ENH: Add SKIP_RULE_DEPENDS option for add_custom_command()

  - Allows make rules to be created with no dependencies.
  - Such rules will not re-run even if the commands themselves change.
  - Useful to create rules that run only if the output is missing.

3 files changed, 11 insertions, 1 deletions

diff --git a/Tests/CustomCommand/CMakeLists.txt b/Tests/CustomCommand/CMakeLists.txt
index 7e9f29c..5ee0519 100644
--- a/Tests/CustomCommand/CMakeLists.txt
+++ b/Tests/CustomCommand/CMakeLists.txt
@@ -151,6 +151,14 @@ ADD_EXECUTABLE(CustomCommand
   ${PROJECT_BINARY_DIR}/generated.c
   ${PROJECT_BINARY_DIR}/not_included.h
   gen_redirect.c # default location for custom commands is in build tree
+  gen_once.c
+  )
+
+# Add a rule with no dependencies.
+ADD_CUSTOM_COMMAND(
+  OUTPUT gen_once.c
+  COMMAND ${CMAKE_COMMAND} -E copy ${PROJECT_SOURCE_DIR}/gen_once.c.in ${PROJECT_BINARY_DIR}/gen_once.c
+  SKIP_RULE_DEPENDS
   )
 
 # Add the rule to create generated.c at build time.  This is placed
diff --git a/Tests/CustomCommand/foo.in b/Tests/CustomCommand/foo.in
index 08c559d..c5ce340 100644
--- a/Tests/CustomCommand/foo.in
+++ b/Tests/CustomCommand/foo.in
@@ -6,10 +6,11 @@
 
 int generated();
 int wrapped();
+int gen_once(void);
 
 int main ()
 {
-  if (generated()*wrapped()*doc() == 3*5*7)
+  if (generated()*wrapped()*doc()*gen_once() == 3*5*7*11)
     {
     FILE* fin = fopen(PROJECT_BINARY_DIR "/not_included.h", "r");
     if(fin)
diff --git a/Tests/CustomCommand/gen_once.c.in b/Tests/CustomCommand/gen_once.c.in
new file mode 100644
index 0000000..dc8eb67
--- /dev/null
+++ b/Tests/CustomCommand/gen_once.c.in
@@ -0,0 +1 @@
+int gen_once(void) { return 11; }