[cmake] generate a mbedtls-config.h without private headers (#5084)

third_party/mbedtls/CMakeLists.txt

@@ -26,15 +26,37 @@
 #  POSSIBILITY OF SUCH DAMAGE.
 #
 
-set(OT_MBEDTLS_DEFAULT_CONFIG_FILE \"${CMAKE_CURRENT_SOURCE_DIR}/mbedtls-config.h\")
+set(OT_MBEDTLS_DEFAULT_CONFIG_FILE \"${CMAKE_CURRENT_BINARY_DIR}/mbedtls-config.h\")
 
 set(OT_MBEDTLS_CONFIG_FILE "" CACHE STRING "The mbedTLS config file")
 
 set(ENABLE_TESTING OFF CACHE BOOL "Disable mbedtls test" FORCE)
 set(ENABLE_PROGRAMS OFF CACHE BOOL "Disable mbetls program" FORCE)
 
+find_program(UNIFDEFALL_EXE unifdefall)
+find_program(SED_EXE sed)
+
 add_subdirectory(repo)
 
+if(UNIFDEFALL_EXE AND SED_EXE)
+    add_custom_target(mbedtls-config.h
+        ${UNIFDEFALL_EXE}
+            "'-D$<JOIN:$<TARGET_PROPERTY:ot-config,INTERFACE_COMPILE_DEFINITIONS>,';'-D>'"
+            "-I$<JOIN:$<TARGET_PROPERTY:ot-config,INTERFACE_INCLUDE_DIRECTORIES>,;-I>"
+            "-I$<JOIN:${OT_PUBLIC_INCLUDES},;-I>"
+            "-I${CMAKE_CURRENT_SOURCE_DIR}/repo/include"
+            "${CMAKE_CURRENT_SOURCE_DIR}/mbedtls-config.h" |
+            ${SED_EXE} '/openthread-core-config\.h/d' >
+            ${OT_MBEDTLS_DEFAULT_CONFIG_FILE}
+        COMMAND_EXPAND_LISTS
+    )
+    add_dependencies(mbedtls mbedtls-config.h)
+    add_dependencies(mbedx509 mbedtls-config.h)
+    add_dependencies(mbedcrypto mbedtls-config.h)
+else()
+    configure_file(mbedtls-config.h mbedtls-config.h COPYONLY)
+endif()
+
 target_compile_definitions(mbedtls
     PUBLIC
         "MBEDTLS_CONFIG_FILE=$<IF:$<BOOL:${OT_MBEDTLS_CONFIG_FILE}>,${OT_MBEDTLS_CONFIG_FILE},${OT_MBEDTLS_DEFAULT_CONFIG_FILE}>"

third_party/mbedtls/mbedtls-config.h

@@ -26,7 +26,9 @@
  *  POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef MBEDTLS_CONFIG_H
+// Spans multiple lines to avoid being processed by unifdef
+#ifndef \
+    MBEDTLS_CONFIG_H
 #define MBEDTLS_CONFIG_H
 
 #include "openthread-core-config.h"
@@ -76,8 +78,7 @@
 #define MBEDTLS_SSL_PROTO_DTLS
 #define MBEDTLS_SSL_TLS_C
 
-#if OPENTHREAD_CONFIG_BORDER_AGENT_ENABLE || OPENTHREAD_CONFIG_COMMISSIONER_ENABLE || \
+#if OPENTHREAD_CONFIG_BORDER_AGENT_ENABLE || OPENTHREAD_CONFIG_COMMISSIONER_ENABLE || OPENTHREAD_CONFIG_COAP_SECURE_API_ENABLE
-    OPENTHREAD_CONFIG_COAP_SECURE_API_ENABLE
 #define MBEDTLS_SSL_COOKIE_C
 #define MBEDTLS_SSL_SRV_C
 #endif
@@ -129,7 +130,9 @@
 
 #define MBEDTLS_SSL_CIPHERSUITES         MBEDTLS_TLS_ECJPAKE_WITH_AES_128_CCM_8
 
-#if defined(MBEDTLS_USER_CONFIG_FILE)
+// Spans multiple lines to avoid being processed by unifdef
+#if defined(\
+    MBEDTLS_USER_CONFIG_FILE)
 #include MBEDTLS_USER_CONFIG_FILE
 #endif