build: make non zephyr/ include prefix configurable

Add a Kconfig to disable non prefixed includes. By setting
`CONFIG_LEGACY_INCLUDE_PATH=n` developers can disable having
`include/zephyr` in the search path. This means that includes such
as `#include <kernel.h>` will no longer work.

Internally, every header should be updated to add the `zephyr/`
prefix to the headers. Only then, will developers be able to use
this config value for their applications.

Signed-off-by: Yuval Peress <peress@google.com>

CMakeLists.txt

@@ -104,9 +104,12 @@ add_library(zephyr_interface INTERFACE)
 # flags that come with zephyr_interface.
 zephyr_library_named(zephyr)
 
+if(CONFIG_LEGACY_INCLUDE_PATH)
+  zephyr_include_directories(include/zephyr)
+endif()
+
 zephyr_include_directories(
   include
-  include/zephyr
   ${PROJECT_BINARY_DIR}/include/generated
   ${USERINCLUDE}
   ${STDINCLUDE}

Kconfig.zephyr

@@ -800,3 +800,15 @@ config COMPAT_INCLUDES
 	  deprecated header files.
 
 endmenu
+
+config LEGACY_INCLUDE_PATH
+	bool "Allow for the legacy include paths (without the zephyr/ prefix)"
+	default y
+	help
+	  Allow applications and libraries to use the Zephyr legacy include
+	  path which does not use the zephyr/ prefix. For example, the
+	  preferred way to include a Zephyr header is to use <zephyr/kernel.h>,
+	  but enabling CONFIG_LEGACY_INCLUDE_PATH will allow developers to
+	  use <kernel.h> instead. This (without the zephyr/ prefix) is
+	  deprecated and should be avoided. Eventually, it will not be
+	  supported.

boards/x86/ehl_crb/CMakeLists.txt

@@ -5,7 +5,8 @@ set_property(GLOBAL APPEND PROPERTY extra_post_build_commands
   -c ${CMAKE_C_COMPILER}
   -o ${CMAKE_OBJCOPY}
   -i ${ZEPHYR_BASE}/include
-  -i ${ZEPHYR_BASE}/include/zephyr
+  $<$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>:-i>
+  $<$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>:${ZEPHYR_BASE}/include/zephyr>
   -f ${PROJECT_BINARY_DIR}/${CONFIG_KERNEL_BIN_NAME}.elf
   $<$<BOOL:${CMAKE_VERBOSE_MAKEFILE}>:--verbose>
   WORKING_DIRECTORY ${PROJECT_BINARY_DIR}

boards/x86/qemu_x86/CMakeLists.txt

@@ -3,7 +3,8 @@ set_property(GLOBAL APPEND PROPERTY extra_post_build_commands
   COMMAND ${PYTHON_EXECUTABLE} ${PROJECT_SOURCE_DIR}/arch/x86/zefi/zefi.py
   -c ${CMAKE_C_COMPILER}
   -i ${ZEPHYR_BASE}/include
-  -i ${ZEPHYR_BASE}/include/zephyr
+  $<$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>:-i>
+  $<$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>:${ZEPHYR_BASE}/include/zephyr>
   -o ${CMAKE_OBJCOPY}
   -f ${PROJECT_BINARY_DIR}/${CONFIG_KERNEL_BIN_NAME}.elf
   $<$<BOOL:${CMAKE_VERBOSE_MAKEFILE}>:--verbose>

boards/x86/up_squared/CMakeLists.txt

@@ -5,7 +5,8 @@ set_property(GLOBAL APPEND PROPERTY extra_post_build_commands
   -c ${CMAKE_C_COMPILER}
   -o ${CMAKE_OBJCOPY}
   -i ${ZEPHYR_BASE}/include
-  -i ${ZEPHYR_BASE}/include/zephyr
+  $<$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>:-i>
+  $<$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>:${ZEPHYR_BASE}/include/zephyr>
   -f ${PROJECT_BINARY_DIR}/${CONFIG_KERNEL_BIN_NAME}.elf
   $<$<BOOL:${CMAKE_VERBOSE_MAKEFILE}>:--verbose>
   WORKING_DIRECTORY ${PROJECT_BINARY_DIR}

cmake/modules/unittest.cmake

@@ -34,8 +34,8 @@ gen_kobj(KOBJ_GEN_DIR)
 list(APPEND INCLUDE
   subsys/testsuite/ztest/include
   subsys/testsuite/include
-  include
   include/zephyr
+  include
   .
 )
 

doc/zephyr.doxyfile.in

@@ -928,8 +928,8 @@ RECURSIVE              = YES
 # Note that relative paths are relative to the directory from which doxygen is
 # run.
 
-EXCLUDE                = @ZEPHYR_BASE@/include/portability/cmsis_os.h \
-                         @ZEPHYR_BASE@/include/portability/cmsis_os2.h
+EXCLUDE                = @ZEPHYR_BASE@/include/zephyr/portability/cmsis_os.h \
+                         @ZEPHYR_BASE@/include/zephyr/portability/cmsis_os2.h
 
 # The EXCLUDE_SYMLINKS tag can be used to select whether or not files or
 # directories that are symbolic links (a Unix file system feature) are excluded

modules/hal_rpi_pico/CMakeLists.txt

@@ -33,6 +33,7 @@ if(CONFIG_HAS_RPI_PICO)
         -DZEPHYR_BASE=${ZEPHYR_BASE}
         -DFLASH_TYPE=${flash_type}
         -DPYTHON_EXECUTABLE=${Python3_EXECUTABLE}
+        -DCONFIG_LEGACY_INCLUDE_PATH=$<BOOL:${CONFIG_LEGACY_INCLUDE_PATH}>
       INSTALL_COMMAND "" # No installation needed
       BUILD_BYPRODUCTS ${rp2_bootloader_prefix}/boot_stage2.S
       BUILD_ALWAYS TRUE

modules/hal_rpi_pico/bootloader/CMakeLists.txt

@@ -38,9 +38,12 @@ target_include_directories(boot_stage2 PUBLIC
   ${rp2040_dir}/hardware_regs/include
   ${common_dir}/pico_base/include
   ${ZEPHYR_BASE}/include
-  ${ZEPHYR_BASE}/include/zephyr
   )
 
+if(CONFIG_LEGACY_INCLUDE_PATH)
+  target_include_directories(boot_stage2 PUBLIC ${ZEPHYR_BASE}/include/zephyr)
+endif()
+
 target_link_options(boot_stage2 PRIVATE
   "-nostartfiles"
   "--specs=nosys.specs"