annotate hgdemandimport/demandimportpy3.py @ 44894:39c598f1c774

sslutil: remove comment referring to unsupported legacy stacks
author Manuel Jacob <me@manueljacob.de>
date Fri, 29 May 2020 22:47:58 +0200
parents a6e12d477595
children 8ed69bd42f10
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1 # demandimportpy3 - global demand-loading of modules for Mercurial
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2 #
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3 # Copyright 2017 Facebook Inc.
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4 #
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5 # This software may be used and distributed according to the terms of the
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6 # GNU General Public License version 2 or any later version.
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7
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8 """Lazy loading for Python 3.6 and above.
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9
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10 This uses the new importlib finder/loader functionality available in Python 3.5
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11 and up. The code reuses most of the mechanics implemented inside importlib.util,
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12 but with a few additions:
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13
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14 * Allow excluding certain modules from lazy imports.
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15 * Expose an interface that's substantially the same as demandimport for
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16 Python 2.
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17
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18 This also has some limitations compared to the Python 2 implementation:
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19
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20 * Much of the logic is per-package, not per-module, so any packages loaded
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21 before demandimport is enabled will not be lazily imported in the future. In
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22 practice, we only expect builtins to be loaded before demandimport is
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23 enabled.
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24 """
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25
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26 # This line is unnecessary, but it satisfies test-check-py3-compat.t.
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27 from __future__ import absolute_import
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28
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29 import contextlib
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30 import importlib.util
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31 import sys
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32
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33 from . import tracing
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34
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35 _deactivated = False
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36
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37 # Python 3.5's LazyLoader doesn't work for some reason.
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38 # https://bugs.python.org/issue26186 is a known issue with extension
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39 # importing. But it appears to not have a meaningful effect with
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40 # Mercurial.
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41 _supported = sys.version_info[0:2] >= (3, 6)
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43
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44 class _lazyloaderex(importlib.util.LazyLoader):
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45 """This is a LazyLoader except it also follows the _deactivated global and
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46 the ignore list.
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47 """
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48
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49 def exec_module(self, module):
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50 """Make the module load lazily."""
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51 with tracing.log('demandimport %s', module):
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52 if _deactivated or module.__name__ in ignores:
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53 self.loader.exec_module(module)
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54 else:
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55 super().exec_module(module)
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58 class LazyFinder(object):
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59 """A wrapper around a ``MetaPathFinder`` that makes loaders lazy.
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60
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61 ``sys.meta_path`` finders have their ``find_spec()`` called to locate a
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62 module. This returns a ``ModuleSpec`` if found or ``None``. The
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63 ``ModuleSpec`` has a ``loader`` attribute, which is called to actually
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64 load a module.
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65
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66 Our class wraps an existing finder and overloads its ``find_spec()`` to
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67 replace the ``loader`` with our lazy loader proxy.
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68
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69 We have to use __getattribute__ to proxy the instance because some meta
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70 path finders don't support monkeypatching.
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71 """
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72
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73 __slots__ = ("_finder",)
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74
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75 def __init__(self, finder):
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76 object.__setattr__(self, "_finder", finder)
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77
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78 def __repr__(self):
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79 return "<LazyFinder for %r>" % object.__getattribute__(self, "_finder")
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80
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81 # __bool__ is canonical Python 3. But check-code insists on __nonzero__ being
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82 # defined via `def`.
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83 def __nonzero__(self):
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84 return bool(object.__getattribute__(self, "_finder"))
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85
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86 __bool__ = __nonzero__
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87
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88 def __getattribute__(self, name):
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89 if name in ("_finder", "find_spec"):
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90 return object.__getattribute__(self, name)
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91
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92 return getattr(object.__getattribute__(self, "_finder"), name)
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93
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94 def __delattr__(self, name):
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95 return delattr(object.__getattribute__(self, "_finder"))
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96
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97 def __setattr__(self, name, value):
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98 return setattr(object.__getattribute__(self, "_finder"), name, value)
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99
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100 def find_spec(self, fullname, path, target=None):
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101 finder = object.__getattribute__(self, "_finder")
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102 try:
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103 find_spec = finder.find_spec
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104 except AttributeError:
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105 loader = finder.find_module(fullname, path)
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106 if loader is None:
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107 spec = None
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108 else:
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109 spec = importlib.util.spec_from_loader(fullname, loader)
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110 else:
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111 spec = find_spec(fullname, path, target)
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112
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113 # Lazy loader requires exec_module().
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114 if (
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115 spec is not None
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116 and spec.loader is not None
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117 and getattr(spec.loader, "exec_module")
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118 ):
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119 spec.loader = _lazyloaderex(spec.loader)
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120
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121 return spec
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122
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123
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124 ignores = set()
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125
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126
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127 def init(ignoreset):
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128 global ignores
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129 ignores = ignoreset
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130
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131
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132 def isenabled():
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133 return not _deactivated and any(
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134 isinstance(finder, LazyFinder) for finder in sys.meta_path
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135 )
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136
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137
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138 def disable():
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139 new_finders = []
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140 for finder in sys.meta_path:
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141 new_finders.append(
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142 finder._finder if isinstance(finder, LazyFinder) else finder
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143 )
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144 sys.meta_path[:] = new_finders
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145
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146
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147 def enable():
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148 if not _supported:
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149 return
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150
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151 new_finders = []
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152 for finder in sys.meta_path:
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153 new_finders.append(
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154 LazyFinder(finder) if not isinstance(finder, LazyFinder) else finder
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155 )
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156 sys.meta_path[:] = new_finders
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157
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158
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159 @contextlib.contextmanager
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160 def deactivated():
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161 # This implementation is a bit different from Python 2's. Python 3
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162 # maintains a per-package finder cache in sys.path_importer_cache (see
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163 # PEP 302). This means that we can't just call disable + enable.
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164 # If we do that, in situations like:
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165 #
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166 # demandimport.enable()
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167 # ...
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168 # from foo.bar import mod1
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169 # with demandimport.deactivated():
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170 # from foo.bar import mod2
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171 #
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172 # mod2 will be imported lazily. (The converse also holds -- whatever finder
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173 # first gets cached will be used.)
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174 #
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175 # Instead, have a global flag the LazyLoader can use.
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176 global _deactivated
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177 demandenabled = isenabled()
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178 if demandenabled:
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179 _deactivated = True
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180 try:
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181 yield
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182 finally:
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183 if demandenabled:
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184 _deactivated = False