# CMP0098

`FindFLEX` runs `flex` in directory `CMAKE_CURRENT_BINARY_DIR` when executing.

The module provides a `FLEX_TARGET` macro which generates FLEX output. In CMake 3.16 and below the macro would generate a custom command that runs `flex` in the current source directory. CMake 3.17 and later prefer to run it in the build directory and use `CMAKE_CURRENT_BINARY_DIR` as the `WORKING_DIRECTORY` of its `add_custom_command()` invocation. This ensures that any implicitly generated file is written relative to the build tree rather than the source tree, unless the generated file is provided as absolute path.

This policy provides compatibility for projects that have not been updated to expect the new behavior.

The `OLD` behavior for this policy is for `FLEX_TARGET` to use the current source directory for the `WORKING_DIRECTORY` and where to generate implicit files. The `NEW` behavior of this policy is to use the current binary directory for the `WORKING_DIRECTORY` relative to which implicit files are generated unless provided as absolute path.

This policy was introduced in CMake version 3.17. Use the `cmake_policy()` command to set it to `OLD` or `NEW` explicitly. Unlike many policies, CMake version 3.18.0-rc4 does not warn when this policy is not set and simply uses `OLD` behavior.

Note

The `OLD` behavior of a policy is `deprecated by definition` and may be removed in a future version of CMake.