FindFLEX: Add policy CMP0098 to run flex in build tree

3 files changed, 44 insertions, 0 deletions

diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index 44ea1a8..eceeac7 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -51,6 +51,14 @@ The :variable:`CMAKE_MINIMUM_REQUIRED_VERSION` variable may also be used
 to determine whether to report an error on use of deprecated macros or
 functions.
 
+Policies Introduced by CMake 3.17
+=================================
+
+.. toctree::
+   :maxdepth: 1
+
+   CMP0098: FindFLEX runs flex in CMAKE_CURRENT_BINARY_DIR when executing. </policy/CMP0098>
+
 Policies Introduced by CMake 3.16
 =================================
 
diff --git a/Help/policy/CMP0098.rst b/Help/policy/CMP0098.rst
new file mode 100644
index 0000000..6d1443b
--- /dev/null
+++ b/Help/policy/CMP0098.rst
@@ -0,0 +1,30 @@
+CMP0098
+-------
+
+:module:`FindFLEX` runs ``flex`` in directory
+:variable:`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 :variable:`CMAKE_CURRENT_BINARY_DIR`
+as the ``WORKING_DIRECTORY`` of its :command:`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
+:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
+Unlike many policies, CMake version |release| does *not* warn
+when this policy is not set and simply uses ``OLD`` behavior.
+
+.. include:: DEPRECATED.txt
diff --git a/Help/release/dev/FindFLEX-work-dir.rst b/Help/release/dev/FindFLEX-work-dir.rst
new file mode 100644
index 0000000..3569185
--- /dev/null
+++ b/Help/release/dev/FindFLEX-work-dir.rst
@@ -0,0 +1,6 @@
+FindFLEX-work-dir
+-----------------
+
+* The :module:`FindFLEX` module's ``FLEX_TARGET`` command now runs ``flex``
+  with :variable:`CMAKE_CURRENT_BINARY_DIR` as the working directory.
+  See policy :policy:`CMP0098`.