use logged deps mtime in dirty calculation

The idea here is that it's possible for a build to complete (writing
its output) but then for Ninja to get interrupted before writing out
the updated dependency information.  In that case the mtime stored in
the deps log (if any) will match the previous output, and we'll know
we need to rebuild the output just to get the deps updated.

1 files changed, 15 insertions, 5 deletions

diff --git a/src/graph.cc b/src/graph.cc
index b11973f..5cc491b 100644
--- a/src/graph.cc
+++ b/src/graph.cc
@@ -61,7 +61,8 @@ bool DependencyScan::RecomputeDirty(Edge* edge, string* err) {
   bool dirty = false;
   edge->outputs_ready_ = true;
 
-  if (!dep_loader_.LoadDeps(edge, err)) {
+  TimeStamp deps_mtime = 0;
+  if (!dep_loader_.LoadDeps(edge, &deps_mtime, err)) {
     if (!err->empty())
       return false;
     // Failed to load dependency info: rebuild to regenerate it.
@@ -112,7 +113,8 @@ bool DependencyScan::RecomputeDirty(Edge* edge, string* err) {
     for (vector<Node*>::iterator i = edge->outputs_.begin();
          i != edge->outputs_.end(); ++i) {
       (*i)->StatIfNecessary(disk_interface_);
-      if (RecomputeOutputDirty(edge, most_recent_input, command, *i)) {
+      if (RecomputeOutputDirty(edge, most_recent_input, deps_mtime,
+                               command, *i)) {
         dirty = true;
         break;
       }
@@ -141,6 +143,7 @@ bool DependencyScan::RecomputeDirty(Edge* edge, string* err) {
 
 bool DependencyScan::RecomputeOutputDirty(Edge* edge,
                                           Node* most_recent_input,
+                                          TimeStamp deps_mtime,
                                           const string& command,
                                           Node* output) {
   if (edge->is_phony()) {
@@ -182,6 +185,12 @@ bool DependencyScan::RecomputeOutputDirty(Edge* edge,
     }
   }
 
+  // Dirty if the output is newer than the deps.
+  if (deps_mtime && output->mtime() > deps_mtime) {
+    EXPLAIN("stored deps info out of date for for %s", output->path().c_str());
+    return true;
+  }
+
   // May also be dirty due to the command changing since the last build.
   // But if this is a generator rule, the command changing does not make us
   // dirty.
@@ -322,10 +331,10 @@ void Node::Dump(const char* prefix) const {
   }
 }
 
-bool ImplicitDepLoader::LoadDeps(Edge* edge, string* err) {
+bool ImplicitDepLoader::LoadDeps(Edge* edge, TimeStamp* mtime, string* err) {
   string deps_type = edge->GetBinding("deps");
   if (!deps_type.empty()) {
-    if (!LoadDepsFromLog(edge, err)) {
+    if (!LoadDepsFromLog(edge, mtime, err)) {
       if (!err->empty())
         return false;
       EXPLAIN("deps for %s are missing", edge->outputs_[0]->path().c_str());
@@ -396,7 +405,8 @@ bool ImplicitDepLoader::LoadDepFile(Edge* edge, const string& path,
   return true;
 }
 
-bool ImplicitDepLoader::LoadDepsFromLog(Edge* edge, string* err) {
+bool ImplicitDepLoader::LoadDepsFromLog(Edge* edge, TimeStamp* deps_mtime,
+                                        string* err) {
   DepsLog::Deps* deps = deps_log_->GetDeps(edge->outputs_[0]);
   if (!deps)
     return false;