fix(3517): super-simplistic fix to avoid costly AST transforms when t… (#4292)

* fix(3517): super-simplistic fix to avoid costly AST transforms when they are not needed

Co-authored-by: Ronny Berndt <ronny@apache.org>

2 files changed, 63 insertions, 3 deletions

diff --git a/share/server/60/rewrite_fun.js b/share/server/60/rewrite_fun.js
index 1b27a9d14..436fd3da1 100644
--- a/share/server/60/rewrite_fun.js
+++ b/share/server/60/rewrite_fun.js
@@ -28,7 +28,7 @@ function rewriteFunInt(fun) {
 
     // If we have a function declaration without an Id, wrap it
     // in an ExpressionStatement and change it into
-    // a FuntionExpression
+    // a FunctionExpression
     if (decl.type == "FunctionDeclaration" && decl.id == null) {
         decl.type = "FunctionExpression";
         ast.body[idx] = {
@@ -41,7 +41,6 @@ function rewriteFunInt(fun) {
     return escodegen.generate(ast);
 }
 
-
 function rewriteFun(funJSON) {
     const fun = JSON.parse(funJSON);
     return JSON.stringify(rewriteFunInt(fun));
@@ -53,4 +52,4 @@ function rewriteFuns(funsJSON) {
         return rewriteFunInt(fun);
     });
     return JSON.stringify(results);
-}
\ No newline at end of file
+}
diff --git a/share/server/60/rewrite_fun_ast_bypass.js b/share/server/60/rewrite_fun_ast_bypass.js
new file mode 100644
index 000000000..d2c43caf1
--- /dev/null
+++ b/share/server/60/rewrite_fun_ast_bypass.js
@@ -0,0 +1,61 @@
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+//
+// Based on the normalizeFunction which can be
+// found here:
+//
+//  https://github.com/dmunch/couch-chakra/blob/master/js/normalizeFunction.js
+
+function rewriteFunInt(fun) {
+    // Skip lengthy AST transforms if the function passed can be
+    // safely wrapped in parentheses.
+    if (fun.startsWith('function') && fun.endsWith('}')) {
+        return '(' + fun + ')'
+    }
+
+    const ast = esprima.parse(fun);
+    let idx = ast.body.length - 1;
+    let decl = {};
+
+    // Search for the first FunctionDeclaration beginning from the end
+    do {
+        decl = ast.body[idx--];
+    } while (idx >= 0 && decl.type !== "FunctionDeclaration");
+    idx++;
+
+    // If we have a function declaration without an Id, wrap it
+    // in an ExpressionStatement and change it into
+    // a FunctionExpression
+    if (decl.type == "FunctionDeclaration" && decl.id == null) {
+        decl.type = "FunctionExpression";
+        ast.body[idx] = {
+            type: "ExpressionStatement",
+            expression: decl
+        };
+    }
+
+    // Generate source from the rewritten AST
+    return escodegen.generate(ast);
+}
+
+function rewriteFun(funJSON) {
+    const fun = JSON.parse(funJSON);
+    return JSON.stringify(rewriteFunInt(fun));
+}
+
+function rewriteFuns(funsJSON) {
+    let funs = JSON.parse(funsJSON);
+    const results = Array.from(funs, (fun) => {
+        return rewriteFunInt(fun);
+    });
+    return JSON.stringify(results);
+}