treewide: Enforce C17 as the minimum required C standard

C99 has been the minimum required C standard version for Zephyr since
its inception. After multiple attempts and discussions, a decision has
been made to upgrade to C17 going forward.
This commits replaces the default C standard from C99 to C17 in the
configuration and build system.

Signed-off-by: Carles Cufi <[email protected]>

Author: carlescufi

CMakeLists.txt

@@ -319,12 +319,6 @@ if(CONFIG_STD_C23)
   set(CSTD c2x)
 elseif(CONFIG_STD_C17)
   set(CSTD c17)
-elseif(CONFIG_STD_C11)
-  set(CSTD c11)
-elseif(CONFIG_STD_C99)
-  set(CSTD c99)
-elseif(CONFIG_STD_C90)
-  set(CSTD c90)
 else()
   message(FATAL_ERROR "Unreachable code. Expected C standard to have been chosen.")
 endif()

Kconfig.zephyr

@@ -355,20 +355,8 @@ endmenu
 
 menu "Compiler Options"
 
-config REQUIRES_STD_C99
-	bool
-	help
-	  Hidden option to select compiler support C99 standard or higher.
-
-config REQUIRES_STD_C11
-	bool
-	select REQUIRES_STD_C99
-	help
-	  Hidden option to select compiler support C11 standard or higher.
-
 config REQUIRES_STD_C17
 	bool
-	select REQUIRES_STD_C11
 	help
 	  Hidden option to select compiler support C17 standard or higher.
 
@@ -381,31 +369,10 @@ config REQUIRES_STD_C23
 choice STD_C
 	prompt "C Standard"
 	default STD_C23 if REQUIRES_STD_C23
-	default STD_C17 if REQUIRES_STD_C17
-	default STD_C11 if REQUIRES_STD_C11
-	default STD_C99
+	default STD_C17
 	help
 	  C Standards.
 
-config STD_C90
-	bool "C90"
-	depends on !REQUIRES_STD_C99
-	help
-	  1989 C standard as completed in 1989 and ratified by ISO/IEC
-	  as ISO/IEC 9899:1990. This version is known as "ANSI C".
-
-config STD_C99
-	bool "C99"
-	depends on !REQUIRES_STD_C11
-	help
-	  1999 C standard.
-
-config STD_C11
-	bool "C11"
-	depends on !REQUIRES_STD_C17
-	help
-	  2011 C standard.
-
 config STD_C17
 	bool "C17"
 	depends on !REQUIRES_STD_C23

arch/Kconfig

@@ -152,12 +152,6 @@ config ARCH_POSIX
 	select BARRIER_OPERATIONS_BUILTIN
 	# POSIX arch based targets get their memory cleared on entry by the host OS
 	select SKIP_BSS_CLEAR
-	# Override the C standard used for compilation to C 2011
-	# This is due to some tests using _Static_assert which is a 2011 feature, but
-	# otherwise relying on compilers supporting it also when set to C99.
-	# This was in general ok, but with some host compilers and C library versions
-	# it led to problems. So we override it to 2011 for the native targets.
-	select REQUIRES_STD_C11
 	help
 	  POSIX (native) architecture
 

cmake/compiler/compiler_features.cmake

@@ -1,18 +1,15 @@
-set(c23id c2x gnu2x)
+set(c23id c2x gnu2x "iso9899:2023" "iso9899:2024")
 set(c17id c17 c18 gnu17 gnu18 "iso9899:2017" "iso9899:2018")
-set(c11id c11 gnu11 "iso9899:2011")
-set(c99id c99 gnu99 "iso9899:1999")
-set(c90id c89 c90 gnu89 gnu90 "iso9899:1990" "iso9899:199409")
 
 set(compile_features_list)
 
 # For each id value above a compile_features_${idval} with a list of supported
 # `c_std_XX` values are created for easy lookup.
 # For example, the settings
-# - `compile_feature_c99` will contain `c_std_90;c_std_99`
-# - `compile_feature_iso9899:2011` will contain `c_std_90;c_std_99;c_std_11`
+# - `compile_feature_c23` will contain `c_std_17;c_std_23`
+# - `compile_feature_iso9899:2023` will contain `c_std_17;c_std_23`
 # that can then be used to set CMAKE_C_COMPILE_FEATURES accordingly.
-foreach(standard 90 99 11 17 23)
+foreach(standard 17 23)
   list(APPEND compile_features_list c_std_${standard})
   foreach(id ${c${standard}id})
     set(compile_features_${id} ${compile_features_list})

modules/nanopb/Kconfig

@@ -6,8 +6,6 @@ config ZEPHYR_NANOPB_MODULE
 
 menuconfig NANOPB
 	bool "Nanopb Support"
-	# Nanopb requires c_std_11 compiler features like _Static_assert
-	select REQUIRES_STD_C11
 	help
 	  This option enables the Nanopb library and generator.
 

tests/subsys/bindesc/definition/testcase.yaml

@@ -19,24 +19,10 @@ tests:
       - qemu_riscv32
       - qemu_riscv32e
       - qemu_riscv64
-  bindesc.define.c99:
-    extra_configs:
-      - CONFIG_STD_C99=y
-  bindesc.define.c11:
-    extra_configs:
-      - CONFIG_STD_C11=y
-  bindesc.define.c17:
+ bindesc.define.c17:
     extra_configs:
       - CONFIG_STD_C17=y
-  bindesc.define.gnu99:
-    extra_configs:
-      - CONFIG_STD_C99=y
-      - CONFIG_GNU_C_EXTENSIONS=y
-  bindesc.define.gnu11:
-    extra_configs:
-      - CONFIG_STD_C11=y
-      - CONFIG_GNU_C_EXTENSIONS=y
-  bindesc.define.gnu17:
+ bindesc.define.gnu17:
     extra_configs:
       - CONFIG_STD_C17=y
       - CONFIG_GNU_C_EXTENSIONS=y

tests/subsys/bindesc/reading/testcase.yaml

@@ -8,24 +8,10 @@ tests:
   bindesc.read:
     platform_allow:
       - native_sim
-  bindesc.read.c99:
-    extra_configs:
-      - CONFIG_STD_C99=y
-  bindesc.read.c11:
-    extra_configs:
-      - CONFIG_STD_C11=y
-  bindesc.read.c17:
+ bindesc.read.c17:
     extra_configs:
       - CONFIG_STD_C17=y
-  bindesc.read.gnu99:
-    extra_configs:
-      - CONFIG_STD_C99=y
-      - CONFIG_GNU_C_EXTENSIONS=y
-  bindesc.read.gnu11:
-    extra_configs:
-      - CONFIG_STD_C11=y
-      - CONFIG_GNU_C_EXTENSIONS=y
-  bindesc.read.gnu17:
+ bindesc.read.gnu17:
     extra_configs:
       - CONFIG_STD_C17=y
       - CONFIG_GNU_C_EXTENSIONS=y