Issue 6538, 6781 - Implement script compilation for snippets

test/snippets.js

Index: test/snippets.js
===================================================================
--- a/test/snippets.js
+++ b/test/snippets.js
@@ -10,16 +10,18 @@
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+/* eslint no-new-func: "off" */

[Manish Jethani, 2018/04/26 13:46:00]

ESLint won't let me use new Function(...) even though it's not the same as eval
[1]

[1]: https://stackoverflow.com/a/4599946

+
 "use strict";
 
 const {createSandbox} = require("./_common");
 
 let SnippetFilter = null;
 let Snippets = null;
 let ElemHide = null;
 let Filter = null;
@@ -185,8 +187,81 @@
   checkParsedScript("Script containing Unicode composite characters",
                     "f\ud83d\ude42\ud83d\ude42 b\ud83d\ude02r",
                     [["f\ud83d\ude42\ud83d\ude42", "b\ud83d\ude02r"]]);
   checkParsedScript("Script with no-op commands", "foo; ;;; ;  ; bar 1",
                     [["foo"], ["bar", "1"]]);
 
   test.done();
 };
+
+exports.testScriptCompilation = function(test)
+{
+  let {compileScript, parseScript} = Snippets;
+
+  let libraries = [
+    `
+      let foo = 0;
+
+      exports.setFoo = function(value)
+      {
+        foo = value;
+      };
+
+      exports.assertFoo = function(expected)
+      {
+        if (foo != expected)
+          throw new Error("Value mismatch");
+      };
+    `
+  ];
+
+  let template = `
+      "use strict";
+      {
+        const libraries = ${JSON.stringify(libraries)};
+
+        const script = {{{script}}};
+
+        let imports = Object.create(null);
+        for (let library of libraries)
+          new Function("exports", library)(imports);
+
+        for (let [name, ...args] of script)
+        {
+          if (Object.prototype.hasOwnProperty.call(imports, name))
+          {
+            let value = imports[name];
+            if (typeof value == "function")
+              value(...args);
+          }
+        }
+      }
+  `;
+
+  function verifyExecutable(script)

[Manish Jethani, 2018/04/26 13:46:00]

I don't know how valuable this is because "template" is essentially
copy-and-paste from the implementation.

+  {
+    let actual = compileScript(script, libraries);
+    let expected = template.replace("{{{script}}}",
+                                    JSON.stringify(parseScript(script)));
+
+    // Trim surrounding spaces because of possible difference in indentation.
+    test.equal(expected.trim(), actual.trim());
+  }
+
+  verifyExecutable("hello 'How are you?'");
+
+  // Test script execution.
+  new Function(compileScript("setFoo 123; assertFoo 123", libraries))();
+
+  // Override setFoo in a second library, without overriding assertFoo. A
+  // couple of things to note here: (1) each library has its own variables;
+  // (2) script execution is stateless, i.e. the values are not retained
+  // between executions. In the example below, assertFoo does not find 456 but
+  // it doesn't find 123 either. It's the initial value 0.
+  new Function(
+    compileScript("setFoo 456; assertFoo 0", [
+      ...libraries, "let foo = 1; exports.setFoo = value => { foo = value; };"
+    ])
+  )();
+
+  test.done();
+};