Merge pull request #5542 from pradyunsg/dev-ops/deprecation-utilities

Introduce a helper function for deprecation

docs/development.rst

@@ -211,6 +211,12 @@ document existing behavior with the intention of covering that behavior with
 the above deprecation process are always acceptable, and will be considered on
 their merits.
 
+.. note::
+
+  pip has a helper function for making deprecation easier for pip maintainers.
+  The supporting documentation can be found in the source code of
+  ``pip._internal.utils.deprecation.deprecated``. The function is not a part of
+  pip's public API.
 
 Release Process
 ===============

src/pip/_internal/index.py

@@ -9,7 +9,6 @@ import os
 import posixpath
 import re
 import sys
-import warnings
 from collections import namedtuple
 
 from pip._vendor import html5lib, requests, six
@@ -29,7 +28,7 @@ from pip._internal.exceptions import (
 )
 from pip._internal.models.index import PyPI
 from pip._internal.pep425tags import get_supported
-from pip._internal.utils.deprecation import RemovedInPip12Warning
+from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.logging import indent_log
 from pip._internal.utils.misc import (
     ARCHIVE_EXTENSIONS, SUPPORTED_EXTENSIONS, cached_property, normalize_path,
@@ -212,10 +211,12 @@ class PackageFinder(object):
         # # dependency_links value
         # # FIXME: also, we should track comes_from (i.e., use Link)
         if self.process_dependency_links:
-            warnings.warn(
+            deprecated(
                 "Dependency Links processing has been deprecated and will be "
                 "removed in a future release.",
-                RemovedInPip12Warning,
+                replacement=None,
+                gone_in="18.2",
+                issue=4187,
             )
             self.dependency_links.extend(links)
 

src/pip/_internal/operations/freeze.py

@@ -4,7 +4,6 @@ import collections
 import logging
 import os
 import re
-import warnings
 
 from pip._vendor import pkg_resources, six
 from pip._vendor.packaging.utils import canonicalize_name
@@ -13,7 +12,7 @@ from pip._vendor.pkg_resources import RequirementParseError
 from pip._internal.exceptions import InstallationError
 from pip._internal.req import InstallRequirement
 from pip._internal.req.req_file import COMMENT_RE
-from pip._internal.utils.deprecation import RemovedInPip12Warning
+from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.misc import (
     dist_is_editable, get_installed_distributions,
 )
@@ -216,10 +215,12 @@ class FrozenRequirement(object):
                         'for this package:'
                     )
                 else:
-                    warnings.warn(
+                    deprecated(
                         "SVN editable detection based on dependency links "
                         "will be dropped in the future.",
-                        RemovedInPip12Warning,
+                        replacement=None,
+                        gone_in="18.2",
+                        issue=4187,
                     )
                     comments.append(
                         '# Installing as editable to satisfy requirement %s:' %

src/pip/_internal/req/req_install.py

@@ -8,7 +8,6 @@ import shutil
 import sys
 import sysconfig
 import traceback
-import warnings
 import zipfile
 from distutils.util import change_root
 from email.parser import FeedParser  # type: ignore
@@ -33,7 +32,7 @@ from pip._internal.locations import (
     PIP_DELETE_MARKER_FILENAME, running_under_virtualenv,
 )
 from pip._internal.req.req_uninstall import UninstallPathSet
-from pip._internal.utils.deprecation import RemovedInPip12Warning
+from pip._internal.utils.deprecation import deprecated
 from pip._internal.utils.hashes import Hashes
 from pip._internal.utils.logging import indent_log
 from pip._internal.utils.misc import (
@@ -582,11 +581,13 @@ class InstallRequirement(object):
 
         if requires is None:
             logging.warn(template, self, "it is missing.")
-            warnings.warn(
+            deprecated(
                 "Future versions of pip may reject packages with "
                 "pyproject.toml files that do not contain the [build-system]"
                 "table and the requires key, as specified in PEP 518.",
-                RemovedInPip12Warning,
+                replacement=None,
+                gone_in="18.2",
+                issue=5416,
             )
 
             # Currently, we're isolating the build based on the presence of the

src/pip/_internal/utils/deprecation.py

@@ -6,68 +6,84 @@ from __future__ import absolute_import
 import logging
 import warnings
 
+from pip._vendor.packaging.version import parse
+
+from pip import __version__ as current_version
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 if MYPY_CHECK_RUNNING:
-    from typing import Any  # noqa: F401
+    from typing import Any, Optional  # noqa: F401
 
 
 class PipDeprecationWarning(Warning):
     pass
 
 
-class Pending(object):
-    pass
-
-
-class RemovedInPip12Warning(PipDeprecationWarning, Pending):
-    pass
+_original_showwarning = None  # type: Any
 
 
 # Warnings <-> Logging Integration
-
-
-_warnings_showwarning = None  # type: Any
-
-
 def _showwarning(message, category, filename, lineno, file=None, line=None):
     if file is not None:
-        if _warnings_showwarning is not None:
-            _warnings_showwarning(
+        if _original_showwarning is not None:
+            _original_showwarning(
                 message, category, filename, lineno, file, line,
             )
+    elif issubclass(category, PipDeprecationWarning):
+        # We use a specially named logger which will handle all of the
+        # deprecation messages for pip.
+        logger = logging.getLogger("pip._internal.deprecations")
+        logger.warning(message)
     else:
-        if issubclass(category, PipDeprecationWarning):
-            # We use a specially named logger which will handle all of the
-            # deprecation messages for pip.
-            logger = logging.getLogger("pip._internal.deprecations")
-
-            # This is purposely using the % formatter here instead of letting
-            # the logging module handle the interpolation. This is because we
-            # want it to appear as if someone typed this entire message out.
-            log_message = "DEPRECATION: %s" % message
-
-            # PipDeprecationWarnings that are Pending still have at least 2
-            # versions to go until they are removed so they can just be
-            # warnings.  Otherwise, they will be removed in the very next
-            # version of pip. We want these to be more obvious so we use the
-            # ERROR logging level.
-            if issubclass(category, Pending):
-                logger.warning(log_message)
-            else:
-                logger.error(log_message)
-        else:
-            _warnings_showwarning(
-                message, category, filename, lineno, file, line,
-            )
+        _original_showwarning(
+            message, category, filename, lineno, file, line,
+        )
 
 
 def install_warning_logger():
     # Enable our Deprecation Warnings
     warnings.simplefilter("default", PipDeprecationWarning, append=True)
 
-    global _warnings_showwarning
+    global _original_showwarning
 
-    if _warnings_showwarning is None:
-        _warnings_showwarning = warnings.showwarning
+    if _original_showwarning is None:
+        _original_showwarning = warnings.showwarning
         warnings.showwarning = _showwarning
+
+
+def deprecated(reason, replacement, gone_in, issue=None):
+    # type: (str, Optional[str], Optional[str], Optional[int]) -> None
+    """Helper to deprecate existing functionality.
+
+    reason:
+        Textual reason shown to the user about why this functionality has
+        been deprecated.
+    replacement:
+        Textual suggestion shown to the user about what alternative
+        functionality they can use.
+    gone_in:
+        The version of pip does this functionality should get removed in.
+        Raises errors if pip's current version is greater than or equal to
+        this.
+    issue:
+        Issue number on the tracker that would serve as a useful place for
+        users to find related discussion and provide feedback.
+
+    Always pass replacement, gone_in and issue as keyword arguments for clarity
+    at the call site.
+    """
+
+    # Construct a nice message.
+    # This is purposely eagerly formatted as we want it to appear as if someone
+    # typed this entire message out.
+    message = "DEPRECATION: " + reason
+    if replacement is not None:
+        message += " A possible replacement is {}.".format(replacement)
+    if issue is not None:
+        url = "https://github.com/pypa/pip/issues/" + str(issue)
+        message += " You can find discussion regarding this at {}.".format(url)
+
+    # Raise as an error if it has to be removed.
+    if gone_in is not None and parse(current_version) >= parse(gone_in):
+        raise PipDeprecationWarning(message)
+    warnings.warn(message, category=PipDeprecationWarning, stacklevel=2)

tests/functional/test_warning.py

@@ -1,21 +1,22 @@
+import textwrap
+
 
 def test_environ(script, tmpdir):
     """$PYTHONWARNINGS was added in python2.7"""
     demo = tmpdir.join('warnings_demo.py')
-    demo.write('''
-from pip._internal.utils import deprecation
-deprecation.install_warning_logger()
+    demo.write(textwrap.dedent('''
+        from logging import basicConfig
+        from pip._internal.utils import deprecation
 
-from logging import basicConfig
-basicConfig()
+        deprecation.install_warning_logger()
+        basicConfig()
 
-from warnings import warn
-warn("deprecated!", deprecation.PipDeprecationWarning)
-''')
+        deprecation.deprecated("deprecated!", replacement=None, gone_in=None)
+    '''))
 
     result = script.run('python', demo, expect_stderr=True)
-    assert result.stderr == \
-        'ERROR:pip._internal.deprecations:DEPRECATION: deprecated!\n'
+    expected = 'WARNING:pip._internal.deprecations:DEPRECATION: deprecated!\n'
+    assert result.stderr == expected
 
     script.environ['PYTHONWARNINGS'] = 'ignore'
     result = script.run('python', demo)