Do not include headers inside __BEGIN_DECLS ... __END_DECLS blocks.

We don't have C++ unsafe headers (anymore).

I added a test to fix_headers.sh that checks if certain "unsafe"
headers are ONLY included inside a __BEGIN_DECLS ... __END_DECLS
(because after all, they are unsafe), as well as checking that
no other header files are included inside such a block. The rationale
of the latter is that if a file is a C header and it declares
function prototypes (otherwise it doesn't matter) and is sometimes
included outside a __BEGIN_DECLS ... __END_DECLS block (from a C++
source file) then it has to be C++ safe and doesn't ever to be
included from inside such a block; while if a file is a C++ header
then obviously it should never be included from such a block.

fix_headers.sh subsequently found several safe headers to be
included from inside such a block, and those that were (apparently
in the past) unsafe were included only sometimes inside such a
block and often outside it. I had a look at those files and saw
that at least an attempt has been made to make them C++ safe,
but especially because they already are included OFTEN outside
a __BEGIN_DECLS ... __END_DECLS (from C++ source files) the
best decision seems to treat them as safe.

This is not risky: .c files that define such functions still
generate C-linkage for their functions. If a C++ unsafe C header
is included outside a __BEGIN_DECLS ... __END_DECLS block then
the only possible result would be an undefined reference to
a function with C++-linkage that will not exist. Aka, when
something links after this commit, then the commit was correct.
I did build all targets and they all linked.

src/drivers/boards/aerocore/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -189,6 +186,8 @@ __BEGIN_DECLS
 		{GPIO_GPIO10_INPUT,      GPIO_GPIO10_OUTPUT,      0}, \
 		{GPIO_GPIO11_INPUT,      GPIO_GPIO11_OUTPUT,      0}, }
 
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/

src/drivers/boards/asc-v1/board_config.h

@@ -50,9 +50,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -259,6 +256,9 @@ __BEGIN_DECLS
 #define TEMP_CONTROL(_on_true)	px4_arch_gpiowrite(GPIO_TEMP_CONT, (_on_true))
 
 #define  FLASH_BASED_PARAMS
+
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/
@@ -351,4 +351,5 @@ bool board_pwr_button_down(void);
 void board_pwr(bool on_not_off);
 
 #endif /* __ASSEMBLY__ */
+
 __END_DECLS

src/drivers/boards/crazyflie/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -168,8 +165,7 @@ __BEGIN_DECLS
 
 #define BOARD_FMU_GPIO_TAB { {0, 0, 0}, }
 
-
+__BEGIN_DECLS
-
 
 /****************************************************************************************************
  * Public Types
@@ -219,9 +215,6 @@ extern void board_peripheral_reset(int ms);
 int nsh_archinitialize(void);
 #endif
 
-
-
-
 /****************************************************************************
  * Name: board_i2c_initialize
  *
@@ -232,7 +225,6 @@ int nsh_archinitialize(void);
 
 int board_i2c_initialize(void);
 
-
 #endif /* __ASSEMBLY__ */
 
 __END_DECLS

src/drivers/boards/mindpx-v2/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -328,6 +325,8 @@ __BEGIN_DECLS
 
 #define BOARD_DMA_ALLOC_POOL_SIZE 5120
 
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/

src/drivers/boards/px4-stm32f4discovery/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -89,6 +86,8 @@ __BEGIN_DECLS
 
 #define BOARD_NAME "PX4_STM32F4DISCOVERY"
 
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/

src/drivers/boards/px4fmu-v1/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -224,6 +221,8 @@ __BEGIN_DECLS
  */
 #define BOARD_HAS_MULTI_PURPOSE_GPIO 1
 
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/

src/drivers/boards/px4fmu-v2/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -271,8 +268,10 @@ __BEGIN_DECLS
 		{GPIO_VDD_5V_PERIPH_OC,  0,                       0}, }
 
 /* This board provides a DMA pool and APIs */
-
 #define BOARD_DMA_ALLOC_POOL_SIZE 5120
+
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/

src/drivers/boards/px4fmu-v4/board_config.h

@@ -47,9 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -298,9 +295,10 @@ __BEGIN_DECLS
 		{GPIO_VDD_BRICK_VALID,   0,                       0}, }
 
 /* This board provides a DMA pool and APIs */
-
 #define BOARD_DMA_ALLOC_POOL_SIZE 5120
 
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/

src/drivers/boards/px4io-v1/board_config.h

@@ -47,7 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 

src/drivers/boards/px4io-v2/board_config.h

@@ -47,7 +47,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -143,4 +142,3 @@
 #define LED_SIGNAL        5  /* LED? + LED? */
 #define LED_ASSERTION     6  /* LED? + LED? + LED? */
 #define LED_PANIC         7  /* N/C  + N/C  + N/C + LED? */
-

src/drivers/boards/tap-v1/board_config.h

@@ -48,9 +48,6 @@
 #include <nuttx/compiler.h>
 #include <stdint.h>
 
-__BEGIN_DECLS
-
-/* these headers are not C++ safe */
 #include <stm32.h>
 #include <arch/board/board.h>
 
@@ -262,6 +259,9 @@ __BEGIN_DECLS
 #define TEMP_CONTROL(_on_true)	px4_arch_gpiowrite(GPIO_TEMP_CONT, (_on_true))
 
 #define  FLASH_BASED_PARAMS
+
+__BEGIN_DECLS
+
 /****************************************************************************************************
  * Public Types
  ****************************************************************************************************/
@@ -320,7 +320,6 @@ extern int board_sdio_initialize(void);
 int nsh_archinitialize(void);
 #endif
 
-
 /************************************************************************************
  * Name: board_pwr_init()
  *
@@ -364,4 +363,5 @@ void board_pwr(bool on_not_off);
 int board_i2c_initialize(void);
 
 #endif /* __ASSEMBLY__ */
+
 __END_DECLS

src/drivers/drv_pwm_output.h

@@ -44,6 +44,9 @@
 #pragma once
 
 #include <px4_defines.h>
+
+#include "uORB/topics/output_pwm.h"
+
 #include <stdint.h>
 #include <sys/ioctl.h>
 
@@ -61,7 +64,6 @@ __BEGIN_DECLS
 #define PWM_OUTPUT_BASE_DEVICE_PATH "/dev/pwm_output"
 #define PWM_OUTPUT0_DEVICE_PATH	"/dev/pwm_output0"
 
-#include <uORB/topics/output_pwm.h>
 #define pwm_output_values output_pwm_s
 
 #ifndef PWM_OUTPUT_MAX_CHANNELS

src/lib/geo/geo.h

@@ -45,7 +45,6 @@
 
 #pragma once
 #include <platforms/px4_defines.h>
-__BEGIN_DECLS
 
 #include "geo_lookup/geo_mag_declination.h"
 
@@ -79,6 +78,8 @@ struct globallocal_converter_reference_s {
 	bool init_done;
 };
 
+__BEGIN_DECLS
+
 /**
  * Checks if global projection was initialized
  * @return true if map was initialized before, false else

src/modules/mavlink/mavlink_bridge_header.h

@@ -42,8 +42,6 @@
 #ifndef MAVLINK_BRIDGE_HEADER_H
 #define MAVLINK_BRIDGE_HEADER_H
 
-__BEGIN_DECLS
-
 #define MAVLINK_USE_CONVENIENCE_FUNCTIONS
 
 /* use efficient approach, see mavlink_helpers.h */
@@ -57,6 +55,7 @@ __BEGIN_DECLS
 #include <v2.0/mavlink_types.h>
 #include <unistd.h>
 
+__BEGIN_DECLS
 
 /* Struct that stores the communication settings of this system.
    you can also define / alter these settings elsewhere, as long

src/modules/systemlib/cpuload.h

@@ -35,8 +35,6 @@
 
 #ifdef CONFIG_SCHED_INSTRUMENTATION
 
-__BEGIN_DECLS
-
 #include <sched.h>
 #include <stdint.h>
 
@@ -58,6 +56,8 @@ struct system_load_s {
 	int sleeping_count;
 };
 
+__BEGIN_DECLS
+
 __EXPORT extern struct system_load_s system_load;
 
 __EXPORT void cpuload_initialize_once(void);

src/modules/systemlib/otp.h

@@ -43,8 +43,6 @@
 #ifndef OTP_H_
 #define OTP_H_
 
-__BEGIN_DECLS
-
 #define ADDR_OTP_START			0x1FFF7800
 #define ADDR_OTP_LOCK_START		0x1FFF7A00
 
@@ -130,6 +128,7 @@ union udid {
 };
 #pragma pack(pop)
 
+__BEGIN_DECLS
 
 /**
  *   s

src/modules/systemlib/printload.h

@@ -41,9 +41,8 @@
 
 #pragma once
 
-__BEGIN_DECLS
-
 #include <px4_config.h>
+
 #include <stdint.h>
 
 #ifndef CONFIG_MAX_TASKS
@@ -63,6 +62,8 @@ struct print_load_s {
 	float interval_time_ms_inv;
 };
 
+__BEGIN_DECLS
+
 __EXPORT void init_print_load_s(uint64_t t, struct print_load_s *s);
 
 __EXPORT void print_load(uint64_t t, int fd, struct print_load_s *print_state);