SCons: Disable C++ exception handling

Upon investigating the extremely slow MSVC build times in #80513, I noticed
that while Godot policy is to never use exceptions, we weren't enforcing it
with compiler flags, and thus still included exception handling code and
stack unwinding.

This is wasteful on multiple aspects:

- Binary size: Around 20% binary size reduction with exceptions disabled
  for both MSVC and GCC binaries.
- Compile time:
  * More than 50% build time reduction with MSVC.
  * 10% to 25% build time reduction with GCC + LTO.
- Performance: Possibly, needs to be benchmarked.

Since users may want to re-enable exceptions in their own thirdparty code
or the libraries they compile with Godot, this behavior can be toggled with
the `disable_exceptions` SCons option, which defaults to true.

9 files changed, 31 insertions, 30 deletions

diff --git a/SConstruct b/SConstruct
index 6968967380..7ea056f839 100644
--- a/SConstruct
+++ b/SConstruct
@@ -193,6 +193,7 @@ opts.Add(BoolVariable("vulkan", "Enable the vulkan rendering driver", True))
 opts.Add(BoolVariable("opengl3", "Enable the OpenGL/GLES3 rendering driver", True))
 opts.Add(BoolVariable("openxr", "Enable the OpenXR driver", True))
 opts.Add(BoolVariable("use_volk", "Use the volk library to load the Vulkan loader dynamically", True))
+opts.Add(BoolVariable("disable_exceptions", "Force disabling exception handling code", True))
 opts.Add("custom_modules", "A list of comma-separated directory paths containing custom modules to build.", "")
 opts.Add(BoolVariable("custom_modules_recursive", "Detect custom modules recursively for each specified path.", True))
 
@@ -710,6 +711,16 @@ if selected_platform in platform_list:
             )
             Exit(255)
 
+    # Disable exception handling. Godot doesn't use exceptions anywhere, and this
+    # saves around 20% of binary size and very significant build time (GH-80513).
+    if env["disable_exceptions"]:
+        if env.msvc:
+            env.Append(CPPDEFINES=[("_HAS_EXCEPTIONS", 0)])
+        else:
+            env.Append(CCFLAGS=["-fno-exceptions"])
+    elif env.msvc:
+        env.Append(CCFLAGS=["/EHsc"])
+
     # Configure compiler warnings
     if env.msvc:  # MSVC
         if env["warnings"] == "no":
@@ -739,9 +750,6 @@ if selected_platform in platform_list:
                 ]
             )
 
-        # Set exception handling model to avoid warnings caused by Windows system headers.
-        env.Append(CCFLAGS=["/EHsc"])
-
         if env["werror"]:
             env.Append(CCFLAGS=["/WX"])
     else:  # GCC, Clang
diff --git a/modules/denoise/SCsub b/modules/denoise/SCsub
index 779ce165d2..967a511e1e 100644
--- a/modules/denoise/SCsub
+++ b/modules/denoise/SCsub
@@ -109,6 +109,15 @@ env_oidn.AppendUnique(CPPDEFINES=["NDEBUG"])  # No assert() even in debug builds
 
 env_thirdparty = env_oidn.Clone()
 env_thirdparty.disable_warnings()
+
+if env["disable_exceptions"]:
+    # OIDN hard-requires exceptions, so we re-enable them here.
+    if env.msvc and ("_HAS_EXCEPTIONS", 0) in env_thirdparty["CPPDEFINES"]:
+        env_thirdparty["CPPDEFINES"].remove(("_HAS_EXCEPTIONS", 0))
+        env_thirdparty.AppendUnique(CCFLAGS=["/EHsc"])
+    elif not env.msvc and "-fno-exceptions" in env_thirdparty["CCFLAGS"]:
+        env_thirdparty["CCFLAGS"].remove("-fno-exceptions")
+
 env_thirdparty.add_source_files(thirdparty_obj, thirdparty_sources)
 env.modules_sources += thirdparty_obj
 
diff --git a/modules/openxr/SCsub b/modules/openxr/SCsub
index f49dc390de..1bd10f1009 100644
--- a/modules/openxr/SCsub
+++ b/modules/openxr/SCsub
@@ -52,10 +52,11 @@ if env["builtin_openxr"]:
 
     env_thirdparty = env_openxr.Clone()
     env_thirdparty.disable_warnings()
+
     env_thirdparty.AppendUnique(CPPDEFINES=["DISABLE_STD_FILESYSTEM"])
+    if env["disable_exceptions"]:
+        env_thirdparty.AppendUnique(CPPDEFINES=["XRLOADER_DISABLE_EXCEPTION_HANDLING", ("JSON_USE_EXCEPTION", 0)])
 
-    if "-fno-exceptions" in env_thirdparty["CXXFLAGS"]:
-        env_thirdparty["CXXFLAGS"].remove("-fno-exceptions")
     env_thirdparty.Append(CPPPATH=[thirdparty_dir + "/src/loader"])
 
     # add in external jsoncpp dependency
diff --git a/platform/android/detect.py b/platform/android/detect.py
index 2860898e5c..33c6565789 100644
--- a/platform/android/detect.py
+++ b/platform/android/detect.py
@@ -170,10 +170,6 @@ def configure(env: "Environment"):
     env["RANLIB"] = compiler_path + "/llvm-ranlib"
     env["AS"] = compiler_path + "/clang"
 
-    # Disable exceptions on template builds
-    if not env.editor_build:
-        env.Append(CXXFLAGS=["-fno-exceptions"])
-
     env.Append(
         CCFLAGS=(
             "-fpic -ffunction-sections -funwind-tables -fstack-protector-strong -fvisibility=hidden -fno-strict-aliasing".split()
diff --git a/platform/ios/detect.py b/platform/ios/detect.py
index a01f4b55db..e11c0b7d91 100644
--- a/platform/ios/detect.py
+++ b/platform/ios/detect.py
@@ -30,7 +30,6 @@ def get_opts():
         ),
         ("IOS_SDK_PATH", "Path to the iOS SDK", ""),
         BoolVariable("ios_simulator", "Build for iOS Simulator", False),
-        BoolVariable("ios_exceptions", "Enable exceptions", False),
         ("ios_triple", "Triple for ios toolchain", ""),
     ]
 
@@ -138,11 +137,6 @@ def configure(env: "Environment"):
         env.Append(ASFLAGS=["-arch", "arm64"])
         env.Append(CPPDEFINES=["NEED_LONG_INT"])
 
-    if env["ios_exceptions"]:
-        env.Append(CCFLAGS=["-fexceptions"])
-    else:
-        env.Append(CCFLAGS=["-fno-exceptions"])
-
     # Temp fix for ABS/MAX/MIN macros in iOS SDK blocking compilation
     env.Append(CCFLAGS=["-Wno-ambiguous-macro"])
 
diff --git a/platform/web/detect.py b/platform/web/detect.py
index 2685cbcd63..dc8f4e0dd9 100644
--- a/platform/web/detect.py
+++ b/platform/web/detect.py
@@ -97,12 +97,9 @@ def configure(env: "Environment"):
     if env["use_assertions"]:
         env.Append(LINKFLAGS=["-s", "ASSERTIONS=1"])
 
-    if env.editor_build:
-        if env["initial_memory"] < 64:
-            print('Note: Forcing "initial_memory=64" as it is required for the web editor.')
-            env["initial_memory"] = 64
-    else:
-        env.Append(CPPFLAGS=["-fno-exceptions"])
+    if env.editor_build and env["initial_memory"] < 64:
+        print('Note: Forcing "initial_memory=64" as it is required for the web editor.')
+        env["initial_memory"] = 64
 
     env.Append(LINKFLAGS=["-s", "INITIAL_MEMORY=%sMB" % env["initial_memory"]])
 
diff --git a/tests/SCsub b/tests/SCsub
index c59ce69b92..d96a1142e4 100644
--- a/tests/SCsub
+++ b/tests/SCsub
@@ -13,10 +13,8 @@ env_tests = env.Clone()
 if env_tests["platform"] == "windows":
     env_tests.Append(CPPDEFINES=[("DOCTEST_THREAD_LOCAL", "")])
 
-# Increase number of addressable sections in object files
-# due to doctest's heavy use of templates and macros.
-if env_tests.msvc:
-    env_tests.Append(CCFLAGS=["/bigobj"])
+if env["disable_exceptions"]:
+    env_tests.Append(CPPDEFINES=["DOCTEST_CONFIG_NO_EXCEPTIONS_BUT_WITH_ALL_ASSERTS"])
 
 env_tests.add_source_files(env.tests_sources, "*.cpp")
 
diff --git a/tests/core/io/test_image.h b/tests/core/io/test_image.h
index 92ab166ae8..1897971113 100644
--- a/tests/core/io/test_image.h
+++ b/tests/core/io/test_image.h
@@ -262,9 +262,7 @@ TEST_CASE("[Image] Modifying pixels of an image") {
 
 		for (const Rect2i &rect : rects) {
 			Ref<Image> img = memnew(Image(img_width, img_height, false, Image::FORMAT_RGBA8));
-			CHECK_NOTHROW_MESSAGE(
-					img->fill_rect(rect, Color(1, 1, 1, 1)),
-					"fill_rect() shouldn't throw for any rect.");
+			img->fill_rect(rect, Color(1, 1, 1, 1));
 			for (int y = 0; y < img->get_height(); y++) {
 				for (int x = 0; x < img->get_width(); x++) {
 					if (rect.abs().has_point(Point2(x, y))) {
@@ -317,7 +315,7 @@ TEST_CASE("[Image] Modifying pixels of an image") {
 	// Pre-multiply Alpha then Convert from RGBA to L8, checking alpha
 	{
 		Ref<Image> gray_image = memnew(Image(3, 3, false, Image::FORMAT_RGBA8));
-		CHECK_NOTHROW_MESSAGE(gray_image->fill_rect(Rect2i(0, 0, 3, 3), Color(1, 1, 1, 0)), "fill_rect() shouldn't throw for any rect.");
+		gray_image->fill_rect(Rect2i(0, 0, 3, 3), Color(1, 1, 1, 0));
 		gray_image->set_pixel(1, 1, Color(1, 1, 1, 1));
 		gray_image->set_pixel(1, 2, Color(0.5, 0.5, 0.5, 0.5));
 		gray_image->set_pixel(2, 1, Color(0.25, 0.05, 0.5, 1.0));
diff --git a/tests/scene/test_viewport.h b/tests/scene/test_viewport.h
index ab17459a41..dd4786977e 100644
--- a/tests/scene/test_viewport.h
+++ b/tests/scene/test_viewport.h
@@ -226,7 +226,7 @@ TEST_CASE("[SceneTree][Viewport] Controls and InputEvent handling") {
 
 	SUBCASE("[Viewport][GuiInputEvent] nullptr as argument doesn't lead to a crash.") {
 		ERR_PRINT_OFF;
-		CHECK_NOTHROW(root->push_input(nullptr));
+		root->push_input(nullptr);
 		ERR_PRINT_ON;
 	}