ENH: Introduce "rule hashes" to help rebuild files when rules change.

  - In CMake 2.4 custom commands would not rebuild when rules changed.
  - In CMake 2.6.0 custom commands have a dependency on build.make
    which causes them to rebuild when changed, but also when any
    source is added or removed.  This is too often.
  - We cannot have a per-rule file because Windows filesystems
    do not deal well with lots of small files.
  - Instead we add a persistent CMakeFiles/CMakeRuleHashes.txt file
    at the top of the build tree that is updated during each
    CMake Generate step.  It records a hash of the build rule for
    each file to be built.  When the hash changes the file is
    removed so that it will be rebuilt.

1 files changed, 6 insertions, 7 deletions

diff --git a/Source/cmMakefileTargetGenerator.cxx b/Source/cmMakefileTargetGenerator.cxx
index 5e724d4..ea0d9b8 100644
--- a/Source/cmMakefileTargetGenerator.cxx
+++ b/Source/cmMakefileTargetGenerator.cxx
@@ -1122,13 +1122,6 @@ void cmMakefileTargetGenerator
   std::vector<std::string> depends;
   this->LocalGenerator->AppendCustomDepend(depends, cc);
 
-  // Add a dependency on the rule file itself.
-  if(!cc.GetSkipRuleDepends())
-    {
-    this->LocalGenerator->AppendRuleDepend(depends,
-                                           this->BuildFileNameFull.c_str());
-    }
-
   // Check whether we need to bother checking for a symbolic output.
   bool need_symbolic = this->GlobalGenerator->GetNeedSymbolicMark();
 
@@ -1147,6 +1140,12 @@ void cmMakefileTargetGenerator
   this->LocalGenerator->WriteMakeRule(*this->BuildFileStream, 0,
                                       o->c_str(), depends, commands,
                                       symbolic);
+
+  // If the rule has changed make sure the output is rebuilt.
+  if(!symbolic)
+    {
+    this->GlobalGenerator->AddRuleHash(cc.GetOutputs(), depends, commands);
+    }
   }
 
   // Write rules to drive building any outputs beyond the first.