Refactor SConstruct, and add scu_build option.

SConstruct

@@ -5,60 +5,64 @@ import sys
 from methods import print_error
 
 
+if not (os.path.isdir("godot-cpp") and os.listdir("godot-cpp")):
+    print_error("""godot-cpp is not available within this folder, as Git submodules haven"t been initialized.
+Run the following command to download godot-cpp:
+
+    git submodule update --init --recursive""")
+    sys.exit(1)
+
+
+# ============================= General Lib Info =============================
+
 libname = "EXTENSION-NAME"
 projectdir = "demo"
 
-localEnv = Environment(tools=["default"], PLATFORM="")
+gdextension_tool = Tool("gdextension")
+
+# ============================= Setup Options =============================
 
+# Load variables from custom.py, in case someone wants to store their own arguments.
+# See https://scons.org/doc/production/HTML/scons-user.html#app-tools // search custom.py
 customs = ["custom.py"]
 customs = [os.path.abspath(path) for path in customs]
-
 opts = Variables(customs, ARGUMENTS)
-opts.Update(localEnv)
 
-Help(opts.GenerateHelpText(localEnv))
+gdextension_tool.options(opts)
 
-env = localEnv.Clone()
+# Remove our custom options to avoid passing to godot-cpp; godot-cpp has its own check for unknown options.
+for opt in opts.options:
+    ARGUMENTS.pop(opt.key, None)
 
-submodule_initialized = False
-dir_name = 'godot-cpp'
-if os.path.isdir(dir_name):
-    if os.listdir(dir_name):
-        submodule_initialized = True
+# ============================= Setup godot-cpp =============================
 
-if not submodule_initialized:
-    print_error("""godot-cpp is not available within this folder, as Git submodules haven't been initialized.
-Run the following command to download godot-cpp:
+godot_cpp_env = SConscript("godot-cpp/SConstruct", {"customs": customs})
 
-    git submodule update --init --recursive""")
-    sys.exit(1)
+gdextension_env = godot_cpp_env.Clone()
+opts.Update(gdextension_env)
+Help(opts.GenerateHelpText(gdextension_env))
 
-env = SConscript("godot-cpp/SConstruct", {"env": env, "customs": customs})
+# ============================= Setup Targets =============================
 
-env.Append(CPPPATH=["src/"])
-sources = Glob("src/*.cpp")
+sources = []
+targets = []
 
-if env["target"] in ["editor", "template_debug"]:
-    try:
-        doc_data = env.GodotCPPDocData("src/gen/doc_data.gen.cpp", source=Glob("doc_classes/*.xml"))
-        sources.append(doc_data)
-    except AttributeError:
-        print("Not including class reference as we're targeting a pre-4.3 baseline.")
+gdextension_tool.generate(gdextension_env, godot_cpp_env, sources)
 
-file = "{}{}{}".format(libname, env["suffix"], env["SHLIBSUFFIX"])
+file = "{}{}{}".format(libname, godot_cpp_env["suffix"], godot_cpp_env["SHLIBSUFFIX"])
 filepath = ""
 
-if env["platform"] == "macos" or env["platform"] == "ios":
-    filepath = "{}.framework/".format(env["platform"])
-    file = "{}.{}.{}".format(libname, env["platform"], env["target"])
+if godot_cpp_env["platform"] == "macos" or godot_cpp_env["platform"] == "ios":
+    filepath = "{}.framework/".format(godot_cpp_env["platform"])
+    file = "{}.{}.{}".format(libname, godot_cpp_env["platform"], godot_cpp_env["target"])
 
-libraryfile = "bin/{}/{}{}".format(env["platform"], filepath, file)
-library = env.SharedLibrary(
+libraryfile = "bin/{}/{}{}".format(godot_cpp_env["platform"], filepath, file)
+library = gdextension_env.SharedLibrary(
     libraryfile,
     source=sources,
 )
+targets.append(library)
 
-copy = env.InstallAs("{}/bin/{}/{}lib{}".format(projectdir, env["platform"], filepath, file), library)
+targets.append(gdextension_env.Install("{}/bin/{}/{}".format(projectdir, godot_cpp_env["platform"], filepath), library))
 
-default_args = [library, copy]
-Default(*default_args)
+Default(targets)

site_scons/site_tools/gdextension.py

@@ -0,0 +1,40 @@
+import pathlib
+from SCons.Tool import Tool
+
+
+def exists(env):
+    return True
+
+def options(opts):
+    # Add custom options here
+    # opts.Add(
+    #     "custom_option",
+    #     "Custom option help text",
+    #     "default_value"
+    # )
+
+    scu_tool = Tool("scu")
+    scu_tool.options(opts)
+
+def generate(env, godot_cpp_env, sources):
+    scu_tool = Tool("scu")
+
+    # read custom options values
+    # custom_option = env["custom_option"]
+
+    env.Append(CPPPATH=["src/"])
+
+    sources.extend([
+        f for f in env.Glob("src/*.cpp") + env.Glob("src/**/*.cpp")
+        # Generated files will be added selectively and maintained by tools.
+        if not "/gen/" in str(f.path)
+    ])
+
+    scu_tool.generate(env, sources)
+
+    if godot_cpp_env["target"] in ["editor", "template_debug"]:
+        try:
+            doc_data = godot_cpp_env.GodotCPPDocData("src/gen/doc_data.gen.cpp", source=env.Glob("doc_classes/*.xml"))
+            sources.append(doc_data)
+        except AttributeError:
+            print("Not including class reference as we're targeting a pre-4.3 baseline.")

site_scons/site_tools/scu.py

@@ -0,0 +1,31 @@
+import pathlib
+from SCons.Variables import BoolVariable
+
+
+def exists(env):
+    return True
+
+def options(opts):
+    opts.Add(
+        BoolVariable(
+            "scu_build",
+            "Use single compilation unit build.",
+            False
+        )
+    )
+
+def generate(env, sources):
+    if not env.get('scu', False):
+        return
+
+    scu_path = pathlib.Path('src/gen/scu.cpp')
+    scu_path.parent.mkdir(exist_ok=True)
+
+    scu_path.write_text(
+        '\n'.join(
+            f'#include "{pathlib.Path(source.path).relative_to("src")}"'
+            for source in sources
+        ) + '\n'
+    )
+
+    sources[:] = [str(scu_path.absolute())]