Teach target_* commands to set INTERFACE properties of IMPORTED targets

Now, several `INTERFACE_*` properties can be set on `IMPORTED` targets,
not only via `set_property` and `set_target_properties` but also via
`target_compile_definitions`, `target_compile_features`,
`target_compile_options`, `target_include_directories`, `target_sources`
and `target_link_libraries`.

Fixes: #15689
Issue: #17197

Help/command/target_compile_definitions.rst

@@ -12,14 +12,15 @@ Add compile definitions to a target.
 Specify compile definitions to use when compiling a given ``<target>``.  The
 named ``<target>`` must have been created by a command such as
 :command:`add_executable` or :command:`add_library` and must not be an
-:ref:`Imported Target <Imported Targets>`.
+:ref:`ALIAS target <Alias Targets>`.
 
 The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to
 specify the scope of the following arguments.  ``PRIVATE`` and ``PUBLIC``
 items will populate the :prop_tgt:`COMPILE_DEFINITIONS` property of
 ``<target>``. ``PUBLIC`` and ``INTERFACE`` items will populate the
-:prop_tgt:`INTERFACE_COMPILE_DEFINITIONS` property of ``<target>``.  The
-following arguments specify compile definitions.  Repeated calls for the
+:prop_tgt:`INTERFACE_COMPILE_DEFINITIONS` property of ``<target>``.
+(:ref:`IMPORTED targets <Imported Targets>` only support ``INTERFACE`` items.)
+The following arguments specify compile definitions.  Repeated calls for the
 same ``<target>`` append items in the order called.
 
 Arguments to ``target_compile_definitions`` may use "generator expressions"

Help/command/target_compile_features.rst

@@ -18,12 +18,13 @@ The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to
 specify the scope of the features.  ``PRIVATE`` and ``PUBLIC`` items will
 populate the :prop_tgt:`COMPILE_FEATURES` property of ``<target>``.
 ``PUBLIC`` and ``INTERFACE`` items will populate the
-:prop_tgt:`INTERFACE_COMPILE_FEATURES` property of ``<target>``.  Repeated
-calls for the same ``<target>`` append items.
+:prop_tgt:`INTERFACE_COMPILE_FEATURES` property of ``<target>``.
+(:ref:`IMPORTED targets <Imported Targets>` only support ``INTERFACE`` items.)
+Repeated calls for the same ``<target>`` append items.
 
 The named ``<target>`` must have been created by a command such as
-:command:`add_executable` or :command:`add_library` and must not be
-an ``IMPORTED`` target.
+:command:`add_executable` or :command:`add_library` and must not be an
+:ref:`ALIAS target <Alias Targets>`.
 
 Arguments to ``target_compile_features`` may use "generator expressions"
 with the syntax ``$<...>``.

Help/command/target_compile_options.rst

@@ -12,8 +12,10 @@ Add compile options to a target.
 Specify compile options to use when compiling a given target.  The
 named ``<target>`` must have been created by a command such as
 :command:`add_executable` or :command:`add_library` and must not be an
-:ref:`IMPORTED Target <Imported Targets>`.  If ``BEFORE`` is specified,
-the content will be prepended to the property instead of being appended.
+:ref:`ALIAS target <Alias Targets>`.
+
+If ``BEFORE`` is specified, the content will be prepended to the property
+instead of being appended.
 
 This command can be used to add any options, but
 alternative commands exist to add preprocessor definitions
@@ -27,8 +29,9 @@ The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to
 specify the scope of the following arguments.  ``PRIVATE`` and ``PUBLIC``
 items will populate the :prop_tgt:`COMPILE_OPTIONS` property of
 ``<target>``.  ``PUBLIC`` and ``INTERFACE`` items will populate the
-:prop_tgt:`INTERFACE_COMPILE_OPTIONS` property of ``<target>``.  The
-following arguments specify compile options.  Repeated calls for the same
+:prop_tgt:`INTERFACE_COMPILE_OPTIONS` property of ``<target>``.
+(:ref:`IMPORTED targets <Imported Targets>` only support ``INTERFACE`` items.)
+The following arguments specify compile options.  Repeated calls for the same
 ``<target>`` append items in the order called.
 
 Arguments to ``target_compile_options`` may use "generator expressions"

Help/command/target_include_directories.rst

@@ -12,7 +12,7 @@ Add include directories to a target.
 Specify include directories to use when compiling a given target.
 The named ``<target>`` must have been created by a command such
 as :command:`add_executable` or :command:`add_library` and must not be an
-:prop_tgt:`IMPORTED` target.
+:ref:`ALIAS target <Alias Targets>`.
 
 If ``BEFORE`` is specified, the content will be prepended to the property
 instead of being appended.
@@ -21,9 +21,9 @@ The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to specify
 the scope of the following arguments.  ``PRIVATE`` and ``PUBLIC`` items will
 populate the :prop_tgt:`INCLUDE_DIRECTORIES` property of ``<target>``.
 ``PUBLIC`` and ``INTERFACE`` items will populate the
-:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES`
-property of ``<target>``.  The following arguments specify include
-directories.
+:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` property of ``<target>``.
+(:ref:`IMPORTED targets <Imported Targets>` only support ``INTERFACE`` items.)
+The following arguments specify include directories.
 
 Specified include directories may be absolute paths or relative paths.
 Repeated calls for the same <target> append items in the order called.  If

Help/command/target_link_libraries.rst

@@ -19,7 +19,8 @@ All of them have the general form::
   target_link_libraries(<target> ... <item>... ...)
 
 The named ``<target>`` must have been created in the current directory by
-a command such as :command:`add_executable` or :command:`add_library`.
+a command such as :command:`add_executable` or :command:`add_library` and
+must not be an :ref:`ALIAS target <Alias Targets>`.
 Repeated calls for the same ``<target>`` append items in the order called.
 Each ``<item>`` may be:
 

Help/command/target_sources.rst

@@ -12,14 +12,15 @@ Add sources to a target.
 Specify sources to use when compiling a given target.  The
 named ``<target>`` must have been created by a command such as
 :command:`add_executable` or :command:`add_library` and must not be an
-:ref:`IMPORTED Target <Imported Targets>`.
+:ref:`ALIAS target <Alias Targets>`.
 
 The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to
 specify the scope of the following arguments.  ``PRIVATE`` and ``PUBLIC``
 items will populate the :prop_tgt:`SOURCES` property of
 ``<target>``.  ``PUBLIC`` and ``INTERFACE`` items will populate the
-:prop_tgt:`INTERFACE_SOURCES` property of ``<target>``.  The
-following arguments specify sources.  Repeated calls for the same
+:prop_tgt:`INTERFACE_SOURCES` property of ``<target>``.
+(:ref:`IMPORTED targets <Imported Targets>` only support ``INTERFACE`` items.)
+The following arguments specify sources.  Repeated calls for the same
 ``<target>`` append items in the order called.
 
 Arguments to ``target_sources`` may use "generator expressions"