SCons: Fix handling of platform-specific tools, notably mingw

Add optional `detect.py` `get_tools` method to let platforms register SCons
tools they need.

This helps move this logic out of SConstruct, keeping platforms more self
contained, and helping thirdparty platforms define their own custom tools.

This logic was also unreliable (the `use_mingw` one would only work if
passed manually on the command line, not in e.g. `get_flags`).

Co-authored-by: Thaddeus Crews <repiteo@outlook.com>

SConstruct

@@ -107,22 +107,11 @@ for x in sorted(glob.glob("platform/*")):
     sys.path.remove(tmppath)
     sys.modules.pop("detect")
 
-custom_tools = ["default"]
-
-platform_arg = ARGUMENTS.get("platform", ARGUMENTS.get("p", False))
-
-if platform_arg == "android":
-    custom_tools = ["clang", "clang++", "as", "ar", "link"]
-elif platform_arg == "web":
-    # Use generic POSIX build toolchain for Emscripten.
-    custom_tools = ["cc", "c++", "ar", "link", "textfile", "zip"]
-elif os.name == "nt" and methods.get_cmdline_bool("use_mingw", False):
-    custom_tools = ["mingw"]
-
 # We let SCons build its default ENV as it includes OS-specific things which we don't
-# want to have to pull in manually.
+# want to have to pull in manually. However we enforce no "tools", which we register
+# further down after parsing our platform-specific configuration.
 # Then we prepend PATH to make it take precedence, while preserving SCons' own entries.
-env = Environment(tools=custom_tools)
+env = Environment(tools=[])
 env.PrependENVPath("PATH", os.getenv("PATH"))
 env.PrependENVPath("PKG_CONFIG_PATH", os.getenv("PKG_CONFIG_PATH"))
 if "TERM" in os.environ:  # Used for colored output.
@@ -168,11 +157,7 @@ if profile:
 opts = Variables(customs, ARGUMENTS)
 
 # Target build options
-if env.scons_version >= (4, 3):
-    opts.Add(["platform", "p"], "Target platform (%s)" % "|".join(platform_list), "")
-else:
-    opts.Add("platform", "Target platform (%s)" % "|".join(platform_list), "")
-    opts.Add("p", "Alias for 'platform'", "")
+opts.Add((["platform", "p"], "Target platform (%s)" % "|".join(platform_list), ""))
 opts.Add(EnumVariable("target", "Compilation target", "editor", ("editor", "template_release", "template_debug")))
 opts.Add(EnumVariable("arch", "CPU architecture", "auto", ["auto"] + architectures, architecture_aliases))
 opts.Add(BoolVariable("dev_build", "Developer build with dev-only debugging code (DEV_ENABLED)", False))
@@ -312,10 +297,7 @@ if env["import_env_vars"]:
 
 # Platform selection: validate input, and add options.
 
-if env.scons_version < (4, 3) and not env["platform"]:
-    env["platform"] = env["p"]
-
-if env["platform"] == "":
+if not env["platform"]:
     # Missing `platform` argument, try to detect platform automatically
     if (
         sys.platform.startswith("linux")
@@ -330,7 +312,7 @@ if env["platform"] == "":
     elif sys.platform == "win32":
         env["platform"] = "windows"
 
-    if env["platform"] != "":
+    if env["platform"]:
         print(f'Automatically detected platform: {env["platform"]}')
 
 # Deprecated aliases kept for compatibility.
@@ -352,7 +334,7 @@ if env["platform"] not in platform_list:
 
     if env["platform"] == "list":
         print(text)
-    elif env["platform"] == "":
+    elif not env["platform"]:
         print_error("Could not detect platform automatically.\n" + text)
     else:
         print_error(f'Invalid target platform "{env["platform"]}".\n' + text)
@@ -434,6 +416,23 @@ env.modules_detected = modules_detected
 opts.Update(env, {**ARGUMENTS, **env.Dictionary()})
 Help(opts.GenerateHelpText(env))
 
+
+# FIXME: Tool assignment happening at this stage is a direct consequence of getting the platform logic AFTER the SCons
+# environment was already been constructed. Fixing this would require a broader refactor where all options are setup
+# ahead of time with native validator/converter functions.
+tmppath = "./platform/" + env["platform"]
+sys.path.insert(0, tmppath)
+import detect
+
+custom_tools = ["default"]
+try:  # Platform custom tools are optional
+    custom_tools = detect.get_tools(env)
+except AttributeError:
+    pass
+for tool in custom_tools:
+    env.Tool(tool)
+
+
 # add default include paths
 
 env.Prepend(CPPPATH=["#"])
@@ -515,10 +514,6 @@ if not env["deprecated"]:
 if env["precision"] == "double":
     env.Append(CPPDEFINES=["REAL_T_IS_DOUBLE"])
 
-tmppath = "./platform/" + env["platform"]
-sys.path.insert(0, tmppath)
-import detect
-
 # Default num_jobs to local cpu count if not user specified.
 # SCons has a peculiarity where user-specified options won't be overridden
 # by SetOption, so we can rely on this to know if we should use our default.
@@ -587,7 +582,7 @@ if env["dev_mode"]:
 if env["production"]:
     env["use_static_cpp"] = methods.get_cmdline_bool("use_static_cpp", True)
     env["debug_symbols"] = methods.get_cmdline_bool("debug_symbols", False)
-    if platform_arg == "android":
+    if env["platform"] == "android":
         env["swappy"] = methods.get_cmdline_bool("swappy", True)
     # LTO "auto" means we handle the preferred option in each platform detect.py.
     env["lto"] = ARGUMENTS.get("lto", "auto")

platform/android/detect.py

@@ -19,6 +19,10 @@ def can_build():
     return os.path.exists(get_env_android_sdk_root())
 
 
+def get_tools(env: "SConsEnvironment"):
+    return ["clang", "clang++", "as", "ar", "link"]
+
+
 def get_opts():
     from SCons.Variables import BoolVariable
 

platform/web/detect.py

@@ -28,6 +28,11 @@ def can_build():
     return WhereIs("emcc") is not None
 
 
+def get_tools(env: "SConsEnvironment"):
+    # Use generic POSIX build toolchain for Emscripten.
+    return ["cc", "c++", "ar", "link", "textfile", "zip"]
+
+
 def get_opts():
     from SCons.Variables import BoolVariable
 

platform/windows/detect.py

@@ -155,6 +155,13 @@ def detect_build_env_arch():
     return ""
 
 
+def get_tools(env: "SConsEnvironment"):
+    if os.name != "nt" or env["use_mingw"]:
+        return ["mingw"]
+    else:
+        return ["default"]
+
+
 def get_opts():
     from SCons.Variables import BoolVariable, EnumVariable
 
@@ -326,10 +333,6 @@ def setup_mingw(env: "SConsEnvironment"):
         print_error("No valid compilers found, use MINGW_PREFIX environment variable to set MinGW path.")
         sys.exit(255)
 
-    env.Tool("mingw")
-    env.AppendUnique(CCFLAGS=env.get("ccflags", "").split())
-    env.AppendUnique(RCFLAGS=env.get("rcflags", "").split())
-
     print("Using MinGW, arch %s" % (env["arch"]))