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# Copyright 2019 The LUCI Authors. All rights reserved.
# Use of this source code is governed under the Apache License, Version 2.0
# that can be found in the LICENSE file.
from itertools import chain
from collections import defaultdict
from future.utils import iteritems, itervalues
class FakeEnviron(object):
"""This is a fake dictionary which is meant to emulate os.environ strictly for
the purposes of interacting with merge_envs.
It supports:
* Any key access is answered with <key>, allowing this to be used as
a % format argument.
* Deleting/setting items sets them to None/value, appropriately.
* `in` checks always returns True
* copy() returns self
The 'formatted' result can be obtained by looking at .data.
def __init__(self): = {}
def __getitem__(self, key):
return '<%s>' % key
def get(self, key, default=None):
return self[key]
def keys(self):
return list(
def iteritems(self):
return iteritems(
def items(self):
return list(iteritems(
def pop(self, key, default=None):
result =, default)[key] = None
return result
def __delitem__(self, key):[key] = None
def __contains__(self, key):
return True
def __setitem__(self, key, value):[key] = value
def copy(self):
return self
def merge_envs(original, overrides, prefixes, suffixes, pathsep):
"""Merges two environments.
Returns a new environment dict with entries from `overrides` overwriting
corresponding entries in `original`. Keys in `overrides` whose value is None
will completely remove the environment variable. Values can contain %(KEY)s
strings, which will be substituted with the values from the original (useful
for amending, as opposed to overwriting, variables like PATH).
Also returns a set of removed keys; this is used by the simulation tests to
retain explicit envvar deletions for the test expectations.
See StepConfig for environment construction rules.
* original (Dict[str, str]|FakeEnviron) - The base "real" environment to
merge into.
* overrides (Dict[str, str|None]) - The values to overwrite with.
* prefixes (Dict[str, List[str]]) - Values to prepend (joined with
`pathsep`) to PATH-like environment variables.
* suffixes (Dict[str, List[str]]) - Values to append (joined with `pathsep`)
to PATH-like environment variables.
* pathsep (str) - The separator to use when adding `prefixes` and `suffixes`
to the env.
Returns (merged_env : Dict[str, str], removed_keys : Set[str])
result = dict(original.items())
removed = set()
if not any((prefixes, suffixes, overrides)):
return result, removed
subst = (original if isinstance(original, FakeEnviron)
else defaultdict(lambda: '', **original))
merged = set()
for k in set(suffixes).union(prefixes):
pfxs = tuple(prefixes.get(k, ()))
sfxs = tuple(suffixes.get(k, ()))
if not (pfxs or sfxs):
# If the same key is defined in "overrides", we need to incorporate with it.
# We'll do so here, and skip it in the "overrides" construction.
if k in overrides:
val = overrides[k]
if val is not None:
# TODO(iannucci): Remove % formatting hacks from recipe engine
# environment processing; all known uses should be using env
# suffix/prefix instead.
val = str(val) % subst
# Not defined. Append "val" iff it is defined in "original" and not empty.
val = original.get(k, '')
if val:
pfxs += (val,)
result[k] = pathsep.join(str(v) for v in chain(pfxs, sfxs))
for k, v in iteritems(overrides):
if k in merged:
if v is None:
result.pop(k, None)
result[k] = str(v) % subst
return result, removed