cmake: zephyr_get_property: implement additional options

Extended the zephyr_get_property() CMake function with several
convenience options:

 - GENEX:
      Uses generator expressions to get the property entries at build
      time, for targets that are not yet fully configured.
      Cannot be used with LANG. Also, CMake will complain if the
      requested property includes $<COMPILE_OPTIONS:...> expressions.

 - TARGET <target>:
      Specifies the target to get the property from. Defaults to
      "zephyr_interface" as before.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

cmake/modules/extensions.cmake

@@ -164,8 +164,8 @@ function(zephyr_ld_options)
     target_ld_options(zephyr_interface INTERFACE ${ARGV})
 endfunction()
 
-# Getter function for extracting information from zephyr_interface. The
-# function supports filtering for specific compile languages, prefixes, and
+# Getter function for extracting information from a target. The function
+# supports filtering for specific compile languages, prefixes, and
 # different output formats.
 #
 # The result is always returned as a generator expression, so its actual
@@ -185,25 +185,36 @@ endfunction()
 #  - DELIMITER <delimiter>:
 #       Specify the output delimiter to use for the list entries. Defaults to
 #       "$<SEMICOLON>". Cannot be used with AS_STRING.
+#  - GENEX:
+#       Use generator expressions to get the property entries at build time,
+#       for targets that are not yet fully configured.
+#       Cannot be used with LANG. Also, CMake will complain if the requested
+#       property includes $<COMPILE_OPTIONS:...> expressions.
 #  - LANG <C|CXX|ASM>:
 #       When set, the property value is filtered for $<COMPILE_LANGUAGE:lang>
 #       entries, and only those matching the given language are kept.
+#       Cannot be used with GENEX.
 #  - PREFIX <prefix>:
 #       Specify a prefix to use for each entry in the output list. Defaults
 #       for INCLUDE_DIRECTORIES (-I), SYSTEM_INCLUDE_DIRECTORIES (-isystem),
 #       COMPILE_DEFINITIONS (-D) and their INTERFACE_ variants are implicit.
 #  - STRIP_PREFIX:
 #       Omit the prefix string, even if implicit or given by PREFIX.
+#  - TARGET <target>:
+#       Specify the target to get the property from. Defaults to
+#       "zephyr_interface".
 
 function(zephyr_get_build_property output)
-  set(options AS_STRING STRIP_PREFIX)
-  set(single_args DELIMITER LANG PREFIX PROPERTY)
+  set(options AS_STRING GENEX STRIP_PREFIX)
+  set(single_args DELIMITER LANG PREFIX PROPERTY TARGET)
   cmake_parse_arguments(args "${options}" "${single_args}" "" ${ARGN})
   zephyr_check_arguments_required_all(zephyr_get_build_property args PROPERTY)
   zephyr_check_arguments_exclusive(zephyr_get_build_property args AS_STRING DELIMITER)
+  zephyr_check_arguments_exclusive(zephyr_get_build_property args GENEX LANG)
   if(args_UNPARSED_ARGUMENTS)
     message(FATAL_ERROR "zephyr_get_build_property() given unknown arguments: ${args_UNPARSED_ARGUMENTS}")
   endif()
+  set_ifndef(args_TARGET "zephyr_interface")
 
   if(args_AS_STRING)
     set(args_DELIMITER " ")
@@ -225,13 +236,17 @@ function(zephyr_get_build_property output)
     set(maybe_prefix "${prefix_${args_PROPERTY}}")
   endif()
 
-  get_property(flags TARGET zephyr_interface PROPERTY ${args_PROPERTY})
-  if(args_LANG)
-    process_flags(${args_LANG} flags output_list)
+  if(args_GENEX)
+    set(genexp_output_list "$<TARGET_PROPERTY:${args_TARGET},${args_PROPERTY}>")
   else()
-    set(output_list "${flags}")
+    get_property(flags TARGET ${args_TARGET} PROPERTY ${args_PROPERTY})
+    if(args_LANG)
+      process_flags(${args_LANG} flags output_list)
+    else()
+      set(output_list "${flags}")
+    endif()
+    string(REPLACE ";" "$<SEMICOLON>" genexp_output_list "${output_list}")
   endif()
-  string(REPLACE ";" "$<SEMICOLON>" genexp_output_list "${output_list}")
 
   set(result_output_list "${maybe_prefix}$<JOIN:${genexp_output_list},${args_DELIMITER}${maybe_prefix}>")
   set(maybe_result_output_list "$<$<BOOL:${genexp_output_list}>:${result_output_list}>")