New bootstrap-p3

azure-pipelines.yml

           echo Executing Build and Tests
           reg add HKLM\SYSTEM\CurrentControlSet\Control\FileSystem /v LongPathsEnabled /t REG_DWORD /d 1 /f || exit 1
           python -m pip install pytest pytest-xdist || exit 1
-          python -u tools/ci.py -B download --cxx cl.exe -T tools\msvc.dds -T2 tools\msvc.p2.dds || exit 1
+          python -u tools/ci.py -B download --cxx cl.exe -T tools\msvc.dds || exit 1
         displayName: Full CI
       - publish: _build/dds.exe
         artifact: DDS Executable - Windows VS2019
           sudo apt install -y python3-minimal g++-8
           python3 -m pip install pytest pytest-xdist
         displayName: Prepare System
-      - script: python3 -u tools/ci.py -B download --cxx g++-8 -T tools/gcc-8.dds -T2 tools/gcc-8.p2.dds
+      - script: python3 -u tools/ci.py -B download --cxx g++-8 -T tools/gcc-8.dds
         displayName: Full CI
       - publish: _build/dds
         artifact: DDS Executable - Linux
       - script: |
           set -eu
           python3 -m pip install pytest pytest-xdist
-          python3 -u tools/ci.py -B download --cxx g++-8 -T tools/gcc-8.dds -T2 tools/gcc-8.p2.dds
+          python3 -u tools/ci.py -B download --cxx g++-8 -T tools/gcc-8.dds
         displayName: Build and Run Unit Tests
       - publish: _build/dds
         artifact: DDS Executable - macOS

tools/ci.py

     if filename is None:
         raise RuntimeError(f'We do not have a prebuilt DDS binary for '
                            f'the "{sys.platform}" platform')
-    url = f'https://github.com/vector-of-bool/dds/releases/download/bootstrap-p2/{filename}'
+    url = f'https://github.com/vector-of-bool/dds/releases/download/bootstrap-p3/{filename}'
 
     print(f'Downloading prebuilt DDS executable: {url}')
     stream = urllib.request.urlopen(url)
     )
     parser.add_argument(
         '--cxx',
-        help='The name/path of the C++ compiler to use.',
-        required=True)
+        help='The name/path of the C++ compiler to use.')
     parser.add_argument(
         '--toolchain',
         '-T',
     args = parser.parse_args(argv)
 
     opts = CIOptions(
-        cxx=Path(args.cxx), toolchain=args.toolchain, skip_deps=args.skip_deps)
+        cxx=Path(args.cxx or 'unspecified'), toolchain=args.toolchain, skip_deps=args.skip_deps)
 
     if args.bootstrap_with == 'build':
+        if args.cxx is None:
+            raise RuntimeError('`--cxx` must be given when using `--bootstrap-with=build`')
         _do_bootstrap_build(opts)
     elif args.bootstrap_with == 'download':
         _do_bootstrap_download()