ENH: Allow empty arguments in external project API

This uses the get_property command to simplify property lookup in the
AddExternalProject module.  It distinguishes for build and install
argument properties the cases of unset and set to empty.

1 files changed, 13 insertions, 28 deletions

diff --git a/Modules/AddExternalProject.cmake b/Modules/AddExternalProject.cmake
index 7dcbe55..4053c19 100644
--- a/Modules/AddExternalProject.cmake
+++ b/Modules/AddExternalProject.cmake
@@ -127,11 +127,7 @@ function(add_external_project_download_command name)
       message(FATAL_ERROR "error: no CVS_MODULE")
     endif()
 
-    get_target_property(tag ${name} AEP_CVS_TAG)
-    set(cvs_tag)
-    if(tag)
-      set(cvs_tag ${tag})
-    endif()
+    get_property(cvs_tag TARGET ${name} PROPERTY AEP_CVS_TAG)
 
     set(args -d ${cvs_repository} -q co ${cvs_tag} -d ${name} ${cvs_module})
 
@@ -164,11 +160,7 @@ function(add_external_project_download_command name)
       message(FATAL_ERROR "error: could not find svn for checkout of ${name}")
     endif()
 
-    get_target_property(tag ${name} AEP_SVN_TAG)
-    set(svn_tag)
-    if(tag)
-      set(svn_tag ${tag})
-    endif()
+    get_property(svn_tag TARGET ${name} PROPERTY AEP_SVN_TAG)
 
     set(args co ${svn_repository} ${svn_tag} ${name})
 
@@ -356,11 +348,7 @@ function(add_external_project_update_command name)
       message(FATAL_ERROR "error: could not find cvs for update of ${name}")
     endif()
 
-    get_target_property(tag ${name} AEP_CVS_TAG)
-    set(cvs_tag)
-    if(tag)
-      set(cvs_tag ${tag})
-    endif()
+    get_property(cvs_tag TARGET ${name} PROPERTY AEP_CVS_TAG)
 
     set(args -d ${cvs_repository} -q up -dP ${cvs_tag})
 
@@ -385,11 +373,7 @@ function(add_external_project_update_command name)
       message(FATAL_ERROR "error: could not find svn for update of ${name}")
     endif()
 
-    get_target_property(tag ${name} AEP_SVN_TAG)
-    set(svn_tag)
-    if(tag)
-      set(svn_tag ${tag})
-    endif()
+    get_property(svn_tag TARGET ${name} PROPERTY AEP_SVN_TAG)
 
     set(args up ${svn_tag})
 
@@ -423,10 +407,7 @@ function(add_external_project_configure_command name)
     sentinels_dir source_dir tmp_dir)
   get_configure_build_working_dir(${name} working_dir)
 
-  get_target_property(file_deps ${name} AEP_FILE_DEPENDS)
-  if(NOT file_deps)
-    set(file_deps)
-  endif()
+  get_property(file_deps TARGET ${name} PROPERTY AEP_FILE_DEPENDS)
   #message(STATUS "info: name='${name}' file_deps='${file_deps}'")
 
   # Create the working_dir for configure, build and install steps:
@@ -504,8 +485,10 @@ function(add_external_project_build_command name)
       endif()
     endif()
 
-    get_target_property(args ${name} AEP_BUILD_ARGS)
-    if(NOT args)
+    get_property(have_args TARGET ${name} PROPERTY AEP_BUILD_ARGS SET)
+    if(have_args)
+      get_target_property(args ${name} AEP_BUILD_ARGS)
+    else()
       set(args)
       if(cfg_cmd_id STREQUAL "cmake")
         set(args --build ${working_dir} --config ${CMAKE_CFG_INTDIR})
@@ -555,8 +538,10 @@ function(add_external_project_install_command name)
       endif()
     endif()
 
-    get_target_property(args ${name} AEP_INSTALL_ARGS)
-    if(NOT args)
+    get_property(have_args TARGET ${name} PROPERTY AEP_INSTALL_ARGS SET)
+    if(have_args)
+      get_target_property(args ${name} AEP_INSTALL_ARGS)
+    else()
       set(args)
       if(cfg_cmd_id STREQUAL "cmake")
         set(args --build ${working_dir} --config ${CMAKE_CFG_INTDIR} --target install)