1 files changed, 126 insertions, 0 deletions

diff --git a/crates/syntax/src/ted.rs b/crates/syntax/src/ted.rs
new file mode 100644
index 000000000..76f950ef9
--- /dev/null
+++ b/crates/syntax/src/ted.rs
@@ -0,0 +1,126 @@
+//! Primitive tree editor, ed for trees.
+//!
+//! The `_raw`-suffixed functions insert elements as is, unsuffixed versions fix
+//! up elements around the edges.
+use std::ops::RangeInclusive;
+
+use parser::T;
+
+use crate::{ast::make, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken};
+
+#[derive(Debug)]
+pub struct Position {
+    repr: PositionRepr,
+}
+
+#[derive(Debug)]
+enum PositionRepr {
+    FirstChild(SyntaxNode),
+    After(SyntaxElement),
+}
+
+impl Position {
+    pub fn after(elem: impl Into<SyntaxElement>) -> Position {
+        let repr = PositionRepr::After(elem.into());
+        Position { repr }
+    }
+    pub fn before(elem: impl Into<SyntaxElement>) -> Position {
+        let elem = elem.into();
+        let repr = match elem.prev_sibling_or_token() {
+            Some(it) => PositionRepr::After(it),
+            None => PositionRepr::FirstChild(elem.parent().unwrap()),
+        };
+        Position { repr }
+    }
+    pub fn first_child_of(node: impl Into<SyntaxNode>) -> Position {
+        let repr = PositionRepr::FirstChild(node.into());
+        Position { repr }
+    }
+    pub fn last_child_of(node: impl Into<SyntaxNode>) -> Position {
+        let node = node.into();
+        let repr = match node.last_child_or_token() {
+            Some(it) => PositionRepr::After(it),
+            None => PositionRepr::FirstChild(node),
+        };
+        Position { repr }
+    }
+}
+
+pub fn insert(position: Position, elem: impl Into<SyntaxElement>) {
+    insert_all(position, vec![elem.into()])
+}
+pub fn insert_raw(position: Position, elem: impl Into<SyntaxElement>) {
+    insert_all_raw(position, vec![elem.into()])
+}
+pub fn insert_all(position: Position, mut elements: Vec<SyntaxElement>) {
+    if let Some(first) = elements.first() {
+        if let Some(ws) = ws_before(&position, first) {
+            elements.insert(0, ws.into())
+        }
+    }
+    if let Some(last) = elements.last() {
+        if let Some(ws) = ws_after(&position, last) {
+            elements.push(ws.into())
+        }
+    }
+    insert_all_raw(position, elements)
+}
+pub fn insert_all_raw(position: Position, elements: Vec<SyntaxElement>) {
+    let (parent, index) = match position.repr {
+        PositionRepr::FirstChild(parent) => (parent, 0),
+        PositionRepr::After(child) => (child.parent().unwrap(), child.index() + 1),
+    };
+    parent.splice_children(index..index, elements);
+}
+
+pub fn remove(elem: impl Into<SyntaxElement>) {
+    let elem = elem.into();
+    remove_all(elem.clone()..=elem)
+}
+pub fn remove_all(range: RangeInclusive<SyntaxElement>) {
+    replace_all(range, Vec::new())
+}
+
+pub fn replace(old: impl Into<SyntaxElement>, new: impl Into<SyntaxElement>) {
+    let old = old.into();
+    replace_all(old.clone()..=old, vec![new.into()])
+}
+pub fn replace_all(range: RangeInclusive<SyntaxElement>, new: Vec<SyntaxElement>) {
+    let start = range.start().index();
+    let end = range.end().index();
+    let parent = range.start().parent().unwrap();
+    parent.splice_children(start..end + 1, new)
+}
+
+pub fn append_child(node: impl Into<SyntaxNode>, child: impl Into<SyntaxElement>) {
+    let position = Position::last_child_of(node);
+    insert(position, child)
+}
+pub fn append_child_raw(node: impl Into<SyntaxNode>, child: impl Into<SyntaxElement>) {
+    let position = Position::last_child_of(node);
+    insert_raw(position, child)
+}
+
+fn ws_before(position: &Position, new: &SyntaxElement) -> Option<SyntaxToken> {
+    let prev = match &position.repr {
+        PositionRepr::FirstChild(_) => return None,
+        PositionRepr::After(it) => it,
+    };
+    ws_between(prev, new)
+}
+fn ws_after(position: &Position, new: &SyntaxElement) -> Option<SyntaxToken> {
+    let next = match &position.repr {
+        PositionRepr::FirstChild(parent) => parent.first_child_or_token()?,
+        PositionRepr::After(sibling) => sibling.next_sibling_or_token()?,
+    };
+    ws_between(new, &next)
+}
+fn ws_between(left: &SyntaxElement, right: &SyntaxElement) -> Option<SyntaxToken> {
+    if left.kind() == SyntaxKind::WHITESPACE || right.kind() == SyntaxKind::WHITESPACE {
+        return None;
+    }
+    if right.kind() == T![;] || right.kind() == T![,] {
+        return None;
+    }
+    Some(make::tokens::single_space().into())
+}