build,scratch: add a nested scratch directory example

Signed-off-by: Gabriel Ferreira <gabrielcarvfer@gmail.com>

build-support/macros-and-definitions.cmake

@@ -537,6 +537,7 @@ macro(process_options)
   else()
     file(GLOB_RECURSE MODULES_CMAKE_FILES src/**/CMakeLists.txt
          contrib/**/CMakeLists.txt examples/**/CMakeLists.txt
+         scratch/**/CMakeLists.txt
     )
     file(
       GLOB
@@ -1517,6 +1518,17 @@ function(set_runtime_outputdirectory target_name output_directory target_prefix)
   endif()
 endfunction(set_runtime_outputdirectory)
 
+function(get_scratch_prefix prefix)
+  # /path/to/ns-3-dev/scratch/nested-subdir
+  set(temp ${CMAKE_CURRENT_SOURCE_DIR})
+  # remove /path/to/ns-3-dev/ to get scratch/nested-subdir
+  string(REPLACE "${PROJECT_SOURCE_DIR}/" "" temp "${temp}")
+  # replace path separators with underlines
+  string(REPLACE "/" "_" temp "${temp}")
+  # save the prefix value to the passed variable
+  set(${prefix} ${temp}_ PARENT_SCOPE)
+endfunction()
+
 function(build_exec)
   # Argument parsing
   set(options IGNORE_PCH STANDALONE)
@@ -1528,6 +1540,13 @@ function(build_exec)
     "BEXEC" "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN}
   )
 
+  # Resolve nested scratch prefixes without user intervention
+  if("${CMAKE_CURRENT_SOURCE_DIR}" MATCHES "scratch"
+     AND "${BEXEC_EXECNAME_PREFIX}" STREQUAL ""
+  )
+    get_scratch_prefix(BEXEC_EXECNAME_PREFIX)
+  endif()
+
   add_executable(
     ${BEXEC_EXECNAME_PREFIX}${BEXEC_EXECNAME} "${BEXEC_SOURCE_FILES}"
   )

scratch/nested-subdir/CMakeLists.txt

@@ -0,0 +1,16 @@
+# Create a custom library
+add_library(
+  scratch-nested-subdir-lib
+  lib/scratch-nested-subdir-library-source.cc
+)
+
+# Link the custom library to the scratch executable
+build_exec(
+  EXECNAME scratch-nested-subdir-executable
+  SOURCE_FILES scratch-nested-subdir-executable.cc
+  LIBRARIES_TO_LINK scratch-nested-subdir-lib
+                    ${libcore}
+  # use "${ns3-libs}" "${ns3-contrib-libs}" in case you want to link to all
+  # enabled modules
+  EXECUTABLE_DIRECTORY_PATH ${CMAKE_OUTPUT_DIRECTORY}/scratch/nested-subdir
+)

scratch/nested-subdir/lib/scratch-nested-subdir-library-header.h

@@ -0,0 +1,32 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+// This header does not provide much functionality but is meant to demonstrate how,
+// in a scratch subdirectory, one can create new programs that are implemented
+// in multiple files and headers.
+
+#include <string>
+
+namespace ns3
+{
+
+/**
+ * Get a message from the subdir.
+ *
+ * \return The message from the subdir
+ */
+std::string ScratchNestedSubdirGetMessage();
+
+} // namespace ns3

scratch/nested-subdir/lib/scratch-nested-subdir-library-source.cc

@@ -0,0 +1,30 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+// This file contains the implementation of the functions declared in the
+// corresponding header file.
+
+#include "scratch-nested-subdir-library-header.h"
+
+namespace ns3
+{
+
+std::string
+ScratchNestedSubdirGetMessage()
+{
+    return "Scratch Nested Subdir";
+}
+
+} // namespace ns3

scratch/nested-subdir/scratch-nested-subdir-executable.cc

@@ -0,0 +1,51 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+// This example shows how to create new simulations that are implemented in
+// multiple files and headers. The structure of this simulation project
+// is as follows:
+//
+// scratch/
+// |  nested-subdir/
+// |  |  - scratch-nested-subdir-executable.cc        // Main simulation file
+// |  |  lib
+// |  |  |  - scratch-nested-subdir-library-header.h  // Additional header
+// |  |  |  - scratch-nested-subdir-library-source.cc // Additional header implementation
+//
+// This file contains the main() function, which calls an external function
+// defined in the "scratch-nested-subdir-library-header.h" header file and
+// implemented in "scratch-nested-subdir-library-source.cc".
+
+#include "lib/scratch-nested-subdir-library-header.h"
+
+#include "ns3/core-module.h"
+
+#include <string>
+
+using namespace ns3;
+
+NS_LOG_COMPONENT_DEFINE("ScratchNestedSubdir");
+
+int
+main(int argc, char* argv[])
+{
+    std::string message = ScratchNestedSubdirGetMessage();
+    NS_LOG_UNCOND(message);
+
+    Simulator::Run();
+    Simulator::Destroy();
+
+    return 0;
+}