Fix Safari share preprocessing

ios/SourceBraidShare/SharePreprocessing.js

@@ -1,6 +1,7 @@
-var ExtensionPreprocessingJS = function() {};
-
-ExtensionPreprocessingJS.prototype = {
+// Safari calls `run` on this global object before presenting the Share
+// Extension. It must be an object, rather than a constructor whose `run`
+// method only exists on its prototype.
+var ExtensionPreprocessingJS = {
   run: function(arguments) {
     var selection = window.getSelection ? window.getSelection().toString() : "";
     var article = document.querySelector("article") || document.querySelector("main") || document.body;

tests/test_ios_share_preprocessing.py

@@ -0,0 +1,58 @@
+import json
+import subprocess
+import unittest
+from pathlib import Path
+
+
+REPOSITORY_ROOT = Path(__file__).resolve().parents[1]
+SCRIPT = REPOSITORY_ROOT / "ios" / "SourceBraidShare" / "SharePreprocessing.js"
+
+
+class SafariSharePreprocessingTests(unittest.TestCase):
+    def test_exposes_a_global_object_that_returns_page_details(self):
+        program = r"""
+const fs = require("fs");
+const vm = require("vm");
+const source = fs.readFileSync(process.argv[1], "utf8");
+const sandbox = {
+  window: {
+    getSelection: () => ({ toString: () => "Selected excerpt" }),
+    location: { href: "https://example.com/article" }
+  },
+  document: {
+    title: "Example article",
+    location: { href: "https://example.com/article" },
+    querySelector: (selector) => selector === "article"
+      ? { innerText: "Readable page text" }
+      : null
+  }
+};
+vm.createContext(sandbox);
+vm.runInContext(source, sandbox);
+if (typeof sandbox.ExtensionPreprocessingJS?.run !== "function") {
+  throw new Error("ExtensionPreprocessingJS must expose run()");
+}
+sandbox.ExtensionPreprocessingJS.run({
+  completionFunction: (value) => process.stdout.write(JSON.stringify(value))
+});
+"""
+        result = subprocess.run(
+            ["node", "-e", program, str(SCRIPT)],
+            check=True,
+            capture_output=True,
+            text=True,
+        )
+
+        self.assertEqual(
+            json.loads(result.stdout),
+            {
+                "url": "https://example.com/article",
+                "title": "Example article",
+                "selectedText": "Selected excerpt",
+                "articleText": "Readable page text",
+            },
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()