Add the 'targets' tool.

This tool list targets by depth or by rule. It can be useful:
- for shell completion script ;
- to know what are the primary targets: ninja -t targets depth 1 ;
- to know targets that are linked: ninja -t rule link ;
- when debugging.

It works by first listing the root nodes and then following the input nodes
of their in edge.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/ninja_jumble.cc b/src/ninja_jumble.cc
index fd2ee18..e6a0de6 100644
--- a/src/ninja_jumble.cc
+++ b/src/ninja_jumble.cc
@@ -182,3 +182,21 @@ void State::AddOut(Edge* edge, const string& path) {
   }
   node->in_edge_ = edge;
 }
+
+vector<Node*> State::RootNodes(string* error)
+{
+  assert(error);
+  vector<Node*> root_nodes;
+  // Search for nodes with no output.
+  for (vector<Edge*>::iterator e = edges_.begin(); e != edges_.end(); ++e)
+    for (vector<Node*>::iterator outs = (*e)->outputs_.begin();
+         outs != (*e)->outputs_.end();
+         ++outs)
+      if ((*outs)->out_edges_.size() == 0)
+        root_nodes.push_back(*outs);
+  if (!edges_.empty() && root_nodes.empty()) {
+    *error = "could not determine root nodes of build graph";
+  }
+  assert(edges_.empty() || !root_nodes.empty());
+  return root_nodes;
+}