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from contextlib import contextmanager
import os
import os.path
from sys import platform
from tempfile import NamedTemporaryFile, TemporaryFile
from webassets.filter import ExternalTool
__all__ = ('Elm')
def excursion(directory):
"""Context-manager that temporarily changes to a new working directory."""
old_dir = os.getcwd()
class Elm(ExternalTool):
"""Elm filter for webassets.
Requires the ``elm-make`` to be available from the system path.
Supports the following external configuration:
The path to the ``elm-make`` binary. If not set, assumes ``elm-make``
is in the system path.
If set the filter will switch to ``source_path`` directory prior to
name = 'elm'
options = {'binary': 'ELM_MAKE_BIN',
'change_directory': 'ELM_MAKE_CHANGE_DIRECTORY'}
max_debug_level = None
def input(self, _in, out, **kw):
Currently Elm does not write to stdout
(, so we need to write
the compiled contents to a temporary file and then read it in order to
output to stdout.
# create a temp file
tmp = NamedTemporaryFile(suffix='.js', delete=False)
tmp.close() # close it so windows can read it
# write to a temp file
elm_make = self.binary or 'elm-make'
change_directory = bool(self.change_directory or False)
source = kw['source_path']
source_dir = os.path.dirname(source)
exec_dir = source_dir if change_directory else os.getcwd()
write_args = [elm_make, source, '--output',, '--yes']
with excursion(exec_dir), TemporaryFile(mode='w') as fake_write_obj:
self.subprocess(write_args, fake_write_obj)
# read the temp file
cat_or_type = 'type' if platform == 'win32' else 'cat'
read_args = [cat_or_type,]
self.subprocess(read_args, out)