FindFLEX: Add a DEFINES_FILE option to specify flex-generated header (#15781)

Modules/FindFLEX.cmake

@@ -27,13 +27,17 @@
 #
 # ::
 #
-#   FLEX_TARGET(Name FlexInput FlexOutput [COMPILE_FLAGS <string>])
+#   FLEX_TARGET(Name FlexInput FlexOutput
+#               [COMPILE_FLAGS <string>]
+#               [DEFINES_FILE <string>]
+#               )
 #
 # which creates a custom command to generate the <FlexOutput> file from
 # the <FlexInput> file.  If COMPILE_FLAGS option is specified, the next
-# parameter is added to the flex command line.  Name is an alias used to
-# get details of this custom command.  Indeed the macro defines the
-# following variables:
+# parameter is added to the flex command line. If flex is configured to
+# output a header file, the DEFINES_FILE option may be used to specify its
+# name. Name is an alias used to get details of this custom command.
+# Indeed the macro defines the following variables:
 #
 # ::
 #
@@ -41,6 +45,7 @@
 #   FLEX_${Name}_OUTPUTS - the source file generated by the custom rule, an
 #   alias for FlexOutput
 #   FLEX_${Name}_INPUT - the flex source file, an alias for ${FlexInput}
+#   FLEX_${Name}_OUTPUT_HEADER - the header flex output, if any.
 #
 #
 #
@@ -147,11 +152,13 @@ if(FLEX_EXECUTABLE)
   #============================================================
   #
   macro(FLEX_TARGET Name Input Output)
+    set(FLEX_TARGET_outputs "${Output}")
     set(FLEX_EXECUTABLE_opts "")
 
     set(FLEX_TARGET_PARAM_OPTIONS)
     set(FLEX_TARGET_PARAM_ONE_VALUE_KEYWORDS
       COMPILE_FLAGS
+      DEFINES_FILE
       )
     set(FLEX_TARGET_PARAM_MULTI_VALUE_KEYWORDS)
 
@@ -163,7 +170,7 @@ if(FLEX_EXECUTABLE)
       ${ARGN}
       )
 
-    set(FLEX_TARGET_usage "FLEX_TARGET(<Name> <Input> <Output> [COMPILE_FLAGS <string>]")
+    set(FLEX_TARGET_usage "FLEX_TARGET(<Name> <Input> <Output> [COMPILE_FLAGS <string>] [DEFINES_FILE <string>]")
 
     if(NOT "${FLEX_TARGET_ARG_UNPARSED_ARGUMENTS}" STREQUAL "")
       message(SEND_ERROR ${FLEX_TARGET_usage})
@@ -172,8 +179,12 @@ if(FLEX_EXECUTABLE)
         set(FLEX_EXECUTABLE_opts "${FLEX_TARGET_ARG_COMPILE_FLAGS}")
         separate_arguments(FLEX_EXECUTABLE_opts)
       endif()
+      if(NOT "${FLEX_TARGET_ARG_DEFINES_FILE}" STREQUAL "")
+        list(APPEND FLEX_TARGET_outputs "${FLEX_TARGET_ARG_DEFINES_FILE}")
+        list(APPEND FLEX_EXECUTABLE_opts --header-file=${FLEX_TARGET_ARG_DEFINES_FILE})
+      endif()
 
-      add_custom_command(OUTPUT ${Output}
+      add_custom_command(OUTPUT ${FLEX_TARGET_outputs}
         COMMAND ${FLEX_EXECUTABLE}
         ARGS ${FLEX_EXECUTABLE_opts} -o${Output} ${Input}
         DEPENDS ${Input}
@@ -184,6 +195,11 @@ if(FLEX_EXECUTABLE)
       set(FLEX_${Name}_OUTPUTS ${Output})
       set(FLEX_${Name}_INPUT ${Input})
       set(FLEX_${Name}_COMPILE_FLAGS ${FLEX_EXECUTABLE_opts})
+      if("${FLEX_TARGET_ARG_DEFINES_FILE}" STREQUAL "")
+        set(FLEX_${Name}_OUTPUT_HEADER "")
+      else()
+        set(FLEX_${Name}_OUTPUT_HEADER ${FLEX_TARGET_ARG_DEFINES_FILE})
+      endif()
     endif()
   endmacro()
   #============================================================