cmake: Add -E copy_directory_if_different

Fixes #21584

Help/manual/cmake.1.rst

@@ -876,6 +876,16 @@ Available commands are:
     The command now fails when the source directory does not exist.
     Previously it succeeded by creating an empty destination directory.
 
+.. option:: copy_directory_if_different <dir>... <destination>
+
+  .. versionadded:: 3.26
+
+  Copy changed content of ``<dir>...`` directories to ``<destination>`` directory.
+  If ``<destination>`` directory does not exist it will be created.
+
+  ``copy_directory_if_different`` does follow symlinks.
+  The command fails when the source directory does not exist.
+
 .. option:: copy_if_different <file>... <destination>
 
   Copy files to ``<destination>`` (either file or directory) if

Help/release/dev/cmake-E-copy-directory-if-different.rst

@@ -0,0 +1,4 @@
+cmake-E-copy-directory-if-different
+-----------------------------------
+
+* The :manual:`cmake(1)` ``-E`` option learned a new ``copy_directory_if_different`` command.

Source/cmcmd.cxx

@@ -110,6 +110,8 @@ void CMakeCommandUsage(std::string const& program)
        "(either file or directory)\n"
     << "  copy_directory <dir>... destination   - copy content of <dir>... "
        "directories to 'destination' directory\n"
+    << "  copy_directory_if_different <dir>... destination   - copy changed content of <dir>... "
+       "directories to 'destination' directory\n"
     << "  copy_if_different <file>... destination  - copy files if it has "
        "changed\n"
     << "  echo [<string>...]        - displays arguments as text\n"
@@ -731,12 +733,15 @@ int cmcmd::ExecuteCMakeCommand(std::vector<std::string> const& args,
       return return_value;
     }
 
-    // Copy directory content
-    if (args[1] == "copy_directory" && args.size() > 3) {
+    // Copy directory contents
+    if ((args[1] == "copy_directory" ||
+         args[1] == "copy_directory_if_different") &&
+        args.size() > 3) {
       // If error occurs we want to continue copying next files.
       bool return_value = false;
+      const bool copy_always = (args[1] == "copy_directory");
       for (auto const& arg : cmMakeRange(args).advance(2).retreat(1)) {
-        if (!cmSystemTools::CopyADirectory(arg, args.back())) {
+        if (!cmSystemTools::CopyADirectory(arg, args.back(), copy_always)) {
           std::cerr << "Error copying directory from \"" << arg << "\" to \""
                     << args.back() << "\".\n";
           return_value = true;

Tests/RunCMake/CommandLine/RunCMakeTest.cmake

@@ -593,6 +593,15 @@ run_cmake_command(E_copy_if_different-three-source-files-target-is-file
 unset(in)
 unset(out)
 
+set(in ${RunCMake_SOURCE_DIR}/copy_input)
+set(out ${RunCMake_BINARY_DIR}/copy_directory_different_output)
+file(REMOVE_RECURSE "${out}")
+file(MAKE_DIRECTORY ${out})
+run_cmake_command(E_copy_directory_if_different
+  ${CMAKE_COMMAND} -E copy_directory_if_different ${in} ${out})
+unset(in)
+unset(out)
+
 set(in ${RunCMake_SOURCE_DIR}/copy_input)
 set(out ${RunCMake_BINARY_DIR}/copy_directory_output)
 set(outfile ${out}/file_for_test.txt)