perf: use getVisitorKeys (sveltejs#381)

prevents some needless recursion into embed

src/embed.ts

@@ -24,6 +24,22 @@ const {
     utils: { removeLines },
 } = doc;
 
+const leaveAlone = new Set([
+    'Script',
+    'Style',
+    'Identifier',
+    'MemberExpression',
+    'CallExpression',
+    'ArrowFunctionExpression',
+]);
+const dontTraverse = new Set(['start', 'end', 'type']);
+
+export function getVisitorKeys(node: any, nonTraversableKeys: Set<string>): string[] {
+    return Object.keys(node).filter((key) => {
+        return !nonTraversableKeys.has(key) && !leaveAlone.has(node.type) && !dontTraverse.has(key);
+    });
+}
+
 // Embed works like this in Prettier v3:
 // - do depth first traversal of all node properties
 // - deepest property is calling embed first

src/index.ts

@@ -2,7 +2,7 @@ import { SupportLanguage, Parser, Printer } from 'prettier';
 import * as prettierPluginBabel from 'prettier/plugins/babel';
 import { hasPragma, print } from './print';
 import { ASTNode } from './print/nodes';
-import { embed } from './embed';
+import { embed, getVisitorKeys } from './embed';
 import { snipScriptAndStyleTagContent } from './lib/snipTagContent';
 
 const babelParser = prettierPluginBabel.parsers.babel;
@@ -62,16 +62,18 @@ export const parsers: Record<string, Parser> = {
         ...babelParser,
         parse: (text: string, options: any) => {
             const ast = babelParser.parse(text, options);
-        
+
             return { ...ast, program: ast.program.body[0].expression };
-        }
-    }
+        },
+    },
 };
 
 export const printers: Record<string, Printer> = {
     'svelte-ast': {
         print,
         embed,
+        // @ts-expect-error Prettier's type definitions are wrong
+        getVisitorKeys,
     },
 };