mingw: make get_msvcr() a noop

This was added back in the day to make mingw use the same CRT as CPython
(https://bugs.python.org/issue870382), but at least with newer mingw-w64 and
ucrt switching the CRT at "runtime" isn't supported anymore. To build a
compatible extension you have to use a ucrt mingw-w64 build, so things match
up and link against the same CRT.

CPython 3.5+ uses ucrt (see https://wiki.python.org/moin/WindowsCompilers), so
anything besides that is no longer relevant, which only leaves vcruntime140.

Since it's not clear what linking against vcruntime140 solves, and there have
been reports of it needing to be patched out:

* #4101
* pypa/distutils#204 (comment)

let's just make it return nothing. Keep get_msvcr() around for now to avoid breaking
code which patched it.

Fixes #204

distutils/cygwinccompiler.py

@@ -9,13 +9,11 @@
 import copy
 import os
 import pathlib
-import re
 import shlex
 import sys
 import warnings
 from subprocess import check_output
 
-from ._collections import RangeMap
 from .errors import (
     CCompilerError,
     CompileError,
@@ -26,42 +24,10 @@
 from .unixccompiler import UnixCCompiler
 from .version import LooseVersion, suppress_known_deprecation
 
-_msvcr_lookup = RangeMap.left(
-    {
-        # MSVC 7.0
-        1300: ['msvcr70'],
-        # MSVC 7.1
-        1310: ['msvcr71'],
-        # VS2005 / MSVC 8.0
-        1400: ['msvcr80'],
-        # VS2008 / MSVC 9.0
-        1500: ['msvcr90'],
-        # VS2010 / MSVC 10.0
-        1600: ['msvcr100'],
-        # VS2012 / MSVC 11.0
-        1700: ['msvcr110'],
-        # VS2013 / MSVC 12.0
-        1800: ['msvcr120'],
-        # VS2015 / MSVC 14.0
-        1900: ['vcruntime140'],
-        2000: RangeMap.undefined_value,
-    },
-)
-
 
 def get_msvcr():
-    """Include the appropriate MSVC runtime library if Python was built
-    with MSVC 7.0 or later.
-    """
-    match = re.search(r'MSC v\.(\d{4})', sys.version)
-    try:
-        msc_ver = int(match.group(1))
-    except AttributeError:
-        return []
-    try:
-        return _msvcr_lookup[msc_ver]
-    except KeyError:
-        raise ValueError(f"Unknown MS Compiler version {msc_ver} ")
+    """No longer needed, but kept for backward compatibility."""
+    return []
 
 
 _runtime_library_dirs_msg = (
@@ -109,8 +75,6 @@ def __init__(self, verbose=False, dry_run=False, force=False):
             linker_so=(f'{self.linker_dll} -mcygwin {shared_option}'),
         )
 
-        # Include the appropriate MSVC runtime library if Python was built
-        # with MSVC 7.0 or later.
         self.dll_libraries = get_msvcr()
 
     @property

distutils/tests/test_cygwinccompiler.py

@@ -71,50 +71,8 @@ def test_check_config_h(self):
         assert check_config_h()[0] == CONFIG_H_OK
 
     def test_get_msvcr(self):
-        # []
-        sys.version = (
-            '2.6.1 (r261:67515, Dec  6 2008, 16:42:21) '
-            '\n[GCC 4.0.1 (Apple Computer, Inc. build 5370)]'
-        )
         assert get_msvcr() == []
 
-        # MSVC 7.0
-        sys.version = (
-            '2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1300 32 bits (Intel)]'
-        )
-        assert get_msvcr() == ['msvcr70']
-
-        # MSVC 7.1
-        sys.version = (
-            '2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bits (Intel)]'
-        )
-        assert get_msvcr() == ['msvcr71']
-
-        # VS2005 / MSVC 8.0
-        sys.version = (
-            '2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1400 32 bits (Intel)]'
-        )
-        assert get_msvcr() == ['msvcr80']
-
-        # VS2008 / MSVC 9.0
-        sys.version = (
-            '2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1500 32 bits (Intel)]'
-        )
-        assert get_msvcr() == ['msvcr90']
-
-        sys.version = (
-            '3.10.0 (tags/v3.10.0:b494f59, Oct  4 2021, 18:46:30) '
-            '[MSC v.1929 32 bit (Intel)]'
-        )
-        assert get_msvcr() == ['vcruntime140']
-
-        # unknown
-        sys.version = (
-            '2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.2000 32 bits (Intel)]'
-        )
-        with pytest.raises(ValueError):
-            get_msvcr()
-
     @pytest.mark.skipif('sys.platform != "cygwin"')
     def test_dll_libraries_not_none(self):
         from distutils.cygwinccompiler import CygwinCCompiler