CMake directory removal code cannot remove content from read-only
directories (a separate bug which will be fixed). Therefore we should
not create them in the StringFileTest. This tweaks the file(COPY) call
to test not giving OWNER_WRITE to files rather than directories.
The file(INSTALL) command has long been undocumented and used only to
implement install() scripts. We now document it and provide a similar
file(COPY) signature which is useful in general-purpose scripts. It
provides the capabilities of install(DIRECTORY) and install(FILES) but
operates immediately instead of contributing to install scripts.
This creates a new mode of the foreach command which allows precise
iteration even over empty elements. This mode may be safely extended
with more keyword arguments in the future. The cost now is possibly
breaking scripts that iterate over a list of items beginning with 'IN',
but there is no other way to extend the syntax in a readable way.
The $ENV{VAR} syntax permits access to environment variables. This
teaches CMake to recognize most characters in the VAR name since some
environments may have variables with non-C-identifier characters.