feat: expand completion snippets and navigate placeholders

src/lsp.rs

@@ -22,6 +22,7 @@ use crate::{
         DocumentEventKind, DocumentSnapshot, PluginUpdate, SemanticToken, SemanticTokenKind,
         SemanticTokenModifier, TextPosition, UpdateEffect,
     },
+    snippet,
 };
 
 const MAX_BODY: usize = 4 * 1024 * 1024;
@@ -683,7 +684,7 @@ impl Runtime {
                             "dynamicRegistration": false, "contextSupport": true,
                             "insertTextMode": 1,
                             "completionItem": {
-                                "snippetSupport": false, "commitCharactersSupport": false,
+                                "snippetSupport": true, "commitCharactersSupport": false,
                                 "insertReplaceSupport": true,
                                 "insertTextModeSupport": {"valueSet": [1]},
                                 "resolveSupport": {"properties": []}
@@ -1030,7 +1031,9 @@ impl Runtime {
         {
             return Ok(());
         }
-        match result.and_then(|value| decode_completion(&snapshot.text, value, &source)) {
+        match result.and_then(|value| {
+            decode_completion(&snapshot.text, value, &source, snapshot.path.as_deref())
+        }) {
             Ok(items) => self.emit(PluginUpdate {
                 request_id: Some(source.request_id),
                 effects: vec![UpdateEffect::Completion {
@@ -2538,6 +2541,7 @@ fn decode_completion(
     text: &str,
     result: &Value,
     source: &Source,
+    path: Option<&str>,
 ) -> Result<Vec<CompletionItem>, String> {
     if result.is_null() {
         return Ok(Vec::new());
@@ -2611,6 +2615,17 @@ fn decode_completion(
             }
         }
     }
+    let word_end = caret_byte
+        + line[caret_byte..]
+            .graphemes(true)
+            .take_while(|cluster| {
+                cluster
+                    .chars()
+                    .next()
+                    .is_some_and(|ch| ch.is_alphanumeric() || ch == '_')
+            })
+            .map(str::len)
+            .sum::<usize>();
     let mut decoded = Vec::with_capacity(items.len());
     let mut bytes = 0usize;
     for item in items {
@@ -2653,8 +2668,8 @@ fn decode_completion(
             })
             .transpose()?
             .unwrap_or(1);
-        // No snippets, indentation adjustment, server commands or lazy edit resolution.
-        if format == 2 || mode == 2 || item.get("command").is_some() {
+        // No indentation adjustment, server commands or lazy edit resolution.
+        if mode == 2 || item.get("command").is_some() {
             continue;
         }
         let explicit = item.get("textEdit");
@@ -2669,7 +2684,7 @@ fn decode_completion(
             (start, end, new_text)
         } else if let Some(range) = default_range {
             let (start, end) = completion_replacement(&lines, range, source)?;
-            (start, end, edit_text.unwrap_or(label))
+            (start, end, edit_text.or(insert).unwrap_or(label))
         } else {
             (
                 TextPosition {
@@ -2693,10 +2708,25 @@ fn decode_completion(
             prefix
         };
         completion_text(new_text, true)?;
+        let (new_text, snippet) = if format == 2 {
+            match snippet::expand(new_text, |name| {
+                completion_variable(name, line, &line[prefix_byte..word_end], source.row, path)
+            }) {
+                Ok((text, snippet)) => (text, Some(snippet)),
+                Err(snippet::Error::Unsupported) => continue,
+                Err(snippet::Error::Invalid) => return Err("invalid completion snippet".into()),
+                Err(snippet::Error::Limit) => {
+                    return Err("completion snippet exceeds expansion limits".into());
+                }
+            }
+        } else {
+            (normalized(new_text).into_owned(), None)
+        };
+        completion_text(&new_text, true)?;
         let mut edits = vec![CompletionEdit {
             start,
             end,
-            text: normalized(new_text).into_owned(),
+            text: new_text,
         }];
         if let Some(additional) = item.get("additionalTextEdits") {
             for edit in additional
@@ -2749,6 +2779,7 @@ fn decode_completion(
                 detail: detail.map(str::to_owned),
                 primary_edit,
                 edits,
+                snippet,
             },
         ));
     }
@@ -2756,6 +2787,38 @@ fn decode_completion(
     Ok(decoded.into_iter().map(|(_, item)| item).collect())
 }
 
+fn completion_variable(
+    name: &str,
+    line: &str,
+    word: &str,
+    row: usize,
+    path: Option<&str>,
+) -> Option<String> {
+    let value = match name {
+        "TM_SELECTED_TEXT" => "",
+        "TM_CURRENT_LINE" => line,
+        "TM_CURRENT_WORD" => word,
+        "TM_LINE_INDEX" => return Some(row.to_string()),
+        "TM_LINE_NUMBER" => return Some((row + 1).to_string()),
+        "TM_FILEPATH" => path.unwrap_or(""),
+        "TM_FILENAME" => path
+            .and_then(|path| Path::new(path).file_name())
+            .and_then(|name| name.to_str())
+            .unwrap_or(""),
+        "TM_FILENAME_BASE" => path
+            .and_then(|path| Path::new(path).file_stem())
+            .and_then(|name| name.to_str())
+            .unwrap_or(""),
+        "TM_DIRECTORY" => path
+            .and_then(|path| Path::new(path).parent())
+            .and_then(|name| name.to_str())
+            .unwrap_or(""),
+        _ => return None,
+    };
+    // Context values have the same per-expansion bound as template text.
+    (value.len() <= 256 * 1024).then(|| value.to_owned())
+}
+
 fn coordinates(value: &Value) -> Result<(usize, usize), String> {
     let line = value["line"]
         .as_u64()
@@ -3077,7 +3140,7 @@ mod tests {
         };
         let at_limit = json!([{"label": "x", "insertText": "x".repeat(MAX_BODY - 1)}]);
         assert_eq!(
-            decode_completion("", &at_limit, &source).unwrap()[0].edits[0]
+            decode_completion("", &at_limit, &source, None).unwrap()[0].edits[0]
                 .text
                 .len(),
             MAX_BODY - 1
@@ -3087,7 +3150,7 @@ mod tests {
             {"label": "y"}
         ]);
         assert!(
-            decode_completion("", &over_limit, &source)
+            decode_completion("", &over_limit, &source, None)
                 .unwrap_err()
                 .contains("4 MiB")
         );