Please change it back to LibIcal_INCLUDE_DIRS. We're following the CMake policies and coding style recommendations

Xxx_INCLUDE_DIRS

The final set of include directories listed in one variable for use by client code. This should not be a cache entry.

if/endif are not needed for pkgconfig calls

use the QUIET keyword for both lines

endif()

mmh i changed it because pkgconfig returns XXX_INCLUDEDIR and I thought so this is the more "stadardized" name.

for the first I can understand, beause we don't want PkgConfig found line shown.
But why QUIT for the second line?

if we don't if/endif the pkgconfig call, we can modify to
if(NOT LibIcal_FOUND)

and it's not :) What should be removed however is ${LibIcal_INCLUDE_DIRS}/libical at the bottom of this file.
This should be part of LibIcal_INCLUDE_DIRS if necessary.

Because we don't need the pkg-config output.
Our policy is that The Find_xxx.cmake modules should only use the pkg-config output as HINTS. The stuff must be found even if the .pc file cannot be found (eg: on Windows).

still missing the QUIET keyword.
Please also rename LibIcal to avoid confusion between the pkgconfig vars and the CMake ones (pick eg 'PC_LibIcal' )

Not needed here, it doesn't exist yet

it's not the right place for that. See below

Remove

+ ${PC_LibIcal_INCLUDEDIR}

That's where we use the pkgconfig result

+ ${PC_LibIcal_LIBDIR}

+ ${PC_LibIcal_LIBDIR}