Add minimal syntax tree implementation

2 files changed, 88 insertions, 2 deletions

diff --git a/minirust.rs b/minirust.rs
new file mode 100644
index 000000000..d92c03bea
--- /dev/null
+++ b/minirust.rs
@@ -0,0 +1,68 @@
+pub struct NodeKind(u16);
+
+pub struct File {
+    text: String,
+    nodes: Vec<NodeData>,
+}
+
+struct NodeData {
+    kind: NodeKind,
+    range: (u32, u32),
+    parent: Option<u32>,
+    first_child: Option<u32>,
+    next_sibling: Option<u32>,
+}
+
+#[derive(Clone, Copy)]
+pub struct Node<'f> {
+    file: &'f File,
+    idx: u32,
+}
+
+pub struct Children<'f> {
+    next: Option<Node<'f>>,
+}
+
+impl File {
+    pub fn root<'f>(&'f self) -> Node<'f> {
+        assert!(!self.nodes.is_empty());
+        Node { file: self, idx: 0 }
+    }
+}
+
+impl<'f> Node<'f> {
+    pub fn kind(&self) -> NodeKind {
+        self.data().kind
+    }
+
+    pub fn text(&self) -> &'f str {
+        let (start, end) = self.data().range;
+        &self.file.text[start as usize..end as usize]
+    }
+
+    pub fn parent(&self) -> Option<Node<'f>> {
+        self.as_node(self.data().parent)
+    }
+
+    pub fn children(&self) -> Children<'f> {
+        Children { next: self.as_node(self.data().first_child) }
+    }
+
+    fn data(&self) -> &'f NodeData {
+        &self.file.nodes[self.idx as usize]
+    }
+
+    fn as_node(&self, idx: Option<u32>) -> Option<Node<'f>> {
+        idx.map(|idx| Node { file: self.file, idx })
+    }
+}
+
+impl<'f> Iterator for Children<'f> {
+    type Item = Node<'f>;
+
+    fn next(&mut self) -> Option<Node<'f>> {
+        let next = self.next;
+        self.next = next.and_then(|node| node.as_node(node.data().next_sibling));
+        next
+    }
+}
diff --git a/rfc.md b/rfc.md
index 9b7c79991..1476cbaf2 100644
--- a/rfc.md
+++ b/rfc.md
@@ -80,7 +80,10 @@ simpler ones.
 
 In contrast, for IDEs it is crucial to have a lossless view of the
 source code because, for example, it's important to preserve comments
-during refactorings.
+during refactorings. Ideally, IDEs should be able to incrementally
+relex and reparse the file as the user types, because syntax tree is
+necessary to correctly handle certain code-editing actions like
+autoindentation or joining lines.
 
 Currently rustc uses the AST approach, which preserves the source code
 information to some extent by storing spans in the AST.
@@ -98,7 +101,7 @@ Not applicable.
 
 This section proposes a new syntax tree data structure, which should
 be suitable for both compiler and IDE. It is heavily inspired by [PSI]
-data structure which used in [IntelliJ] based IDEs and in the Kotlin
+data structure which used in [IntelliJ] based IDEs and in the [Kotlin]
 compiler.
 
 
@@ -107,6 +110,21 @@ compiler.
 [Kotlin]: https://kotlinlang.org/
 
 
+The main idea is to store the minimal amount of information in the
+tree itself, and instead lean heavily on the source code string for
+the actual data about identifier names, constant values etc.
+
+All nodes in the tree are of the same type and store a constant for
+the syntactic category of the element and a range in the source code.
+
+Here is a minimal implementation of this data structure:
+
+
+```Rust
+```
+
+
+
 # Drawbacks
 [drawbacks]: #drawbacks