Switch to C++20 (#8657)

* Update doc about C++ version agreement.

* Update vscode setting.

* Update std version of external code.

* Update std version.

* Fix warnings about incrementing volatile variables.

* Fix warnings about lambda capture.

* Fix Windows build errors.

* Fix problem of mixing MetaString and MetaName in comparations.

Author: asfernandes

.vscode/c_cpp_properties.json

@@ -13,7 +13,7 @@
             ],
             "compilerPath": "/usr/bin/clang",
             "cStandard": "c17",
-            "cppStandard": "c++17",
+            "cppStandard": "c++20",
             "intelliSenseMode": "linux-clang-x64"
         }
     ],

CMakeLists.txt

@@ -205,14 +205,14 @@ if (MINGW)
     set(CMAKE_STATIC_LIBRARY_PREFIX)
 
     add_definitions(-D_WIN32_WINNT=0x0600)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse4 -std=c++17")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse4 -std=c++20")
 endif()
 
 if (UNIX)
     set(OS_DIR posix)
 
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fPIC")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC -msse4 -std=c++17")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC -msse4 -std=c++20")
 
     if (NOT CMAKE_CROSSCOMPILING)
         set(LIB_readline readline)

builds/docker/linux/arm32-arm64/Dockerfile

@@ -185,15 +185,15 @@ RUN cd ~/build && \
 	tar xvf icu4c-${ARG_ICU_VERSION}-src.tgz --strip 1 -C icu4c-${ARG_ICU_VERSION}-src && \
 	mkdir icu4c-${ARG_ICU_VERSION}-build-x86_64 && \
 	cd icu4c-${ARG_ICU_VERSION}-build-x86_64 && \
-	CXXFLAGS='-std=c++17 -static-libstdc++' ../icu4c-${ARG_ICU_VERSION}-src/source/runConfigureICU \
+	CXXFLAGS='-std=c++20 -static-libstdc++' ../icu4c-${ARG_ICU_VERSION}-src/source/runConfigureICU \
 		Linux \
 		--host=x86_64-pc-linux-gnu && \
 	make -j${ARG_CPUCOUNT}
 
 RUN cd ~/build && \
 	mkdir icu4c-${ARG_ICU_VERSION}-build && \
 	cd icu4c-${ARG_ICU_VERSION}-build && \
-	CXXFLAGS='-std=c++17 -static-libstdc++' ../icu4c-${ARG_ICU_VERSION}-src/source/runConfigureICU \
+	CXXFLAGS='-std=c++20 -static-libstdc++' ../icu4c-${ARG_ICU_VERSION}-src/source/runConfigureICU \
 		Linux \
 		--host=${ARG_TARGET_ARCH} \
 		--with-cross-build=/home/ctng/build/icu4c-${ARG_ICU_VERSION}-build-x86_64 \

builds/docker/linux/x86-x64/Dockerfile

@@ -183,7 +183,7 @@ RUN cd ~/build && \
 	tar xvf icu4c-${ARG_ICU_VERSION}-src.tgz --strip 1 -C icu4c-${ARG_ICU_VERSION}-src && \
 	mkdir icu4c-${ARG_ICU_VERSION}-build && \
 	cd icu4c-${ARG_ICU_VERSION}-build && \
-	CXXFLAGS='-std=c++17 -static-libstdc++' setarch $ARG_SET_ARCH ../icu4c-${ARG_ICU_VERSION}-src/source/runConfigureICU \
+	CXXFLAGS='-std=c++20 -static-libstdc++' setarch $ARG_SET_ARCH ../icu4c-${ARG_ICU_VERSION}-src/source/runConfigureICU \
 		Linux \
 		--host=${ARG_TARGET_ARCH} \
 		--prefix=/home/ctng/x-tools/${ARG_TARGET_ARCH}/${ARG_TARGET_ARCH}/sysroot/usr/local \

builds/posix/Makefile.in.plugins_examples

@@ -36,7 +36,7 @@ else
   DefaultTarget := Release
 endif
 
-CPPFLAGS += -std=c++17 -I$(FB_BUILD)/include
+CPPFLAGS += -std=c++20 -I$(FB_BUILD)/include
 
 include     $(ROOT)/gen/make.defaults
 

builds/posix/make.defaults

@@ -111,7 +111,7 @@ GLOB_OPTIONS:=
 #____________________________________________________________________________
 
 # Global c++ flags: firebird needs no RTTI, choose build standard and c++ specific warnings level
-PLUSPLUS_FLAGS:= -fno-rtti -std=c++17 -Werror=delete-incomplete -Werror=return-type
+PLUSPLUS_FLAGS:= -fno-rtti -std=c++20 -Werror=delete-incomplete -Werror=return-type
 
 # If this is defined then we use special rules useful for developers only
 IsDeveloper = @DEVEL_FLG@

builds/posix/prefix.freebsd_amd64

@@ -26,4 +26,4 @@ DEV_FLAGS=-ggdb -DFREEBSD -DAMD64 -pipe -MMD -p -fPIC -Wall -Wno-non-virtual-dto
 # This file must be compiled with SSE4.2 support
 %/CRC32C.o: CXXFLAGS += -msse4
 
-CXXFLAGS := $(CXXFLAGS) -std=c++17
+CXXFLAGS := $(CXXFLAGS) -std=c++20

builds/win32/msvc15/FirebirdCommon.props

@@ -23,7 +23,7 @@
       <WarningLevel>Level3</WarningLevel>
       <SuppressStartupBanner>true</SuppressStartupBanner>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
-      <LanguageStandard>stdcpp17</LanguageStandard>
+      <LanguageStandard>stdcpp20</LanguageStandard>
       <CompileAs>Default</CompileAs>
       <UseFullPaths>false</UseFullPaths>
       <MultiProcessorCompilation>true</MultiProcessorCompilation>

configure.ac

@@ -1078,7 +1078,7 @@ dnl if 64-bit mode, then archive tool, ar, needs -X64 option
 fi
 
 XE_SAVE_ENV()
-CXXFLAGS="$CXXFLAGS -std=c++17"
+CXXFLAGS="$CXXFLAGS -std=c++20"
 AC_CACHE_CHECK([whether the C++ compiler understands noexcept], [ac_cv_cxx_noexcept], [
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[int f(int x) noexcept { return x + 1; }]], [[]])],
 	[ac_cv_cxx_noexcept=yes], [ac_cv_cxx_noexcept=no])])

doc/README.modern_cpp.md

@@ -1,12 +1,10 @@
 # Modern C++ features
 
-It's allowed to use in Firebird internal code C++ features up to and including C++17.
+It's allowed to use in Firebird internal code C++ features up to and including C++20.
 
 Public files (as API headers) is limited to C++11.
 
 Exceptions to these rules should be listed below and must be agreed by the team,
 discussing in the devel list or by pull request.
 
-## Allowed features
-
-### C++20
+## Disallowed features