Look up header dependencies on the first-output build

Ninja has special syntax to specify the first output of the given node.
E.g. it builds foo.o for foo.cc^. However, it doesn't work for
headers, as headers usually doesn't appear in the regular dependency
tree.

After this change, Ninja looks up header dependencies from .ninja_deps
to pick up a build target, so that it builds foo.o for foo.h^.

4 files changed, 54 insertions, 8 deletions

diff --git a/src/deps_log.cc b/src/deps_log.cc
index eb81a37..42e5326 100644
--- a/src/deps_log.cc
+++ b/src/deps_log.cc
@@ -310,6 +310,19 @@ DepsLog::Deps* DepsLog::GetDeps(Node* node) {
   return deps_[node->id()];
 }
 
+Node* DepsLog::GetFirstReverseDepsNode(Node* node) {
+  for (size_t id = 0; id < deps_.size(); ++id) {
+    Deps* deps = deps_[id];
+    if (!deps)
+      continue;
+    for (int i = 0; i < deps->node_count; ++i) {
+      if (deps->nodes[i] == node)
+        return nodes_[id];
+    }
+  }
+  return NULL;
+}
+
 bool DepsLog::Recompact(const string& path, string* err) {
   METRIC_RECORD(".ninja_deps recompact");
 
diff --git a/src/deps_log.h b/src/deps_log.h
index 3812a28..1336078 100644
--- a/src/deps_log.h
+++ b/src/deps_log.h
@@ -86,6 +86,7 @@ struct DepsLog {
   };
   bool Load(const string& path, State* state, string* err);
   Deps* GetDeps(Node* node);
+  Node* GetFirstReverseDepsNode(Node* node);
 
   /// Rewrite the known log entries, throwing away old data.
   bool Recompact(const string& path, string* err);
diff --git a/src/deps_log_test.cc b/src/deps_log_test.cc
index 89f7be1..7daca90 100644
--- a/src/deps_log_test.cc
+++ b/src/deps_log_test.cc
@@ -476,4 +476,31 @@ TEST_F(DepsLogTest, TruncatedRecovery) {
   }
 }
 
+TEST_F(DepsLogTest, ReverseDepsNodes) {
+  State state;
+  DepsLog log;
+  string err;
+  EXPECT_TRUE(log.OpenForWrite(kTestFilename, &err));
+  ASSERT_EQ("", err);
+
+  vector<Node*> deps;
+  deps.push_back(state.GetNode("foo.h", 0));
+  deps.push_back(state.GetNode("bar.h", 0));
+  log.RecordDeps(state.GetNode("out.o", 0), 1, deps);
+
+  deps.clear();
+  deps.push_back(state.GetNode("foo.h", 0));
+  deps.push_back(state.GetNode("bar2.h", 0));
+  log.RecordDeps(state.GetNode("out2.o", 0), 2, deps);
+
+  log.Close();
+
+  Node* rev_deps = log.GetFirstReverseDepsNode(state.GetNode("foo.h", 0));
+  EXPECT_TRUE(rev_deps == state.GetNode("out.o", 0) ||
+              rev_deps == state.GetNode("out2.o", 0));
+
+  rev_deps = log.GetFirstReverseDepsNode(state.GetNode("bar.h", 0));
+  EXPECT_TRUE(rev_deps == state.GetNode("out.o", 0));
+}
+
 }  // anonymous namespace
diff --git a/src/ninja.cc b/src/ninja.cc
index 30f89c2..3a7ebbc 100644
--- a/src/ninja.cc
+++ b/src/ninja.cc
@@ -282,15 +282,20 @@ Node* NinjaMain::CollectTarget(const char* cpath, string* err) {
   if (node) {
     if (first_dependent) {
       if (node->out_edges().empty()) {
-        *err = "'" + path + "' has no out edge";
-        return NULL;
-      }
-      Edge* edge = node->out_edges()[0];
-      if (edge->outputs_.empty()) {
-        edge->Dump();
-        Fatal("edge has no outputs");
+        Node* rev_deps = deps_log_.GetFirstReverseDepsNode(node);
+        if (!rev_deps) {
+          *err = "'" + path + "' has no out edge";
+          return NULL;
+        }
+        node = rev_deps;
+      } else {
+        Edge* edge = node->out_edges()[0];
+        if (edge->outputs_.empty()) {
+          edge->Dump();
+          Fatal("edge has no outputs");
+        }
+        node = edge->outputs_[0];
       }
-      node = edge->outputs_[0];
     }
     return node;
   } else {