Add uast filter_func argument

Signed-off-by: Carlos Martín <carlos.martin.sanchez@gmail.com>

README.md

@@ -244,6 +244,32 @@ Instead of setting a filter for each level of the query, you can use the `flat`
 }
 ```
 
+There is an **experimental** argument o pass a sort of UDF (User Defined Function) to filter the nodes with any arbitrary code. The JavaScript code must be set as a string for `filter_func`. `node` and `result` are accesible as global variables. For example,
+
+- `filter_func: "result = node.token.length > 15;"`
+- `filter_func: "result = node.internal_type !== 'Comment' && node.token.length > 0;"`
+
+```graphql
+{
+  allRepositories {
+    id
+    refs(name: "HEAD") {
+      commit {
+        files(language: "Go") {
+          path
+          size
+          uast(language: "Go", flat: true, filter_func:
+            "result = node.token.length > 15;") {
+            token
+            internal_type
+          }
+        }
+      }
+    }
+  }
+}
+```
+
 ## Advanced Usage
 
 ### Run from Sources

data/resolvers.js

@@ -1,5 +1,7 @@
 import mysqlPool from './connectors';
 
+const vm = require('vm');
+
 const PROTO_PATH = `${__dirname}/../proto/generated.proto`;
 
 const grpc = require('grpc');
@@ -165,8 +167,21 @@ function flattenUastArr(uast, args) {
 }
 
 function uastFilter(node, args) {
-  return (!args.token || node.token === args.token) &&
-         (!args.internal_type || node.internal_type === args.internal_type);
+  let good =
+    (!args.token || node.token === args.token) &&
+    (!args.internal_type || node.internal_type === args.internal_type);
+
+  if (good && args.filter_func !== undefined) {
+    // This is experimental, nodejs does not claim vm to be secure to execute
+    // untrusted code
+    const sandbox = { node, result: false };
+    vm.createContext(sandbox);
+    vm.runInContext(args.filter_func, sandbox);
+
+    good = sandbox.result;
+  }
+
+  return good;
 }
 
 function uastQuery(sql, args) {

data/schema.js

@@ -69,6 +69,17 @@ type Blob {
     language: String!,
     internal_type: String,
     token: String,
+    """
+    **EXPERIMENTAL**
+
+    A string with JS code. 'node' and 'result' are global variables.
+
+    e.g. "result = node.token.length > 15;"
+    """
+    filter_func: String,
+    """
+    Flatten the tree allowing you filter nodes ignoring the tree level they are at.
+    """
     flat: Boolean): [UASTNode]!
 
   """
@@ -104,6 +115,17 @@ type File {
     language: String!,
     internal_type: String,
     token: String,
+    """
+    **EXPERIMENTAL**
+
+    A string with JS code. 'node' and 'result' are global variables.
+
+    e.g. "result = node.token.length > 15;"
+    """
+    filter_func: String,
+    """
+    Flatten the tree allowing you filter nodes ignoring the tree level they are at.
+    """
     flat: Boolean): [UASTNode]!
 
   """
@@ -125,6 +147,17 @@ type UASTNode {
   children(
     internal_type: String,
     token: String,
+    """
+    **EXPERIMENTAL**
+
+    A string with JS code. 'node' and 'result' are global variables.
+
+    e.g. "result = node.token.length > 15;"
+    """
+    filter_func: String,
+    """
+    Flatten the tree allowing you filter nodes ignoring the tree level they are at.
+    """
     flat: Boolean): [UASTNode]!
 
   """