7 files changed, 83 insertions, 56 deletions

diff --git a/crates/libsyntax2/src/algo/visit.rs b/crates/libsyntax2/src/algo/visit.rs
index dc5afa5a9..55eb72f59 100644
--- a/crates/libsyntax2/src/algo/visit.rs
+++ b/crates/libsyntax2/src/algo/visit.rs
@@ -1,5 +1,5 @@
 use std::marker::PhantomData;
-use {SyntaxNodeRef, AstNode, SyntaxRoot};
+use {SyntaxNodeRef, AstNode, RefRoot};
 
 
 pub fn visitor<'a, T>() -> impl Visitor<'a, Output=T> {
@@ -10,7 +10,7 @@ pub trait Visitor<'a>: Sized {
     type Output;
     fn accept(self, node: SyntaxNodeRef<'a>) -> Option<Self::Output>;
     fn visit<N, F>(self, f: F) -> Vis<Self, N, F>
-        where N: AstNode<&'a SyntaxRoot>,
+        where N: AstNode<RefRoot<'a>>,
               F: FnOnce(N) -> Self::Output,
     {
         Vis { inner: self, f, ph: PhantomData }
@@ -40,7 +40,7 @@ pub struct Vis<V, N, F> {
 impl<'a, V, N, F> Visitor<'a> for Vis<V, N, F>
     where
         V: Visitor<'a>,
-        N: AstNode<&'a SyntaxRoot>,
+        N: AstNode<RefRoot<'a>>,
         F: FnOnce(N) -> <V as Visitor<'a>>::Output,
 {
     type Output = <V as Visitor<'a>>::Output;
diff --git a/crates/libsyntax2/src/ast/generated.rs b/crates/libsyntax2/src/ast/generated.rs
index be3f73f7e..4fc405c8a 100644
--- a/crates/libsyntax2/src/ast/generated.rs
+++ b/crates/libsyntax2/src/ast/generated.rs
@@ -1,13 +1,12 @@
-use std::sync::Arc;
 use {
     ast,
-    SyntaxNode, SyntaxRoot, TreeRoot, AstNode,
+    SyntaxNode, OwnedRoot, TreeRoot, AstNode,
     SyntaxKind::*,
 };
 
 // ArrayType
 #[derive(Debug, Clone, Copy)]
-pub struct ArrayType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ArrayType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -25,7 +24,7 @@ impl<R: TreeRoot> ArrayType<R> {}
 
 // Attr
 #[derive(Debug, Clone, Copy)]
-pub struct Attr<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct Attr<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -50,7 +49,7 @@ impl<R: TreeRoot> Attr<R> {
 
 // ConstDef
 #[derive(Debug, Clone, Copy)]
-pub struct ConstDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ConstDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -70,7 +69,7 @@ impl<R: TreeRoot> ConstDef<R> {}
 
 // DynTraitType
 #[derive(Debug, Clone, Copy)]
-pub struct DynTraitType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct DynTraitType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -88,7 +87,7 @@ impl<R: TreeRoot> DynTraitType<R> {}
 
 // EnumDef
 #[derive(Debug, Clone, Copy)]
-pub struct EnumDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct EnumDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -108,7 +107,7 @@ impl<R: TreeRoot> EnumDef<R> {}
 
 // File
 #[derive(Debug, Clone, Copy)]
-pub struct File<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct File<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -132,7 +131,7 @@ impl<R: TreeRoot> File<R> {
 
 // FnDef
 #[derive(Debug, Clone, Copy)]
-pub struct FnDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct FnDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -152,7 +151,7 @@ impl<R: TreeRoot> FnDef<R> {}
 
 // FnPointerType
 #[derive(Debug, Clone, Copy)]
-pub struct FnPointerType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct FnPointerType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -170,7 +169,7 @@ impl<R: TreeRoot> FnPointerType<R> {}
 
 // ForType
 #[derive(Debug, Clone, Copy)]
-pub struct ForType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ForType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -188,7 +187,7 @@ impl<R: TreeRoot> ForType<R> {}
 
 // ImplItem
 #[derive(Debug, Clone, Copy)]
-pub struct ImplItem<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ImplItem<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -206,7 +205,7 @@ impl<R: TreeRoot> ImplItem<R> {}
 
 // ImplTraitType
 #[derive(Debug, Clone, Copy)]
-pub struct ImplTraitType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ImplTraitType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -224,7 +223,7 @@ impl<R: TreeRoot> ImplTraitType<R> {}
 
 // Module
 #[derive(Debug, Clone, Copy)]
-pub struct Module<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct Module<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -244,7 +243,7 @@ impl<R: TreeRoot> Module<R> {}
 
 // Name
 #[derive(Debug, Clone, Copy)]
-pub struct Name<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct Name<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -262,7 +261,7 @@ impl<R: TreeRoot> Name<R> {}
 
 // NameRef
 #[derive(Debug, Clone, Copy)]
-pub struct NameRef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct NameRef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -280,7 +279,7 @@ impl<R: TreeRoot> NameRef<R> {}
 
 // NamedField
 #[derive(Debug, Clone, Copy)]
-pub struct NamedField<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct NamedField<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -300,7 +299,7 @@ impl<R: TreeRoot> NamedField<R> {}
 
 // NeverType
 #[derive(Debug, Clone, Copy)]
-pub struct NeverType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct NeverType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -318,7 +317,7 @@ impl<R: TreeRoot> NeverType<R> {}
 
 // NominalDef
 #[derive(Debug, Clone, Copy)]
-pub enum NominalDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub enum NominalDef<R: TreeRoot = OwnedRoot> {
     StructDef(StructDef<R>),
     EnumDef(EnumDef<R>),
 }
@@ -344,7 +343,7 @@ impl<R: TreeRoot> NominalDef<R> {}
 
 // ParenType
 #[derive(Debug, Clone, Copy)]
-pub struct ParenType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ParenType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -362,7 +361,7 @@ impl<R: TreeRoot> ParenType<R> {}
 
 // PathType
 #[derive(Debug, Clone, Copy)]
-pub struct PathType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct PathType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -380,7 +379,7 @@ impl<R: TreeRoot> PathType<R> {}
 
 // PlaceholderType
 #[derive(Debug, Clone, Copy)]
-pub struct PlaceholderType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct PlaceholderType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -398,7 +397,7 @@ impl<R: TreeRoot> PlaceholderType<R> {}
 
 // PointerType
 #[derive(Debug, Clone, Copy)]
-pub struct PointerType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct PointerType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -416,7 +415,7 @@ impl<R: TreeRoot> PointerType<R> {}
 
 // ReferenceType
 #[derive(Debug, Clone, Copy)]
-pub struct ReferenceType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct ReferenceType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -434,7 +433,7 @@ impl<R: TreeRoot> ReferenceType<R> {}
 
 // SliceType
 #[derive(Debug, Clone, Copy)]
-pub struct SliceType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct SliceType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -452,7 +451,7 @@ impl<R: TreeRoot> SliceType<R> {}
 
 // StaticDef
 #[derive(Debug, Clone, Copy)]
-pub struct StaticDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct StaticDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -472,7 +471,7 @@ impl<R: TreeRoot> StaticDef<R> {}
 
 // StructDef
 #[derive(Debug, Clone, Copy)]
-pub struct StructDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct StructDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -498,7 +497,7 @@ impl<R: TreeRoot> StructDef<R> {
 
 // TokenTree
 #[derive(Debug, Clone, Copy)]
-pub struct TokenTree<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct TokenTree<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -516,7 +515,7 @@ impl<R: TreeRoot> TokenTree<R> {}
 
 // TraitDef
 #[derive(Debug, Clone, Copy)]
-pub struct TraitDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct TraitDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -536,7 +535,7 @@ impl<R: TreeRoot> TraitDef<R> {}
 
 // TupleType
 #[derive(Debug, Clone, Copy)]
-pub struct TupleType<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct TupleType<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -554,7 +553,7 @@ impl<R: TreeRoot> TupleType<R> {}
 
 // TypeDef
 #[derive(Debug, Clone, Copy)]
-pub struct TypeDef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct TypeDef<R: TreeRoot = OwnedRoot> {
     syntax: SyntaxNode<R>,
 }
 
@@ -574,7 +573,7 @@ impl<R: TreeRoot> TypeDef<R> {}
 
 // TypeRef
 #[derive(Debug, Clone, Copy)]
-pub enum TypeRef<R: TreeRoot = Arc<SyntaxRoot>> {
+pub enum TypeRef<R: TreeRoot = OwnedRoot> {
     ParenType(ParenType<R>),
     TupleType(TupleType<R>),
     NeverType(NeverType<R>),
diff --git a/crates/libsyntax2/src/ast/mod.rs b/crates/libsyntax2/src/ast/mod.rs
index 9b9200f99..b52230e9c 100644
--- a/crates/libsyntax2/src/ast/mod.rs
+++ b/crates/libsyntax2/src/ast/mod.rs
@@ -1,12 +1,10 @@
 mod generated;
 
-use std::sync::Arc;
-
 use itertools::Itertools;
 use smol_str::SmolStr;
 
 use {
-    SyntaxNode, SyntaxNodeRef, SyntaxRoot, TreeRoot, SyntaxError,
+    SyntaxNode, SyntaxNodeRef, OwnedRoot, TreeRoot, SyntaxError,
     SyntaxKind::*,
 };
 pub use self::generated::*;
@@ -37,7 +35,7 @@ pub trait AttrsOwner<R: TreeRoot>: AstNode<R> {
     }
 }
 
-impl File<Arc<SyntaxRoot>> {
+impl File<OwnedRoot> {
     pub fn parse(text: &str) -> Self {
         File::cast(::parse(text)).unwrap()
     }
@@ -45,7 +43,7 @@ impl File<Arc<SyntaxRoot>> {
 
 impl<R: TreeRoot> File<R> {
     pub fn errors(&self) -> Vec<SyntaxError> {
-        self.syntax().root.errors.clone()
+        self.syntax().root.syntax_root().errors.clone()
     }
 }
 
diff --git a/crates/libsyntax2/src/lib.rs b/crates/libsyntax2/src/lib.rs
index feef542c4..0e40fb65f 100644
--- a/crates/libsyntax2/src/lib.rs
+++ b/crates/libsyntax2/src/lib.rs
@@ -45,7 +45,7 @@ pub use {
     lexer::{tokenize, Token},
     syntax_kinds::SyntaxKind,
     text_unit::{TextRange, TextUnit},
-    yellow::{SyntaxNode, SyntaxNodeRef, SyntaxRoot, TreeRoot, SyntaxError},
+    yellow::{SyntaxNode, SyntaxNodeRef, OwnedRoot, RefRoot, TreeRoot, SyntaxError},
 };
 
 
diff --git a/crates/libsyntax2/src/utils.rs b/crates/libsyntax2/src/utils.rs
index 1fbb872a5..4f60aa2a8 100644
--- a/crates/libsyntax2/src/utils.rs
+++ b/crates/libsyntax2/src/utils.rs
@@ -1,13 +1,13 @@
 use std::fmt::Write;
 use {
     algo::walk::{walk, WalkEvent},
-    SyntaxNode,
+    SyntaxNode, TreeRoot,
 };
 
 /// Parse a file and create a string representation of the resulting parse tree.
 pub fn dump_tree(syntax: &SyntaxNode) -> String {
     let syntax = syntax.as_ref();
-    let mut errors: Vec<_> = syntax.root.errors.iter().cloned().collect();
+    let mut errors: Vec<_> = syntax.root.syntax_root().errors.iter().cloned().collect();
     errors.sort_by_key(|e| e.offset);
     let mut err_pos = 0;
     let mut level = 0;
diff --git a/crates/libsyntax2/src/yellow/mod.rs b/crates/libsyntax2/src/yellow/mod.rs
index ff3bb221b..3c4510fe7 100644
--- a/crates/libsyntax2/src/yellow/mod.rs
+++ b/crates/libsyntax2/src/yellow/mod.rs
@@ -4,7 +4,6 @@ mod red;
 mod syntax;
 
 use std::{
-    ops::Deref,
     sync::Arc,
     ptr,
 };
@@ -15,17 +14,48 @@ pub(crate) use self::{
     red::RedNode,
 };
 
-pub trait TreeRoot: Deref<Target=SyntaxRoot> + Clone + Send + Sync {}
-
 #[derive(Debug)]
 pub struct SyntaxRoot {
     red: RedNode,
     pub(crate) errors: Vec<SyntaxError>,
 }
 
-impl TreeRoot for Arc<SyntaxRoot> {}
+pub trait TreeRoot: Clone + Send + Sync {
+    fn borrowed(&self) -> RefRoot;
+    fn owned(&self) -> OwnedRoot;
+
+    #[doc(hidden)]
+    fn syntax_root(&self) -> &SyntaxRoot;
+}
+#[derive(Clone, Debug)]
+pub struct OwnedRoot(Arc<SyntaxRoot>);
+#[derive(Clone, Copy, Debug)]
+pub struct RefRoot<'a>(&'a OwnedRoot); // TODO: shared_from_this instead of double indirection
 
-impl<'a> TreeRoot for &'a SyntaxRoot {}
+impl TreeRoot for OwnedRoot {
+    fn borrowed(&self) -> RefRoot {
+        RefRoot(&self)
+    }
+    fn owned(&self) -> OwnedRoot {
+        self.clone()
+    }
+
+    fn syntax_root(&self) -> &SyntaxRoot {
+        &*self.0
+    }
+}
+
+impl<'a> TreeRoot for RefRoot<'a> {
+    fn borrowed(&self) -> RefRoot {
+        *self
+    }
+    fn owned(&self) -> OwnedRoot {
+        self.0.clone()
+    }
+    fn syntax_root(&self) -> &SyntaxRoot {
+        self.0.syntax_root()
+    }
+}
 
 impl SyntaxRoot {
     pub(crate) fn new(green: GreenNode, errors: Vec<SyntaxError>) -> SyntaxRoot {
diff --git a/crates/libsyntax2/src/yellow/syntax.rs b/crates/libsyntax2/src/yellow/syntax.rs
index bb390751a..ef82ba408 100644
--- a/crates/libsyntax2/src/yellow/syntax.rs
+++ b/crates/libsyntax2/src/yellow/syntax.rs
@@ -3,14 +3,14 @@ use std::{fmt, sync::Arc};
 use smol_str::SmolStr;
 
 use {
-    yellow::{RedNode, TreeRoot, SyntaxRoot, RedPtr},
+    yellow::{RedNode, TreeRoot, SyntaxRoot, RedPtr, RefRoot, OwnedRoot},
     SyntaxKind::{self, *},
     TextRange, TextUnit,
 };
 
 
 #[derive(Clone, Copy)]
-pub struct SyntaxNode<R: TreeRoot = Arc<SyntaxRoot>> {
+pub struct SyntaxNode<R: TreeRoot = OwnedRoot> {
     pub(crate) root: R,
     // Guaranteed to not dangle, because `root` holds a
     // strong reference to red's ancestor
@@ -28,7 +28,7 @@ impl<R1: TreeRoot, R2: TreeRoot> PartialEq<SyntaxNode<R1>> for SyntaxNode<R2> {
 
 impl<R: TreeRoot> Eq for SyntaxNode<R> {}
 
-pub type SyntaxNodeRef<'a> = SyntaxNode<&'a SyntaxRoot>;
+pub type SyntaxNodeRef<'a> = SyntaxNode<RefRoot<'a>>;
 
 #[test]
 fn syntax_node_ref_is_copy() {
@@ -42,18 +42,18 @@ pub struct SyntaxError {
     pub offset: TextUnit,
 }
 
-impl SyntaxNode<Arc<SyntaxRoot>> {
+impl SyntaxNode<OwnedRoot> {
     pub(crate) fn new_owned(root: SyntaxRoot) -> Self {
-        let root = Arc::new(root);
-        let red = RedPtr::new(&root.red);
+        let root = OwnedRoot(Arc::new(root));
+        let red = RedPtr::new(&root.syntax_root().red);
         SyntaxNode { root, red }
     }
 }
 
 impl<R: TreeRoot> SyntaxNode<R> {
-    pub fn as_ref<'a>(&'a self) -> SyntaxNode<&'a SyntaxRoot> {
+    pub fn as_ref<'a>(&'a self) -> SyntaxNode<RefRoot<'a>> {
         SyntaxNode {
-            root: &*self.root,
+            root: self.root.borrowed(),
             red: self.red,
         }
     }