Core: Bump C++ Standard to C++20

Author: Repiteo

SConstruct

@@ -665,16 +665,16 @@ cc_version_metadata1 = cc_version["metadata1"]
 
 if cc_version_major == -1:
     print_warning(
-        "Couldn't detect compiler version, skipping version checks. "
-        "Build may fail if the compiler doesn't support C++17 fully."
+        "Couldn't detect compiler version, skipping version checks. Build may "
+        "fail if the compiler doesn't support C++20 fully."
     )
 elif methods.using_gcc(env):
-    if cc_version_major < 9:
+    if cc_version_major < 11:
         print_error(
-            "Detected GCC version older than 9, which does not fully support "
-            "C++17, or has bugs when compiling Godot. Supported versions are 9 "
-            "and later. Use a newer GCC version, or Clang 6 or later by passing "
-            '"use_llvm=yes" to the SCons command line.'
+            "Detected GCC version older than 11, which does not fully support "
+            "C++20. Supported versions are GCC 11 and later. Use a newer GCC "
+            'version, or Clang 13 or later by passing "use_llvm=yes" to the '
+            "SCons command line."
         )
         Exit(255)
     elif cc_version_metadata1 == "win32":
@@ -689,47 +689,31 @@ elif methods.using_clang(env):
     # Apple LLVM versions differ from upstream LLVM version \o/, compare
     # in https://en.wikipedia.org/wiki/Xcode#Toolchain_versions
     if methods.is_apple_clang(env):
-        if cc_version_major < 10:
+        if cc_version_major < 15:
             print_error(
-                "Detected Apple Clang version older than 10, which does not fully "
-                "support C++17. Supported versions are Apple Clang 10 and later."
+                "Detected Apple Clang version older than 15, which does not fully "
+                "support C++20. Supported versions are Apple Clang 15 and later."
             )
             Exit(255)
-        elif env["debug_paths_relative"] and cc_version_major < 12:
-            print_warning(
-                "Apple Clang < 12 doesn't support -ffile-prefix-map, disabling `debug_paths_relative` option."
-            )
-            env["debug_paths_relative"] = False
     else:
-        if cc_version_major < 6:
+        if cc_version_major < 13:
             print_error(
-                "Detected Clang version older than 6, which does not fully support "
-                "C++17. Supported versions are Clang 6 and later."
+                "Detected Clang version older than 13, which does not fully support "
+                "C++20. Supported versions are Clang 13 and later."
             )
             Exit(255)
-        elif env["debug_paths_relative"] and cc_version_major < 10:
-            print_warning("Clang < 10 doesn't support -ffile-prefix-map, disabling `debug_paths_relative` option.")
-            env["debug_paths_relative"] = False
 
 elif env.msvc:
-    # Ensure latest minor builds of Visual Studio 2017/2019.
-    # https://github.com/godotengine/godot/pull/94995#issuecomment-2336464574
-    if cc_version_major == 16 and cc_version_minor < 11:
-        print_error(
-            "Detected Visual Studio 2019 version older than 16.11, which has bugs "
-            "when compiling Godot. Use a newer VS2019 version, or VS2022."
-        )
-        Exit(255)
-    if cc_version_major == 15 and cc_version_minor < 9:
+    if cc_version_major < 16:
         print_error(
-            "Detected Visual Studio 2017 version older than 15.9, which has bugs "
-            "when compiling Godot. Use a newer VS2017 version, or VS2019/VS2022."
+            "Detected Visual Studio version older than 2019, which does not fully "
+            "support C++20. Supported versions are Visual Studio 2019 and later."
         )
         Exit(255)
-    if cc_version_major < 15:
+    elif cc_version_major == 16 and cc_version_minor < 11:
         print_error(
-            "Detected Visual Studio 2015 or earlier, which is unsupported in Godot. "
-            "Supported versions are Visual Studio 2017 and later."
+            "Detected Visual Studio 2019 version older than 16.11, which does not "
+            "fully support C++20. Use a newer VS2019 version, or VS2022."
         )
         Exit(255)
 
@@ -840,22 +824,17 @@ if env["lto"] != "none":
     print("Using LTO: " + env["lto"])
 
 # Set our C and C++ standard requirements.
-# C++17 is required as we need guaranteed copy elision as per GH-36436.
-# Prepending to make it possible to override.
 # This needs to come after `configure`, otherwise we don't have env.msvc.
 if not env.msvc:
     # Specifying GNU extensions support explicitly, which are supported by
-    # both GCC and Clang. Both currently default to gnu17 and gnu++17.
+    # both GCC and Clang. Both currently default to gnu17 and gnu++20.
     env.Prepend(CFLAGS=["-std=gnu17"])
-    env.Prepend(CXXFLAGS=["-std=gnu++17"])
+    env.Prepend(CXXFLAGS=["-std=gnu++20"])
 else:
     # MSVC started offering C standard support with Visual Studio 2019 16.8, which covers all
-    # of our supported VS2019 & VS2022 versions; VS2017 will only pass the C++ standard.
-    env.Prepend(CXXFLAGS=["/std:c++17"])
-    if cc_version_major < 16:
-        print_warning("Visual Studio 2017 cannot specify a C-Standard.")
-    else:
-        env.Prepend(CFLAGS=["/std:c17"])
+    # of our supported VS2019 & VS2022 versions.
+    env.Prepend(CFLAGS=["/std:c17"])
+    env.Prepend(CXXFLAGS=["/std:c++20"])
     # MSVC is non-conforming with the C++ standard by default, so we enable more conformance.
     # Note that this is still not complete conformance, as certain Windows-related headers
     # don't compile under complete conformance.
@@ -913,22 +892,15 @@ if env.msvc and not methods.using_clang(env):  # MSVC
 else:  # GCC, Clang
     common_warnings = []
     if methods.using_gcc(env):
-        common_warnings += ["-Wshadow", "-Wno-misleading-indentation"]
-        if cc_version_major < 11:
-            # Regression in GCC 9/10, spams so much in our variadic templates
-            # that we need to outright disable it.
-            common_warnings += ["-Wno-type-limits"]
+        common_warnings += ["-Wshadow", "-Wno-misleading-indentation", "-Wenum-conversion"]
         if cc_version_major == 12:
             # Regression in GCC 12, false positives in our error macros, see GH-58747.
             common_warnings += ["-Wno-return-type"]
-        if cc_version_major >= 11:
-            common_warnings += ["-Wenum-conversion"]
     elif methods.using_clang(env) or methods.using_emcc(env):
-        common_warnings += ["-Wshadow-field-in-constructor", "-Wshadow-uncaptured-local"]
+        common_warnings += ["-Wshadow-field-in-constructor", "-Wshadow-uncaptured-local", "-Wenum-conversion"]
         # We often implement `operator<` for structs of pointers as a requirement
         # for putting them in `Set` or `Map`. We don't mind about unreliable ordering.
         common_warnings += ["-Wno-ordered-compare-function-pointers"]
-        common_warnings += ["-Wenum-conversion"]
 
     # clang-cl will interpret `-Wall` as `-Weverything`, workaround with compatibility cast.
     env["WARNLEVEL"] = "-Wall" if not env.msvc else "-W3"
@@ -940,19 +912,14 @@ else:  # GCC, Clang
             env.AppendUnique(
                 CCFLAGS=[
                     "-Walloc-zero",
+                    "-Wattribute-alias=2",
                     "-Wduplicated-branches",
                     "-Wduplicated-cond",
+                    "-Wlogical-op",
                     "-Wstringop-overflow=4",
                 ]
             )
             env.AppendUnique(CXXFLAGS=["-Wplacement-new=1", "-Wvirtual-inheritance"])
-            # Need to fix a warning with AudioServer lambdas before enabling.
-            # if cc_version_major != 9:  # GCC 9 had a regression (GH-36325).
-            #    env.Append(CXXFLAGS=["-Wnoexcept"])
-            if cc_version_major >= 9:
-                env.AppendUnique(CCFLAGS=["-Wattribute-alias=2"])
-            if cc_version_major >= 11:  # Broke on MethodBind templates before GCC 11.
-                env.AppendUnique(CCFLAGS=["-Wlogical-op"])
         elif methods.using_clang(env) or methods.using_emcc(env):
             env.AppendUnique(CCFLAGS=["-Wimplicit-fallthrough"])
     elif env["warnings"] == "all":
@@ -968,8 +935,6 @@ else:  # GCC, Clang
 # Configure external includes.
 if env.msvc:
     if not methods.using_clang(env):
-        if cc_version_major < 16 or (cc_version_major == 16 and cc_version_minor < 10):
-            env.AppendUnique(CCFLAGS=["/experimental:external"])
         env.AppendUnique(CCFLAGS=["/external:anglebrackets"])
     env.AppendUnique(CCFLAGS=["/external:W0"])
     env["EXTINCPREFIX"] = "/external:I"

core/os/spin_lock.h

@@ -93,7 +93,7 @@ static_assert(std::atomic_bool::is_always_lock_free);
 
 class SpinLock {
 	union {
-		mutable std::atomic<bool> locked = ATOMIC_VAR_INIT(false);
+		mutable std::atomic<bool> locked = false;
 		char aligner[Thread::CACHE_LINE_BYTES];
 	};
 

core/typedefs.h

@@ -36,9 +36,9 @@
 
 // IWYU pragma: always_keep
 
-// Ensure that C++ standard is at least C++17.
+// Ensure that C++ standard is at least C++20.
 // If on MSVC, also ensures that the `Zc:__cplusplus` flag is present.
-static_assert(__cplusplus >= 201703L, "Minimum of C++17 required.");
+static_assert(__cplusplus >= 202002L, "Minimum of C++20 required.");
 
 // IWYU pragma: begin_exports
 

drivers/metal/SCsub

@@ -33,11 +33,6 @@ env_thirdparty.disable_warnings()
 env_thirdparty.add_source_files(thirdparty_obj, thirdparty_sources)
 env_metal.drivers_sources += thirdparty_obj
 
-# Enable C++20 for the Objective-C++ Metal code, which uses C++20 concepts.
-if "-std=gnu++17" in env_metal["CXXFLAGS"]:
-    env_metal["CXXFLAGS"].remove("-std=gnu++17")
-env_metal.Append(CXXFLAGS=["-std=gnu++20"])
-
 # Enable module support
 env_metal.Append(CCFLAGS=["-fmodules", "-fcxx-modules"])
 

modules/mono/mono_gc_handle.h

@@ -48,7 +48,11 @@ struct GCHandleIntPtr {
 	_FORCE_INLINE_ bool operator==(const GCHandleIntPtr &p_other) { return value == p_other.value; }
 	_FORCE_INLINE_ bool operator!=(const GCHandleIntPtr &p_other) { return value != p_other.value; }
 
+	// FIXME: C++20 doesn't allow aggregate initializers to bypass deleted constructors.
+	// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1008r1.pdf
+#if 0
 	GCHandleIntPtr() = delete;
+#endif
 };
 }
 

thirdparty/README.md

@@ -1043,6 +1043,7 @@ Patches:
 
 - `0001-revert-tvglines-bezier-precision.patch` (GH-96658)
 - `0002-use-heap-alloc.patch` (GH-109530)
+- `0003-cpp20-explicit-namespace.patch` (GH-100749)
 
 
 ## tinyexr

thirdparty/thorvg/patches/0003-cpp20-explicit-namespace.patch

@@ -0,0 +1,24 @@
+diff --git a/thirdparty/thorvg/src/loaders/svg/tvgSvgSceneBuilder.cpp b/thirdparty/thorvg/src/loaders/svg/tvgSvgSceneBuilder.cpp
+index 175739250a..5c2b36d394 100644
+--- a/thirdparty/thorvg/src/loaders/svg/tvgSvgSceneBuilder.cpp
++++ b/thirdparty/thorvg/src/loaders/svg/tvgSvgSceneBuilder.cpp
+@@ -218 +218 @@ static bool _appendClipUseNode(SvgLoaderData& loaderData, SvgNode* node, Shape*
+-    return _appendClipShape(loaderData, child, shape, vBox, svgPath, identity((const Matrix*)(&finalTransform)) ? nullptr : &finalTransform);
++    return _appendClipShape(loaderData, child, shape, vBox, svgPath, tvg::identity((const Matrix*)(&finalTransform)) ? nullptr : &finalTransform);
+diff --git a/thirdparty/thorvg/src/renderer/sw_engine/tvgSwFill.cpp b/thirdparty/thorvg/src/renderer/sw_engine/tvgSwFill.cpp
+index e012465b70..380e547dcf 100644
+--- a/thirdparty/thorvg/src/renderer/sw_engine/tvgSwFill.cpp
++++ b/thirdparty/thorvg/src/renderer/sw_engine/tvgSwFill.cpp
+@@ -231 +231 @@ bool _prepareLinear(SwFill* fill, const LinearGradient* linear, const Matrix& tr
+-    bool isTransformation = !identity((const Matrix*)(&gradTransform));
++    bool isTransformation = !tvg::identity((const Matrix*)(&gradTransform));
+@@ -298 +298 @@ bool _prepareRadial(SwFill* fill, const RadialGradient* radial, const Matrix& tr
+-    bool isTransformation = !identity((const Matrix*)(&gradTransform));
++    bool isTransformation = !tvg::identity((const Matrix*)(&gradTransform));
+diff --git a/thirdparty/thorvg/src/renderer/tvgPaint.cpp b/thirdparty/thorvg/src/renderer/tvgPaint.cpp
+index e00c2c1954..873e65527b 100644
+--- a/thirdparty/thorvg/src/renderer/tvgPaint.cpp
++++ b/thirdparty/thorvg/src/renderer/tvgPaint.cpp
+@@ -316 +316 @@ bool Paint::Impl::bounds(float* x, float* y, float* w, float* h, bool transforme
+-    if (!transformed || identity(&m)) {
++    if (!transformed || tvg::identity(&m)) {

thirdparty/thorvg/src/loaders/svg/tvgSvgSceneBuilder.cpp

@@ -215,7 +215,7 @@ static bool _appendClipUseNode(SvgLoaderData& loaderData, SvgNode* node, Shape*
     }
     if (child->transform) finalTransform *= *child->transform;
 
-    return _appendClipShape(loaderData, child, shape, vBox, svgPath, identity((const Matrix*)(&finalTransform)) ? nullptr : &finalTransform);
+    return _appendClipShape(loaderData, child, shape, vBox, svgPath, tvg::identity((const Matrix*)(&finalTransform)) ? nullptr : &finalTransform);
 }
 
 

thirdparty/thorvg/src/renderer/sw_engine/tvgSwFill.cpp

@@ -228,7 +228,7 @@ bool _prepareLinear(SwFill* fill, const LinearGradient* linear, const Matrix& tr
     fill->linear.offset = -fill->linear.dx * x1 - fill->linear.dy * y1;
 
     auto gradTransform = linear->transform();
-    bool isTransformation = !identity((const Matrix*)(&gradTransform));
+    bool isTransformation = !tvg::identity((const Matrix*)(&gradTransform));
 
     if (isTransformation) {
         gradTransform = transform * gradTransform;
@@ -295,7 +295,7 @@ bool _prepareRadial(SwFill* fill, const RadialGradient* radial, const Matrix& tr
     if (fill->radial.a > 0) fill->radial.invA = 1.0f / fill->radial.a;
 
     auto gradTransform = radial->transform();
-    bool isTransformation = !identity((const Matrix*)(&gradTransform));
+    bool isTransformation = !tvg::identity((const Matrix*)(&gradTransform));
 
     if (isTransformation) gradTransform = transform * gradTransform;
     else {

thirdparty/thorvg/src/renderer/tvgPaint.cpp

@@ -316,7 +316,7 @@ bool Paint::Impl::bounds(float* x, float* y, float* w, float* h, bool transforme
     const auto& m = this->transform(origin);
 
     //Case: No transformed, quick return!
-    if (!transformed || identity(&m)) {
+    if (!transformed || tvg::identity(&m)) {
         PAINT_METHOD(ret, bounds(x, y, w, h, stroking));
         return ret;
     }