feat: expand completion snippets and navigate placeholders

src/plugin.rs

@@ -113,6 +113,22 @@ pub struct CompletionEdit {
     pub text: String,
 }
 
+/// Expanded snippet tabstops, in byte offsets relative to the primary edit text.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct CompletionSnippet {
+    /// Positive tabstops in ascending order, followed by the final zero tabstop.
+    pub tabstops: Vec<SnippetTabstop>,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct SnippetTabstop {
+    pub index: u32,
+    /// Repeated occurrences of the same tabstop are edited together.
+    pub ranges: Vec<std::ops::Range<usize>>,
+    /// Enclosing numbered stops per occurrence, outermost first; parallel to ranges.
+    pub ancestors: Vec<Vec<u32>>,
+}
+
 /// Protocol-independent completion text and its atomic document edits.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct CompletionItem {
@@ -121,6 +137,7 @@ pub struct CompletionItem {
     /// Index of the primary replacement; other edits never determine caret placement.
     pub primary_edit: usize,
     pub edits: Vec<CompletionEdit>,
+    pub snippet: Option<CompletionSnippet>,
 }
 
 #[derive(Debug, Deserialize)]