Allow target commands to be invoked with no items (#14325).

Code such as

 target_include_directories(foo PRIVATE ${items})

should not work or break based on whether items is defined or not.

Source/cmTargetPropCommandBase.cxx

@@ -19,7 +19,7 @@ bool cmTargetPropCommandBase
 ::HandleArguments(std::vector<std::string> const& args, const char *prop,
                  ArgumentFlags flags)
 {
-  if(args.size() < 3)
+  if(args.size() < 2)
     {
     this->SetError("called with incorrect number of arguments");
     return false;
@@ -53,7 +53,7 @@ bool cmTargetPropCommandBase
 
   if ((flags & PROCESS_SYSTEM) && args[argIndex] == "SYSTEM")
     {
-    if (args.size() < 4)
+    if (args.size() < 3)
       {
       this->SetError("called with incorrect number of arguments");
       return false;
@@ -65,7 +65,7 @@ bool cmTargetPropCommandBase
   bool prepend = false;
   if ((flags & PROCESS_BEFORE) && args[argIndex] == "BEFORE")
     {
-    if (args.size() < 4)
+    if (args.size() < 3)
       {
       this->SetError("called with incorrect number of arguments");
       return false;

Tests/CMakeCommands/target_compile_definitions/CMakeLists.txt

@@ -20,3 +20,8 @@ target_compile_definitions(consumer
   PRIVATE $<TARGET_PROPERTY:target_compile_definitions,INTERFACE_COMPILE_DEFINITIONS>
   -DDASH_D_DEFINE
 )
+
+# Test no items
+target_compile_definitions(consumer
+  PRIVATE
+)

Tests/CMakeCommands/target_compile_options/CMakeLists.txt

@@ -33,3 +33,8 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
       "DO_GNU_TESTS"
   )
 endif()
+
+# Test no items
+target_compile_options(consumer
+  PRIVATE
+)

Tests/CMakeCommands/target_include_directories/CMakeLists.txt

@@ -47,3 +47,17 @@ target_include_directories(consumer
     $<TARGET_PROPERTY:target_include_directories,INTERFACE_INCLUDE_DIRECTORIES>
   relative_dir
 )
+
+# Test no items
+target_include_directories(consumer
+  PRIVATE
+)
+target_include_directories(consumer
+  BEFORE PRIVATE
+)
+target_include_directories(consumer
+  SYSTEM BEFORE PRIVATE
+)
+target_include_directories(consumer
+  SYSTEM PRIVATE
+)