cmake: escape json input string

Escape the json input string given to `to_yaml()` function and the
content given to `yaml_set()` function.

This ensures that a string like `foo\bar` becomes `foo\\bar` during
internal CMake json processing and when written to the file it becomes
`foo\bar`.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>

cmake/modules/extensions.cmake

@@ -3037,6 +3037,16 @@ endfunction()
 # This function extends the CMake string function by providing additional
 # manipulation arguments to CMake string.
 #
+# ESCAPE:   Ensure that any single '\' in the input string is escaped with the
+#           escape char '\'. For example the string 'foo\bar' will be escaped
+#           so that it becomes 'foo\\bar'.
+#           Backslashes which are already escaped will not be escaped further,
+#           for example 'foo\\bar' will not be modified.
+#           This is useful for handling of windows path separator in strings or
+#           when strings contains newline escapes such as '\n' and this can
+#           cause issues when writing to a file where a '\n' is desired in the
+#           string instead of a newline.
+#
 # SANITIZE: Ensure that the output string does not contain any special
 #           characters. Special characters, such as -, +, =, $, etc. are
 #           converted to underscores '_'.
@@ -3048,9 +3058,11 @@ endfunction()
 #
 # returns the updated string
 function(zephyr_string)
-  set(options SANITIZE TOUPPER)
+  set(options SANITIZE TOUPPER ESCAPE)
   cmake_parse_arguments(ZEPHYR_STRING "${options}" "" "" ${ARGN})
 
+  zephyr_check_flags_exclusive(${CMAKE_CURRENT_FUNCTION} ZEPHYR_STRING SANITIZE ESCAPE)
+
   if (NOT ZEPHYR_STRING_UNPARSED_ARGUMENTS)
     message(FATAL_ERROR "Function zephyr_string() called without a return variable")
   endif()
@@ -3068,6 +3080,13 @@ function(zephyr_string)
     string(TOUPPER ${work_string} work_string)
   endif()
 
+  if(ZEPHYR_STRING_ESCAPE)
+    # If a single '\' is discovered, such as 'foo\bar', then it must be escaped like: 'foo\\bar'
+    # \\1 and \\2 are keeping the match patterns, the \\\\ --> \\ meaning an escaped '\',
+    # which then becomes a single '\' in the final string.
+    string(REGEX REPLACE "([^\\][\\])([^\\])" "\\1\\\\\\2" work_string "${ZEPHYR_STRING_UNPARSED_ARGUMENTS}")
+  endif()
+
   set(${return_arg} ${work_string} PARENT_SCOPE)
 endfunction()
 

cmake/modules/yaml.cmake

@@ -422,9 +422,11 @@ function(yaml_set)
       internal_yaml_list_initializer(json_string ${genex})
       string(JSON json_content SET "${json_content}" ${ARG_YAML_KEY} "${json_string}")
     endif()
-    internal_yaml_list_append(json_content ${genex} "${ARG_YAML_KEY}" ${ARG_YAML_LIST})
+    zephyr_string(ESCAPE escape_list "${ARG_YAML_LIST}")
+    internal_yaml_list_append(json_content ${genex} "${ARG_YAML_KEY}" ${escape_list})
   else()
-    string(JSON json_content SET "${json_content}" ${ARG_YAML_KEY} "\"${ARG_YAML_VALUE}\"")
+    zephyr_string(ESCAPE escape_value "${ARG_YAML_VALUE}")
+    string(JSON json_content SET "${json_content}" ${ARG_YAML_KEY} "\"${escape_value}\"")
   endif()
 
   zephyr_set(JSON "${json_content}" SCOPE ${ARG_YAML_NAME})
@@ -539,7 +541,8 @@ function(yaml_save)
   endif()
 endfunction()
 
-function(to_yaml json level yaml genex)
+function(to_yaml in_json level yaml genex)
+  zephyr_string(ESCAPE json "${in_json}")
   if(level GREATER 0)
     math(EXPR level_dec "${level} - 1")
     set(indent_${level} "${indent_${level_dec}}  ")