Add script to simplify local testing

.gitignore

@@ -1,4 +1,2 @@
 # Emacs backup files
 *~
-
-build/

README.md

@@ -22,6 +22,20 @@ Having set up that hook will ensure that all the automated tests are run prior t
 That executable is now on your default path, so you can now run `godot` from the command line and the automated tests will work.
 You can still create a shortcut to that executable on your Desktop for ease of mouse access, though there's real value to just opening the project you want from the command line.
 
+### Locally testing the HTML build
+
+[The Godot documentation](https://docs.godotengine.org/en/stable/tutorials/export/exporting_for_web.html#serving-the-files) describes the approach that we can use
+to locally test a web build. This requires using the [`serve.py`](build/web/serve.py)
+Python script, which comes from the [Godot Engine repository](https://raw.githubusercontent.com/godotengine/godot/master/platform/web/serve.py) and is copied locally into
+the [`build/web`](build/web) folder.
+
+First, export the project as an HTML5 Web build as normal.
+Then, from the [build/web](build/web) directory, run:
+```bash
+python serve.py --root .
+```
+
+It should bring up a browser that loads the web build from the build folder.
 
 ### Per-Developer Project Settings Override
 

build/web/serve.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+from http.server import HTTPServer, SimpleHTTPRequestHandler, test  # type: ignore
+from pathlib import Path
+import os
+import sys
+import argparse
+import subprocess
+
+
+class CORSRequestHandler(SimpleHTTPRequestHandler):
+    def end_headers(self):
+        self.send_header("Cross-Origin-Opener-Policy", "same-origin")
+        self.send_header("Cross-Origin-Embedder-Policy", "require-corp")
+        self.send_header("Access-Control-Allow-Origin", "*")
+        super().end_headers()
+
+
+def shell_open(url):
+    if sys.platform == "win32":
+        os.startfile(url)
+    else:
+        opener = "open" if sys.platform == "darwin" else "xdg-open"
+        subprocess.call([opener, url])
+
+
+def serve(root, port, run_browser):
+    os.chdir(root)
+
+    if run_browser:
+        # Open the served page in the user's default browser.
+        print("Opening the served URL in the default browser (use `--no-browser` or `-n` to disable this).")
+        shell_open(f"http://127.0.0.1:{port}")
+
+    test(CORSRequestHandler, HTTPServer, port=port)
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-p", "--port", help="port to listen on", default=8060, type=int)
+    parser.add_argument(
+        "-r", "--root", help="path to serve as root (relative to `platform/web/`)", default="../../bin", type=Path
+    )
+    browser_parser = parser.add_mutually_exclusive_group(required=False)
+    browser_parser.add_argument(
+        "-n", "--no-browser", help="don't open default web browser automatically", dest="browser", action="store_false"
+    )
+    parser.set_defaults(browser=True)
+    args = parser.parse_args()
+
+    # Change to the directory where the script is located,
+    # so that the script can be run from any location.
+    os.chdir(Path(__file__).resolve().parent)
+
+    serve(args.root, args.port, args.browser)