Fix pip-install to respect --ignore-requires-python.

Author: cjerdonek

news/6371.bugfix

@@ -0,0 +1,2 @@
+Fix ``pip install`` to respect ``--ignore-requires-python`` when evaluating
+links.

src/pip/_internal/cli/base_command.py

@@ -326,11 +326,15 @@ def _build_package_finder(
         platform=None,         # type: Optional[str]
         python_versions=None,  # type: Optional[List[str]]
         abi=None,              # type: Optional[str]
-        implementation=None    # type: Optional[str]
+        implementation=None,   # type: Optional[str]
+        ignore_requires_python=None,  # type: Optional[bool]
     ):
         # type: (...) -> PackageFinder
         """
         Create a package finder appropriate to this requirement command.
+
+        :param ignore_requires_python: Whether to ignore incompatible
+            "Requires-Python" values in links. Defaults to False.
         """
         index_urls = [options.index_url] + options.extra_index_urls
         if options.no_index:
@@ -352,4 +356,5 @@ def _build_package_finder(
             abi=abi,
             implementation=implementation,
             prefer_binary=options.prefer_binary,
+            ignore_requires_python=ignore_requires_python,
         )

src/pip/_internal/commands/install.py

@@ -297,6 +297,7 @@ def run(self, options, args):
                 python_versions=python_versions,
                 abi=options.abi,
                 implementation=options.implementation,
+                ignore_requires_python=options.ignore_requires_python,
             )
             build_delete = (not (options.no_clean or options.build_dir))
             wheel_cache = WheelCache(options.cache_dir, options.format_control)

src/pip/_internal/index.py

@@ -256,10 +256,20 @@ def _get_html_page(link, session=None):
     return None
 
 
-def _check_link_requires_python(link, version_info):
+def _check_link_requires_python(
+    link,  # type: Link
+    version_info,  # type: Tuple[int, ...]
+    ignore_requires_python=False,  # type: bool
+):
+    # type: (...) -> bool
     """
-    Return whether the link's Requires-Python supports the given Python
-    version.
+    Return whether the given Python version is compatible with a link's
+    "Requires-Python" value.
+
+    :param version_info: The Python version to use to check, as a 3-tuple
+        of ints (major-minor-micro).
+    :param ignore_requires_python: Whether to ignore the "Requires-Python"
+        value if the given Python version isn't compatible.
     """
     try:
         support_this_python = check_requires_python(
@@ -273,11 +283,18 @@ def _check_link_requires_python(link, version_info):
     else:
         if not support_this_python:
             version = '.'.join(map(str, version_info))
+            if not ignore_requires_python:
+                logger.debug(
+                    'Link requires a different Python (%s not in: %r): %s',
+                    version, link.requires_python, link,
+                )
+                return False
+
             logger.debug(
-                'Link requires a different Python (%s not in: %r): %s',
+                'Ignoring failed Requires-Python check (%s not in: %r) '
+                'for link: %s',
                 version, link.requires_python, link,
             )
-            return False
 
     return True
 
@@ -295,6 +312,7 @@ def __init__(
         prefer_binary=False,   # type: bool
         allow_all_prereleases=False,  # type: bool
         py_version_info=None,  # type: Optional[Tuple[int, ...]]
+        ignore_requires_python=None,  # type: Optional[bool]
     ):
         # type: (...) -> None
         """
@@ -303,12 +321,17 @@ def __init__(
             representing a major-minor-micro version, to use to check both
             the Python version embedded in the filename and the package's
             "Requires-Python" metadata. Defaults to `sys.version_info[:3]`.
+        :param ignore_requires_python: Whether to ignore incompatible
+            "Requires-Python" values in links. Defaults to False.
         """
         if py_version_info is None:
             py_version_info = sys.version_info[:3]
+        if ignore_requires_python is None:
+            ignore_requires_python = False
 
         py_version = '.'.join(map(str, py_version_info[:2]))
 
+        self._ignore_requires_python = ignore_requires_python
         self._prefer_binary = prefer_binary
         self._py_version = py_version
         self._py_version_info = py_version_info
@@ -383,6 +406,7 @@ def evaluate_link(self, link, search):
 
         supports_python = _check_link_requires_python(
             link, version_info=self._py_version_info,
+            ignore_requires_python=self._ignore_requires_python,
         )
         if not supports_python:
             # Return None for the reason text to suppress calling
@@ -575,7 +599,8 @@ def create(
         versions=None,  # type: Optional[List[str]]
         abi=None,  # type: Optional[str]
         implementation=None,  # type: Optional[str]
-        prefer_binary=False  # type: bool
+        prefer_binary=False,  # type: bool
+        ignore_requires_python=None,  # type: Optional[bool]
     ):
         # type: (...) -> PackageFinder
         """Create a PackageFinder.
@@ -599,6 +624,8 @@ def create(
             to pep425tags.py in the get_supported() method.
         :param prefer_binary: Whether to prefer an old, but valid, binary
             dist over a new source dist.
+        :param ignore_requires_python: Whether to ignore incompatible
+            "Requires-Python" values in links. Defaults to False.
         """
         if session is None:
             raise TypeError(
@@ -634,6 +661,7 @@ def create(
         candidate_evaluator = CandidateEvaluator(
             valid_tags=valid_tags, prefer_binary=prefer_binary,
             allow_all_prereleases=allow_all_prereleases,
+            ignore_requires_python=ignore_requires_python,
         )
 
         # If we don't have TLS enabled, then WARN if anyplace we're looking

tests/unit/test_index.py

@@ -34,20 +34,34 @@ def check_caplog(caplog, expected_level, expected_message):
     assert record.message == expected_message
 
 
-def test_check_link_requires_python__incompatible_python(caplog):
+@pytest.mark.parametrize('ignore_requires_python, expected', [
+    (None, (
+        False, 'DEBUG',
+        "Link requires a different Python (3.6.5 not in: '== 3.6.4'): "
+        "https://example.com"
+    )),
+    (True, (
+        True, 'DEBUG',
+        "Ignoring failed Requires-Python check (3.6.5 not in: '== 3.6.4') "
+        "for link: https://example.com"
+    )),
+])
+def test_check_link_requires_python__incompatible_python(
+    caplog, ignore_requires_python, expected,
+):
     """
-    Test the log message for an incompatible Python.
+    Test an incompatible Python.
     """
+    expected_return, expected_level, expected_message = expected
     link = Link('https://example.com', requires_python='== 3.6.4')
     caplog.set_level(logging.DEBUG)
-    actual = _check_link_requires_python(link, version_info=(3, 6, 5))
-    assert actual == False
-
-    expected_message = (
-        "Link requires a different Python (3.6.5 not in: '== 3.6.4'): "
-        "https://example.com"
+    actual = _check_link_requires_python(
+        link, version_info=(3, 6, 5),
+        ignore_requires_python=ignore_requires_python,
     )
-    check_caplog(caplog, 'DEBUG', expected_message)
+    assert actual == expected_return
+
+    check_caplog(caplog, expected_level, expected_message)
 
 
 def test_check_link_requires_python__invalid_requires(caplog):
@@ -57,7 +71,7 @@ def test_check_link_requires_python__invalid_requires(caplog):
     link = Link('https://example.com', requires_python='invalid')
     caplog.set_level(logging.DEBUG)
     actual = _check_link_requires_python(link, version_info=(3, 6, 5))
-    assert actual == True
+    assert actual
 
     expected_message = (
         "Ignoring invalid Requires-Python ('invalid') for link: "