p.error("expected literal");
+                }
+            }
+            L_PAREN => meta_item_arg_list(p),
+            _ => (),
+        }
+        meta_item.complete(p, META_ITEM);
+    } else {
+        p.error("expected attribute value");
+    }
+}
+
+fn meta_item_arg_list(p: &mut Parser) {
+    assert!(p.at(L_PAREN));
+    p.bump();
+    loop {
+        match p.current() {
+            EOF | R_PAREN => break,
+            IDENT => meta_item(p),
+            c => if expressions::literal(p).is_none() {
+                let message = "expected attribute";
+
+                if items::ITEM_FIRST.contains(c) {
+                    p.error(message);
+                    return;
+                }
+
+                let err = p.start();
+                p.error(message);
+                p.bump();
+                err.complete(p, ERROR);
+                continue;
+            },
+        }
+        if !p.at(R_PAREN) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_PAREN);
+}
diff --git a/crates/libsyntax2/src/grammar/expressions/atom.rs b/crates/libsyntax2/src/grammar/expressions/atom.rs
new file mode 100644
index 000000000..af9f47c5e
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/expressions/atom.rs
@@ -0,0 +1,348 @@
+use super::*;
+
+// test expr_literals
+// fn foo() {
+//     let _ = true;
+//     let _ = false;
+//     let _ = 1;
+//     let _ = 2.0;
+//     let _ = b'a';
+//     let _ = 'b';
+//     let _ = "c";
+//     let _ = r"d";
+//     let _ = b"e";
+//     let _ = br"f";
+// }
+const LITERAL_FIRST: TokenSet =
+    token_set![TRUE_KW, FALSE_KW, INT_NUMBER, FLOAT_NUMBER, BYTE, CHAR,
+               STRING, RAW_STRING, BYTE_STRING, RAW_BYTE_STRING];
+
+pub(crate) fn literal(p: &mut Parser) -> Option<CompletedMarker> {
+    if !LITERAL_FIRST.contains(p.current()) {
+        return None;
+    }
+    let m = p.start();
+    p.bump();
+    Some(m.complete(p, LITERAL))
+}
+
+pub(super) const ATOM_EXPR_FIRST: TokenSet =
+    token_set_union![
+        LITERAL_FIRST,
+        token_set![L_PAREN, PIPE, MOVE_KW, IF_KW, WHILE_KW, MATCH_KW, UNSAFE_KW, L_CURLY, RETURN_KW,
+                   IDENT, SELF_KW, SUPER_KW, COLONCOLON ],
+    ];
+
+pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<CompletedMarker> {
+    match literal(p) {
+        Some(m) => return Some(m),
+        None => (),
+    }
+    if paths::is_path_start(p) {
+        return Some(path_expr(p, r));
+    }
+    let la = p.nth(1);
+    let done = match p.current() {
+        L_PAREN => tuple_expr(p),
+        L_BRACK => array_expr(p),
+        PIPE => lambda_expr(p),
+        MOVE_KW if la == PIPE => lambda_expr(p),
+        IF_KW => if_expr(p),
+        WHILE_KW => while_expr(p),
+        LOOP_KW => loop_expr(p),
+        FOR_KW => for_expr(p),
+        MATCH_KW => match_expr(p),
+        UNSAFE_KW if la == L_CURLY => block_expr(p),
+        L_CURLY => block_expr(p),
+        RETURN_KW => return_expr(p),
+        _ => {
+            p.err_and_bump("expected expression");
+            return None;
+        }
+    };
+    Some(done)
+}
+
+// test tuple_expr
+// fn foo() {
+//     ();
+//     (1);
+//     (1,);
+// }
+fn tuple_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_PAREN));
+    let m = p.start();
+    p.expect(L_PAREN);
+
+    let mut saw_comma = false;
+    let mut saw_expr = false;
+    while !p.at(EOF) && !p.at(R_PAREN) {
+        saw_expr = true;
+        expr(p);
+        if !p.at(R_PAREN) {
+            saw_comma = true;
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_PAREN);
+    m.complete(p, if saw_expr && !saw_comma { PAREN_EXPR } else { TUPLE_EXPR })
+}
+
+// test array_expr
+// fn foo() {
+//     [];
+//     [1];
+//     [1, 2,];
+//     [1; 2];
+// }
+fn array_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_BRACK));
+    let m = p.start();
+    p.bump();
+    if p.eat(R_BRACK) {
+        return m.complete(p, ARRAY_EXPR);
+    }
+    expr(p);
+    if p.eat(SEMI) {
+        expr(p);
+        p.expect(R_BRACK);
+        return m.complete(p, ARRAY_EXPR);
+    }
+    while !p.at(EOF) && !p.at(R_BRACK) {
+        p.expect(COMMA);
+        if !p.at(R_BRACK) {
+            expr(p);
+        }
+    }
+    p.expect(R_BRACK);
+    m.complete(p, ARRAY_EXPR)
+}
+
+// test lambda_expr
+// fn foo() {
+//     || ();
+//     || -> i32 { 92 };
+//     |x| x;
+//     move |x: i32,| x;
+// }
+fn lambda_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(PIPE) || (p.at(MOVE_KW) && p.nth(1) == PIPE));
+    let m = p.start();
+    p.eat(MOVE_KW);
+    params::param_list_opt_types(p);
+    if fn_ret_type(p) {
+        block(p);
+    } else {
+        expr(p);
+    }
+    m.complete(p, LAMBDA_EXPR)
+}
+
+// test if_expr
+// fn foo() {
+//     if true {};
+//     if true {} else {};
+//     if true {} else if false {} else {};
+//     if S {};
+// }
+fn if_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(IF_KW));
+    let m = p.start();
+    p.bump();
+    cond(p);
+    block(p);
+    if p.at(ELSE_KW) {
+        p.bump();
+        if p.at(IF_KW) {
+            if_expr(p);
+        } else {
+            block(p);
+        }
+    }
+    m.complete(p, IF_EXPR)
+}
+
+// test while_expr
+// fn foo() {
+//     while true {};
+//     while let Some(x) = it.next() {};
+// }
+fn while_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(WHILE_KW));
+    let m = p.start();
+    p.bump();
+    cond(p);
+    block(p);
+    m.complete(p, WHILE_EXPR)
+}
+
+// test loop_expr
+// fn foo() {
+//     loop {};
+// }
+fn loop_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(LOOP_KW));
+    let m = p.start();
+    p.bump();
+    block(p);
+    m.complete(p, LOOP_EXPR)
+}
+
+// test for_expr
+// fn foo() {
+//     for x in [] {};
+// }
+fn for_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(FOR_KW));
+    let m = p.start();
+    p.bump();
+    patterns::pattern(p);
+    p.expect(IN_KW);
+    expr_no_struct(p);
+    block(p);
+    m.complete(p, FOR_EXPR)
+}
+
+// test cond
+// fn foo() { if let Some(_) = None {} }
+fn cond(p: &mut Parser) {
+    if p.eat(LET_KW) {
+        patterns::pattern(p);
+        p.expect(EQ);
+    }
+    expr_no_struct(p)
+}
+
+// test match_expr
+// fn foo() {
+//     match () { };
+//     match S {};
+// }
+fn match_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(MATCH_KW));
+    let m = p.start();
+    p.bump();
+    expr_no_struct(p);
+    p.eat(L_CURLY);
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        // test match_arms_commas
+        // fn foo() {
+        //     match () {
+        //         _ => (),
+        //         _ => {}
+        //         _ => ()
+        //     }
+        // }
+        if match_arm(p).is_block() {
+            p.eat(COMMA);
+        } else if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+    m.complete(p, MATCH_EXPR)
+}
+
+// test match_arm
+// fn foo() {
+//     match () {
+//         _ => (),
+//         X | Y if Z => (),
+//     };
+// }
+fn match_arm(p: &mut Parser) -> BlockLike {
+    let m = p.start();
+    loop {
+        patterns::pattern(p);
+        if !p.eat(PIPE) {
+            break;
+        }
+    }
+    if p.eat(IF_KW) {
+        expr_no_struct(p);
+    }
+    p.expect(FAT_ARROW);
+    let ret = expr_stmt(p);
+    m.complete(p, MATCH_ARM);
+    ret
+}
+
+// test block_expr
+// fn foo() {
+//     {};
+//     unsafe {};
+// }
+pub(super) fn block_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_CURLY) || p.at(UNSAFE_KW) && p.nth(1) == L_CURLY);
+    let m = p.start();
+    p.eat(UNSAFE_KW);
+    p.bump();
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        match p.current() {
+            LET_KW => let_stmt(p),
+            _ => {
+                // test block_items
+                // fn a() { fn b() {} }
+                let m = p.start();
+                match items::maybe_item(p) {
+                    items::MaybeItem::Item(kind) => {
+                        m.complete(p, kind);
+                    }
+                    items::MaybeItem::Modifiers => {
+                        m.abandon(p);
+                        p.error("expected an item");
+                    }
+                    // test pub_expr
+                    // fn foo() { pub 92; } //FIXME
+                    items::MaybeItem::None => {
+                        let is_blocklike = expressions::expr_stmt(p) == BlockLike::Block;
+                        if p.eat(SEMI) || (is_blocklike && !p.at(R_CURLY)) {
+                            m.complete(p, EXPR_STMT);
+                        } else {
+                            m.abandon(p);
+                        }
+                    }
+                }
+            }
+        }
+    }
+    p.expect(R_CURLY);
+    m.complete(p, BLOCK_EXPR)
+}
+
+// test let_stmt;
+// fn foo() {
+//     let a;
+//     let b: i32;
+//     let c = 92;
+//     let d: i32 = 92;
+// }
+fn let_stmt(p: &mut Parser) {
+    assert!(p.at(LET_KW));
+    let m = p.start();
+    p.bump();
+    patterns::pattern(p);
+    if p.at(COLON) {
+        types::ascription(p);
+    }
+    if p.eat(EQ) {
+        expressions::expr(p);
+    }
+    p.expect(SEMI);
+    m.complete(p, LET_STMT);
+}
+
+// test return_expr
+// fn foo() {
+//     return;
+//     return 92;
+// }
+fn return_expr(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(RETURN_KW));
+    let m = p.start();
+    p.bump();
+    if EXPR_FIRST.contains(p.current()) {
+        expr(p);
+    }
+    m.complete(p, RETURN_EXPR)
+}
diff --git a/crates/libsyntax2/src/grammar/expressions/mod.rs b/crates/libsyntax2/src/grammar/expressions/mod.rs
new file mode 100644
index 000000000..dcbb1e2a8
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/expressions/mod.rs
@@ -0,0 +1,379 @@
+mod atom;
+
+use super::*;
+pub(super) use self::atom::literal;
+
+const EXPR_FIRST: TokenSet = LHS_FIRST;
+
+pub(super) fn expr(p: &mut Parser) -> BlockLike {
+    let r = Restrictions { forbid_structs: false, prefer_stmt: false };
+    expr_bp(p, r, 1)
+}
+
+pub(super) fn expr_stmt(p: &mut Parser) -> BlockLike {
+    let r = Restrictions { forbid_structs: false, prefer_stmt: true };
+    expr_bp(p, r, 1)
+}
+
+fn expr_no_struct(p: &mut Parser) {
+    let r = Restrictions { forbid_structs: true, prefer_stmt: false };
+    expr_bp(p, r, 1);
+}
+
+// test block
+// fn a() {}
+// fn b() { let _ = 1; }
+// fn c() { 1; 2; }
+// fn d() { 1; 2 }
+pub(super) fn block(p: &mut Parser) {
+    if !p.at(L_CURLY) {
+        p.error("expected block");
+        return;
+    }
+    atom::block_expr(p);
+}
+
+#[derive(Clone, Copy)]
+struct Restrictions {
+    forbid_structs: bool,
+    prefer_stmt: bool,
+}
+
+enum Op {
+    Simple,
+    Composite(SyntaxKind, u8),
+}
+
+fn current_op(p: &Parser) -> (u8, Op) {
+    if p.at_compound2(PLUS, EQ) {
+        return (1, Op::Composite(PLUSEQ, 2));
+    }
+    if p.at_compound2(MINUS, EQ) {
+        return (1, Op::Composite(MINUSEQ, 2));
+    }
+    if p.at_compound3(L_ANGLE, L_ANGLE, EQ) {
+        return (1, Op::Composite(SHLEQ, 3));
+    }
+    if p.at_compound3(R_ANGLE, R_ANGLE, EQ) {
+        return (1, Op::Composite(SHREQ, 3));
+    }
+    if p.at_compound2(PIPE, PIPE) {
+        return (3, Op::Composite(PIPEPIPE, 2));
+    }
+    if p.at_compound2(AMP, AMP) {
+        return (4, Op::Composite(AMPAMP, 2));
+    }
+    if p.at_compound2(L_ANGLE, EQ) {
+        return (5, Op::Composite(LTEQ, 2));
+    }
+    if p.at_compound2(R_ANGLE, EQ) {
+        return (5, Op::Composite(GTEQ, 2));
+    }
+    if p.at_compound2(L_ANGLE, L_ANGLE) {
+        return (9, Op::Composite(SHL, 2));
+    }
+    if p.at_compound2(R_ANGLE, R_ANGLE) {
+        return (9, Op::Composite(SHR, 2));
+    }
+
+    let bp = match p.current() {
+        EQ => 1,
+        DOTDOT => 2,
+        EQEQ | NEQ | L_ANGLE | R_ANGLE => 5,
+        PIPE => 6,
+        CARET => 7,
+        AMP => 8,
+        MINUS | PLUS => 10,
+        STAR | SLASH | PERCENT => 11,
+        _ => 0,
+    };
+    (bp, Op::Simple)
+}
+
+// Parses expression with binding power of at least bp.
+fn expr_bp(p: &mut Parser, r: Restrictions, bp: u8) -> BlockLike {
+    let mut lhs = match lhs(p, r) {
+        Some(lhs) => {
+            // test stmt_bin_expr_ambiguity
+            // fn foo() {
+            //     let _ = {1} & 2;
+            //     {1} &2;
+            // }
+            if r.prefer_stmt && is_block(lhs.kind()) {
+                return BlockLike::Block;
+            }
+            lhs
+        }
+        None => return BlockLike::NotBlock,
+    };
+
+    loop {
+        let is_range = p.current() == DOTDOT;
+        let (op_bp, op) = current_op(p);
+        if op_bp < bp {
+            break;
+        }
+        let m = lhs.precede(p);
+        match op {
+            Op::Simple => p.bump(),
+            Op::Composite(kind, n) => {
+                p.bump_compound(kind, n);
+            }
+        }
+        expr_bp(p, r, op_bp + 1);
+        lhs = m.complete(p, if is_range { RANGE_EXPR } else { BIN_EXPR });
+    }
+    BlockLike::NotBlock
+}
+
+// test no_semi_after_block
+// fn foo() {
+//     if true {}
+//     loop {}
+//     match () {}
+//     while true {}
+//     for _ in () {}
+//     {}
+//     {}
+// }
+fn is_block(kind: SyntaxKind) -> bool {
+    match kind {
+        IF_EXPR | WHILE_EXPR | FOR_EXPR | LOOP_EXPR | MATCH_EXPR | BLOCK_EXPR => true,
+        _ => false,
+    }
+}
+
+const LHS_FIRST: TokenSet =
+    token_set_union![
+        token_set![AMP, STAR, EXCL, DOTDOT, MINUS],
+        atom::ATOM_EXPR_FIRST,
+    ];
+
+fn lhs(p: &mut Parser, r: Restrictions) -> Option<CompletedMarker> {
+    let m;
+    let kind = match p.current() {
+        // test ref_expr
+        // fn foo() {
+        //     let _ = &1;
+        //     let _ = &mut &f();
+        // }
+        AMP => {
+            m = p.start();
+            p.bump();
+            p.eat(MUT_KW);
+            REF_EXPR
+        }
+        // test unary_expr
+        // fn foo() {
+        //     **&1;
+        //     !!true;
+        //     --1;
+        // }
+        STAR | EXCL | MINUS => {
+            m = p.start();
+            p.bump();
+            PREFIX_EXPR
+        }
+        DOTDOT => {
+            m = p.start();
+            p.bump();
+            expr_bp(p, r, 2);
+            return Some(m.complete(p, RANGE_EXPR));
+        }
+        _ => {
+            let lhs = atom::atom_expr(p, r)?;
+            return Some(postfix_expr(p, r, lhs));
+        }
+    };
+    expr_bp(p, r, 255);
+    Some(m.complete(p, kind))
+}
+
+fn postfix_expr(p: &mut Parser, r: Restrictions, mut lhs: CompletedMarker) -> CompletedMarker {
+    let mut allow_calls = !r.prefer_stmt || !is_block(lhs.kind());
+    loop {
+        lhs = match p.current() {
+            // test stmt_postfix_expr_ambiguity
+            // fn foo() {
+            //     match () {
+            //         _ => {}
+            //         () => {}
+            //         [] => {}
+            //     }
+            // }
+            L_PAREN if allow_calls => call_expr(p, lhs),
+            L_BRACK if allow_calls => index_expr(p, lhs),
+            DOT if p.nth(1) == IDENT => if p.nth(2) == L_PAREN || p.nth(2) == COLONCOLON {
+                method_call_expr(p, lhs)
+            } else {
+                field_expr(p, lhs)
+            },
+            DOT if p.nth(1) == INT_NUMBER => field_expr(p, lhs),
+            // test postfix_range
+            // fn foo() { let x = 1..; }
+            DOTDOT if !EXPR_FIRST.contains(p.nth(1)) => {
+                let m = lhs.precede(p);
+                p.bump();
+                m.complete(p, RANGE_EXPR)
+            }
+            QUESTION => try_expr(p, lhs),
+            AS_KW => cast_expr(p, lhs),
+            _ => break,
+        };
+        allow_calls = true
+    }
+    lhs
+}
+
+// test call_expr
+// fn foo() {
+//     let _ = f();
+//     let _ = f()(1)(1, 2,);
+// }
+fn call_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(L_PAREN));
+    let m = lhs.precede(p);
+    arg_list(p);
+    m.complete(p, CALL_EXPR)
+}
+
+// test index_expr
+// fn foo() {
+//     x[1][2];
+// }
+fn index_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(L_BRACK));
+    let m = lhs.precede(p);
+    p.bump();
+    expr(p);
+    p.expect(R_BRACK);
+    m.complete(p, INDEX_EXPR)
+}
+
+// test method_call_expr
+// fn foo() {
+//     x.foo();
+//     y.bar::<T>(1, 2,);
+// }
+fn method_call_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(
+        p.at(DOT) && p.nth(1) == IDENT
+            && (p.nth(2) == L_PAREN || p.nth(2) == COLONCOLON)
+    );
+    let m = lhs.precede(p);
+    p.bump();
+    name_ref(p);
+    type_args::type_arg_list(p, true);
+    arg_list(p);
+    m.complete(p, METHOD_CALL_EXPR)
+}
+
+// test field_expr
+// fn foo() {
+//     x.foo;
+//     x.0.bar;
+// }
+fn field_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(DOT) && (p.nth(1) == IDENT || p.nth(1) == INT_NUMBER));
+    let m = lhs.precede(p);
+    p.bump();
+    if p.at(IDENT) {
+        name_ref(p)
+    } else {
+        p.bump()
+    }
+    m.complete(p, FIELD_EXPR)
+}
+
+// test try_expr
+// fn foo() {
+//     x?;
+// }
+fn try_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(QUESTION));
+    let m = lhs.precede(p);
+    p.bump();
+    m.complete(p, TRY_EXPR)
+}
+
+// test cast_expr
+// fn foo() {
+//     82 as i32;
+// }
+fn cast_expr(p: &mut Parser, lhs: CompletedMarker) -> CompletedMarker {
+    assert!(p.at(AS_KW));
+    let m = lhs.precede(p);
+    p.bump();
+    types::type_(p);
+    m.complete(p, CAST_EXPR)
+}
+
+fn arg_list(p: &mut Parser) {
+    assert!(p.at(L_PAREN));
+    let m = p.start();
+    p.bump();
+    while !p.at(R_PAREN) && !p.at(EOF) {
+        expr(p);
+        if !p.at(R_PAREN) && !p.expect(COMMA) {
+            break;
+        }
+    }
+    p.eat(R_PAREN);
+    m.complete(p, ARG_LIST);
+}
+
+// test path_expr
+// fn foo() {
+//     let _ = a;
+//     let _ = a::b;
+//     let _ = ::a::<b>;
+//     let _ = format!();
+// }
+fn path_expr(p: &mut Parser, r: Restrictions) -> CompletedMarker {
+    assert!(paths::is_path_start(p));
+    let m = p.start();
+    paths::expr_path(p);
+    match p.current() {
+        L_CURLY if !r.forbid_structs => {
+            struct_lit(p);
+            m.complete(p, STRUCT_LIT)
+        }
+        EXCL => {
+            items::macro_call_after_excl(p);
+            m.complete(p, MACRO_CALL)
+        }
+        _ => m.complete(p, PATH_EXPR)
+    }
+}
+
+// test struct_lit
+// fn foo() {
+//     S {};
+//     S { x, y: 32, };
+//     S { x, y: 32, ..Default::default() };
+// }
+fn struct_lit(p: &mut Parser) {
+    assert!(p.at(L_CURLY));
+    p.bump();
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        match p.current() {
+            IDENT => {
+                let m = p.start();
+                name_ref(p);
+                if p.eat(COLON) {
+                    expr(p);
+                }
+                m.complete(p, STRUCT_LIT_FIELD);
+            }
+            DOTDOT => {
+                p.bump();
+                expr(p);
+            }
+            _ => p.err_and_bump("expected identifier"),
+        }
+        if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+}
diff --git a/crates/libsyntax2/src/grammar/items/consts.rs b/crates/libsyntax2/src/grammar/items/consts.rs
new file mode 100644
index 000000000..b11949b49
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/items/consts.rs
@@ -0,0 +1,21 @@
+use super::*;
+
+pub(super) fn static_item(p: &mut Parser) {
+    const_or_static(p, STATIC_KW)
+}
+
+pub(super) fn const_item(p: &mut Parser) {
+    const_or_static(p, CONST_KW)
+}
+
+fn const_or_static(p: &mut Parser, kw: SyntaxKind) {
+    assert!(p.at(kw));
+    p.bump();
+    p.eat(MUT_KW); // TODO: validator to forbid const mut
+    name(p);
+    types::ascription(p);
+    if p.eat(EQ) {
+        expressions::expr(p);
+    }
+    p.expect(SEMI);
+}
diff --git a/crates/libsyntax2/src/grammar/items/mod.rs b/crates/libsyntax2/src/grammar/items/mod.rs
new file mode 100644
index 000000000..3bf906f85
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/items/mod.rs
@@ -0,0 +1,332 @@
+use super::*;
+
+mod consts;
+mod structs;
+mod traits;
+mod use_item;
+
+// test mod_contents
+// fn foo() {}
+// macro_rules! foo {}
+// foo::bar!();
+// super::baz! {}
+// struct S;
+pub(super) fn mod_contents(p: &mut Parser, stop_on_r_curly: bool) {
+    attributes::inner_attributes(p);
+    while !p.at(EOF) && !(stop_on_r_curly && p.at(R_CURLY)) {
+        item_or_macro(p, stop_on_r_curly)
+    }
+}
+
+pub(super) fn item_or_macro(p: &mut Parser, stop_on_r_curly: bool) {
+    let m = p.start();
+    match maybe_item(p) {
+        MaybeItem::Item(kind) => {
+            m.complete(p, kind);
+        }
+        MaybeItem::None => {
+            if paths::is_path_start(p) {
+                match macro_call(p) {
+                    BlockLike::Block => (),
+                    BlockLike::NotBlock => {
+                        p.expect(SEMI);
+                    }
+                }
+                m.complete(p, MACRO_CALL);
+            } else {
+                m.abandon(p);
+                if p.at(L_CURLY) {
+                    error_block(p, "expected an item");
+                } else if !p.at(EOF) && !(stop_on_r_curly && p.at(R_CURLY)) {
+                    p.err_and_bump("expected an item");
+                } else {
+                    p.error("expected an item");
+                }
+            }
+        }
+        MaybeItem::Modifiers => {
+            p.error("expected fn, trait or impl");
+            m.complete(p, ERROR);
+        }
+    }
+}
+
+pub(super) const ITEM_FIRST: TokenSet =
+    token_set![EXTERN_KW, MOD_KW, USE_KW, STRUCT_KW, ENUM_KW, FN_KW, PUB_KW, POUND];
+
+pub(super) enum MaybeItem {
+    None,
+    Item(SyntaxKind),
+    Modifiers,
+}
+
+pub(super) fn maybe_item(p: &mut Parser) -> MaybeItem {
+    attributes::outer_attributes(p);
+    visibility(p);
+    if let Some(kind) = items_without_modifiers(p) {
+        return MaybeItem::Item(kind);
+    }
+
+    let mut has_mods = false;
+    // modifiers
+    has_mods |= p.eat(CONST_KW);
+
+    // test unsafe_block_in_mod
+    // fn foo(){} unsafe { } fn bar(){}
+    if p.at(UNSAFE_KW) && p.nth(1) != L_CURLY {
+        p.eat(UNSAFE_KW);
+        has_mods = true;
+    }
+    if p.at(EXTERN_KW) {
+        has_mods = true;
+        abi(p);
+    }
+    if p.at(IDENT) && p.at_contextual_kw("auto") && p.nth(1) == TRAIT_KW {
+        p.bump_remap(AUTO_KW);
+        has_mods = true;
+    }
+    if p.at(IDENT) && p.at_contextual_kw("default") && p.nth(1) == IMPL_KW {
+        p.bump_remap(DEFAULT_KW);
+        has_mods = true;
+    }
+
+    // items
+    let kind = match p.current() {
+        // test extern_fn
+        // extern fn foo() {}
+
+        // test const_fn
+        // const fn foo() {}
+
+        // test const_unsafe_fn
+        // const unsafe fn foo() {}
+
+        // test unsafe_extern_fn
+        // unsafe extern "C" fn foo() {}
+
+        // test unsafe_fn
+        // unsafe fn foo() {}
+        FN_KW => {
+            function(p);
+            FUNCTION
+        }
+
+        // test unsafe_trait
+        // unsafe trait T {}
+
+        // test auto_trait
+        // auto trait T {}
+
+        // test unsafe_auto_trait
+        // unsafe auto trait T {}
+        TRAIT_KW => {
+            traits::trait_item(p);
+            TRAIT_ITEM
+        }
+
+        // test unsafe_impl
+        // unsafe impl Foo {}
+
+        // test default_impl
+        // default impl Foo {}
+
+        // test unsafe_default_impl
+        // unsafe default impl Foo {}
+        IMPL_KW => {
+            traits::impl_item(p);
+            IMPL_ITEM
+        }
+        _ => return if has_mods {
+            MaybeItem::Modifiers
+        } else {
+            MaybeItem::None
+        }
+    };
+
+    MaybeItem::Item(kind)
+}
+
+fn items_without_modifiers(p: &mut Parser) -> Option<SyntaxKind> {
+    let la = p.nth(1);
+    let kind = match p.current() {
+        // test extern_crate
+        // extern crate foo;
+        EXTERN_KW if la == CRATE_KW => {
+            extern_crate_item(p);
+            EXTERN_CRATE_ITEM
+        }
+        TYPE_KW => {
+            type_item(p);
+            TYPE_ITEM
+        }
+        MOD_KW => {
+            mod_item(p);
+            MOD_ITEM
+        }
+        STRUCT_KW => {
+            structs::struct_item(p);
+            if p.at(SEMI) {
+                p.err_and_bump(
+                    "expected item, found `;`\n\
+                     consider removing this semicolon"
+                );
+            }
+            STRUCT_ITEM
+        }
+        ENUM_KW => {
+            structs::enum_item(p);
+            ENUM_ITEM
+        }
+        USE_KW => {
+            use_item::use_item(p);
+            USE_ITEM
+        }
+        CONST_KW if (la == IDENT || la == MUT_KW) => {
+            consts::const_item(p);
+            CONST_ITEM
+        }
+        STATIC_KW => {
+            consts::static_item(p);
+            STATIC_ITEM
+        }
+        // test extern_block
+        // extern {}
+        EXTERN_KW if la == L_CURLY || ((la == STRING || la == RAW_STRING) && p.nth(2) == L_CURLY) => {
+            abi(p);
+            extern_block(p);
+            EXTERN_BLOCK_EXPR
+        }
+        _ => return None,
+    };
+    Some(kind)
+}
+
+fn extern_crate_item(p: &mut Parser) {
+    assert!(p.at(EXTERN_KW));
+    p.bump();
+    assert!(p.at(CRATE_KW));
+    p.bump();
+    name(p);
+    alias(p);
+    p.expect(SEMI);
+}
+
+fn extern_block(p: &mut Parser) {
+    assert!(p.at(L_CURLY));
+    p.bump();
+    p.expect(R_CURLY);
+}
+
+fn function(p: &mut Parser) {
+    assert!(p.at(FN_KW));
+    p.bump();
+
+    name(p);
+    // test function_type_params
+    // fn foo<T: Clone + Copy>(){}
+    type_params::type_param_list(p);
+
+    if p.at(L_PAREN) {
+        params::param_list(p);
+    } else {
+        p.error("expected function arguments");
+    }
+    // test function_ret_type
+    // fn foo() {}
+    // fn bar() -> () {}
+    fn_ret_type(p);
+
+    // test function_where_clause
+    // fn foo<T>() where T: Copy {}
+    type_params::where_clause(p);
+
+    // test fn_decl
+    // trait T { fn foo(); }
+    if !p.eat(SEMI) {
+        expressions::block(p);
+    }
+}
+
+// test type_item
+// type Foo = Bar;
+fn type_item(p: &mut Parser) {
+    assert!(p.at(TYPE_KW));
+    p.bump();
+
+    name(p);
+
+    // test type_item_type_params
+    // type Result<T> = ();
+    type_params::type_param_list(p);
+
+    if p.at(COLON) {
+        type_params::bounds(p);
+    }
+
+    // test type_item_where_clause
+    // type Foo where Foo: Copy = ();
+    type_params::where_clause(p);
+
+    if p.eat(EQ) {
+        types::type_(p);
+    }
+    p.expect(SEMI);
+}
+
+fn mod_item(p: &mut Parser) {
+    assert!(p.at(MOD_KW));
+    p.bump();
+
+    name(p);
+    if !p.eat(SEMI) {
+        if p.expect(L_CURLY) {
+            mod_contents(p, true);
+            p.expect(R_CURLY);
+        }
+    }
+}
+
+fn macro_call(p: &mut Parser) -> BlockLike {
+    assert!(paths::is_path_start(p));
+    paths::use_path(p);
+    macro_call_after_excl(p)
+}
+
+pub(super) fn macro_call_after_excl(p: &mut Parser) -> BlockLike {
+    p.expect(EXCL);
+    p.eat(IDENT);
+    let flavor = match p.current() {
+        L_CURLY => {
+            token_tree(p);
+            BlockLike::Block
+        }
+        L_PAREN | L_BRACK => {
+            token_tree(p);
+            BlockLike::NotBlock
+        }
+        _ => {
+            p.error("expected `{`, `[`, `(`");
+            BlockLike::NotBlock
+        },
+    };
+
+    flavor
+}
+
+fn token_tree(p: &mut Parser) {
+    let closing_paren_kind = match p.current() {
+        L_CURLY => R_CURLY,
+        L_PAREN => R_PAREN,
+        L_BRACK => R_BRACK,
+        _ => unreachable!(),
+    };
+    p.bump();
+    while !p.at(EOF) && !p.at(closing_paren_kind) {
+        match p.current() {
+            L_CURLY | L_PAREN | L_BRACK => token_tree(p),
+            R_CURLY | R_PAREN | R_BRACK => p.err_and_bump("unmatched brace"),
+            _ => p.bump()
+        }
+    };
+    p.expect(closing_paren_kind);
+}
diff --git a/crates/libsyntax2/src/grammar/items/structs.rs b/crates/libsyntax2/src/grammar/items/structs.rs
new file mode 100644
index 000000000..67616eaad
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/items/structs.rs
@@ -0,0 +1,116 @@
+use super::*;
+
+pub(super) fn struct_item(p: &mut Parser) {
+    assert!(p.at(STRUCT_KW));
+    p.bump();
+
+    name(p);
+    type_params::type_param_list(p);
+    match p.current() {
+        WHERE_KW => {
+            type_params::where_clause(p);
+            match p.current() {
+                SEMI => {
+                    p.bump();
+                    return;
+                }
+                L_CURLY => named_fields(p),
+                _ => {
+                    //TODO: special case `(` error message
+                    p.error("expected `;` or `{`");
+                    return;
+                }
+            }
+        }
+        SEMI => {
+            p.bump();
+            return;
+        }
+        L_CURLY => named_fields(p),
+        L_PAREN => {
+            pos_fields(p);
+            p.expect(SEMI);
+        }
+        _ => {
+            p.error("expected `;`, `{`, or `(`");
+            return;
+        }
+    }
+}
+
+pub(super) fn enum_item(p: &mut Parser) {
+    assert!(p.at(ENUM_KW));
+    p.bump();
+    name(p);
+    type_params::type_param_list(p);
+    type_params::where_clause(p);
+    if p.expect(L_CURLY) {
+        while !p.at(EOF) && !p.at(R_CURLY) {
+            let var = p.start();
+            attributes::outer_attributes(p);
+            if p.at(IDENT) {
+                name(p);
+                match p.current() {
+                    L_CURLY => named_fields(p),
+                    L_PAREN => pos_fields(p),
+                    EQ => {
+                        p.bump();
+                        expressions::expr(p);
+                    }
+                    _ => (),
+                }
+                var.complete(p, ENUM_VARIANT);
+            } else {
+                var.abandon(p);
+                p.err_and_bump("expected enum variant");
+            }
+            if !p.at(R_CURLY) {
+                p.expect(COMMA);
+            }
+        }
+        p.expect(R_CURLY);
+    }
+}
+
+fn named_fields(p: &mut Parser) {
+    assert!(p.at(L_CURLY));
+    p.bump();
+    while !p.at(R_CURLY) && !p.at(EOF) {
+        named_field(p);
+        if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+
+    fn named_field(p: &mut Parser) {
+        let field = p.start();
+        visibility(p);
+        if p.at(IDENT) {
+            name(p);
+            p.expect(COLON);
+            types::type_(p);
+            field.complete(p, NAMED_FIELD);
+        } else {
+            field.abandon(p);
+            p.err_and_bump("expected field declaration");
+        }
+    }
+}
+
+fn pos_fields(p: &mut Parser) {
+    if !p.expect(L_PAREN) {
+        return;
+    }
+    while !p.at(R_PAREN) && !p.at(EOF) {
+        let pos_field = p.start();
+        visibility(p);
+        types::type_(p);
+        pos_field.complete(p, POS_FIELD);
+
+        if !p.at(R_PAREN) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_PAREN);
+}
diff --git a/crates/libsyntax2/src/grammar/items/traits.rs b/crates/libsyntax2/src/grammar/items/traits.rs
new file mode 100644
index 000000000..0b9fb2b0b
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/items/traits.rs
@@ -0,0 +1,87 @@
+use super::*;
+
+// test trait_item
+// trait T<U>: Hash + Clone where U: Copy {}
+pub(super) fn trait_item(p: &mut Parser) {
+    assert!(p.at(TRAIT_KW));
+    p.bump();
+    name(p);
+    type_params::type_param_list(p);
+    if p.at(COLON) {
+        type_params::bounds(p);
+    }
+    type_params::where_clause(p);
+    p.expect(L_CURLY);
+    // test trait_item_items
+    // impl F {
+    //     type A: Clone;
+    //     const B: i32;
+    //     fn foo() {}
+    //     fn bar(&self);
+    // }
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        item_or_macro(p, true);
+    }
+    p.expect(R_CURLY);
+}
+
+// test impl_item
+// impl Foo {}
+pub(super) fn impl_item(p: &mut Parser) {
+    assert!(p.at(IMPL_KW));
+    p.bump();
+    if choose_type_params_over_qpath(p) {
+        type_params::type_param_list(p);
+    }
+
+    // TODO: never type
+    // impl ! {}
+
+    // test impl_item_neg
+    // impl !Send for X {}
+    p.eat(EXCL);
+    types::type_(p);
+    if p.eat(FOR_KW) {
+        types::type_(p);
+    }
+    type_params::where_clause(p);
+    p.expect(L_CURLY);
+
+    // test impl_item_items
+    // impl F {
+    //     type A = i32;
+    //     const B: i32 = 92;
+    //     fn foo() {}
+    //     fn bar(&self) {}
+    // }
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        item_or_macro(p, true);
+    }
+    p.expect(R_CURLY);
+}
+
+fn choose_type_params_over_qpath(p: &Parser) -> bool {
+    // There's an ambiguity between generic parameters and qualified paths in impls.
+    // If we see `<` it may start both, so we have to inspect some following tokens.
+    // The following combinations can only start generics,
+    // but not qualified paths (with one exception):
+    //     `<` `>` - empty generic parameters
+    //     `<` `#` - generic parameters with attributes
+    //     `<` (LIFETIME|IDENT) `>` - single generic parameter
+    //     `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
+    //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
+    //     `<` (LIFETIME|IDENT) `=` - generic parameter with a default
+    // The only truly ambiguous case is
+    //     `<` IDENT `>` `::` IDENT ...
+    // we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
+    // because this is what almost always expected in practice, qualified paths in impls
+    // (`impl <Type>::AssocTy { ... }`) aren't even allowed by type checker at the moment.
+    if !p.at(L_ANGLE) {
+        return false;
+    }
+    if p.nth(1) == POUND || p.nth(1) == R_ANGLE {
+        return true;
+    }
+    (p.nth(1) == LIFETIME || p.nth(1) == IDENT)
+        && (p.nth(2) == R_ANGLE || p.nth(2) == COMMA || p.nth(2) == COLON || p.nth(2) == EQ)
+}
diff --git a/crates/libsyntax2/src/grammar/items/use_item.rs b/crates/libsyntax2/src/grammar/items/use_item.rs
new file mode 100644
index 000000000..a3f7f0da8
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/items/use_item.rs
@@ -0,0 +1,66 @@
+use super::*;
+
+pub(super) fn use_item(p: &mut Parser) {
+    assert!(p.at(USE_KW));
+    p.bump();
+    use_tree(p);
+    p.expect(SEMI);
+}
+
+fn use_tree(p: &mut Parser) {
+    let la = p.nth(1);
+    let m = p.start();
+    match (p.current(), la) {
+        (STAR, _) => p.bump(),
+        (COLONCOLON, STAR) => {
+            p.bump();
+            p.bump();
+        }
+        (L_CURLY, _) | (COLONCOLON, L_CURLY) => {
+            if p.at(COLONCOLON) {
+                p.bump();
+            }
+            nested_trees(p);
+        }
+        _ if paths::is_path_start(p) => {
+            paths::use_path(p);
+            match p.current() {
+                AS_KW => {
+                    alias(p);
+                }
+                COLONCOLON => {
+                    p.bump();
+                    match p.current() {
+                        STAR => {
+                            p.bump();
+                        }
+                        L_CURLY => nested_trees(p),
+                        _ => {
+                            // is this unreachable?
+                            p.error("expected `{` or `*`");
+                        }
+                    }
+                }
+                _ => (),
+            }
+        }
+        _ => {
+            m.abandon(p);
+            p.err_and_bump("expected one of `*`, `::`, `{`, `self`, `super`, `indent`");
+            return;
+        }
+    }
+    m.complete(p, USE_TREE);
+}
+
+fn nested_trees(p: &mut Parser) {
+    assert!(p.at(L_CURLY));
+    p.bump();
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        use_tree(p);
+        if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+}
diff --git a/crates/libsyntax2/src/grammar/mod.rs b/crates/libsyntax2/src/grammar/mod.rs
new file mode 100644
index 000000000..e1329044d
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/mod.rs
@@ -0,0 +1,161 @@
+//! This is the actual "grammar" of the Rust language.
+//!
+//! Each function in this module and its children corresponds
+//! to a production of the format grammar. Submodules roughly
+//! correspond to different *areas* of the grammar. By convention,
+//! each submodule starts with `use super::*` import and exports
+//! "public" productions via `pub(super)`.
+//!
+//! See docs for `Parser` to learn about API, available to the grammar,
+//! and see docs for `Event` to learn how this actually manages to
+//! produce parse trees.
+//!
+//! Code in this module also contains inline tests, which start with
+//! `// test name-of-the-test` comment and look like this:
+//!
+//! ```
+//! // test function_with_zero_parameters
+//! // fn foo() {}
+//! ```
+//!
+//! After adding a new inline-test, run `cargo collect-tests` to extract
+//! it as a standalone text-fixture into `tests/data/parser/inline`, and
+//! run `cargo test` once to create the "gold" value.
+mod attributes;
+mod expressions;
+mod items;
+mod params;
+mod paths;
+mod patterns;
+mod type_args;
+mod type_params;
+mod types;
+
+use {
+    parser_api::{CompletedMarker, Parser, TokenSet},
+    SyntaxKind::{self, *},
+};
+
+pub(crate) fn file(p: &mut Parser) {
+    let file = p.start();
+    p.eat(SHEBANG);
+    items::mod_contents(p, false);
+    file.complete(p, FILE);
+}
+
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum BlockLike {
+    Block,
+    NotBlock,
+}
+
+impl BlockLike {
+    fn is_block(self) -> bool { self == BlockLike::Block }
+}
+
+fn visibility(p: &mut Parser) {
+    match p.current() {
+        PUB_KW => {
+            let m = p.start();
+            p.bump();
+            if p.at(L_PAREN) {
+                match p.nth(1) {
+                    // test crate_visibility
+                    // pub(crate) struct S;
+                    // pub(self) struct S;
+                    // pub(self) struct S;
+                    // pub(self) struct S;
+                    CRATE_KW | SELF_KW | SUPER_KW => {
+                        p.bump();
+                        p.bump();
+                        p.expect(R_PAREN);
+                    }
+                    IN_KW => {
+                        p.bump();
+                        p.bump();
+                        paths::use_path(p);
+                        p.expect(R_PAREN);
+                    }
+                    _ => (),
+                }
+            }
+            m.complete(p, VISIBILITY);
+        }
+        // test crate_keyword_vis
+        // crate fn main() { }
+        CRATE_KW => {
+            let m = p.start();
+            p.bump();
+            m.complete(p, VISIBILITY);
+        }
+        _ => (),
+    }
+}
+fn alias(p: &mut Parser) -> bool {
+    if p.at(AS_KW) {
+        let alias = p.start();
+        p.bump();
+        name(p);
+        alias.complete(p, ALIAS);
+    }
+    true //FIXME: return false if three are errors
+}
+
+fn abi(p: &mut Parser) {
+    assert!(p.at(EXTERN_KW));
+    let abi = p.start();
+    p.bump();
+    match p.current() {
+        STRING | RAW_STRING => p.bump(),
+        _ => (),
+    }
+    abi.complete(p, ABI);
+}
+
+fn fn_ret_type(p: &mut Parser) -> bool {
+    if p.at(THIN_ARROW) {
+        p.bump();
+        types::type_(p);
+        true
+    } else {
+        false
+    }
+}
+
+fn name(p: &mut Parser) {
+    if p.at(IDENT) {
+        let m = p.start();
+        p.bump();
+        m.complete(p, NAME);
+    } else {
+        p.error("expected a name");
+    }
+}
+
+fn name_ref(p: &mut Parser) {
+    if p.at(IDENT) {
+        let m = p.start();
+        p.bump();
+        m.complete(p, NAME_REF);
+    } else {
+        p.error("expected identifier");
+    }
+}
+
+fn error_block(p: &mut Parser, message: &str) {
+    assert!(p.at(L_CURLY));
+    let err = p.start();
+    p.error(message);
+    p.bump();
+    let mut level: u32 = 1;
+    while level > 0 && !p.at(EOF) {
+        match p.current() {
+            L_CURLY => level += 1,
+            R_CURLY => level -= 1,
+            _ => (),
+        }
+        p.bump();
+    }
+    err.complete(p, ERROR);
+}
diff --git a/crates/libsyntax2/src/grammar/params.rs b/crates/libsyntax2/src/grammar/params.rs
new file mode 100644
index 000000000..32e905cb2
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/params.rs
@@ -0,0 +1,116 @@
+use super::*;
+
+// test param_list
+// fn a() {}
+// fn b(x: i32) {}
+// fn c(x: i32, ) {}
+// fn d(x: i32, y: ()) {}
+pub(super) fn param_list(p: &mut Parser) {
+    list_(p, Flavor::Normal)
+}
+
+// test param_list_opt_patterns
+// fn foo<F: FnMut(&mut Foo<'a>)>(){}
+pub(super) fn param_list_opt_patterns(p: &mut Parser) {
+    list_(p, Flavor::OptionalPattern)
+}
+
+pub(super) fn param_list_opt_types(p: &mut Parser) {
+    list_(p, Flavor::OptionalType)
+}
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+enum Flavor {
+    OptionalType,
+    OptionalPattern,
+    Normal,
+}
+
+impl Flavor {
+    fn type_required(self) -> bool {
+        match self {
+            Flavor::OptionalType => false,
+            _ => true,
+        }
+    }
+}
+
+fn list_(p: &mut Parser, flavor: Flavor) {
+    let (bra, ket) = if flavor.type_required() {
+        (L_PAREN, R_PAREN)
+    } else {
+        (PIPE, PIPE)
+    };
+    assert!(p.at(bra));
+    let m = p.start();
+    p.bump();
+    if flavor.type_required() {
+        self_param(p);
+    }
+    while !p.at(EOF) && !p.at(ket) {
+        value_parameter(p, flavor);
+        if !p.at(ket) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(ket);
+    m.complete(p, PARAM_LIST);
+}
+
+fn value_parameter(p: &mut Parser, flavor: Flavor) {
+    let m = p.start();
+    match flavor {
+        Flavor::OptionalType | Flavor::Normal => {
+            patterns::pattern(p);
+            if p.at(COLON) || flavor.type_required() {
+                types::ascription(p)
+            }
+        },
+        // test value_parameters_no_patterns
+        // type F = Box<Fn(a: i32, &b: &i32, &mut c: &i32, ())>;
+        Flavor::OptionalPattern => {
+            let la0 = p.current();
+            let la1 = p.nth(1);
+            let la2 = p.nth(2);
+            let la3 = p.nth(3);
+            if la0 == IDENT && la1 == COLON
+                || la0 == AMP && la1 == IDENT && la2 == COLON
+                || la0 == AMP && la1 == MUT_KW && la2 == IDENT && la3 == COLON {
+                patterns::pattern(p);
+                types::ascription(p);
+            } else {
+                types::type_(p);
+            }
+        },
+    }
+    m.complete(p, PARAM);
+}
+
+// test self_param
+// impl S {
+//     fn a(self) {}
+//     fn b(&self,) {}
+//     fn c(&'a self,) {}
+//     fn d(&'a mut self, x: i32) {}
+// }
+fn self_param(p: &mut Parser) {
+    let la1 = p.nth(1);
+    let la2 = p.nth(2);
+    let la3 = p.nth(3);
+    let n_toks = match (p.current(), la1, la2, la3) {
+        (SELF_KW, _, _, _) => 1,
+        (AMP, SELF_KW, _, _) => 2,
+        (AMP, MUT_KW, SELF_KW, _) => 3,
+        (AMP, LIFETIME, SELF_KW, _) => 3,
+        (AMP, LIFETIME, MUT_KW, SELF_KW) => 4,
+        _ => return,
+    };
+    let m = p.start();
+    for _ in 0..n_toks {
+        p.bump();
+    }
+    m.complete(p, SELF_PARAM);
+    if !p.at(R_PAREN) {
+        p.expect(COMMA);
+    }
+}
diff --git a/crates/libsyntax2/src/grammar/paths.rs b/crates/libsyntax2/src/grammar/paths.rs
new file mode 100644
index 000000000..c277e2a6b
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/paths.rs
@@ -0,0 +1,86 @@
+use super::*;
+
+pub(super) fn is_path_start(p: &Parser) -> bool {
+    match p.current() {
+        IDENT | SELF_KW | SUPER_KW | COLONCOLON => true,
+        _ => false,
+    }
+}
+
+pub(super) fn use_path(p: &mut Parser) {
+    path(p, Mode::Use)
+}
+
+pub(super) fn type_path(p: &mut Parser) {
+    path(p, Mode::Type)
+}
+
+pub(super) fn expr_path(p: &mut Parser) {
+    path(p, Mode::Expr)
+}
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+enum Mode {
+    Use,
+    Type,
+    Expr,
+}
+
+fn path(p: &mut Parser, mode: Mode) {
+    if !is_path_start(p) {
+        return;
+    }
+    let path = p.start();
+    path_segment(p, mode, true);
+    let mut qual = path.complete(p, PATH);
+    loop {
+        let use_tree = match p.nth(1) {
+            STAR | L_CURLY => true,
+            _ => false,
+        };
+        if p.at(COLONCOLON) && !use_tree {
+            let path = qual.precede(p);
+            p.bump();
+            path_segment(p, mode, false);
+            let path = path.complete(p, PATH);
+            qual = path;
+        } else {
+            break;
+        }
+    }
+}
+
+fn path_segment(p: &mut Parser, mode: Mode, first: bool) {
+    let segment = p.start();
+    if first {
+        p.eat(COLONCOLON);
+    }
+    match p.current() {
+        IDENT => {
+            name_ref(p);
+            path_generic_args(p, mode);
+        }
+        SELF_KW | SUPER_KW => p.bump(),
+        _ => {
+            p.error("expected identifier");
+        }
+    };
+    segment.complete(p, PATH_SEGMENT);
+}
+
+fn path_generic_args(p: &mut Parser, mode: Mode) {
+    match mode {
+        Mode::Use => return,
+        Mode::Type => {
+            // test path_fn_trait_args
+            // type F = Box<Fn(x: i32) -> ()>;
+            if p.at(L_PAREN) {
+                params::param_list_opt_patterns(p);
+                fn_ret_type(p);
+            } else {
+                type_args::type_arg_list(p, false)
+            }
+        },
+        Mode::Expr => type_args::type_arg_list(p, true),
+    }
+}
diff --git a/crates/libsyntax2/src/grammar/patterns.rs b/crates/libsyntax2/src/grammar/patterns.rs
new file mode 100644
index 000000000..436f3b26d
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/patterns.rs
@@ -0,0 +1,204 @@
+use super::*;
+
+pub(super) fn pattern(p: &mut Parser) {
+    if let Some(lhs) = atom_pat(p) {
+        // test range_pat
+        // fn main() {
+        //     match 92 { 0 ... 100 => () }
+        // }
+        if p.at(DOTDOTDOT) {
+            let m = lhs.precede(p);
+            p.bump();
+            atom_pat(p);
+            m.complete(p, RANGE_PAT);
+        }
+    }
+}
+
+fn atom_pat(p: &mut Parser) -> Option<CompletedMarker> {
+    let la0 = p.nth(0);
+    let la1 = p.nth(1);
+    if la0 == REF_KW || la0 == MUT_KW
+        || (la0 == IDENT && !(la1 == COLONCOLON || la1 == L_PAREN || la1 == L_CURLY)) {
+        return Some(bind_pat(p, true));
+    }
+    if paths::is_path_start(p) {
+        return Some(path_pat(p));
+    }
+
+    // test literal_pattern
+    // fn main() {
+    //     match () {
+    //         92 => (),
+    //         'c' => (),
+    //         "hello" => (),
+    //     }
+    // }
+    match expressions::literal(p) {
+        Some(m) => return Some(m),
+        None => (),
+    }
+
+    let m = match la0 {
+        UNDERSCORE => placeholder_pat(p),
+        AMP => ref_pat(p),
+        L_PAREN => tuple_pat(p),
+        L_BRACK => slice_pat(p),
+        _ => {
+            p.err_and_bump("expected pattern");
+            return None;
+        }
+    };
+    Some(m)
+}
+
+// test path_part
+// fn foo() {
+//     let foo::Bar = ();
+//     let ::Bar = ();
+//     let Bar { .. } = ();
+//     let Bar(..) = ();
+// }
+fn path_pat(p: &mut Parser) -> CompletedMarker {
+    let m = p.start();
+    paths::expr_path(p);
+    let kind = match p.current() {
+        L_PAREN => {
+            tuple_pat_fields(p);
+            TUPLE_STRUCT_PAT
+        }
+        L_CURLY => {
+            struct_pat_fields(p);
+            STRUCT_PAT
+        }
+        _ => PATH_PAT
+    };
+    m.complete(p, kind)
+}
+
+// test tuple_pat_fields
+// fn foo() {
+//     let S() = ();
+//     let S(_) = ();
+//     let S(_,) = ();
+//     let S(_, .. , x) = ();
+// }
+fn tuple_pat_fields(p: &mut Parser) {
+    assert!(p.at(L_PAREN));
+    p.bump();
+    while !p.at(EOF) && !p.at(R_PAREN) {
+        match p.current() {
+            DOTDOT => p.bump(),
+            _ => pattern(p),
+        }
+        if !p.at(R_PAREN) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_PAREN);
+}
+
+// test struct_pat_fields
+// fn foo() {
+//     let S {} = ();
+//     let S { f, ref mut g } = ();
+//     let S { h: _, ..} = ();
+//     let S { h: _, } = ();
+// }
+fn struct_pat_fields(p: &mut Parser) {
+    assert!(p.at(L_CURLY));
+    p.bump();
+    while !p.at(EOF) && !p.at(R_CURLY) {
+        match p.current() {
+            DOTDOT => p.bump(),
+            IDENT if p.nth(1) == COLON => {
+                p.bump();
+                p.bump();
+                pattern(p);
+            }
+            _ => {
+                bind_pat(p, false);
+            }
+        }
+        if !p.at(R_CURLY) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_CURLY);
+}
+
+// test placeholder_pat
+// fn main() { let _ = (); }
+fn placeholder_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(UNDERSCORE));
+    let m = p.start();
+    p.bump();
+    m.complete(p, PLACEHOLDER_PAT)
+}
+
+// test ref_pat
+// fn main() {
+//     let &a = ();
+//     let &mut b = ();
+// }
+fn ref_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(AMP));
+    let m = p.start();
+    p.bump();
+    p.eat(MUT_KW);
+    pattern(p);
+    m.complete(p, REF_PAT)
+}
+
+// test tuple_pat
+// fn main() {
+//     let (a, b, ..) = ();
+// }
+fn tuple_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_PAREN));
+    let m = p.start();
+    tuple_pat_fields(p);
+    m.complete(p, TUPLE_PAT)
+}
+
+// test slice_pat
+// fn main() {
+//     let [a, b, ..] = [];
+// }
+fn slice_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(L_BRACK));
+    let m = p.start();
+    p.bump();
+    while !p.at(EOF) && !p.at(R_BRACK) {
+        match p.current() {
+            DOTDOT => p.bump(),
+            _ => pattern(p),
+        }
+        if !p.at(R_BRACK) {
+            p.expect(COMMA);
+        }
+    }
+    p.expect(R_BRACK);
+
+    m.complete(p, SLICE_PAT)
+}
+
+// test bind_pat
+// fn main() {
+//     let a = ();
+//     let mut b = ();
+//     let ref c = ();
+//     let ref mut d = ();
+//     let e @ _ = ();
+//     let ref mut f @ g @ _ = ();
+// }
+fn bind_pat(p: &mut Parser, with_at: bool) -> CompletedMarker {
+    let m = p.start();
+    p.eat(REF_KW);
+    p.eat(MUT_KW);
+    name(p);
+    if with_at && p.eat(AT) {
+        pattern(p);
+    }
+    m.complete(p, BIND_PAT)
+}
diff --git a/crates/libsyntax2/src/grammar/type_args.rs b/crates/libsyntax2/src/grammar/type_args.rs
new file mode 100644
index 000000000..5b960f10b
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/type_args.rs
@@ -0,0 +1,48 @@
+use super::*;
+
+pub(super) fn type_arg_list(p: &mut Parser, colon_colon_required: bool) {
+    let m;
+    match (colon_colon_required, p.nth(0), p.nth(1)) {
+        (_, COLONCOLON, L_ANGLE) => {
+            m = p.start();
+            p.bump();
+            p.bump();
+        }
+        (false, L_ANGLE, _) => {
+            m = p.start();
+            p.bump();
+        }
+        _ => return,
+    };
+
+    while !p.at(EOF) && !p.at(R_ANGLE) {
+        type_arg(p);
+        if !p.at(R_ANGLE) && !p.expect(COMMA) {
+            break;
+        }
+    }
+    p.expect(R_ANGLE);
+    m.complete(p, TYPE_ARG_LIST);
+}
+
+// test type_arg
+// type A = B<'static, i32, Item=u64>
+fn type_arg(p: &mut Parser) {
+    let m = p.start();
+    match p.current() {
+        LIFETIME => {
+            p.bump();
+            m.complete(p, LIFETIME_ARG);
+        }
+        IDENT if p.nth(1) == EQ => {
+            name_ref(p);
+            p.bump();
+            types::type_(p);
+            m.complete(p, ASSOC_TYPE_ARG);
+        }
+        _ => {
+            types::type_(p);
+            m.complete(p, TYPE_ARG);
+        }
+    }
+}
diff --git a/crates/libsyntax2/src/grammar/type_params.rs b/crates/libsyntax2/src/grammar/type_params.rs
new file mode 100644
index 000000000..0a3e8fd07
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/type_params.rs
@@ -0,0 +1,127 @@
+use super::*;
+
+pub(super) fn type_param_list(p: &mut Parser) {
+    if !p.at(L_ANGLE) {
+        return;
+    }
+    let m = p.start();
+    p.bump();
+
+    while !p.at(EOF) && !p.at(R_ANGLE) {
+        match p.current() {
+            LIFETIME => lifetime_param(p),
+            IDENT => type_param(p),
+            _ => p.err_and_bump("expected type parameter"),
+        }
+        if !p.at(R_ANGLE) && !p.expect(COMMA) {
+            break;
+        }
+    }
+    p.expect(R_ANGLE);
+    m.complete(p, TYPE_PARAM_LIST);
+
+    fn lifetime_param(p: &mut Parser) {
+        assert!(p.at(LIFETIME));
+        let m = p.start();
+        p.bump();
+        if p.at(COLON) {
+            lifetime_bounds(p);
+        }
+        m.complete(p, LIFETIME_PARAM);
+    }
+
+    fn type_param(p: &mut Parser) {
+        assert!(p.at(IDENT));
+        let m = p.start();
+        name(p);
+        if p.at(COLON) {
+            bounds(p);
+        }
+        // test type_param_default
+        // struct S<T = i32>;
+        if p.at(EQ) {
+            p.bump();
+            types::type_(p)
+        }
+        m.complete(p, TYPE_PARAM);
+    }
+}
+
+// test type_param_bounds
+// struct S<T: 'a + ?Sized + (Copy)>;
+pub(super) fn bounds(p: &mut Parser) {
+    assert!(p.at(COLON));
+    p.bump();
+    bounds_without_colon(p);
+}
+
+fn lifetime_bounds(p: &mut Parser) {
+    assert!(p.at(COLON));
+    p.bump();
+    while p.at(LIFETIME) {
+        p.bump();
+        if !p.eat(PLUS) {
+            break;
+        }
+    }
+}
+
+pub(super) fn bounds_without_colon(p: &mut Parser) {
+    loop {
+        let has_paren = p.eat(L_PAREN);
+        p.eat(QUESTION);
+        if p.at(FOR_KW) {
+            //TODO
+        }
+        if p.at(LIFETIME) {
+            p.bump();
+        } else if paths::is_path_start(p) {
+            paths::type_path(p);
+        } else {
+            break;
+        }
+        if has_paren {
+            p.expect(R_PAREN);
+        }
+        if !p.eat(PLUS) {
+            break;
+        }
+    }
+}
+
+// test where_clause
+// fn foo()
+// where
+//    'a: 'b + 'c,
+//    T: Clone + Copy + 'static,
+//    Iterator::Item: 'a,
+// {}
+pub(super) fn where_clause(p: &mut Parser) {
+    if !p.at(WHERE_KW) {
+        return;
+    }
+    let m = p.start();
+    p.bump();
+    loop {
+        if !(paths::is_path_start(p) || p.current() == LIFETIME) {
+            break
+        }
+        where_predicate(p);
+        if p.current() != L_CURLY && p.current() != SEMI {
+            p.expect(COMMA);
+        }
+    }
+    m.complete(p, WHERE_CLAUSE);
+}
+
+fn where_predicate(p: &mut Parser) {
+    let m = p.start();
+    if p.at(LIFETIME) {
+        p.eat(LIFETIME);
+        lifetime_bounds(p)
+    } else {
+        types::path_type(p);
+        bounds(p);
+    }
+    m.complete(p, WHERE_PRED);
+}
diff --git a/crates/libsyntax2/src/grammar/types.rs b/crates/libsyntax2/src/grammar/types.rs
new file mode 100644
index 000000000..0d8c6bfba
--- /dev/null
+++ b/crates/libsyntax2/src/grammar/types.rs
@@ -0,0 +1,212 @@
+use super::*;
+
+pub(super) fn type_(p: &mut Parser) {
+    match p.current() {
+        L_PAREN => paren_or_tuple_type(p),
+        EXCL => never_type(p),
+        STAR => pointer_type(p),
+        L_BRACK => array_or_slice_type(p),
+        AMP => reference_type(p),
+        UNDERSCORE => placeholder_type(p),
+        FN_KW | UNSAFE_KW | EXTERN_KW => fn_pointer_type(p),
+        FOR_KW => for_type(p),
+        IMPL_KW => impl_trait_type(p),
+        _ if paths::is_path_start(p) => path_type(p),
+        _ => {
+            p.error("expected type");
+        }
+    }
+}
+
+pub(super) fn ascription(p: &mut Parser) {
+    p.expect(COLON);
+    type_(p)
+}
+
+fn type_no_plus(p: &mut Parser) {
+    type_(p);
+}
+
+fn paren_or_tuple_type(p: &mut Parser) {
+    assert!(p.at(L_PAREN));
+    let m = p.start();
+    p.bump();
+    let mut n_types: u32 = 0;
+    let mut trailing_comma: bool = false;
+    while !p.at(EOF) && !p.at(R_PAREN) {
+        n_types += 1;
+        type_(p);
+        if p.eat(COMMA) {
+            trailing_comma = true;
+        } else {
+            trailing_comma = false;
+            break;
+        }
+    }
+    p.expect(R_PAREN);
+
+    let kind = if n_types == 1 && !trailing_comma {
+        // test paren_type
+        // type T = (i32);
+        PAREN_TYPE
+    } else {
+        // test unit_type
+        // type T = ();
+
+        // test singleton_tuple_type
+        // type T = (i32,);
+        TUPLE_TYPE
+    };
+    m.complete(p, kind);
+}
+
+// test never_type
+// type Never = !;
+fn never_type(p: &mut Parser) {
+    assert!(p.at(EXCL));
+    let m = p.start();
+    p.bump();
+    m.complete(p, NEVER_TYPE);
+}
+
+fn pointer_type(p: &mut Parser) {
+    assert!(p.at(STAR));
+    let m = p.start();
+    p.bump();
+
+    match p.current() {
+        // test pointer_type_mut
+        // type M = *mut ();
+        // type C = *mut ();
+        MUT_KW | CONST_KW => p.bump(),
+        _ => {
+            // test pointer_type_no_mutability
+            // type T = *();
+            p.error(
+                "expected mut or const in raw pointer type \
+                 (use `*mut T` or `*const T` as appropriate)",
+            );
+        }
+    };
+
+    type_no_plus(p);
+    m.complete(p, POINTER_TYPE);
+}
+
+fn array_or_slice_type(p: &mut Parser) {
+    assert!(p.at(L_BRACK));
+    let m = p.start();
+    p.bump();
+
+    type_(p);
+    let kind = match p.current() {
+        // test slice_type
+        // type T = [()];
+        R_BRACK => {
+            p.bump();
+            SLICE_TYPE
+        }
+
+        // test array_type
+        // type T = [(); 92];
+        SEMI => {
+            p.bump();
+            expressions::expr(p);
+            p.expect(R_BRACK);
+            ARRAY_TYPE
+        }
+        // test array_type_missing_semi
+        // type T = [() 92];
+        _ => {
+            p.error("expected `;` or `]`");
+            SLICE_TYPE
+        }
+    };
+    m.complete(p, kind);
+}
+
+// test reference_type;
+// type A = &();
+// type B = &'static ();
+// type C = &mut ();
+fn reference_type(p: &mut Parser) {
+    assert!(p.at(AMP));
+    let m = p.start();
+    p.bump();
+    p.eat(LIFETIME);
+    p.eat(MUT_KW);
+    type_no_plus(p);
+    m.complete(p, REFERENCE_TYPE);
+}
+
+// test placeholder_type
+// type Placeholder = _;
+fn placeholder_type(p: &mut Parser) {
+    assert!(p.at(UNDERSCORE));
+    let m = p.start();
+    p.bump();
+    m.complete(p, PLACEHOLDER_TYPE);
+}
+
+// test fn_pointer_type
+// type A = fn();
+// type B = unsafe fn();
+// type C = unsafe extern "C" fn();
+fn fn_pointer_type(p: &mut Parser) {
+    let m = p.start();
+    p.eat(UNSAFE_KW);
+    if p.at(EXTERN_KW) {
+        abi(p);
+    }
+    // test fn_pointer_type_missing_fn
+    // type F = unsafe ();
+    if !p.eat(FN_KW) {
+        m.abandon(p);
+        p.error("expected `fn`");
+        return;
+    }
+
+    params::param_list_opt_patterns(p);
+    // test fn_pointer_type_with_ret
+    // type F = fn() -> ();
+    fn_ret_type(p);
+    m.complete(p, FN_POINTER_TYPE);
+}
+
+// test for_type
+// type A = for<'a> fn() -> ();
+fn for_type(p: &mut Parser) {
+    assert!(p.at(FOR_KW));
+    let m = p.start();
+    p.bump();
+    type_params::type_param_list(p);
+    type_(p);
+    m.complete(p, FOR_TYPE);
+}
+
+// test impl_trait_type
+// type A = impl Iterator<Item=Foo<'a>> + 'a;
+fn impl_trait_type(p: &mut Parser) {
+    assert!(p.at(IMPL_KW));
+    let m = p.start();
+    p.bump();
+    type_params::bounds_without_colon(p);
+    m.complete(p, IMPL_TRAIT_TYPE);
+}
+
+// test path_type
+// type A = Foo;
+// type B = ::Foo;
+// type C = self::Foo;
+// type D = super::Foo;
+pub(super) fn path_type(p: &mut Parser) {
+    assert!(paths::is_path_start(p));
+    let m = p.start();
+    paths::type_path(p);
+    // test path_type_with_bounds
+    // fn foo() -> Box<T + 'f> {}
+    if p.eat(PLUS) {
+        type_params::bounds_without_colon(p);
+    }
+    m.complete(p, PATH_TYPE);
+}
diff --git a/crates/libsyntax2/src/lexer/classes.rs b/crates/libsyntax2/src/lexer/classes.rs
new file mode 100644
index 000000000..4235d2648
--- /dev/null
+++ b/crates/libsyntax2/src/lexer/classes.rs
@@ -0,0 +1,26 @@
+use unicode_xid::UnicodeXID;
+
+pub fn is_ident_start(c: char) -> bool {
+    (c >= 'a' && c <= 'z')
+        || (c >= 'A' && c <= 'Z')
+        || c == '_'
+        || (c > '\x7f' && UnicodeXID::is_xid_start(c))
+}
+
+pub fn is_ident_continue(c: char) -> bool {
+    (c >= 'a' && c <= 'z')
+        || (c >= 'A' && c <= 'Z')
+        || (c >= '0' && c <= '9')
+        || c == '_'
+        || (c > '\x7f' && UnicodeXID::is_xid_continue(c))
+}
+
+pub fn is_whitespace(c: char) -> bool {
+    //FIXME: use is_pattern_whitespace
+    //https://github.com/behnam/rust-unic/issues/192
+    c.is_whitespace()
+}
+
+pub fn is_dec_digit(c: char) -> bool {
+    '0' <= c && c <= '9'
+}
diff --git a/crates/libsyntax2/src/lexer/comments.rs b/crates/libsyntax2/src/lexer/comments.rs
new file mode 100644
index 000000000..01acb6515
--- /dev/null
+++ b/crates/libsyntax2/src/lexer/comments.rs
@@ -0,0 +1,57 @@
+use lexer::ptr::Ptr;
+
+use SyntaxKind::{self, *};
+
+pub(crate) fn scan_shebang(ptr: &mut Ptr) -> bool {
+    if ptr.next_is('!') && ptr.nnext_is('/') {
+        ptr.bump();
+        ptr.bump();
+        bump_until_eol(ptr);
+        true
+    } else {
+        false
+    }
+}
+
+fn scan_block_comment(ptr: &mut Ptr) -> Option<SyntaxKind> {
+    if ptr.next_is('*') {
+        ptr.bump();
+        let mut depth: u32 = 1;
+        while depth > 0 {
+            if ptr.next_is('*') && ptr.nnext_is('/') {
+                depth -= 1;
+                ptr.bump();
+                ptr.bump();
+            } else if ptr.next_is('/') && ptr.nnext_is('*') {
+                depth += 1;
+                ptr.bump();
+                ptr.bump();
+            } else if ptr.bump().is_none() {
+                break;
+            }
+        }
+        Some(COMMENT)
+    } else {
+        None
+    }
+}
+
+pub(crate) fn scan_comment(ptr: &mut Ptr) -> Option<SyntaxKind> {
+    if ptr.next_is('/') {
+        bump_until_eol(ptr);
+        Some(COMMENT)
+    } else {
+        scan_block_comment(ptr)
+    }
+}
+
+fn bump_until_eol(ptr: &mut Ptr) {
+    loop {
+        if ptr.next_is('\n') || ptr.next_is('\r') && ptr.nnext_is('\n') {
+            return;
+        }
+        if ptr.bump().is_none() {
+            break;
+        }
+    }
+}
diff --git a/crates/libsyntax2/src/lexer/mod.rs b/crates/libsyntax2/src/lexer/mod.rs
new file mode 100644
index 000000000..f8fdc41ac
--- /dev/null
+++ b/crates/libsyntax2/src/lexer/mod.rs
@@ -0,0 +1,209 @@
+mod classes;
+mod comments;
+mod numbers;
+mod ptr;
+mod strings;
+
+use {
+    SyntaxKind::{self, *},
+    TextUnit,
+};
+
+use self::{
+    classes::*,
+    comments::{scan_comment, scan_shebang},
+    numbers::scan_number,
+    ptr::Ptr,
+    strings::{
+        is_string_literal_start, scan_byte_char_or_string, scan_char, scan_raw_string, scan_string,
+    },
+};
+
+/// A token of Rust source.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Token {
+    /// The kind of token.
+    pub kind: SyntaxKind,
+    /// The length of the token.
+    pub len: TextUnit,
+}
+
+/// Break a string up into its component tokens
+pub fn tokenize(text: &str) -> Vec<Token> {
+    let mut text = text;
+    let mut acc = Vec::new();
+    while !text.is_empty() {
+        let token = next_token(text);
+        acc.push(token);
+        let len: u32 = token.len.into();
+        text = &text[len as usize..];
+    }
+    acc
+}
+
+/// Get the next token from a string
+pub fn next_token(text: &str) -> Token {
+    assert!(!text.is_empty());
+    let mut ptr = Ptr::new(text);
+    let c = ptr.bump().unwrap();
+    let kind = next_token_inner(c, &mut ptr);
+    let len = ptr.into_len();
+    Token { kind, len }
+}
+
+fn next_token_inner(c: char, ptr: &mut Ptr) -> SyntaxKind {
+    if is_whitespace(c) {
+        ptr.bump_while(is_whitespace);
+        return WHITESPACE;
+    }
+
+    match c {
+        '#' => if scan_shebang(ptr) {
+            return SHEBANG;
+        },
+        '/' => if let Some(kind) = scan_comment(ptr) {
+            return kind;
+        },
+        _ => (),
+    }
+
+    let ident_start = is_ident_start(c) && !is_string_literal_start(c, ptr.next(), ptr.nnext());
+    if ident_start {
+        return scan_ident(c, ptr);
+    }
+
+    if is_dec_digit(c) {
+        let kind = scan_number(c, ptr);
+        scan_literal_suffix(ptr);
+        return kind;
+    }
+
+    // One-byte tokens.
+    if let Some(kind) = SyntaxKind::from_char(c) {
+        return kind;
+    }
+
+    match c {
+        // Multi-byte tokens.
+        '.' => {
+            return match (ptr.next(), ptr.nnext()) {
+                (Some('.'), Some('.')) => {
+                    ptr.bump();
+                    ptr.bump();
+                    DOTDOTDOT
+                }
+                (Some('.'), Some('=')) => {
+                    ptr.bump();
+                    ptr.bump();
+                    DOTDOTEQ
+                }
+                (Some('.'), _) => {
+                    ptr.bump();
+                    DOTDOT
+                }
+                _ => DOT,
+            };
+        }
+        ':' => {
+            return match ptr.next() {
+                Some(':') => {
+                    ptr.bump();
+                    COLONCOLON
+                }
+                _ => COLON,
+            };
+        }
+        '=' => {
+            return match ptr.next() {
+                Some('=') => {
+                    ptr.bump();
+                    EQEQ
+                }
+                Some('>') => {
+                    ptr.bump();
+                    FAT_ARROW
+                }
+                _ => EQ,
+            };
+        }
+        '!' => {
+            return match ptr.next() {
+                Some('=') => {
+                    ptr.bump();
+                    NEQ
+                }
+                _ => EXCL,
+            };
+        }
+        '-' => {
+            return if ptr.next_is('>') {
+                ptr.bump();
+                THIN_ARROW
+            } else {
+                MINUS
+            };
+        }
+
+        // If the character is an ident start not followed by another single
+        // quote, then this is a lifetime name:
+        '\'' => {
+            return if ptr.next_is_p(is_ident_start) && !ptr.nnext_is('\'') {
+                ptr.bump();
+                while ptr.next_is_p(is_ident_continue) {
+                    ptr.bump();
+                }
+                // lifetimes shouldn't end with a single quote
+                // if we find one, then this is an invalid character literal
+                if ptr.next_is('\'') {
+                    ptr.bump();
+                    return CHAR; // TODO: error reporting
+                }
+                LIFETIME
+            } else {
+                scan_char(ptr);
+                scan_literal_suffix(ptr);
+                CHAR
+            };
+        }
+        'b' => {
+            let kind = scan_byte_char_or_string(ptr);
+            scan_literal_suffix(ptr);
+            return kind;
+        }
+        '"' => {
+            scan_string(ptr);
+            scan_literal_suffix(ptr);
+            return STRING;
+        }
+        'r' => {
+            scan_raw_string(ptr);
+            scan_literal_suffix(ptr);
+            return RAW_STRING;
+        }
+        _ => (),
+    }
+    ERROR
+}
+
+fn scan_ident(c: char, ptr: &mut Ptr) -> SyntaxKind {
+    let is_single_letter = match ptr.next() {
+        None => true,
+        Some(c) if !is_ident_continue(c) => true,
+        _ => false,
+    };
+    if is_single_letter {
+        return if c == '_' { UNDERSCORE } else { IDENT };
+    }
+    ptr.bump_while(is_ident_continue);
+    if let Some(kind) = SyntaxKind::from_keyword(ptr.current_token_text()) {
+        return kind;
+    }
+    IDENT
+}
+
+fn scan_literal_suffix(ptr: &mut Ptr) {
+    if ptr.next_is_p(is_ident_start) {
+        ptr.bump();
+    }
+    ptr.bump_while(is_ident_continue);
+}
diff --git a/crates/libsyntax2/src/lexer/numbers.rs b/crates/libsyntax2/src/lexer/numbers.rs
new file mode 100644
index 000000000..5c4641a2d
--- /dev/null
+++ b/crates/libsyntax2/src/lexer/numbers.rs
@@ -0,0 +1,67 @@
+use lexer::classes::*;
+use lexer::ptr::Ptr;
+
+use SyntaxKind::{self, *};
+
+pub(crate) fn scan_number(c: char, ptr: &mut Ptr) -> SyntaxKind {
+    if c == '0' {
+        match ptr.next().unwrap_or('\0') {
+            'b' | 'o' => {
+                ptr.bump();
+                scan_digits(ptr, false);
+            }
+            'x' => {
+                ptr.bump();
+                scan_digits(ptr, true);
+            }
+            '0'...'9' | '_' | '.' | 'e' | 'E' => {
+                scan_digits(ptr, true);
+            }
+            _ => return INT_NUMBER,
+        }
+    } else {
+        scan_digits(ptr, false);
+    }
+
+    // might be a float, but don't be greedy if this is actually an
+    // integer literal followed by field/method access or a range pattern
+    // (`0..2` and `12.foo()`)
+    if ptr.next_is('.') && !(ptr.nnext_is('.') || ptr.nnext_is_p(is_ident_start)) {
+        // might have stuff after the ., and if it does, it needs to start
+        // with a number
+        ptr.bump();
+        scan_digits(ptr, false);
+        scan_float_exponent(ptr);
+        return FLOAT_NUMBER;
+    }
+    // it might be a float if it has an exponent
+    if ptr.next_is('e') || ptr.next_is('E') {
+        scan_float_exponent(ptr);
+        return FLOAT_NUMBER;
+    }
+    INT_NUMBER
+}
+
+fn scan_digits(ptr: &mut Ptr, allow_hex: bool) {
+    while let Some(c) = ptr.next() {
+        match c {
+            '_' | '0'...'9' => {
+                ptr.bump();
+            }
+            'a'...'f' | 'A'...'F' if allow_hex => {
+                ptr.bump();
+            }
+            _ => return,
+        }
+    }
+}
+
+fn scan_float_exponent(ptr: &mut Ptr) {
+    if ptr.next_is('e') || ptr.next_is('E') {
+        ptr.bump();
+        if ptr.next_is('-') || ptr.next_is('+') {
+            ptr.bump();
+        }
+        scan_digits(ptr, false);
+    }
+}
diff --git a/crates/libsyntax2/src/lexer/ptr.rs b/crates/libsyntax2/src/lexer/ptr.rs
new file mode 100644
index 000000000..d1391fd5f
--- /dev/null
+++ b/crates/libsyntax2/src/lexer/ptr.rs
@@ -0,0 +1,74 @@
+use TextUnit;
+
+use std::str::Chars;
+
+pub(crate) struct Ptr<'s> {
+    text: &'s str,
+    len: TextUnit,
+}
+
+impl<'s> Ptr<'s> {
+    pub fn new(text: &'s str) -> Ptr<'s> {
+        Ptr {
+            text,
+            len: 0.into(),
+        }
+    }
+
+    pub fn into_len(self) -> TextUnit {
+        self.len
+    }
+
+    pub fn next(&self) -> Option<char> {
+        self.chars().next()
+    }
+
+    pub fn nnext(&self) -> Option<char> {
+        let mut chars = self.chars();
+        chars.next()?;
+        chars.next()
+    }
+
+    pub fn next_is(&self, c: char) -> bool {
+        self.next() == Some(c)
+    }
+
+    pub fn nnext_is(&self, c: char) -> bool {
+        self.nnext() == Some(c)
+    }
+
+    pub fn next_is_p<P: Fn(char) -> bool>(&self, p: P) -> bool {
+        self.next().map(p) == Some(true)
+    }
+
+    pub fn nnext_is_p<P: Fn(char) -> bool>(&self, p: P) -> bool {
+        self.nnext().map(p) == Some(true)
+    }
+
+    pub fn bump(&mut self) -> Option<char> {
+        let ch = self.chars().next()?;
+        self.len += TextUnit::of_char(ch);
+        Some(ch)
+    }
+
+    pub fn bump_while<F: Fn(char) -> bool>(&mut self, pred: F) {
+        loop {
+            match self.next() {
+                Some(c) if pred(c) => {
+                    self.bump();
+                }
+                _ => return,
+            }
+        }
+    }
+
+    pub fn current_token_text(&self) -> &str {
+        let len: u32 = self.len.into();
+        &self.text[..len as usize]
+    }
+
+    fn chars(&self) -> Chars {
+        let len: u32 = self.len.into();
+        self.text[len as usize..].chars()
+    }
+}
diff --git a/crates/libsyntax2/src/lexer/strings.rs b/crates/libsyntax2/src/lexer/strings.rs
new file mode 100644
index 000000000..e3704fbb3
--- /dev/null
+++ b/crates/libsyntax2/src/lexer/strings.rs
@@ -0,0 +1,106 @@
+use SyntaxKind::{self, *};
+
+use lexer::ptr::Ptr;
+
+pub(crate) fn is_string_literal_start(c: char, c1: Option<char>, c2: Option<char>) -> bool {
+    match (c, c1, c2) {
+        ('r', Some('"'), _)
+        | ('r', Some('#'), _)
+        | ('b', Some('"'), _)
+        | ('b', Some('\''), _)
+        | ('b', Some('r'), Some('"'))
+        | ('b', Some('r'), Some('#')) => true,
+        _ => false,
+    }
+}
+
+pub(crate) fn scan_char(ptr: &mut Ptr) {
+    if ptr.bump().is_none() {
+        return; // TODO: error reporting is upper in the stack
+    }
+    scan_char_or_byte(ptr);
+    if !ptr.next_is('\'') {
+        return; // TODO: error reporting
+    }
+    ptr.bump();
+}
+
+pub(crate) fn scan_byte_char_or_string(ptr: &mut Ptr) -> SyntaxKind {
+    // unwrapping and not-exhaustive match are ok
+    // because of string_literal_start
+    let c = ptr.bump().unwrap();
+    match c {
+        '\'' => {
+            scan_byte(ptr);
+            BYTE
+        }
+        '"' => {
+            scan_byte_string(ptr);
+            BYTE_STRING
+        }
+        'r' => {
+            scan_raw_byte_string(ptr);
+            RAW_BYTE_STRING
+        }
+        _ => unreachable!(),
+    }
+}
+
+pub(crate) fn scan_string(ptr: &mut Ptr) {
+    while let Some(c) = ptr.bump() {
+        if c == '"' {
+            return;
+        }
+    }
+}
+
+pub(crate) fn scan_raw_string(ptr: &mut Ptr) {
+    if !ptr.next_is('"') {
+        return;
+    }
+    ptr.bump();
+
+    while let Some(c) = ptr.bump() {
+        if c == '"' {
+            return;
+        }
+    }
+}
+
+fn scan_byte(ptr: &mut Ptr) {
+    if ptr.next_is('\'') {
+        ptr.bump();
+        return;
+    }
+    ptr.bump();
+    if ptr.next_is('\'') {
+        ptr.bump();
+        return;
+    }
+}
+
+fn scan_byte_string(ptr: &mut Ptr) {
+    while let Some(c) = ptr.bump() {
+        if c == '"' {
+            return;
+        }
+    }
+}
+
+fn scan_raw_byte_string(ptr: &mut Ptr) {
+    if !ptr.next_is('"') {
+        return;
+    }
+    ptr.bump();
+
+    while let Some(c) = ptr.bump() {
+        if c == '"' {
+            return;
+        }
+    }
+}
+
+fn scan_char_or_byte(ptr: &mut Ptr) {
+    //FIXME: deal with escape sequencies
+    ptr.bump();
+}
diff --git a/crates/libsyntax2/src/lib.rs b/crates/libsyntax2/src/lib.rs
new file mode 100644
index 000000000..ca33618a0
--- /dev/null
+++ b/crates/libsyntax2/src/lib.rs
@@ -0,0 +1,55 @@
+//! An experimental implementation of [Rust RFC#2256 libsyntax2.0][rfc#2256].
+//!
+//! The intent is to be an IDE-ready parser, i.e. one that offers
+//!
+//! - easy and fast incremental re-parsing,
+//! - graceful handling of errors, and
+//! - maintains all information in the source file.
+//!
+//! For more information, see [the RFC][rfc#2265], or [the working draft][RFC.md].
+//!
+//!   [rfc#2256]: <https://github.com/rust-lang/rfcs/pull/2256>
+//!   [RFC.md]: <https://github.com/matklad/libsyntax2/blob/master/docs/RFC.md>
+
+#![forbid(
+    missing_debug_implementations,
+    unconditional_recursion,
+    future_incompatible
+)]
+#![deny(bad_style, missing_docs)]
+#![allow(missing_docs)]
+//#![warn(unreachable_pub)] // rust-lang/rust#47816
+
+extern crate itertools;
+extern crate text_unit;
+extern crate unicode_xid;
+extern crate drop_bomb;
+extern crate parking_lot;
+
+pub mod algo;
+pub mod ast;
+mod lexer;
+#[macro_use]
+mod parser_api;
+mod grammar;
+mod parser_impl;
+
+mod syntax_kinds;
+mod smol_str;
+mod yellow;
+/// Utilities for simple uses of the parser.
+pub mod utils;
+
+pub use {
+    ast::{AstNode, File},
+    lexer::{tokenize, Token},
+    syntax_kinds::SyntaxKind,
+    text_unit::{TextRange, TextUnit},
+    yellow::{SyntaxNode, SyntaxNodeRef, SyntaxRoot, TreeRoot, SyntaxError},
+};
+
+
+pub fn parse(text: &str) -> SyntaxNode {
+    let tokens = tokenize(&text);
+    parser_impl::parse::<yellow::GreenBuilder>(text, &tokens)
+}
diff --git a/crates/libsyntax2/src/parser_api.rs b/crates/libsyntax2/src/parser_api.rs
new file mode 100644
index 000000000..c78c6e43a
--- /dev/null
+++ b/crates/libsyntax2/src/parser_api.rs
@@ -0,0 +1,195 @@
+use {
+    parser_impl::ParserImpl,
+    SyntaxKind::{self, ERROR},
+    drop_bomb::DropBomb,
+};
+
+#[derive(Clone, Copy)]
+pub(crate) struct TokenSet(pub(crate) u128);
+
+fn mask(kind: SyntaxKind) -> u128 {
+    1u128 << (kind as usize)
+}
+
+impl TokenSet {
+    pub fn contains(&self, kind: SyntaxKind) -> bool {
+        self.0 & mask(kind) != 0
+    }
+}
+
+#[macro_export]
+macro_rules! token_set {
+    ($($t:ident),*) => { TokenSet($(1u128 << ($t as usize))|*) };
+    ($($t:ident),* ,) => { token_set!($($t),*) };
+}
+
+#[macro_export]
+macro_rules! token_set_union {
+    ($($ts:expr),*) => { TokenSet($($ts.0)|*) };
+    ($($ts:expr),* ,) => { token_set_union!($($ts),*) };
+}
+
+#[test]
+fn token_set_works_for_tokens() {
+    use SyntaxKind::*;
+    let ts = token_set! { EOF, SHEBANG };
+    assert!(ts.contains(EOF));
+    assert!(ts.contains(SHEBANG));
+    assert!(!ts.contains(PLUS));
+}
+
+/// `Parser` struct provides the low-level API for
+/// navigating through the stream of tokens and
+/// constructing the parse tree. The actual parsing
+/// happens in the `grammar` module.
+///
+/// However, the result of this `Parser` is not a real
+/// tree, but rather a flat stream of events of the form
+/// "start expression, consume number literal,
+/// finish expression". See `Event` docs for more.
+pub(crate) struct Parser<'t>(pub(super) ParserImpl<'t>);
+
+impl<'t> Parser<'t> {
+    /// Returns the kind of the current token.
+    /// If parser has already reached the end of input,
+    /// the special `EOF` kind is returned.
+    pub(crate) fn current(&self) -> SyntaxKind {
+        self.nth(0)
+    }
+
+    /// Lookahead operation: returns the kind of the next nth
+    /// token.
+    pub(crate) fn nth(&self, n: u32) -> SyntaxKind {
+        self.0.nth(n)
+    }
+
+    /// Checks if the current token is `kind`.
+    pub(crate) fn at(&self, kind: SyntaxKind) -> bool {
+        self.current() == kind
+    }
+
+    pub(crate) fn at_compound2(&self, c1: SyntaxKind, c2: SyntaxKind) -> bool {
+        self.0.at_compound2(c1, c2)
+    }
+
+    pub(crate) fn at_compound3(&self, c1: SyntaxKind, c2: SyntaxKind, c3: SyntaxKind) -> bool {
+        self.0.at_compound3(c1, c2, c3)
+    }
+
+    /// Checks if the current token is contextual keyword with text `t`.
+    pub(crate) fn at_contextual_kw(&self, t: &str) -> bool {
+        self.0.at_kw(t)
+    }
+
+    /// Starts a new node in the syntax tree. All nodes and tokens
+    /// consumed between the `start` and the corresponding `Marker::complete`
+    /// belong to the same node.
+    pub(crate) fn start(&mut self) -> Marker {
+        Marker::new(self.0.start())
+    }
+
+    /// Advances the parser by one token.
+    pub(crate) fn bump(&mut self) {
+        self.0.bump();
+    }
+
+    /// Advances the parser by one token, remapping its kind.
+    /// This is useful to create contextual keywords from
+    /// identifiers. For example, the lexer creates an `union`
+    /// *identifier* token, but the parser remaps it to the
+    /// `union` keyword, and keyword is what ends up in the
+    /// final tree.
+    pub(crate) fn bump_remap(&mut self, kind: SyntaxKind) {
+        self.0.bump_remap(kind);
+    }
+
+    /// Advances the parser by `n` tokens, remapping its kind.
+    /// This is useful to create compound tokens from parts. For
+    /// example, an `<<` token is two consecutive remapped `<` tokens
+    pub(crate) fn bump_compound(&mut self, kind: SyntaxKind, n: u8) {
+        self.0.bump_compound(kind, n);
+    }
+
+    /// Emit error with the `message`
+    /// TODO: this should be much more fancy and support
+    /// structured errors with spans and notes, like rustc
+    /// does.
+    pub(crate) fn error<T: Into<String>>(&mut self, message: T) {
+        self.0.error(message.into())
+    }
+
+    /// Consume the next token if it is `kind`.
+    pub(crate) fn eat(&mut self, kind: SyntaxKind) -> bool {
+        if !self.at(kind) {
+            return false;
+        }
+        self.bump();
+        true
+    }
+
+    /// Consume the next token if it is `kind` or emit an error
+    /// otherwise.
+    pub(crate) fn expect(&mut self, kind: SyntaxKind) -> bool {
+        if self.eat(kind) {
+            return true;
+        }
+        self.error(format!("expected {:?}", kind));
+        false
+    }
+
+    /// Create an error node and consume the next token.
+    pub(crate) fn err_and_bump(&mut self, message: &str) {
+        let m = self.start();
+        self.error(message);
+        self.bump();
+        m.complete(self, ERROR);
+    }
+}
+
+/// See `Parser::start`.
+pub(crate) struct Marker {
+    pos: u32,
+    bomb: DropBomb,
+}
+
+impl Marker {
+    fn new(pos: u32) -> Marker {
+        Marker {
+            pos,
+            bomb: DropBomb::new("Marker must be either completed or abandoned"),
+        }
+    }
+
+    /// Finishes the syntax tree node and assigns `kind` to it.
+    pub(crate) fn complete(mut self, p: &mut Parser, kind: SyntaxKind) -> CompletedMarker {
+        self.bomb.defuse();
+        p.0.complete(self.pos, kind);
+        CompletedMarker(self.pos, kind)
+    }
+
+    /// Abandons the syntax tree node. All its children
+    /// are attached to its parent instead.
+    pub(crate) fn abandon(mut self, p: &mut Parser) {
+        self.bomb.defuse();
+        p.0.abandon(self.pos);
+    }
+}
+
+pub(crate) struct CompletedMarker(u32, SyntaxKind);
+
+impl CompletedMarker {
+    /// This one is tricky :-)
+    /// This method allows to create a new node which starts
+    /// *before* the current one. That is, parser could start
+    /// node `A`, then complete it, and then after parsing the
+    /// whole `A`, decide that it should have started some node
+    /// `B` before starting `A`. `precede` allows to do exactly
+    /// that. See also docs about `forward_parent` in `Event::Start`.
+    pub(crate) fn precede(self, p: &mut Parser) -> Marker {
+        Marker::new(p.0.precede(self.0))
+    }
+
+    pub(crate) fn kind(&self) -> SyntaxKind {
+        self.1
+    }
+}
diff --git a/crates/libsyntax2/src/parser_impl/event.rs b/crates/libsyntax2/src/parser_impl/event.rs
new file mode 100644
index 000000000..9fd56b996
--- /dev/null
+++ b/crates/libsyntax2/src/parser_impl/event.rs
@@ -0,0 +1,154 @@
+//! This module provides a way to construct a `File`.
+//! It is intended to be completely decoupled from the
+//! parser, so as to allow to evolve the tree representation
+//! and the parser algorithm independently.
+//!
+//! The `Sink` trait is the bridge between the parser and the
+//! tree builder: the parser produces a stream of events like
+//! `start node`, `finish node`, and `FileBuilder` converts
+//! this stream to a real tree.
+use std::mem;
+use {
+    lexer::Token,
+    parser_impl::Sink,
+    SyntaxKind::{self, TOMBSTONE},
+};
+
+
+/// `Parser` produces a flat list of `Event`s.
+/// They are converted to a tree-structure in
+/// a separate pass, via `TreeBuilder`.
+#[derive(Debug)]
+pub(crate) enum Event {
+    /// This event signifies the start of the node.
+    /// It should be either abandoned (in which case the
+    /// `kind` is `TOMBSTONE`, and the event is ignored),
+    /// or completed via a `Finish` event.
+    ///
+    /// All tokens between a `Start` and a `Finish` would
+    /// become the children of the respective node.
+    ///
+    /// For left-recursive syntactic constructs, the parser produces
+    /// a child node before it sees a parent. `forward_parent`
+    /// exists to allow to tweak parent-child relationships.
+    ///
+    /// Consider this path
+    ///
+    /// foo::bar
+    ///
+    /// The events for it would look like this:
+    ///
+    ///
+    /// START(PATH) IDENT('foo') FINISH START(PATH) COLONCOLON IDENT('bar') FINISH
+    ///       |                          /\
+    ///       |                          |
+    ///       +------forward-parent------+
+    ///
+    /// And the tree would look like this
+    ///