Add a directory property to list subdirectories

Add a SUBDIRECTORIES directory property to allow project code to
traverse the directory structure of itself as CMake sees it.

Help/manual/cmake-properties.7.rst

@@ -73,6 +73,7 @@ Properties on Directories
    /prop_dir/RULE_LAUNCH_COMPILE
    /prop_dir/RULE_LAUNCH_CUSTOM
    /prop_dir/RULE_LAUNCH_LINK
+   /prop_dir/SUBDIRECTORIES
    /prop_dir/TEST_INCLUDE_FILE
    /prop_dir/VARIABLES
    /prop_dir/VS_GLOBAL_SECTION_POST_section

Help/prop_dir/SUBDIRECTORIES.rst

+SUBDIRECTORIES
+--------------
+
+This read-only directory property contains a
+:ref:`;-list <CMake Language Lists>` of subdirectories processed so far by
+the :command:`add_subdirectory` or :command:`subdirs` commands.  Each entry is
+the absolute path to the source directory (containing the ``CMakeLists.txt``
+file).  This is suitable to pass to the :command:`get_property` command
+``DIRECTORY`` option.
+
+.. note::
+
+  The :command:`subdirs` command does not process its arguments until
+  after the calling directory is fully processed.  Therefore looking
+  up this property in the current directory will not see them.

Help/release/dev/directory-list-targets-and-subdirs.rst

+directory-list-targets-and-subdirs
+----------------------------------
+
+* A :prop_dir:`SUBDIRECTORIES` directory property was added to
+  get the list of subdirectories added by a project in a directory.

Source/cmState.cxx

@@ -29,6 +29,8 @@
 #include <string.h>
 #include <utility>
 
+static std::string const kSUBDIRECTORIES = "SUBDIRECTORIES";
+
 struct cmState::SnapshotDataType
 {
   cmState::PositionType ScopeParent;
@@ -1670,6 +1672,18 @@ const char* cmState::Directory::GetProperty(const std::string& prop,
     }
     return "";
   }
+  if (prop == kSUBDIRECTORIES) {
+    std::vector<std::string> child_dirs;
+    std::vector<cmState::Snapshot> const& children =
+      this->DirectoryState->Children;
+    for (std::vector<cmState::Snapshot>::const_iterator ci = children.begin();
+         ci != children.end(); ++ci) {
+      child_dirs.push_back(ci->GetDirectory().GetCurrentSource());
+    }
+    output = cmJoin(child_dirs, ";");
+    return output.c_str();
+  }
+
   if (prop == "LISTFILE_STACK") {
     std::vector<std::string> listFiles;
     cmState::Snapshot snp = this->Snapshot_;

Tests/RunCMake/get_property/directory_properties-stderr.txt

@@ -3,4 +3,8 @@ get_property: --><--
 get_directory_property: -->value<--
 get_property: -->value<--
 get_directory_property: --><--
-get_property: --><--$
+get_property: --><--
+get_directory_property: -->[^<;]*Tests/RunCMake/get_property/directory_properties<--
+get_property: -->[^<;]*Tests/RunCMake/get_property/directory_properties<--
+get_directory_property: -->[^<;]*Tests/RunCMake/get_property/directory_properties/sub1;[^<;]*Tests/RunCMake/get_property/directory_properties/sub2<--
+get_property: -->[^<;]*Tests/RunCMake/get_property/directory_properties/sub1;[^<;]*Tests/RunCMake/get_property/directory_properties/sub2<--$

Tests/RunCMake/get_property/directory_properties.cmake

@@ -13,3 +13,7 @@ set_directory_properties(PROPERTIES empty "" custom value)
 check_directory_property("${CMAKE_CURRENT_SOURCE_DIR}" empty)
 check_directory_property("${CMAKE_CURRENT_SOURCE_DIR}" custom)
 check_directory_property("${CMAKE_CURRENT_SOURCE_DIR}" noexist)
+
+add_subdirectory(directory_properties)
+check_directory_property("${CMAKE_CURRENT_SOURCE_DIR}" SUBDIRECTORIES)
+check_directory_property("${CMAKE_CURRENT_SOURCE_DIR}/directory_properties" SUBDIRECTORIES)

Tests/RunCMake/get_property/directory_properties/CMakeLists.txt

+add_subdirectory(sub1)
+subdirs(sub2)