ALIAS: Add support for set_property and set_target_properties commands

Currently, getting properties from an ALIAS target retrieves the property
from the target which the alias references while setting properties results
in an error. This relaxes set_property and set_target_properties to
accept ALIAS targets and act on the referenced target, mirroring the get
behavior.

An error is raised when setting ALIAS_GLOBAL or ALIASED_TARGET on an ALIAS
target.

Closes: #19445

Help/command/add_executable.rst

@@ -112,11 +112,16 @@ Alias Executables
 ``ALIAS`` targets can be used as targets to read properties
 from, executables for custom commands and custom targets.  They can also be
 tested for existence with the regular :command:`if(TARGET)` subcommand.
-The ``<name>`` may not be used to modify properties of ``<target>``, that
-is, it may not be used as the operand of :command:`set_property`,
-:command:`set_target_properties`, :command:`target_link_libraries` etc.
 An ``ALIAS`` target may not be installed or exported.
 
+.. versionchanged:: 4.5
+  The ``<name>`` may be used as the operand of :command:`set_property` and
+  :command:`set_target_properties` to modify properties of ``<target>``.  It
+  may not be used with the commands :command:`target_link_libraries`,
+  :command:`target_compile_definitions` etc.  CMake 4.4 and earlier did not
+  allow the ``<name>`` to modify properties of ``<target>`` with
+  :command:`set_property` and :command:`set_target_properties`.
+
 See Also
 ^^^^^^^^
 

Help/command/add_library.rst

@@ -317,12 +317,17 @@ Alias Libraries
 
 ``ALIAS`` targets can be used as linkable targets and as targets to
 read properties from.  They can also be tested for existence with the
-regular :command:`if(TARGET)` subcommand.  The ``<name>`` may not be used
-to modify properties of ``<target>``, that is, it may not be used as the
-operand of :command:`set_property`, :command:`set_target_properties`,
-:command:`target_link_libraries` etc.  An ``ALIAS`` target may not be
+regular :command:`if(TARGET)` subcommand.  An ``ALIAS`` target may not be
 installed or exported.
 
+.. versionchanged:: 4.5
+  The ``<name>`` may be used as the operand of :command:`set_property` and
+  :command:`set_target_properties` to modify properties of ``<target>``.  It
+  may not be used with the commands :command:`target_link_libraries`,
+  :command:`target_compile_definitions` etc.  CMake 4.4 and earlier did not
+  allow the ``<name>`` to modify properties of ``<target>`` with
+  :command:`set_property` and :command:`set_target_properties`.
+
 See Also
 ^^^^^^^^
 

Help/command/set_property.rst

@@ -40,7 +40,9 @@ It must be one of the following:
   Scope may name zero or more existing targets.
   See also the :command:`set_target_properties` command.
 
-  :ref:`Alias Targets` do not support setting target properties.
+  .. versionchanged:: 4.5
+    If ``<target>`` is an :ref:`Alias Target <Alias Targets>`, properties are
+    set on the target which the alias references.
 
 ``FILE_SET``
   .. versionadded:: 4.3

Help/command/set_target_properties.rst

@@ -15,7 +15,9 @@ set next.  You can use any prop value pair you want and extract it
 later with the :command:`get_property` or :command:`get_target_property`
 command.
 
-:ref:`Alias Targets` do not support setting target properties.
+.. versionchanged:: 4.5
+  If ``<targets>`` contains :ref:`Alias Targets`, properties are set on the
+  corresponding target referenced by each alias.
 
 See Also
 ^^^^^^^^

Help/manual/cmake-buildsystem.7.rst

@@ -1429,9 +1429,16 @@ target, which may be an :prop_tgt:`IMPORTED` target from a package, or an
   target_link_libraries(exe1 Upstream::lib1)
 
 ``ALIAS`` targets are not mutable, installable or exportable.  They are
-entirely local to the buildsystem description.  A name can be tested for
-whether it is an ``ALIAS`` name by reading the :prop_tgt:`ALIASED_TARGET`
-property from it:
+entirely local to the buildsystem description.
+
+.. versionchanged:: 4.5
+  ``ALIAS`` targets may be used as the operand for :command:`set_property` and
+  similar commands used to modify properties of targets.  The commands operate
+  on the target which the alias references.  CMake 4.4 and earlier did not
+  allow modifying targets via an ``ALIAS``.
+
+A name can be tested for whether it is an ``ALIAS`` name by reading the
+:prop_tgt:`ALIASED_TARGET` property from it:
 
 .. code-block:: cmake
 

Help/release/dev/alias-transparency.rst

@@ -0,0 +1,6 @@
+alias-transparency
+------------------
+
+* The :command:`set_property` and :command:`set_target_properties` commands
+  now accept :ref:`Alias Targets`. Properties are set on the target which
+  the alias references.

Source/cmSetPropertyCommand.cxx

@@ -709,11 +709,14 @@ bool HandleTargetMode(cmExecutionStatus& status,
                       bool appendMode, bool remove)
 {
   for (std::string const& name : names) {
-    if (status.GetMakefile().IsAlias(name)) {
-      status.SetError("can not be used on an ALIAS target.");
-      return false;
+    // Better error message for alias properties set on an alias target.
+    if (propertyName == "ALIASED_TARGET" || propertyName == "ALIAS_GLOBAL") {
+      if (status.GetMakefile().IsAlias(name)) {
+        status.SetError(cmStrCat("can not set property ", propertyName,
+                                 " on an ALIAS target: ", name));
+        return false;
+      }
     }
-
     if (cmTarget* target = status.GetMakefile().FindTargetToUse(name)) {
       if (target->IsSymbolic()) {
         status.SetError("can not be used on a SYMBOLIC target.");

Source/cmSetTargetPropertiesCommand.cxx

@@ -35,10 +35,6 @@ bool cmSetTargetPropertiesCommand(std::vector<std::string> const& args,
 
   // loop over all the targets
   for (std::string const& tname : cmStringRange{ args.begin(), propsIter }) {
-    if (mf.IsAlias(tname)) {
-      status.SetError("can not be used on an ALIAS target.");
-      return false;
-    }
     if (cmTarget* target = mf.FindTargetToUse(tname)) {
       if (target->IsSymbolic()) {
         status.SetError("can not be used on a SYMBOLIC target.");
@@ -46,6 +42,14 @@ bool cmSetTargetPropertiesCommand(std::vector<std::string> const& args,
       }
       // loop through all the props and set them
       for (auto k = propsIter + 1; k != args.end(); k += 2) {
+        // Better error message for alias properties set on an alias target.
+        if (*k == "ALIASED_TARGET" || *k == "ALIAS_GLOBAL") {
+          if (mf.IsAlias(tname)) {
+            status.SetError(cmStrCat("can not set property ", *k,
+                                     " on an ALIAS target: ", tname));
+            return false;
+          }
+        }
         target->SetProperty(*k, *(k + 1));
         target->CheckProperty(*k, &mf);
       }

Tests/RunCMake/alias_targets/RunCMakeTest.cmake

@@ -12,8 +12,10 @@ run_cmake(imported-global-target)
 run_cmake(imported-target)
 run_cmake(alias-target)
 run_cmake(set_property)
+run_cmake(set_property-ALIAS_GLOBAL)
 run_cmake(get_property)
 run_cmake(set_target_properties)
+run_cmake(set_target_properties-ALIAS_GLOBAL)
 run_cmake(target_link_libraries)
 run_cmake(target_include_directories)
 run_cmake(export)

Tests/RunCMake/alias_targets/set_property-ALIAS_GLOBAL-stderr.txt

@@ -0,0 +1,2 @@
+CMake Error at set_property-ALIAS_GLOBAL\.cmake:[0-9]+ \(set_property\):
+  set_property can not set property ALIAS_GLOBAL on an ALIAS target: alias

Tests/RunCMake/alias_targets/set_property-ALIAS_GLOBAL.cmake

@@ -0,0 +1,6 @@
+enable_language(CXX)
+
+add_library(foo empty.cpp)
+add_library(alias ALIAS foo)
+
+set_property(TARGET alias PROPERTY ALIAS_GLOBAL something)

Tests/RunCMake/alias_targets/set_property-stderr.txt

@@ -1,4 +0,0 @@
-CMake Error at set_property\.cmake:8 \(set_property\):
-  set_property can not be used on an ALIAS target\.
-Call Stack \(most recent call first\):
-  CMakeLists\.txt:3 \(include\)

Tests/RunCMake/alias_targets/set_property.cmake

@@ -6,3 +6,8 @@ add_library(foo empty.cpp)
 add_library(alias ALIAS foo)
 
 set_property(TARGET alias PROPERTY ANYTHING 1)
+
+get_target_property(val foo ANYTHING)
+if(NOT val STREQUAL "1")
+  message(SEND_ERROR "set_property(): Target property 'ANYTHING' set on ALIAS 'alias' has wrong value on aliased target 'foo': '${val}' instead of '1'.")
+endif()

Tests/RunCMake/alias_targets/set_target_properties-ALIAS_GLOBAL-stderr.txt

@@ -0,0 +1,3 @@
+CMake Error at set_target_properties-ALIAS_GLOBAL\.cmake:[0-9]+ \(set_target_properties\):
+  set_target_properties can not set property ALIAS_GLOBAL on an ALIAS target:
+  alias

Tests/RunCMake/alias_targets/set_target_properties-ALIAS_GLOBAL.cmake

@@ -0,0 +1,6 @@
+enable_language(CXX)
+
+add_library(foo empty.cpp)
+add_library(alias ALIAS foo)
+
+set_target_properties(alias PROPERTIES ALIAS_GLOBAL something)

Tests/RunCMake/alias_targets/set_target_properties-stderr.txt

@@ -1,4 +0,0 @@
-CMake Error at set_target_properties\.cmake:8 \(set_target_properties\):
-  set_target_properties can not be used on an ALIAS target\.
-Call Stack \(most recent call first\):
-  CMakeLists\.txt:3 \(include\)

Tests/RunCMake/alias_targets/set_target_properties.cmake

@@ -6,3 +6,8 @@ add_library(foo empty.cpp)
 add_library(alias ALIAS foo)
 
 set_target_properties(alias PROPERTIES ANYTHING 1)
+
+get_target_property(val foo ANYTHING)
+if(NOT val STREQUAL "1")
+  message(SEND_ERROR "set_target_properties(): Target property 'ANYTHING' set on ALIAS 'alias' has wrong value on aliased target 'foo': '${val}' instead of '1'.")
+endif()