1 files changed, 87 insertions, 4 deletions

diff --git a/third_party/aom/build/cmake/util.cmake b/third_party/aom/build/cmake/util.cmake
index a0c705691..b70ec4013 100644
--- a/third_party/aom/build/cmake/util.cmake
+++ b/third_party/aom/build/cmake/util.cmake
@@ -13,19 +13,21 @@ if(AOM_BUILD_CMAKE_UTIL_CMAKE_)
 endif() # AOM_BUILD_CMAKE_UTIL_CMAKE_
 set(AOM_BUILD_CMAKE_UTIL_CMAKE_ 1)
 
+# Directory where generated sources will be written.
+set(AOM_GEN_SRC_DIR "${AOM_CONFIG_DIR}/gen_src")
+
 # Creates dummy source file in $AOM_CONFIG_DIR named $basename.$extension and
 # returns the full path to the dummy source file via the $out_file_path
 # parameter.
-function(create_dummy_source_file basename extension out_file_path)
-  set(dummy_source_file "${AOM_CONFIG_DIR}/${basename}_dummy.${extension}")
+macro(create_dummy_source_file basename extension out_file_path)
+  set(dummy_source_file "${AOM_GEN_SRC_DIR}/${basename}_dummy.${extension}")
   file(
     WRITE
       "${dummy_source_file}" "// Generated file. DO NOT EDIT!\n"
       "// ${target_name} needs a ${extension} file to force link language, \n"
       "// or to silence a harmless CMake warning: Ignore me.\n"
       "void ${target_name}_dummy_function(void) {}\n")
-  set(${out_file_path} ${dummy_source_file} PARENT_SCOPE)
-endfunction()
+endmacro()
 
 # Convenience function for adding a dummy source file to $target_name using
 # $extension as the file extension. Wraps create_dummy_source_file().
@@ -86,3 +88,84 @@ function(set_compiler_launcher launcher_flag launcher_name)
   endif()
 endfunction()
 
+# Sentinel value used to detect when a variable has been set via the -D argument
+# passed to CMake on the command line.
+set(cmake_cmdline_helpstring "No help, variable specified on the command line.")
+
+# Wrapper macro for set() that does some book keeping to help with storage of
+# build configuration information.
+#
+# Sets the default value for variable $name when the value of $name has not
+# already been set via the CMake command line.
+#
+# The names of variables defaulted through this macro are added to
+# $AOM_CONFIG_VARS to facilitate build logging and diagnostics.
+macro(set_aom_detect_var name value type helpstring)
+  unset(list_index)
+  list(FIND AOM_DETECT_VARS ${name} list_index)
+  if(${list_index} EQUAL -1)
+    list(APPEND AOM_DETECT_VARS ${name})
+  endif()
+
+  # Update the variable only when it does not carry the CMake assigned help
+  # string for variables specified via the command line.
+  unset(cache_helpstring)
+  get_property(cache_helpstring CACHE ${name} PROPERTY HELPSTRING)
+  if(NOT "${cache_helpstring}" STREQUAL "${cmake_cmdline_helpstring}")
+    set(${name} ${value} CACHE ${type} "${helpstring}")
+    mark_as_advanced(${name})
+  else()
+    message(
+      WARNING
+        "${name} has been set by CMake, but it may be overridden by the build "
+        "system during environment detection")
+  endif()
+endmacro()
+
+# Wrapper macro for set() that does some book keeping to help with storage of
+# build configuration information.
+#
+# Sets the default value for variable $name when the value of $name has not
+# already been set via the CMake command line.
+#
+# The names of variables defaulted through this macro are added to
+# $AOM_CONFIG_VARS to facilitate build logging and diagnostics.
+macro(set_aom_config_var name value type helpstring)
+  unset(list_index)
+  list(FIND AOM_CONFIG_VARS ${name} list_index)
+  if(${list_index} EQUAL -1)
+    list(APPEND AOM_CONFIG_VARS ${name})
+  endif()
+
+  # Update the variable only when it does not carry the CMake assigned help
+  # string for variables specified via the command line.
+  unset(cache_helpstring)
+  get_property(cache_helpstring CACHE ${name} PROPERTY HELPSTRING)
+  if(NOT "${cache_helpstring}" STREQUAL "${cmake_cmdline_helpstring}")
+    set(${name} ${value} CACHE ${type} "${helpstring}")
+  endif()
+endmacro()
+
+# Wrapper macro for option() that does some book keeping to help with storage of
+# build configuration information.
+#
+# Sets the default value for variable $name when the value of $name has not
+# already been set via the CMake command line.
+#
+# The names of variables defaulted through this macro are added to
+# $AOM_OPTION_VARS to facilitate build logging and diagnostics.
+macro(set_aom_option_var name helpstring value)
+  unset(list_index)
+  list(FIND AOM_OPTION_VARS ${name} list_index)
+  if(${list_index} EQUAL -1)
+    list(APPEND AOM_OPTION_VARS ${name})
+  endif()
+
+  # Update the variable only when it does not carry the CMake assigned help
+  # string for variables specified via the command line.
+  unset(cache_helpstring)
+  get_property(cache_helpstring CACHE ${name} PROPERTY HELPSTRING)
+  if(NOT "${cache_helpstring}" STREQUAL "${cmake_cmdline_helpstring}")
+    option(${name} "${helpstring}" ${value})
+  endif()
+endmacro()