Allow using pydevd as a regular dependency.
Submitted upstream at: https://github.com/microsoft/debugpy/pull/1586

diff --git a/setup.py b/setup.py
index 1bfba237..afffc6b2 100644
--- a/setup.py
+++ b/setup.py
@@ -11,6 +11,8 @@ import subprocess
 import sys
 
 
+BUNDLE_DEBUGPY = not (os.getenv("BUNDLE_DEBUGPY").strip().lower() == "0")
+
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 import versioneer  # noqa
 
@@ -18,12 +20,14 @@ del sys.path[0]
 
 sys.path.insert(0, os.path.join(os.path.dirname(os.path.abspath(__file__)), "src"))
 import debugpy
-import debugpy._vendored
+
+if BUNDLE_DEBUGPY:
+    import debugpy._vendored
 
 del sys.path[0]
 
-
-PYDEVD_ROOT = debugpy._vendored.project_root("pydevd")
+if BUNDLE_DEBUGPY:
+    PYDEVD_ROOT = debugpy._vendored.project_root("pydevd")
 DEBUGBY_ROOT = os.path.dirname(os.path.abspath(debugpy.__file__))
 
 
@@ -46,7 +50,7 @@ def get_buildplatform():
 # relevant setuptools versions.
 class ExtModules(list):
     def __bool__(self):
-        return True
+        return BUNDLE_DEBUGPY
 
 
 def override_build(cmds):
@@ -147,7 +151,28 @@ if __name__ == "__main__":
 
     cmds = versioneer.get_cmdclass()
     override_build(cmds)
-    override_build_py(cmds)
+    if BUNDLE_DEBUGPY:
+        override_build_py(cmds)
+
+    data = {"debugpy": ["ThirdPartyNotices.txt"]}
+    packages = [
+        "debugpy",
+        "debugpy.adapter",
+        "debugpy.common",
+        "debugpy.launcher",
+        "debugpy.server",
+    ]
+    if BUNDLE_DEBUGPY:
+        data.update(
+            {
+                "debugpy._vendored": [
+                    # pydevd extensions must be built before this list can
+                    # be computed properly, so it is populated in the
+                    # overridden build_py.finalize_options().
+                ]
+            }
+        )
+        packages.append("debugpy._vendored")
 
     setuptools.setup(
         name="debugpy",
@@ -177,23 +202,10 @@ if __name__ == "__main__":
             "License :: OSI Approved :: MIT License",
         ],
         package_dir={"": "src"},
-        packages=[
-            "debugpy",
-            "debugpy.adapter",
-            "debugpy.common",
-            "debugpy.launcher",
-            "debugpy.server",
-            "debugpy._vendored",
-        ],
-        package_data={
-            "debugpy": ["ThirdPartyNotices.txt"],
-            "debugpy._vendored": [
-                # pydevd extensions must be built before this list can be computed properly,
-                # so it is populated in the overridden build_py.finalize_options().
-            ],
-        },
+        packages=packages,
+        package_data=data,
         ext_modules=ExtModules(),
-        has_ext_modules=lambda: True,
+        has_ext_modules=lambda: BUNDLE_DEBUGPY,
         cmdclass=cmds,
         **extras
     )
diff --git a/src/debugpy/__init__.py b/src/debugpy/__init__.py
index 975bec79..512219d7 100644
--- a/src/debugpy/__init__.py
+++ b/src/debugpy/__init__.py
@@ -24,6 +24,13 @@ __all__ = [  # noqa
 
 import sys
 
+try:
+    import debugpy._vendored  # noqa
+
+    is_pydevd_bundled = True
+except ImportError:
+    is_pydevd_bundled = False
+
 assert sys.version_info >= (3, 7), (
     "Python 3.6 and below is not supported by this version of debugpy; "
     "use debugpy 1.5.1 or earlier."
diff --git a/src/debugpy/_vendored/force_pydevd.py b/src/debugpy/_vendored/force_pydevd.py
index cfd89275..99622f8c 100644
--- a/src/debugpy/_vendored/force_pydevd.py
+++ b/src/debugpy/_vendored/force_pydevd.py
@@ -3,7 +3,6 @@
 # for license information.
 
 from importlib import import_module
-import os
 import warnings
 
 from . import check_modules, prefix_matcher, preimport, vendored
@@ -17,23 +16,12 @@ if _unvendored:
     # raise ImportError(msg)
     warnings.warn(msg + ':\n {}'.format('\n  '.join(_unvendored)))
 
-# If debugpy logging is enabled, enable it for pydevd as well
-if "DEBUGPY_LOG_DIR" in os.environ:
-    os.environ[str("PYDEVD_DEBUG")] = str("True")
-    os.environ[str("PYDEVD_DEBUG_FILE")] = os.environ["DEBUGPY_LOG_DIR"] + str("/debugpy.pydevd.log")
-
-# Disable pydevd frame-eval optimizations only if unset, to allow opt-in.
-if "PYDEVD_USE_FRAME_EVAL" not in os.environ:
-    os.environ[str("PYDEVD_USE_FRAME_EVAL")] = str("NO")
-
 # Constants must be set before importing any other pydevd module
-# # due to heavy use of "from" in them.
+# due to heavy use of "from" in them.
 with warnings.catch_warnings():
     warnings.simplefilter("ignore", category=DeprecationWarning)
     with vendored('pydevd'):
         pydevd_constants = import_module('_pydevd_bundle.pydevd_constants')
-# We limit representation size in our representation provider when needed.
-pydevd_constants.MAXIMUM_VARIABLE_REPRESENTATION_SIZE = 2 ** 32
 
 # Now make sure all the top-level modules and packages in pydevd are
 # loaded.  Any pydevd modules that aren't loaded at this point, will
@@ -50,32 +38,3 @@ with warnings.catch_warnings():
         'pydevd_plugins',
         'pydevd',
     ])
-
-# When pydevd is imported it sets the breakpoint behavior, but it needs to be
-# overridden because by default pydevd will connect to the remote debugger using
-# its own custom protocol rather than DAP.
-import pydevd  # noqa
-import debugpy  # noqa
-
-
-def debugpy_breakpointhook():
-    debugpy.breakpoint()
-
-
-pydevd.install_breakpointhook(debugpy_breakpointhook)
-
-# Ensure that pydevd uses JSON protocol
-from _pydevd_bundle import pydevd_constants
-from _pydevd_bundle import pydevd_defaults
-pydevd_defaults.PydevdCustomization.DEFAULT_PROTOCOL = pydevd_constants.HTTP_JSON_PROTOCOL
-
-# Enable some defaults related to debugpy such as sending a single notification when
-# threads pause and stopping on any exception.
-pydevd_defaults.PydevdCustomization.DEBUG_MODE = 'debugpy-dap'
-
-# This is important when pydevd attaches automatically to a subprocess. In this case, we have to
-# make sure that debugpy is properly put back in the game for users to be able to use it.
-pydevd_defaults.PydevdCustomization.PREIMPORT = '%s;%s' % (
-    os.path.dirname(os.path.dirname(debugpy.__file__)), 
-    'debugpy._vendored.force_pydevd'
-)
diff --git a/src/debugpy/server/__init__.py b/src/debugpy/server/__init__.py
index 42d5367f..a27c6bf4 100644
--- a/src/debugpy/server/__init__.py
+++ b/src/debugpy/server/__init__.py
@@ -2,6 +2,70 @@
 # Licensed under the MIT License. See LICENSE in the project root
 # for license information.
 
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+from importlib import import_module
+import os
+
 # "force_pydevd" must be imported first to ensure (via side effects)
 # that the debugpy-vendored copy of pydevd gets used.
-import debugpy._vendored.force_pydevd  # noqa
+import debugpy
+
+# If debugpy logging is enabled, enable it for pydevd as well
+if "DEBUGPY_LOG_DIR" in os.environ:
+    os.environ[str("PYDEVD_DEBUG")] = str("True")
+    os.environ[str("PYDEVD_DEBUG_FILE")] = os.environ["DEBUGPY_LOG_DIR"] + str(
+        "/debugpy.pydevd.log"
+    )
+
+# Disable pydevd frame-eval optimizations only if unset, to allow opt-in.
+if "PYDEVD_USE_FRAME_EVAL" not in os.environ:
+    os.environ[str("PYDEVD_USE_FRAME_EVAL")] = str("NO")
+
+BUNDLE_DEBUGPY = bool(os.getenv("BUNDLE_DEBUGPY"))
+
+# Constants must be set before importing any other pydevd module
+# due to heavy use of "from" in them.
+if BUNDLE_DEBUGPY:
+    try:
+        import debugpy._vendored.force_pydevd  # noqa
+    except Exception as e:
+        raise e
+else:
+    pydevd_constants = import_module("_pydevd_bundle.pydevd_constants")
+
+# We limit representation size in our representation provider when needed.
+pydevd_constants.MAXIMUM_VARIABLE_REPRESENTATION_SIZE = 2**32
+
+# When pydevd is imported it sets the breakpoint behavior, but it needs to be
+# overridden because by default pydevd will connect to the remote debugger using
+# its own custom protocol rather than DAP.
+import pydevd  # noqa
+import debugpy  # noqa
+
+
+def debugpy_breakpointhook():
+    debugpy.breakpoint()
+
+
+pydevd.install_breakpointhook(debugpy_breakpointhook)
+
+# Ensure that pydevd uses JSON protocol
+from _pydevd_bundle import pydevd_constants
+from _pydevd_bundle import pydevd_defaults
+
+pydevd_defaults.PydevdCustomization.DEFAULT_PROTOCOL = (
+    pydevd_constants.HTTP_JSON_PROTOCOL
+)
+
+# Enable some defaults related to debugpy such as sending a single notification when
+# threads pause and stopping on any exception.
+pydevd_defaults.PydevdCustomization.DEBUG_MODE = "debugpy-dap"
+
+# This is important when pydevd attaches automatically to a subprocess. In this case, we have to
+# make sure that debugpy is properly put back in the game for users to be able to use it.
+if not BUNDLE_DEBUGPY:
+    pydevd_defaults.PydevdCustomization.PREIMPORT = "%s;%s" % (
+        os.path.dirname(os.path.dirname(debugpy.__file__)),
+        "debugpy._vendored.force_pydevd",
+    )
diff --git a/src/debugpy/server/attach_pid_injected.py b/src/debugpy/server/attach_pid_injected.py
index a8df6e1e..06e49600 100644
--- a/src/debugpy/server/attach_pid_injected.py
+++ b/src/debugpy/server/attach_pid_injected.py
@@ -6,6 +6,7 @@
 
 import os
 
+import debugpy
 
 __file__ = os.path.abspath(__file__)
 _debugpy_dir = os.path.dirname(os.path.dirname(os.path.dirname(__file__)))
@@ -28,25 +29,29 @@ def attach(setup):
                 def on_critical(msg):
                     print(msg, file=sys.stderr)
 
-                pydevd_attach_to_process_path = os.path.join(
-                    _debugpy_dir,
-                    "debugpy",
-                    "_vendored",
-                    "pydevd",
-                    "pydevd_attach_to_process",
-                )
-                assert os.path.exists(pydevd_attach_to_process_path)
-                sys.path.insert(0, pydevd_attach_to_process_path)
+                if not debugpy.is_pydevd_bundled:
+                    from pydevd_attach_to_process import attach_script
+                else:
+                    pydevd_attach_to_process_path = os.path.join(
+                        _debugpy_dir,
+                        "debugpy",
+                        "_vendored",
+                        "pydevd",
+                        "pydevd_attach_to_process",
+                    )
+                    assert os.path.exists(pydevd_attach_to_process_path)
+                    sys.path.insert(0, pydevd_attach_to_process_path)
 
-                # NOTE: that it's not a part of the pydevd PYTHONPATH
-                import attach_script
+                    # NOTE: that it's not a part of the pydevd PYTHONPATH
+                    import attach_script
 
                 attach_script.fix_main_thread_id(
                     on_warn=on_warn, on_exception=on_exception, on_critical=on_critical
                 )
 
-                # NOTE: At this point it should be safe to remove this.
-                sys.path.remove(pydevd_attach_to_process_path)
+                if debugpy.is_pydevd_bundled:
+                    # NOTE: At this point it should be safe to remove this.
+                    sys.path.remove(pydevd_attach_to_process_path)
             except:
                 import traceback
 
diff --git a/tests/tests/test_vendoring.py b/tests/tests/test_vendoring.py
index 9cf44220..3188eb9e 100644
--- a/tests/tests/test_vendoring.py
+++ b/tests/tests/test_vendoring.py
@@ -3,6 +3,12 @@
 # for license information.
 
 
+import pytest
+
+import debugpy
+
+
+@pytest.mark.skipif(not debugpy.is_pydevd_bundled, reason="pydevd is not bundled")
 def test_vendoring(pyfile):
     @pyfile
     def import_debugpy():
-- 
2.41.0