Noissue - [emscripten] Always process source files in the same order to get reliable builds

compile

 #!/usr/bin/env python
 
 import argparse
 import os
 import subprocess
 import sys
 
 BASE_DIR = os.path.dirname(__file__)
 SOURCE_DIR = os.path.join(BASE_DIR, 'compiled')
 SOURCE_FILES = [
@@ skipping 50 matching lines @@
         subprocess.check_call([env['NODE_JS'], BINDINGS_GENERATOR],
                               stdout=file)
 
 
 def run_compiler(env, debug=False, tracing=False):
     params = [
         env['PYTHON'], os.path.join(env['EMSCRIPTEN'], 'emcc'),
         '-o', COMPILER_OUTPUT,
         '--post-js', BINDINGS_OUTPUT,
     ]
-    params.extend(SOURCE_FILES)
+    # Order matters. We sort source files so that we always get the same

[sergei, 2017/03/23 15:06:15]

It looks strange, what is the difference between different order of cpp files
and why is the alphabetical order correct?
If there is a different behavior then I would assume that there is some bug with
some global variables.

[Wladimir Palant, 2017/03/24 06:02:13]

There is no "correct" order but each order will produce a slightly different
result - presumably, this difference to cased by the optimizer. The point is
having reproducible builds (e.g. Mozilla would want to verify that the file
matches the source code in their reviews).

+    # results for the same source code.
+    params.extend(sorted(SOURCE_FILES))
     params.extend('-D' + flag for flag in DEFINES)
     for key, value in GENERATION_PARAMS.iteritems():
         params.extend(['-s', '{}={}'.format(key, str(value))])
     if debug:
         params.append('-g1')
     if tracing:
         params.append('--tracing')
     params.extend(ADDITIONAL_PARAMS)
     subprocess.check_call(params, env=env)
 
@@ skipping 16 matching lines @@
     parser.add_argument(
         '-t', '--tracing',
         action='store_true',
         help='Enable memory tracing'
     )
     args = parser.parse_args()
 
     env = getenv(args.emscripten_config)
     generate_bindings(env)
     run_compiler(env, debug=args.debug, tracing=args.tracing)