snippets: Discard placeholder text for the `$0` tabstop

helix-core/src/snippets/active.rs

@@ -252,4 +252,21 @@ mod tests {
         snippet.map(edit.changes());
         assert!(!snippet.is_valid(&Selection::point(4)))
     }
+
+    #[test]
+    fn tabstop_zero_with_placeholder() {
+        // The `$0` tabstop should not have placeholder text. When we receive a snippet like this
+        // (from older versions of clangd for example) we should discard the placeholder text.
+        let snippet = Snippet::parse("sizeof(${0:expression-or-type})").unwrap();
+        let mut doc = Rope::from("\n");
+        let (transaction, _, snippet) = snippet.render(
+            &doc,
+            &Selection::point(0),
+            |_| (0, 0),
+            &mut SnippetRenderCtx::test_ctx(),
+        );
+        assert!(transaction.apply(&mut doc));
+        assert_eq!(doc, "sizeof()\n");
+        assert!(ActiveSnippet::new(snippet).is_none());
+    }
 }

helix-core/src/snippets/elaborate.rs

@@ -178,9 +178,16 @@ impl Snippet {
         &mut self,
         idx: usize,
         parent: Option<TabstopIdx>,
-        default: Vec<parser::SnippetElement>,
+        mut default: Vec<parser::SnippetElement>,
     ) -> TabstopIdx {
         let idx = TabstopIdx::elaborate(idx);
+        if idx == LAST_TABSTOP_IDX && !default.is_empty() {
+            // Older versions of clangd for example may send a snippet like `${0:placeholder}`
+            // which is considered by VSCode to be a misuse of the `$0` tabstop.
+            log::warn!("Discarding placeholder text for the `$0` tabstop ({default:?}). \
+                The `$0` tabstop signifies the final cursor position and should not include placeholder text.");
+            default.clear();
+        }
         let default = self.elaborate(default, Some(idx));
         self.tabstops.push(Tabstop {
             idx,