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.

1 files changed, 18 insertions, 3 deletions

diff --git a/Source/cmAddCustomCommandCommand.cxx b/Source/cmAddCustomCommandCommand.cxx
index 5912a79f0e..afbdc70c4f 100644
--- a/Source/cmAddCustomCommandCommand.cxx
+++ b/Source/cmAddCustomCommandCommand.cxx
@@ -40,6 +40,7 @@ bool cmAddCustomCommandCommand
   std::vector<std::string> depends, outputs, output;
   bool verbatim = false;
   bool append = false;
+  bool skip_rule_depends = false;
   std::string implicit_depends_lang;
   cmCustomCommand::ImplicitDependsList implicit_depends;
 
@@ -103,6 +104,11 @@ bool cmAddCustomCommandCommand
       {
       verbatim = true;
       }
+    else if(copy == "SKIP_RULE_DEPENDS")
+      {
+      doing = doing_nothing;
+      skip_rule_depends = true;
+      }
     else if(copy == "APPEND")
       {
       append = true;
@@ -310,8 +316,8 @@ bool cmAddCustomCommandCommand
                                              working.c_str(), false,
                                              escapeOldStyle);
 
-    // Add implicit dependency scanning requests if any were given.
-    if(!implicit_depends.empty())
+    // Get the rule object to add some extra information.
+    if(!implicit_depends.empty() || skip_rule_depends)
       {
       bool okay = false;
       if(cmSourceFile* sf =
@@ -320,7 +326,16 @@ bool cmAddCustomCommandCommand
         if(cmCustomCommand* cc = sf->GetCustomCommand())
           {
           okay = true;
-          cc->SetImplicitDepends(implicit_depends);
+
+          // Add implicit dependency scanning requests if any were
+          // given.
+          if(!implicit_depends.empty())
+            {
+            cc->SetImplicitDepends(implicit_depends);
+            }
+
+          // Set the rule dependency state.
+          cc->SetSkipRuleDepends(skip_rule_depends);
           }
         }
       if(!okay)