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# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at
from __future__ import absolute_import, print_function, unicode_literals
from abc import (
import errno
import io
import itertools
import os
import six
import time
from contextlib import contextmanager
from mach.mixin.logging import LoggingMixin
import mozpack.path as mozpath
from ..preprocessor import Preprocessor
from ..pythonutil import iter_modules_in_path
from ..util import (
from import ContextDerived
from ..frontend.reader import EmptyConfig
from .configenvironment import ConfigEnvironment
from mozbuild.base import ExecutionSummary
class BuildBackend(LoggingMixin):
"""Abstract base class for build backends.
A build backend is merely a consumer of the build configuration (the output
of the frontend processing). It does something with said data. What exactly
is the discretion of the specific implementation.
__metaclass__ = ABCMeta
def __init__(self, environment):
assert isinstance(environment, (ConfigEnvironment, EmptyConfig))
self.environment = environment
# Files whose modification should cause a new read and backend
# generation.
self.backend_input_files = set()
# Files generated by the backend.
self._backend_output_files = set()
self._environments = {}
self._environments[environment.topobjdir] = environment
# The number of backend files created.
self._created_count = 0
# The number of backend files updated.
self._updated_count = 0
# The number of unchanged backend files.
self._unchanged_count = 0
# The number of deleted backend files.
self._deleted_count = 0
# The total wall time spent in the backend. This counts the time the
# backend writes out files, etc.
self._execution_time = 0.0
# Mapping of changed file paths to diffs of the changes.
self.file_diffs = {}
self.dry_run = False
def summary(self):
return ExecutionSummary(
self.__class__.__name__.replace("Backend", "")
+ " backend executed in {execution_time:.2f}s\n "
"{total:d} total backend files; "
"{created:d} created; "
"{updated:d} updated; "
"{unchanged:d} unchanged; "
"{deleted:d} deleted",
total=self._created_count + self._updated_count + self._unchanged_count,
def _init(self):
"""Hook point for child classes to perform actions during __init__.
This exists so child classes don't need to implement __init__.
def consume(self, objs):
"""Consume a stream of TreeMetadata instances.
This is the main method of the interface. This is what takes the
frontend output and does something with it.
Child classes are not expected to implement this method. Instead, the
base class consumes objects and calls methods (possibly) implemented by
child classes.
# Previously generated files.
list_file = mozpath.join(
self.environment.topobjdir, "backend.%s" % self.__class__.__name__
backend_output_list = set()
if os.path.exists(list_file):
with open(list_file) as fh:
mozpath.normsep(p) for p in
for obj in objs:
obj_start = time.time()
if not self.consume_object(obj) and not isinstance(self, PartialBackend):
raise Exception("Unhandled object of type %s" % type(obj))
self._execution_time += time.time() - obj_start
if isinstance(obj, ContextDerived) and not isinstance(self, PartialBackend):
self.backend_input_files |= obj.context_all_paths
# Pull in all loaded Python as dependencies so any Python changes that
# could influence our output result in a rescan.
self.backend_input_files |= set(
iter_modules_in_path(self.environment.topsrcdir, self.environment.topobjdir)
finished_start = time.time()
self._execution_time += time.time() - finished_start
# Purge backend files created in previous run, but not created anymore
delete_files = backend_output_list - self._backend_output_files
for path in delete_files:
full_path = mozpath.join(self.environment.topobjdir, path)
with, mode="r", encoding="utf-8") as existing:
old_content =
if old_content:
self.file_diffs[full_path] = simple_diff(
full_path, old_content.splitlines(), None
except IOError:
if not self.dry_run:
self._deleted_count += 1
except OSError:
# Remove now empty directories
for dir in set(mozpath.dirname(d) for d in delete_files):
except OSError:
# Write out the list of backend files generated, if it changed.
if backend_output_list != self._backend_output_files:
with self._write_file(list_file) as fh:
# Always update its mtime if we're not in dry-run mode.
if not self.dry_run:
with open(list_file, "a"):
os.utime(list_file, None)
# Write out the list of input files for the backend
with self._write_file("" % list_file) as fh:
"\n".join(sorted(mozpath.normsep(f) for f in self.backend_input_files))
def consume_object(self, obj):
"""Consumes an individual TreeMetadata instance.
This is the main method used by child classes to react to build
def consume_finished(self):
"""Called when consume() has completed handling all objects."""
def build(self, config, output, jobs, verbose, what=None):
"""Called when 'mach build' is executed.
This should return the status value of a subprocess, where 0 denotes
success and any other value is an error code. A return value of None
indicates that the default 'make -f' should run.
return None
def _write_purgecaches(self, config):
"""Write .purgecaches sentinels.
The purgecaches mechanism exists to allow the platform to
invalidate the XUL cache (which includes some JS) at application
startup-time. The application checks for .purgecaches in the
application directory, which varies according to
--enable-application. There's a further wrinkle on macOS, where
the real application directory is part of a Cocoa bundle
produced from the regular application directory by the build
system. In this case, we write to both locations, since the
build system recreates the Cocoa bundle from the contents of the
regular application directory and might remove a sentinel
created here.
app = config.substs["MOZ_BUILD_APP"]
if app == "mobile/android":
# In order to take effect, .purgecaches sentinels would need to be
# written to the Android device file system.
root = mozpath.join(config.topobjdir, "dist", "bin")
if app == "browser":
root = mozpath.join(config.topobjdir, "dist", "bin", "browser")
purgecaches_dirs = [root]
if app == "browser" and "cocoa" == config.substs["MOZ_WIDGET_TOOLKIT"]:
bundledir = mozpath.join(
for dir in purgecaches_dirs:
with open(mozpath.join(dir, ".purgecaches"), "wt") as f:
def post_build(self, config, output, jobs, verbose, status):
"""Called late during 'mach build' execution, after `build(...)` has finished.
`status` is the status value returned from `build(...)`.
In the case where `build` returns `None`, this is called after
the default `make` command has completed, with the status of
that command.
This should return the status value from `build(...)`, or the
status value of a subprocess, where 0 denotes success and any
other value is an error code.
If an exception is raised, |mach build| will fail with a
non-zero exit code.
return status
def _write_file(self, path=None, fh=None, readmode="rU"):
"""Context manager to write a file.
This is a glorified wrapper around FileAvoidWrite with integration to
update the summary data on this instance.
Example usage:
with self._write_file('foo.txt') as fh:
fh.write('hello world')
if path is not None:
assert fh is None
fh = FileAvoidWrite(
path, capture_diff=True, dry_run=self.dry_run, readmode=readmode
assert fh is not None
dirname = mozpath.dirname(
except OSError as error:
if error.errno != errno.EEXIST:
yield fh
mozpath.relpath(, self.environment.topobjdir)
existed, updated = fh.close()
if fh.diff:
self.file_diffs[] = fh.diff
if not existed:
self._created_count += 1
elif updated:
self._updated_count += 1
self._unchanged_count += 1
def _get_preprocessor(self, obj):
"""Returns a preprocessor with a few predefined values depending on
the given BaseConfigSubstitution(-like) object, and all the substs
in the current environment."""
pp = Preprocessor()
srcdir = mozpath.dirname(obj.input_path)
k: " ".join(v) if isinstance(v, list) else v
for k, v in six.iteritems(obj.config.substs)
srcdir_rel=mozpath.relpath(srcdir, mozpath.dirname(obj.output_path)),
relativesrcdir=mozpath.relpath(srcdir, obj.topsrcdir) or ".",
DEPTH=mozpath.relpath(obj.topobjdir, mozpath.dirname(obj.output_path))
or ".",
with self._write_file(obj.output_path) as fh:
pp.out = fh
yield pp
class PartialBackend(BuildBackend):
"""A PartialBackend is a BuildBackend declaring that its consume_object
method may not handle all build configuration objects it's passed, and
that it's fine."""
def HybridBackend(*backends):
"""A HybridBackend is the combination of one or more PartialBackends
with a non-partial BuildBackend.
Build configuration objects are passed to each backend, stopping at the
first of them that declares having handled them.
assert len(backends) >= 2
assert all(issubclass(b, PartialBackend) for b in backends[:-1])
assert not (issubclass(backends[-1], PartialBackend))
assert all(issubclass(b, BuildBackend) for b in backends)
class TheHybridBackend(BuildBackend):
def __init__(self, environment):
self._backends = [b(environment) for b in backends]
super(TheHybridBackend, self).__init__(environment)
def consume_object(self, obj):
return any(b.consume_object(obj) for b in self._backends)
def consume_finished(self):
for backend in self._backends:
for attr in (
setattr(self, attr, sum(getattr(b, attr) for b in self._backends))
for b in self._backends:
for attr in ("backend_input_files", "_backend_output_files"):
files = getattr(self, attr)
files |= getattr(b, attr)
name = "+".join(
(b.__name__.replace("Backend", "") for b in backends[:-1]),
(b.__name__ for b in backends[-1:]),
return type(str(name), (TheHybridBackend,), {})