Cleanup scons support and remove config file parsing (emscripten-core…

…#7249)

This change is precursor to removing EMSCRIPTEN_ROOT from
the emscripten config file. Now scons requires EMSCRIPTEN_ROOT
to be set explicitly in the environment.

The rational for this change is that having the EMSCRIPTEN_ROOT
set in the config can leave is in a contradictory state.  e.g.
when emcc runs from location X but the config file says EMSCRIPTEN_ROOT
is location Y.  In most cases it is the tool entry point that dictates
the root directory.

The only exception was scons which was trying to imply the root
based on the config.

Also importantly this change removes the `exec` of the config file from
scons which should allow is to be more strict in how we parse and
evaluate the config file in `tools/shared.py` since it will hopefully
soon be the only consumer.

.flake8

@@ -4,6 +4,7 @@ ignore = E111,E114,E501,E261,E266,E121,E402,E241
 # exclude = ./third_party/,emmaken.py,./tools/scons/,./tools/ports/,./tests/
 filename =
   */emcc.py
+  */emscons.py
   */emscripten.py
   */tools/shared.py
   */tools/response_file.py

emscons

@@ -1,20 +1,11 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python
 
-'''
-Wrapping the scons invocation, EMSCRIPTEN_TOOL_PATH is set in the process
-environment, and can be used to locate the emscripten SCons Tool.
-Example:
-# Load emscripten Tool
-my_env = Environment(tools=['emscripten'], toolpath=[os.environ['EMSCRIPTEN_TOOL_PATH']])
-'''
+# This script should work in python 2 *or* 3. It loads the main code using
+# python_selector, which may pick a different version.
 
-import os, subprocess, sys
-from tools import shared
+from tools import python_selector
 
-tool_path = os.path.join(shared.path_from_root('tools'), 'scons', 'site_scons', 'site_tools', 'emscripten')
-
-env = os.environ.copy()
-env[ 'EMSCRIPTEN_TOOL_PATH' ] = tool_path
-
-exit(subprocess.call(sys.argv[1:], env=env))
+import sys
 
+if __name__ == '__main__':
+  python_selector.run(__file__)

emscons.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python2
+"""Wrapping the scons invocation, EMSCRIPTEN_TOOL_PATH is set in the process
+environment, and can be used to locate the emscripten SCons Tool.
+
+Example:
+
+# Load emscripten Tool
+my_env = Environment(tools=['emscripten'], toolpath=[os.environ['EMSCRIPTEN_TOOL_PATH']])
+"""
+
+import os
+import subprocess
+import sys
+from tools import shared
+
+tool_path = os.path.join(shared.path_from_root('tools'), 'scons', 'site_scons', 'site_tools', 'emscripten')
+
+env = os.environ.copy()
+env['EMSCRIPTEN_TOOL_PATH'] = tool_path
+
+sys.exit(subprocess.call(sys.argv[1:], env=env))

tests/runner.py

@@ -144,6 +144,16 @@ def env_modify(updates):
     os.environ.update(old_env)
 
 
+# Decorator version of env_modify
+def with_env_modify(updates):
+  def decorated(f):
+    def modified(self):
+      with env_modify(updates):
+        return f(self)
+    return modified
+  return decorated
+
+
 @contextlib.contextmanager
 def chdir(dir):
   """A context manager that performs actions in the given directory."""

tests/scons/SConstruct

@@ -1,5 +1,5 @@
-env = Environment()
+import os
+env = Environment(toolpath=[os.environ.get('EMSCRIPTEN_TOOL_PATH')])
 env.Tool('emscripten')
 env.Append(CXXFLAGS='-std=c++11')
 env.Program('scons_integration', ['integration.cpp', 'other.c'])
-

tests/test_other.py

@@ -27,13 +27,15 @@
 from tools.shared import EMCC, EMXX, EMAR, EMRANLIB, PYTHON, FILE_PACKAGER, WINDOWS, MACOS, LLVM_ROOT, EMCONFIG, TEMP_DIR, EM_BUILD_VERBOSE
 from tools.shared import CLANG, CLANG_CC, CLANG_CPP, LLVM_AR
 from tools.shared import COMPILER_ENGINE, NODE_JS, SPIDERMONKEY_ENGINE, JS_ENGINES, V8_ENGINE
-from runner import RunnerCore, path_from_root, get_zlib_library, no_wasm_backend, needs_dlfcn, env_modify, no_windows
+from runner import RunnerCore, path_from_root, get_zlib_library, no_wasm_backend, needs_dlfcn, env_modify, no_windows, chdir, with_env_modify
 from tools import jsrun, shared
 import tools.line_endings
 import tools.js_optimizer
 import tools.tempfiles
 import tools.duplicate_function_eliminator
 
+scons_path = Building.which('scons')
+
 
 class temp_directory(object):
   def __enter__(self):
@@ -2260,17 +2262,28 @@ def test_debuginfo(self):
           else:
             self.assertIn('strip-debug', opts)
 
-  def test_scons(self): # also incidentally tests c++11 integration in llvm 3.1
-    scons_path = Building.which('scons')
-    if not scons_path:
-      self.skipTest('Skipping other.test_scons: The tool "scons" was not found in PATH!')
-    try_delete(os.path.join(self.get_dir(), 'test'))
-    shutil.copytree(path_from_root('tests', 'scons'), os.path.join(self.get_dir(), 'test'))
-    shutil.copytree(path_from_root('tools', 'scons', 'site_scons'), os.path.join(self.get_dir(), 'test', 'site_scons'))
-    os.chdir(os.path.join(self.get_dir(), 'test'))
-    run_process(['scons'])
-    output = run_js('scons_integration.js', assert_returncode=5)
-    assert 'If you see this - the world is all right!' in output
+  @unittest.skipIf(not scons_path, 'scons not found in PATH')
+  @with_env_modify({'EMSCRIPTEN_ROOT': path_from_root()})
+  def test_scons(self):
+    # this test copies the site_scons directory alongside the test
+    shutil.copytree(path_from_root('tests', 'scons'), 'test')
+    shutil.copytree(path_from_root('tools', 'scons', 'site_scons'), os.path.join('test', 'site_scons'))
+    with chdir('test'):
+      run_process(['scons'])
+      output = run_js('scons_integration.js', assert_returncode=5)
+    self.assertContained('If you see this - the world is all right!', output)
+
+  @unittest.skipIf(not scons_path, 'scons not found in PATH')
+  @with_env_modify({'EMSCRIPTEN_TOOLPATH': path_from_root('tools', 'scons', 'site_scons'),
+                    'EMSCRIPTEN_ROOT': path_from_root()})
+  def test_emscons(self):
+    # uses the emscons wrapper which requires EMSCRIPTEN_TOOLPATH to find
+    # site_scons
+    shutil.copytree(path_from_root('tests', 'scons'), 'test')
+    with chdir('test'):
+      run_process([path_from_root('emscons'), 'scons'])
+      output = run_js('scons_integration.js', assert_returncode=5)
+    self.assertContained('If you see this - the world is all right!', output)
 
   def test_embind(self):
     environ = os.environ.copy()

tools/scons/site_scons/site_tools/emscripten/emscripten.py

@@ -6,41 +6,25 @@
 
 from __future__ import print_function
 import os
-import sys
 
 
 def generate(env, emscripten_path=None, **kw):
   """ SCons tool entry point """
 
-  # Try to find emscripten
-  # Use same method as Emscripten's shared.py
-  EM_CONFIG = os.environ.get('EM_CONFIG')
-  if not EM_CONFIG:
-    EM_CONFIG = os.path.expanduser('~/.emscripten')
-
   if emscripten_path is None:
-
-    CONFIG_FILE = os.path.expanduser(EM_CONFIG)
-    try:
-      exec(open(CONFIG_FILE, 'r').read())
-    except Exception, e:
-      print('Error in evaluating %s (at %s): %s' % (EM_CONFIG, CONFIG_FILE, str(e)), file=sys.stderr)
-      sys.exit(1)
-
-    emscripten_path = EMSCRIPTEN_ROOT # noqa
-
-  env['EMSCRIPTEN_ROOT'] = emscripten_path
+    emscripten_path = os.environ.get('EMSCRIPTEN_ROOT')
+    if not emscripten_path:
+      raise 'Unable to find emscripten. Please set EMSCRIPTEN_ROOT'
 
   # SCons does not by default invoke the compiler with the
   # environment variabls from the parent calling process,
   # so manually route all environment variables referenced
   # by Emscripten to the child.
-  env['ENV']['EM_CONFIG'] = EM_CONFIG
   for var in ['EM_CACHE', 'EMCC_DEBUG', 'EMSCRIPTEN_NATIVE_OPTIMIZER', 'EMTEST_BROWSER',
               'EMMAKEN_JUST_CONFIGURE', 'EMCC_CFLAGS', 'EMCC_LEAVE_INPUTS_RAW', 'EMCC_TEMP_DIR',
               'EMCC_AUTODEBUG', 'EMMAKEN_JUST_CONFIGURE_RECURSE', 'EMCONFIGURE_JS', 'CONFIGURE_CC',
               'EMMAKEN_COMPILER', 'EMMAKEN_CFLAGS', 'EMCC_FAST_COMPILER', 'EMCC_JSOPT_BLACKLIST',
-              'MOZ_DISABLE_AUTO_SAFE_MODE', 'EMSCRIPTEN_TOOL_PATH', 'EMCC_STDERR_FILE',
+              'MOZ_DISABLE_AUTO_SAFE_MODE', 'EMCC_STDERR_FILE',
               'EMSCRIPTEN_SUPPRESS_USAGE_WARNING', 'EM_SAVE_DIR', 'NODE_PATH', 'EMCC_JSOPT_MIN_CHUNK_SIZE',
               'EMCC_JSOPT_MAX_CHUNK_SIZE', 'EMCC_SAVE_OPT_TEMP', 'EMCC_CORES', 'EMCC_NO_OPT_SORT',
               'EMCC_BUILD_DIR', 'EM_POPEN_WORKAROUND', 'EMCC_DEBUG_SAVE', 'EMCC_SKIP_SANITY_CHECK',