Fix and improve the build system

- Fix automatic architecture detection
- Fix compiling with MinGW on Linux
  - MinGW on Windows is still not working though
- Default to Clang on macOS
- Remove redundant `use_custom_api_file` option
- Format SConstruct using Flake8

This closes #245.

SConstruct

@@ -1,6 +1,7 @@
-#!python
+#!/usr/bin/env python
 
-import os, subprocess, platform, sys
+import os
+import sys
 
 
 def add_sources(sources, dir, extension):
@@ -8,7 +9,8 @@ def add_sources(sources, dir, extension):
         if f.endswith('.' + extension):
             sources.append(dir + '/' + f)
 
-# Try to detect the host platform automatically
+
+# Try to detect the host platform automatically.
 # This is used if no `platform` argument is passed
 if sys.platform.startswith('linux'):
     host_platform = 'linux'
@@ -17,50 +19,86 @@ elif sys.platform == 'darwin':
 elif sys.platform == 'win32':
     host_platform = 'windows'
 else:
-    raise ValueError('Could not detect platform automatically, please specify with platform=<platform>')
+    raise ValueError(
+        'Could not detect platform automatically, please specify with '
+        'platform=<platform>'
+    )
 
 opts = Variables([], ARGUMENTS)
-
+opts.Add(EnumVariable(
-opts.Add(EnumVariable('platform', 'Target platform', host_platform,
+    'platform',
+    'Target platform',
+    host_platform,
     allowed_values=('linux', 'osx', 'windows'),
-                    ignorecase=2))
+    ignorecase=2
-opts.Add(EnumVariable('bits', 'Target platform bits', 'default', ('default', '32', '64')))
+))
-opts.Add(BoolVariable('use_llvm', 'Use the LLVM compiler - only effective when targeting Linux', False))
+opts.Add(EnumVariable(
-opts.Add(BoolVariable('use_mingw', 'Use the MinGW compiler - only effective on Windows', False))
+    'bits',
+    'Target platform bits',
+    'default',
+    ('default', '32', '64')
+))
+opts.Add(BoolVariable(
+    'use_llvm',
+    'Use the LLVM compiler - only effective when targeting Linux',
+    False
+))
+opts.Add(BoolVariable(
+    'use_mingw',
+    'Use the MinGW compiler instead of MSVC - only effective on Windows',
+    False
+))
 # Must be the same setting as used for cpp_bindings
-opts.Add(EnumVariable('target', 'Compilation target', 'debug',
+opts.Add(EnumVariable(
+    'target',
+    'Compilation target',
+    'debug',
     allowed_values=('debug', 'release'),
-                    ignorecase=2))
+    ignorecase=2
-opts.Add(PathVariable('headers_dir', 'Path to the directory containing Godot headers', 'godot_headers', PathVariable.PathIsDir))
+))
-opts.Add(BoolVariable('use_custom_api_file', 'Use a custom JSON API file', False))
+opts.Add(PathVariable(
-opts.Add(PathVariable('custom_api_file', 'Path to the custom JSON API file', None, PathVariable.PathIsFile))
+    'headers_dir',
-opts.Add(BoolVariable('generate_bindings', 'Generate GDNative API bindings', False))
+    'Path to the directory containing Godot headers',
-
+    'godot_headers',
-unknown = opts.UnknownVariables()
+    PathVariable.PathIsDir
-if unknown:
+))
-    print("Unknown variables:" + unknown.keys())
+opts.Add(PathVariable(
-    Exit(1)
+    'custom_api_file',
+    'Path to a custom JSON API file',
+    None,
+    PathVariable.PathIsFile
+))
+opts.Add(BoolVariable(
+    'generate_bindings',
+    'Generate GDNative API bindings',
+    False
+))
 
 env = Environment()
 opts.Update(env)
 Help(opts.GenerateHelpText(env))
 
-# This makes sure to keep the session environment variables on Windows
+is64 = sys.maxsize > 2**32
-# This way, you can run SCons in a Visual Studio 2017 prompt and it will find all the required tools
+if (
-if env['platform'] == 'windows':
+    env['TARGET_ARCH'] == 'amd64' or
+    env['TARGET_ARCH'] == 'emt64' or
+    env['TARGET_ARCH'] == 'x86_64'
+):
+    is64 = True
+
+if env['bits'] == 'default':
+    env['bits'] = '64' if is64 else '32'
+
+# This makes sure to keep the session environment variables on Windows.
+# This way, you can run SCons in a Visual Studio 2017 prompt and it will find
+# all the required tools
+if host_platform == 'windows':
     if env['bits'] == '64':
         env = Environment(TARGET_ARCH='amd64')
     elif env['bits'] == '32':
         env = Environment(TARGET_ARCH='x86')
-    else:
-        print("Warning: bits argument not specified, target arch is=" + env['TARGET_ARCH'])
-    opts.Update(env)
 
-is64 = False
+    opts.Update(env)
-if (env['platform'] == 'osx' or env['TARGET_ARCH'] == 'amd64' or env['TARGET_ARCH'] == 'emt64' or env['TARGET_ARCH'] == 'x86_64'):
-    is64 = True
-if env['bits'] == 'default':
-    env['bits'] = '64' if is64 else '32'
 
 if env['platform'] == 'linux':
     if env['use_llvm']:
@@ -82,11 +120,22 @@ if env['platform'] == 'linux':
         env.Append(LINKFLAGS=['-m32'])
 
 elif env['platform'] == 'osx':
+    # Use Clang on macOS by default
+    env['CXX'] = 'clang++'
+
     if env['bits'] == '32':
-        raise ValueError('Only 64-bit builds are supported for the macOS target.')
+        raise ValueError(
+            'Only 64-bit builds are supported for the macOS target.'
+        )
 
     env.Append(CCFLAGS=['-g', '-std=c++14', '-arch', 'x86_64'])
-    env.Append(LINKFLAGS=['-arch', 'x86_64', '-framework', 'Cocoa', '-Wl,-undefined,dynamic_lookup'])
+    env.Append(LINKFLAGS=[
+        '-arch',
+        'x86_64',
+        '-framework',
+        'Cocoa',
+        '-Wl,-undefined,dynamic_lookup',
+    ])
 
     if env['target'] == 'debug':
         env.Append(CCFLAGS=['-Og'])
@@ -101,40 +150,56 @@ elif env['platform'] == 'windows':
             env.Append(CCFLAGS=['/EHsc', '/D_DEBUG', '/MDd'])
         elif env['target'] == 'release':
             env.Append(CCFLAGS=['/O2', '/EHsc', '/DNDEBUG', '/MD'])
-    else:
+
-        # MinGW
+    elif host_platform == 'linux':
+        # Cross-compilation using MinGW
         if env['bits'] == '64':
             env['CXX'] = 'x86_64-w64-mingw32-g++'
         elif env['bits'] == '32':
             env['CXX'] = 'i686-w64-mingw32-g++'
 
+    # Native or cross-compilation using MinGW
+    if host_platform == 'linux' or env['use_mingw']:
         env.Append(CCFLAGS=['-g', '-O3', '-std=c++14', '-Wwrite-strings'])
-        env.Append(LINKFLAGS=['--static', '-Wl,--no-undefined', '-static-libgcc', '-static-libstdc++'])
+        env.Append(LINKFLAGS=[
+            '--static',
+            '-Wl,--no-undefined',
+            '-static-libgcc',
+            '-static-libstdc++',
+        ])
 
-
+env.Append(CPPPATH=[
-env.Append(CPPPATH=['.', env['headers_dir'], 'include', 'include/gen', 'include/core'])
+    '.',
+    env['headers_dir'],
+    'include',
+    'include/gen',
+    'include/core',
+])
 
 # Generate bindings?
 json_api_file = ''
 
-if env['use_custom_api_file']:
+if 'custom_api_file' in env:
     json_api_file = env['custom_api_file']
 else:
     json_api_file = os.path.join(os.getcwd(), 'godot_headers', 'api.json')
 
 if env['generate_bindings']:
     # Actually create the bindings here
-
     import binding_generator
 
     binding_generator.generate_bindings(json_api_file)
 
-# source to compile
+# Sources to compile
 sources = []
 add_sources(sources, 'src/core', 'cpp')
 add_sources(sources, 'src/gen', 'cpp')
 
 library = env.StaticLibrary(
-    target='bin/' + 'libgodot-cpp.{}.{}.{}'.format(env['platform'], env['target'], env['bits']), source=sources
+    target='bin/' + 'libgodot-cpp.{}.{}.{}'.format(
+        env['platform'],
+        env['target'],
+        env['bits'],
+    ), source=sources
 )
 Default(library)

binding_generator.py

@@ -1,4 +1,4 @@
-#!python
+#!/usr/bin/env python
 
 import json