Split textDocument/formatting TextEdit with diff

crates/rust-analyzer/src/diff.rs

@@ -0,0 +1,53 @@
+//! Generate minimal `TextEdit`s from different text versions
+use dissimilar::Chunk;
+use ide::{TextEdit, TextRange, TextSize};
+
+pub(crate) fn diff(left: &str, right: &str) -> TextEdit {
+    let chunks = dissimilar::diff(left, right);
+    textedit_from_chunks(chunks)
+}
+
+fn textedit_from_chunks(chunks: Vec<dissimilar::Chunk>) -> TextEdit {
+    let mut builder = TextEdit::builder();
+    let mut pos = TextSize::default();
+
+    let mut chunks = chunks.into_iter().peekable();
+    while let Some(chunk) = chunks.next() {
+        if let (Chunk::Delete(deleted), Some(&Chunk::Insert(inserted))) = (chunk, chunks.peek()) {
+            chunks.next().unwrap();
+            let deleted_len = TextSize::of(deleted);
+            builder.replace(TextRange::at(pos, deleted_len), inserted.into());
+            pos += deleted_len;
+            continue;
+        }
+
+        match chunk {
+            Chunk::Equal(text) => {
+                pos += TextSize::of(text);
+            }
+            Chunk::Delete(deleted) => {
+                let deleted_len = TextSize::of(deleted);
+                builder.delete(TextRange::at(pos, deleted_len));
+                pos += deleted_len;
+            }
+            Chunk::Insert(inserted) => {
+                builder.insert(pos, inserted.into());
+            }
+        }
+    }
+    builder.finish()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn diff_applies() {
+        let mut original = String::from("fn foo(a:u32){\n}");
+        let result = "fn foo(a: u32) {}";
+        let edit = diff(&original, result);
+        edit.apply(&mut original);
+        assert_eq!(original, result);
+    }
+}