Clean up and simplify existing mach bootstrap

- Default to interactive mode and remove the `--interactive` flag
- Use `--force` to skip interactivity
- Change MSVC dependency storage organization on disk: put each version
  into its own folder and directly refer to the versioned folders,
  providing immutability and making the installation list redundant
- Reuse `host_triple()` function to fix broken bootstrapper dispatching
- Simplify code:
  - Remove or inline many unused and redudant functions and variables
  - Prefer plain functions to classes
  - Consolidate into fewer files, remove unnecessary bootstrapper/ dir
- Improve Python style
- Sort dependency list

python/servo/bootstrap.py

@@ -0,0 +1,110 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import absolute_import, print_function
+
+from distutils.spawn import find_executable
+import os
+import subprocess
+import sys
+
+import servo.packages as packages
+from servo.util import extract, download_file, host_triple
+
+
+def windows_gnu(context, force=False):
+    '''Bootstrapper for msys2 based environments for building in Windows.'''
+
+    if not find_executable('pacman'):
+        print(
+            'The Windows GNU bootstrapper only works with msys2 with pacman. '
+            'Get msys2 at http://msys2.github.io/'
+        )
+        return 1
+
+    # Ensure repositories are up to date
+    command = ['pacman', '--sync', '--refresh']
+    subprocess.check_call(command)
+
+    # Install packages
+    command = ['pacman', '--sync', '--needed']
+    if force:
+        command.append('--noconfirm')
+    subprocess.check_call(command + list(packages.WINDOWS_GNU))
+
+    # Downgrade GCC to 5.4.0-1
+    gcc_pkgs = ["gcc", "gcc-ada", "gcc-fortran", "gcc-libgfortran", "gcc-libs", "gcc-objc"]
+    gcc_version = "5.4.0-1"
+    mingw_url = "http://repo.msys2.org/mingw/x86_64/mingw-w64-x86_64-{}-{}-any.pkg.tar.xz"
+    gcc_list = [mingw_url.format(gcc, gcc_version) for gcc in gcc_pkgs]
+
+    # Note: `--upgrade` also does downgrades
+    downgrade_command = ['pacman', '--upgrade']
+    if force:
+        downgrade_command.append('--noconfirm')
+    subprocess.check_call(downgrade_command + gcc_list)
+
+
+def windows_msvc(context, force=False):
+    '''Bootstrapper for MSVC building on Windows.'''
+
+    deps_dir = os.path.join(context.sharedir, "msvc-dependencies")
+    deps_url = "https://servo-rust.s3.amazonaws.com/msvc-deps/"
+
+    def version(package):
+        return packages.WINDOWS_MSVC[package]
+
+    def package_dir(package):
+        return os.path.join(deps_dir, package, version(package))
+
+    to_install = {}
+    for package in packages.WINDOWS_MSVC:
+        # Don't install CMake if it already exists in PATH
+        if package == "cmake" and find_executable(package):
+            continue
+
+        if not os.path.isdir(package_dir(package)):
+            to_install[package] = version(package)
+
+    if not to_install:
+        return 0
+
+    print("Installing missing MSVC dependencies...")
+    for package in to_install:
+        full_spec = '{}-{}'.format(package, version(package))
+
+        parent_dir = os.path.dirname(package_dir(package))
+        if not os.path.isdir(parent_dir):
+            os.makedirs(parent_dir)
+
+        zip_path = package_dir(package) + ".zip"
+        if not os.path.isfile(zip_path):
+            zip_url = "{}{}.zip".format(deps_url, full_spec)
+            download_file(full_spec, zip_url, zip_path)
+
+        print("Extracting {}...".format(full_spec), end='')
+        extract(zip_path, deps_dir)
+        print("done")
+
+        extracted_path = os.path.join(deps_dir, full_spec)
+        os.rename(extracted_path, package_dir(package))
+
+    return 0
+
+
+def bootstrap(context, force=False):
+    '''Dispatches to the right bootstrapping function for the OS.'''
+
+    bootstrapper = None
+
+    if "windows-gnu" in host_triple():
+        bootstrapper = windows_gnu
+    elif "windows-msvc" in host_triple():
+        bootstrapper = windows_msvc
+
+    if bootstrapper is None:
+        print('Bootstrap support is not yet available for your OS.')
+        return 1
+
+    return bootstrapper(context, force=force)