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diff --git a/src/tools/rust-analyzer/crates/syntax/src/lib.rs b/src/tools/rust-analyzer/crates/syntax/src/lib.rs
new file mode 100644
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+++ b/src/tools/rust-analyzer/crates/syntax/src/lib.rs
@@ -0,0 +1,358 @@
+//! Syntax Tree library used throughout the rust analyzer.
+//!
+//! Properties:
+//!   - easy and fast incremental re-parsing
+//!   - graceful handling of errors
+//!   - full-fidelity representation (*any* text can be precisely represented as
+//!     a syntax tree)
+//!
+//! For more information, see the [RFC]. Current implementation is inspired by
+//! the [Swift] one.
+//!
+//! The most interesting modules here are `syntax_node` (which defines concrete
+//! syntax tree) and `ast` (which defines abstract syntax tree on top of the
+//! CST). The actual parser live in a separate `parser` crate, though the
+//! lexer lives in this crate.
+//!
+//! See `api_walkthrough` test in this file for a quick API tour!
+//!
+//! [RFC]: <https://github.com/rust-lang/rfcs/pull/2256>
+//! [Swift]: <https://github.com/apple/swift/blob/13d593df6f359d0cb2fc81cfaac273297c539455/lib/Syntax/README.md>
+
+#![warn(rust_2018_idioms, unused_lifetimes, semicolon_in_expressions_from_macros)]
+
+#[allow(unused)]
+macro_rules! eprintln {
+    ($($tt:tt)*) => { stdx::eprintln!($($tt)*) };
+}
+
+mod syntax_node;
+mod syntax_error;
+mod parsing;
+mod validation;
+mod ptr;
+mod token_text;
+#[cfg(test)]
+mod tests;
+
+pub mod algo;
+pub mod ast;
+#[doc(hidden)]
+pub mod fuzz;
+pub mod utils;
+pub mod ted;
+pub mod hacks;
+
+use std::{marker::PhantomData, sync::Arc};
+
+use stdx::format_to;
+use text_edit::Indel;
+
+pub use crate::{
+    ast::{AstNode, AstToken},
+    ptr::{AstPtr, SyntaxNodePtr},
+    syntax_error::SyntaxError,
+    syntax_node::{
+        PreorderWithTokens, RustLanguage, SyntaxElement, SyntaxElementChildren, SyntaxNode,
+        SyntaxNodeChildren, SyntaxToken, SyntaxTreeBuilder,
+    },
+    token_text::TokenText,
+};
+pub use parser::{SyntaxKind, T};
+pub use rowan::{
+    api::Preorder, Direction, GreenNode, NodeOrToken, SyntaxText, TextRange, TextSize,
+    TokenAtOffset, WalkEvent,
+};
+pub use smol_str::SmolStr;
+
+/// `Parse` is the result of the parsing: a syntax tree and a collection of
+/// errors.
+///
+/// Note that we always produce a syntax tree, even for completely invalid
+/// files.
+#[derive(Debug, PartialEq, Eq)]
+pub struct Parse<T> {
+    green: GreenNode,
+    errors: Arc<Vec<SyntaxError>>,
+    _ty: PhantomData<fn() -> T>,
+}
+
+impl<T> Clone for Parse<T> {
+    fn clone(&self) -> Parse<T> {
+        Parse { green: self.green.clone(), errors: self.errors.clone(), _ty: PhantomData }
+    }
+}
+
+impl<T> Parse<T> {
+    fn new(green: GreenNode, errors: Vec<SyntaxError>) -> Parse<T> {
+        Parse { green, errors: Arc::new(errors), _ty: PhantomData }
+    }
+
+    pub fn syntax_node(&self) -> SyntaxNode {
+        SyntaxNode::new_root(self.green.clone())
+    }
+    pub fn errors(&self) -> &[SyntaxError] {
+        &*self.errors
+    }
+}
+
+impl<T: AstNode> Parse<T> {
+    pub fn to_syntax(self) -> Parse<SyntaxNode> {
+        Parse { green: self.green, errors: self.errors, _ty: PhantomData }
+    }
+
+    pub fn tree(&self) -> T {
+        T::cast(self.syntax_node()).unwrap()
+    }
+
+    pub fn ok(self) -> Result<T, Arc<Vec<SyntaxError>>> {
+        if self.errors.is_empty() {
+            Ok(self.tree())
+        } else {
+            Err(self.errors)
+        }
+    }
+}
+
+impl Parse<SyntaxNode> {
+    pub fn cast<N: AstNode>(self) -> Option<Parse<N>> {
+        if N::cast(self.syntax_node()).is_some() {
+            Some(Parse { green: self.green, errors: self.errors, _ty: PhantomData })
+        } else {
+            None
+        }
+    }
+}
+
+impl Parse<SourceFile> {
+    pub fn debug_dump(&self) -> String {
+        let mut buf = format!("{:#?}", self.tree().syntax());
+        for err in self.errors.iter() {
+            format_to!(buf, "error {:?}: {}\n", err.range(), err);
+        }
+        buf
+    }
+
+    pub fn reparse(&self, indel: &Indel) -> Parse<SourceFile> {
+        self.incremental_reparse(indel).unwrap_or_else(|| self.full_reparse(indel))
+    }
+
+    fn incremental_reparse(&self, indel: &Indel) -> Option<Parse<SourceFile>> {
+        // FIXME: validation errors are not handled here
+        parsing::incremental_reparse(self.tree().syntax(), indel, self.errors.to_vec()).map(
+            |(green_node, errors, _reparsed_range)| Parse {
+                green: green_node,
+                errors: Arc::new(errors),
+                _ty: PhantomData,
+            },
+        )
+    }
+
+    fn full_reparse(&self, indel: &Indel) -> Parse<SourceFile> {
+        let mut text = self.tree().syntax().text().to_string();
+        indel.apply(&mut text);
+        SourceFile::parse(&text)
+    }
+}
+
+/// `SourceFile` represents a parse tree for a single Rust file.
+pub use crate::ast::SourceFile;
+
+impl SourceFile {
+    pub fn parse(text: &str) -> Parse<SourceFile> {
+        let (green, mut errors) = parsing::parse_text(text);
+        let root = SyntaxNode::new_root(green.clone());
+
+        errors.extend(validation::validate(&root));
+
+        assert_eq!(root.kind(), SyntaxKind::SOURCE_FILE);
+        Parse { green, errors: Arc::new(errors), _ty: PhantomData }
+    }
+}
+
+/// Matches a `SyntaxNode` against an `ast` type.
+///
+/// # Example:
+///
+/// ```ignore
+/// match_ast! {
+///     match node {
+///         ast::CallExpr(it) => { ... },
+///         ast::MethodCallExpr(it) => { ... },
+///         ast::MacroCall(it) => { ... },
+///         _ => None,
+///     }
+/// }
+/// ```
+#[macro_export]
+macro_rules! match_ast {
+    (match $node:ident { $($tt:tt)* }) => { match_ast!(match ($node) { $($tt)* }) };
+
+    (match ($node:expr) {
+        $( $( $path:ident )::+ ($it:pat) => $res:expr, )*
+        _ => $catch_all:expr $(,)?
+    }) => {{
+        $( if let Some($it) = $($path::)+cast($node.clone()) { $res } else )*
+        { $catch_all }
+    }};
+}
+
+/// This test does not assert anything and instead just shows off the crate's
+/// API.
+#[test]
+fn api_walkthrough() {
+    use ast::{HasModuleItem, HasName};
+
+    let source_code = "
+        fn foo() {
+            1 + 1
+        }
+    ";
+    // `SourceFile` is the main entry point.
+    //
+    // The `parse` method returns a `Parse` -- a pair of syntax tree and a list
+    // of errors. That is, syntax tree is constructed even in presence of errors.
+    let parse = SourceFile::parse(source_code);
+    assert!(parse.errors().is_empty());
+
+    // The `tree` method returns an owned syntax node of type `SourceFile`.
+    // Owned nodes are cheap: inside, they are `Rc` handles to the underling data.
+    let file: SourceFile = parse.tree();
+
+    // `SourceFile` is the root of the syntax tree. We can iterate file's items.
+    // Let's fetch the `foo` function.
+    let mut func = None;
+    for item in file.items() {
+        match item {
+            ast::Item::Fn(f) => func = Some(f),
+            _ => unreachable!(),
+        }
+    }
+    let func: ast::Fn = func.unwrap();
+
+    // Each AST node has a bunch of getters for children. All getters return
+    // `Option`s though, to account for incomplete code. Some getters are common
+    // for several kinds of node. In this case, a trait like `ast::NameOwner`
+    // usually exists. By convention, all ast types should be used with `ast::`
+    // qualifier.
+    let name: Option<ast::Name> = func.name();
+    let name = name.unwrap();
+    assert_eq!(name.text(), "foo");
+
+    // Let's get the `1 + 1` expression!
+    let body: ast::BlockExpr = func.body().unwrap();
+    let stmt_list: ast::StmtList = body.stmt_list().unwrap();
+    let expr: ast::Expr = stmt_list.tail_expr().unwrap();
+
+    // Enums are used to group related ast nodes together, and can be used for
+    // matching. However, because there are no public fields, it's possible to
+    // match only the top level enum: that is the price we pay for increased API
+    // flexibility
+    let bin_expr: &ast::BinExpr = match &expr {
+        ast::Expr::BinExpr(e) => e,
+        _ => unreachable!(),
+    };
+
+    // Besides the "typed" AST API, there's an untyped CST one as well.
+    // To switch from AST to CST, call `.syntax()` method:
+    let expr_syntax: &SyntaxNode = expr.syntax();
+
+    // Note how `expr` and `bin_expr` are in fact the same node underneath:
+    assert!(expr_syntax == bin_expr.syntax());
+
+    // To go from CST to AST, `AstNode::cast` function is used:
+    let _expr: ast::Expr = match ast::Expr::cast(expr_syntax.clone()) {
+        Some(e) => e,
+        None => unreachable!(),
+    };
+
+    // The two properties each syntax node has is a `SyntaxKind`:
+    assert_eq!(expr_syntax.kind(), SyntaxKind::BIN_EXPR);
+
+    // And text range:
+    assert_eq!(expr_syntax.text_range(), TextRange::new(32.into(), 37.into()));
+
+    // You can get node's text as a `SyntaxText` object, which will traverse the
+    // tree collecting token's text:
+    let text: SyntaxText = expr_syntax.text();
+    assert_eq!(text.to_string(), "1 + 1");
+
+    // There's a bunch of traversal methods on `SyntaxNode`:
+    assert_eq!(expr_syntax.parent().as_ref(), Some(stmt_list.syntax()));
+    assert_eq!(stmt_list.syntax().first_child_or_token().map(|it| it.kind()), Some(T!['{']));
+    assert_eq!(
+        expr_syntax.next_sibling_or_token().map(|it| it.kind()),
+        Some(SyntaxKind::WHITESPACE)
+    );
+
+    // As well as some iterator helpers:
+    let f = expr_syntax.ancestors().find_map(ast::Fn::cast);
+    assert_eq!(f, Some(func));
+    assert!(expr_syntax.siblings_with_tokens(Direction::Next).any(|it| it.kind() == T!['}']));
+    assert_eq!(
+        expr_syntax.descendants_with_tokens().count(),
+        8, // 5 tokens `1`, ` `, `+`, ` `, `!`
+           // 2 child literal expressions: `1`, `1`
+           // 1 the node itself: `1 + 1`
+    );
+
+    // There's also a `preorder` method with a more fine-grained iteration control:
+    let mut buf = String::new();
+    let mut indent = 0;
+    for event in expr_syntax.preorder_with_tokens() {
+        match event {
+            WalkEvent::Enter(node) => {
+                let text = match &node {
+                    NodeOrToken::Node(it) => it.text().to_string(),
+                    NodeOrToken::Token(it) => it.text().to_string(),
+                };
+                format_to!(buf, "{:indent$}{:?} {:?}\n", " ", text, node.kind(), indent = indent);
+                indent += 2;
+            }
+            WalkEvent::Leave(_) => indent -= 2,
+        }
+    }
+    assert_eq!(indent, 0);
+    assert_eq!(
+        buf.trim(),
+        r#"
+"1 + 1" BIN_EXPR
+  "1" LITERAL
+    "1" INT_NUMBER
+  " " WHITESPACE
+  "+" PLUS
+  " " WHITESPACE
+  "1" LITERAL
+    "1" INT_NUMBER
+"#
+        .trim()
+    );
+
+    // To recursively process the tree, there are three approaches:
+    // 1. explicitly call getter methods on AST nodes.
+    // 2. use descendants and `AstNode::cast`.
+    // 3. use descendants and `match_ast!`.
+    //
+    // Here's how the first one looks like:
+    let exprs_cast: Vec<String> = file
+        .syntax()
+        .descendants()
+        .filter_map(ast::Expr::cast)
+        .map(|expr| expr.syntax().text().to_string())
+        .collect();
+
+    // An alternative is to use a macro.
+    let mut exprs_visit = Vec::new();
+    for node in file.syntax().descendants() {
+        match_ast! {
+            match node {
+                ast::Expr(it) => {
+                    let res = it.syntax().text().to_string();
+                    exprs_visit.push(res);
+                },
+                _ => (),
+            }
+        }
+    }
+    assert_eq!(exprs_cast, exprs_visit);
+}