Set output mtime of phony edges to latest inputs

This is a partial cherrypick of https://github.com/ninja-build/ninja/pull/1964/
which fixes a build correctness bug for phony edges. Previously, actions
with implicit dependencies on phony targets would not rerun if the
inputs to these phony targets were changed.

Test: Manually verified bug fix with repro case described in b/232030877#comment27
Test: New unit test
Change-Id: I1d58abb9c46e9a31f0cb3b44bf45e87f8f301209

3 files changed, 52 insertions, 0 deletions

diff --git a/src/graph.cc b/src/graph.cc
index b7a3c7c..682182e 100644
--- a/src/graph.cc
+++ b/src/graph.cc
@@ -49,6 +49,12 @@ bool Node::Stat(DiskInterface* disk_interface, string* err) {
   }
 }
 
+void Node::UpdatePhonyMtime(TimeStamp mtime) {
+  if (!exists()) {
+    mtime_ = std::max(mtime_, mtime);
+  }
+}
+
 bool Node::LStat(
   DiskInterface* disk_interface, bool* is_dir, bool* is_symlink, string* err) {
   assert(in_edge() != nullptr);
@@ -427,6 +433,12 @@ bool DependencyScan::RecomputeOutputsDirty(Edge* edge, Node* most_recent_input,
           return true;
         }
       }
+
+      // Update the mtime with the newest input. Dependents can thus call mtime()
+      // on the fake node and get the latest mtime of the dependencies
+      if (most_recent_input) {
+        (*o)->UpdatePhonyMtime(most_recent_input->mtime());
+      }
       continue;
     }
     if (RecomputeOutputDirty(edge, most_recent_input, command_hash, *o)) {
diff --git a/src/graph.h b/src/graph.h
index 3472c07..33a42fc 100644
--- a/src/graph.h
+++ b/src/graph.h
@@ -119,6 +119,9 @@ struct Node {
   /// Only use when lstat() is desired (output files)
   bool LStat(DiskInterface* disk_interface, bool* is_dir, bool* is_symlink, string* err);
 
+  /// If the file doesn't exist, set the mtime_ from its dependencies
+  void UpdatePhonyMtime(TimeStamp mtime);
+
   /// Return false on error.
   bool StatIfNecessary(DiskInterface* disk_interface, string* err) {
     if (status_known())
diff --git a/src/graph_test.cc b/src/graph_test.cc
index de39980..427334f 100644
--- a/src/graph_test.cc
+++ b/src/graph_test.cc
@@ -1189,3 +1189,40 @@ TEST_F(GraphTest, GetAllPathsInCycles) {
   std::vector<std::string> expected_path = {"f", "d", "c", "b", "a"};
   ASSERT_TRUE(paths_f_to_a[0] == expected_path);
 }
+
+// Check that phony's dependencies' mtimes are propagated.
+TEST_F(GraphTest, PhonyDepsMtimes) {
+  string err;
+  ASSERT_NO_FATAL_FAILURE(AssertParse(&state_,
+"rule touch\n"
+" command = touch $out\n"
+"build in_ph: phony in1\n"
+"build out1: touch in_ph\n"
+));
+  fs_.Create("in1", "");
+  fs_.Create("out1", "");
+  Node* out1 = GetNode("out1");
+  Node* in1  = GetNode("in1");
+
+  EXPECT_TRUE(scan_.RecomputeDirty(GetNode("out1"), NULL, &err));
+  EXPECT_TRUE(!out1->dirty());
+
+  // Get the mtime of out1
+  ASSERT_TRUE(in1->Stat(&fs_, &err));
+  ASSERT_TRUE(out1->Stat(&fs_, &err));
+  TimeStamp out1Mtime1 = out1->mtime();
+  TimeStamp in1Mtime1 = in1->mtime();
+
+  // Touch in1. This should cause out1 to be dirty
+  state_.Reset();
+  fs_.Tick();
+  fs_.Create("in1", "");
+
+  ASSERT_TRUE(in1->Stat(&fs_, &err));
+  EXPECT_GT(in1->mtime(), in1Mtime1);
+
+  EXPECT_TRUE(scan_.RecomputeDirty(GetNode("out1"), NULL, &err));
+  EXPECT_GT(in1->mtime(), in1Mtime1);
+  EXPECT_EQ(out1->mtime(), out1Mtime1);
+  EXPECT_TRUE(out1->dirty());
+}