Cleanup source file dependency tracing logic

In cmTarget we trace the dependencies of source files in the target to
bring in all custom commands needed to generate them.  We clean up the
implementation to use simpler logic and better method names.  The new
approach is based on the observation that a source file is actually an
input (dependency) of the rule that it runs (compiler or custom) even in
the case that it is generated (another .rule file has the rule to
generate it).

Source/cmTarget.cxx

@@ -1087,12 +1087,14 @@ private:
   cmTarget* Target;
   cmMakefile* Makefile;
   cmGlobalGenerator* GlobalGenerator;
-  std::queue<cmStdString> DependencyQueue;
+  std::queue<cmSourceFile*> SourceQueue;
-  std::set<cmStdString> DependenciesQueued;
+  std::set<cmSourceFile*> SourcesQueued;
+  typedef std::map<cmStdString, cmSourceFile*> NameMapType;
+  NameMapType NameMap;
 
-  void QueueOnce(std::string const& name);
+  void QueueSource(cmSourceFile* sf);
-  void QueueOnce(std::vector<std::string> const& names);
+  void FollowName(std::string const& name);
-  void QueueDependencies(cmSourceFile* sf);
+  void FollowNames(std::vector<std::string> const& names);
   bool IsUtility(std::string const& dep);
   void CheckCustomCommand(cmCustomCommand const& cc);
   void CheckCustomCommands(const std::vector<cmCustomCommand>& commands);
@@ -1113,19 +1115,14 @@ cmTargetTraceDependencies
   for(std::vector<cmSourceFile*>::const_iterator si = sources.begin();
       si != sources.end(); ++si)
     {
-    // Queue the source file itself in case it is generated.
+    this->QueueSource(*si);
-    this->QueueOnce((*si)->GetFullPath());
-
-    // Queue the dependencies of the source file in case they are
-    // generated.
-    this->QueueDependencies(*si);
     }
 
   // Queue the VS project file to check dependencies on the rule to
   // generate it.
   if(vsProjectFile)
     {
-    this->QueueOnce(vsProjectFile);
+    this->FollowName(vsProjectFile);
     }
 
   // Queue pre-build, pre-link, and post-build rule dependencies.
@@ -1138,42 +1135,71 @@ cmTargetTraceDependencies
 void cmTargetTraceDependencies::Trace()
 {
   // Process one dependency at a time until the queue is empty.
-  while(!this->DependencyQueue.empty())
+  while(!this->SourceQueue.empty())
     {
-    // Get the next dependency in from queue.
+    // Get the next source from the queue.
-    std::string dep = this->DependencyQueue.front();
+    cmSourceFile* sf = this->SourceQueue.front();
-    this->DependencyQueue.pop();
+    this->SourceQueue.pop();
 
-    // Check if we know how to generate this dependency.
+    // Queue dependencies added explicitly by the user.
-    if(cmSourceFile* sf =
+    if(const char* additionalDeps = sf->GetProperty("OBJECT_DEPENDS"))
-       this->Makefile->GetSourceFileWithOutput(dep.c_str()))
       {
-      // Queue dependencies needed to generate this file.
+      std::vector<std::string> objDeps;
-      this->QueueDependencies(sf);
+      cmSystemTools::ExpandListArgument(additionalDeps, objDeps);
+      this->FollowNames(objDeps);
+      }
 
-      // Make sure this file is in the target.
+    // Queue the source needed to generate this file, if any.
-      this->Target->AddSourceFile(sf);
+    this->FollowName(sf->GetFullPath());
+
+    // Queue dependencies added programatically by commands.
+    this->FollowNames(sf->GetDepends());
+
+    // Queue custom command dependencies.
+    if(cmCustomCommand const* cc = sf->GetCustomCommand())
+      {
+      this->CheckCustomCommand(*cc);
       }
     }
 }
 
 //----------------------------------------------------------------------------
-void cmTargetTraceDependencies::QueueOnce(std::string const& name)
+void cmTargetTraceDependencies::QueueSource(cmSourceFile* sf)
 {
-  if(this->DependenciesQueued.insert(name).second)
+  if(this->SourcesQueued.insert(sf).second)
     {
-    this->DependencyQueue.push(name);
+    this->SourceQueue.push(sf);
+
+    // Make sure this file is in the target.
+    this->Target->AddSourceFile(sf);
+    }
+}
+
+//----------------------------------------------------------------------------
+void cmTargetTraceDependencies::FollowName(std::string const& name)
+{
+  NameMapType::iterator i = this->NameMap.find(name);
+  if(i == this->NameMap.end())
+    {
+    // Check if we know how to generate this file.
+    cmSourceFile* sf = this->Makefile->GetSourceFileWithOutput(name.c_str());
+    NameMapType::value_type entry(name, sf);
+    i = this->NameMap.insert(entry).first;
+    }
+  if(cmSourceFile* sf = i->second)
+    {
+    this->QueueSource(sf);
     }
 }
 
 //----------------------------------------------------------------------------
 void
-cmTargetTraceDependencies::QueueOnce(std::vector<std::string> const& names)
+cmTargetTraceDependencies::FollowNames(std::vector<std::string> const& names)
 {
   for(std::vector<std::string>::const_iterator i = names.begin();
       i != names.end(); ++i)
     {
-    this->QueueOnce(*i);
+    this->FollowName(*i);
     }
 }
 
@@ -1226,28 +1252,6 @@ bool cmTargetTraceDependencies::IsUtility(std::string const& dep)
   return false;
 }
 
-//----------------------------------------------------------------------------
-void cmTargetTraceDependencies::QueueDependencies(cmSourceFile* sf)
-{
-  // Queue dependency added explicitly by the user.
-  if(const char* additionalDeps = sf->GetProperty("OBJECT_DEPENDS"))
-    {
-    std::vector<std::string> objDeps;
-    cmSystemTools::ExpandListArgument(additionalDeps, objDeps);
-    this->QueueOnce(objDeps);
-    }
-
-  // Queue dependencies added programatically by commands.
-  this->QueueOnce(sf->GetDepends());
-
-  // Queue custom command dependencies.
-  if(cmCustomCommand const* cc = sf->GetCustomCommand())
-    {
-    this->CheckCustomCommand(*cc);
-    }
-
-}
-
 //----------------------------------------------------------------------------
 void
 cmTargetTraceDependencies
@@ -1283,7 +1287,7 @@ cmTargetTraceDependencies
       {
       // The dependency does not name a target and may be a file we
       // know how to generate.  Queue it.
-      this->QueueOnce(dep);
+      this->FollowName(dep);
       }
     }
 }