CMake: Is there a way to get a list of imported targets that belong to a package

Question

Sometimes I wish I could get a list of the imported targets that belong to a package. Is there a variable that holds them?

This would allow me to write something like this

find_package(Qt5 CONFIG REQUIRED)
message("Imported Qt5 targets: ${Qt5_IMPORTED_TARGETS}") # speculative code

With my current knowledge I have to rely on the documentation of the package to give me the names of all imported targets. Reading them from a variable or property would be easier.

Answer 1

CMake 3.21 introduced the directory property IMPORTED_TARGETS that can be used to get a list of all imported targets. This can be used to derive a list of targets that were imported by a single find_package() call when it is queried before and after the call to find_package(). The code could look something like this:

...
get_property(importTargets DIRECTORY "${CMAKE_SOURCE_DIR}" PROPERTY IMPORTED_TARGETS)

find_package(Qt5 COMPONENTS Core Widgets REQUIRED)

get_property(importTargetsAfter DIRECTORY "${CMAKE_SOURCE_DIR}" PROPERTY IMPORTED_TARGETS)
list(REMOVE_ITEM importTargetsAfter ${importTargets})

message("${importTargetsAfter}")
...

Usually it is good enough to only print the list of all imported targets and guess from the names which of them were imported by the package of interest.

Answer 2

Not precisely what you asked for, but for Qt5, one can do:

cmake_minimum_required(VERSION 3.14)

project(so)

find_package(Qt5 COMPONENTS Core Widgets REQUIRED)

get_cmake_property(_variableNames VARIABLES)
foreach(_variableName ${_variableNames})
  if(_variableName MATCHES "^Qt5.*LIBRARIES")
      message(STATUS "${_variableName}")
      message(STATUS "\t${${_variableName}}")
  endif()
endforeach()

Example output:

-- Qt5Core_LIBRARIES
--  Qt5::Core
-- Qt5Gui_EGL_LIBRARIES
--  Qt5::Gui_EGL
-- Qt5Gui_LIBRARIES
--  Qt5::Gui
-- Qt5Gui_OPENGL_LIBRARIES
--  Qt5::Gui_GL
-- Qt5Widgets_LIBRARIES
--  Qt5::Widgets
-- Configuring done
-- Generating done
-- Build files have been written to: /path/to/build

Caveat with approach: One needs to know the component names.