cmake: zephyr_get_build_property: implement additional options

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

 - AS_STRING:
      Returns the result as a string rather than a list. Equivalent to
      specifying DELIMITER " ".

 - 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.

 - PREFIX <prefix>:
      Specifies a custom prefix to use for each entry in the output
      list. Defaults to the standard compiler flag prefix for the given
      property.

 - 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

@@ -164,7 +164,7 @@ function(zephyr_ld_options)
     target_ld_options(zephyr_interface INTERFACE ${ARGV})
 endfunction()
 
-# Getter function for extracting build information from
+# Getter function for extracting build information from a target, by default
 # 'zephyr_interface'. The function supports filtering for specific compile
 # languages, custom prefixes, and different output formats.
 #
@@ -179,29 +179,51 @@ endfunction()
 #   - 'prop' is the CMake target property to get
 #
 # Options:
+#   - AS_STRING:
+#       Return the result as a string rather than a list. Equivalent to
+#       specifying DELIMITER " ".
 #  - DELIMITER <delimiter>:
 #       Specify the output delimiter to use for the list entries. Defaults to
 #       "$<SEMICOLON>".
+#  - 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 custom prefix to use for each entry in the output list.
+#       Defaults to the standard compiler flag prefix for the given property.
 #  - STRIP_PREFIX:
-#       Omit the compiler flag prefix (-I, -D, etc.).
+#       Omit the compiler flag prefix (-I, -D, etc.). Equivalent to 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 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(zephyr_get_build_property PROPERTY)
   if(args_UNPARSED_ARGUMENTS)
     message(FATAL_ERROR "zephyr_get_build_prop_for_lang() given unknown "
             "arguments: ${args_UNPARSED_ARGUMENTS}")
   endif()
+  set_ifndef(args_TARGET "zephyr_interface")
 
-  set_ifndef(args_DELIMITER "$<SEMICOLON>")
+  if(args_AS_STRING)
+    set(args_DELIMITER " ")
+  else()
+    set_ifndef(args_DELIMITER "$<SEMICOLON>")
+  endif()
 
   if(args_STRIP_PREFIX)
     set(maybe_prefix "")
+  elseif(args_PREFIX)
+    set(maybe_prefix "${args_PREFIX}")
   elseif(args_PROPERTY MATCHES "^(INTERFACE_)?COMPILE_DEFINITIONS$")
     set(maybe_prefix "-D")
   elseif(args_PROPERTY MATCHES "^(INTERFACE_)?INCLUDE_DIRECTORIES$")
@@ -212,13 +234,21 @@ function(zephyr_get_build_property output)
     set(maybe_prefix "")
   endif()
 
-  get_property(flags TARGET zephyr_interface PROPERTY ${args_PROPERTY})
-  if(args_LANG)
-    process_flags(${args_LANG} flags output_list)
+  if(args_LANG AND args_GENEX)
+    message(FATAL_ERROR "zephyr_get_build_property(): GENEX cannot be used with LANG.")
+  endif()
+
+  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}>")