fbcode_builder: getdeps: add envfuncs.py

Summary:
Add some helpers for manipulating environment variables
that will hold either compiler flags or paths.

These are used in later diffs when setting up arguments/environment
for eg: cmake.

Reviewed By: sinancepel, simpkins

Differential Revision: D14690993

fbshipit-source-id: 7f9753cd99d968550fe9e3ba8b7017a44683061e

build/fbcode_builder/getdeps/envfuncs.py

+#!/usr/bin/env python
+# Copyright (c) 2019-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree. An additional grant
+# of patent rights can be found in the PATENTS file in the same directory.
+
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import os
+import shlex
+import sys
+
+
+class Env(object):
+    def __init__(self, src=None):
+        self._dict = {}
+        self.update(src or os.environ)
+
+    def update(self, src):
+        for k, v in src.items():
+            self.set(k, v)
+
+    def copy(self):
+        return Env(self._dict)
+
+    def _key(self, key):
+        # The `str` cast may not appear to be needed, but without it we run
+        # into issues when passing the environment to subprocess.  The main
+        # issue is that in python2 `os.environ` (which is the initial source
+        # of data for the environment) uses byte based strings, but this
+        # project uses `unicode_literals`.  `subprocess` will raise an error
+        # if the environment that it is passed has a mixture of byte and
+        # unicode strings.
+        # It is simplest to force everthing to be `str` for the sake of
+        # consistency.
+        key = str(key)
+        if sys.platform.startswith("win"):
+            # Windows env var names are case insensitive but case preserving.
+            # An implementation of PAR files on windows gets confused if
+            # the env block contains keys with conflicting case, so make a
+            # pass over the contents to remove any.
+            # While this O(n) scan is technically expensive and gross, it
+            # is practically not a problem because the volume of calls is
+            # relatively low and the cost of manipulating the env is dwarfed
+            # by the cost of spawning a process on windows.  In addition,
+            # since the processes that we run are expensive anyway, this
+            # overhead is not the worst thing to worry about.
+            for k in list(self._dict.keys()):
+                if str(k).lower() == key.lower():
+                    return k
+        elif key in self._dict:
+            return key
+        return None
+
+    def get(self, key, defval=None):
+        key = self._key(key)
+        if key is None:
+            return defval
+        return self._dict[key]
+
+    def __getitem__(self, key):
+        val = self.get(key)
+        if key is None:
+            raise KeyError(key)
+        return val
+
+    def unset(self, key):
+        if key is None:
+            raise KeyError("attempting to unset env[None]")
+
+        key = self._key(key)
+        if key:
+            del self._dict[key]
+
+    def __delitem__(self, key):
+        self.unset(key)
+
+    def __repr__(self):
+        return repr(self._dict)
+
+    def set(self, key, value):
+        if key is None:
+            raise KeyError("attempting to assign env[None] = %r" % value)
+
+        if value is None:
+            raise ValueError("attempting to assign env[%s] = None" % key)
+
+        # The `str` conversion is important to avoid triggering errors
+        # with subprocess if we pass in a unicode value; see commentary
+        # in the `_key` method.
+        key = str(key)
+        value = str(value)
+
+        # The `unset` call is necessary on windows where the keys are
+        # case insensitive.   Since this dict is case sensitive, simply
+        # assigning the value to the new key is not sufficient to remove
+        # the old value.  The `unset` call knows how to match keys and
+        # remove any potential duplicates.
+        self.unset(key)
+        self._dict[key] = value
+
+    def __setitem__(self, key, value):
+        self.set(key, value)
+
+    def __iter__(self):
+        return self._dict.__iter__()
+
+    def __len__(self):
+        return len(self._dict)
+
+    def keys(self):
+        return self._dict.keys()
+
+    def values(self):
+        return self._dict.values()
+
+    def items(self):
+        return self._dict.items()
+
+
+def add_path_entry(env, name, item, append=True, separator=os.pathsep):
+    """ Cause `item` to be added to the path style env var named
+    `name` held in the `env` dict.  `append` specifies whether
+    the item is added to the end (the default) or should be
+    prepended if `name` already exists. """
+    val = env.get(name, "")
+    if len(val) > 0:
+        val = val.split(separator)
+    else:
+        val = []
+    if append:
+        val.append(item)
+    else:
+        val.insert(0, item)
+    env.set(name, separator.join(val))
+
+
+def add_flag(env, name, flag, append=True):
+    """ Cause `flag` to be added to the CXXFLAGS-style env var named
+    `name` held in the `env` dict.  `append` specifies whether the
+    flag is added to the end (the default) or should be prepended if
+    `name` already exists. """
+    val = shlex.split(env.get(name, ""))
+    if append:
+        val.append(flag)
+    else:
+        val.insert(0, flag)
+    env.set(name, " ".join(val))
+
+
+def path_search(env, exename, defval=None):
+    """ Search for exename in the PATH specified in env.
+    exename is eg: `ninja` and this function knows to append a .exe
+    to the end on windows.
+    Returns the path to the exe if found, or None if either no
+    PATH is set in env or no executable is found. """
+
+    path = env.get("PATH", None)
+    if path is None:
+        return defval
+
+    is_win = sys.platform.startswith("win")
+    if is_win:
+        exename = "%s.exe" % exename
+
+    for bindir in path.split(os.pathsep):
+        full_name = os.path.join(bindir, exename)
+        if os.path.exists(full_name) and os.path.isfile(full_name):
+            if not is_win and not os.access(full_name, os.X_OK):
+                continue
+            return full_name
+
+    return None