install: Teach CODE,SCRIPT modes to evaluate generator expressions

This also introduces CMP0087 which will keep the OLD behaviour of not
evaluating generator expressions

Fixes: #15785

1 files changed, 29 insertions, 0 deletions

diff --git a/Help/policy/CMP0087.rst b/Help/policy/CMP0087.rst
new file mode 100644
index 0000000..4c45b99
--- /dev/null
+++ b/Help/policy/CMP0087.rst
@@ -0,0 +1,29 @@
+CMP0087
+-------
+
+:command:`install(CODE)` and :command:`install(SCRIPT)` support generator
+expressions.
+
+In CMake 3.13 and earlier, :command:`install(CODE)` and
+:command:`install(SCRIPT)` did not evaluate generator expressions.  CMake 3.14
+and later will evaluate generator expressions for :command:`install(CODE)` and
+:command:`install(SCRIPT)`.
+
+The ``OLD`` behavior of this policy is for :command:`install(CODE)` and
+:command:`install(SCRIPT)` to not evaluate generator expressions.  The ``NEW``
+behavior is to evaluate generator expressions for :command:`install(CODE)` and
+:command:`install(SCRIPT)`.
+
+Note that it is the value of this policy setting at the end of the directory
+scope that is important, not its setting at the time of the call to
+:command:`install(CODE)` or :command:`install(SCRIPT)`.  This has implications
+for calling these commands from places that have their own policy scope but not
+their own directory scope (e.g. from files brought in via :command:`include()`
+rather than :command:`add_subdirectory()`).
+
+This policy was introduced in CMake version 3.14.  CMake version
+|release| warns when the policy is not set and uses ``OLD`` behavior.
+Use the :command:`cmake_policy` command to set it to ``OLD`` or ``NEW``
+explicitly.
+
+.. include:: DEPRECATED.txt