Find flex executable and provides a macro to generate custom build rules

The module defines the following variables:

FLEX_FOUND - true is flex executable is found
FLEX_EXECUTABLE - the path to the flex executable
FLEX_VERSION - the version of flex
FLEX_LIBRARIES - The flex libraries
FLEX_INCLUDE_DIRS - The path to the flex headers

The minimum required version of flex can be specified using the standard syntax, e.g. find_package(FLEX 2.5.13)

If flex is found on the system, the module provides the macro:

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. 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:

FLEX_${Name}_DEFINED - true is the macro ran successfully
FLEX_${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.

Flex scanners often use tokens defined by Bison: the code generated by Flex depends of the header generated by Bison. This module also defines a macro:


which adds the required dependency between a scanner and a parser where <FlexTarget> and <BisonTarget> are the first parameters of respectively FLEX_TARGET and BISON_TARGET macros.

BISON_TARGET(MyParser parser.y ${CMAKE_CURRENT_BINARY_DIR}/parser.cpp)
FLEX_TARGET(MyScanner lexer.l  ${CMAKE_CURRENT_BINARY_DIR}/lexer.cpp)