add ssr fragment for expressions

Author: matklad

crates/ide_ssr/src/fragments.rs

@@ -35,3 +35,17 @@ pub(crate) fn item(s: &str) -> Result<SyntaxNode, ()> {
     }
     Ok(node.syntax().clone())
 }
+
+pub(crate) fn expr(s: &str) -> Result<SyntaxNode, ()> {
+    let template = "const _: () = {};";
+    let input = template.replace("{}", s);
+    let parse = syntax::SourceFile::parse(&input);
+    if !parse.errors().is_empty() {
+        return Err(());
+    }
+    let node = parse.tree().syntax().descendants().find_map(ast::Expr::cast).ok_or(())?;
+    if node.to_string() != s {
+        return Err(());
+    }
+    Ok(node.syntax().clone())
+}

crates/ide_ssr/src/parsing.rs

@@ -74,8 +74,8 @@ impl ParsedRule {
         };
 
         let raw_template_stmt = raw_template.map(ast::Stmt::parse);
-        if let raw_template_expr @ Some(Ok(_)) = raw_template.map(ast::Expr::parse) {
-            builder.try_add(ast::Expr::parse(&raw_pattern), raw_template_expr);
+        if let raw_template_expr @ Some(Ok(_)) = raw_template.map(fragments::expr) {
+            builder.try_add2(fragments::expr(&raw_pattern), raw_template_expr);
         } else {
             builder.try_add(ast::Expr::parse(&raw_pattern), raw_template_stmt.clone());
         }