Expose more details in FileReader::ReadFile signature

Return a status so callers can distinguish a missing file from an empty
file.  This allows our VirtualFileSystem test infrastructure to report
as missing any file for which it has no entry.

1 files changed, 9 insertions, 2 deletions

diff --git a/src/graph.cc b/src/graph.cc
index 9e65675..98f1461 100644
--- a/src/graph.cc
+++ b/src/graph.cc
@@ -395,8 +395,15 @@ bool ImplicitDepLoader::LoadDeps(Edge* edge, string* err) {
 bool ImplicitDepLoader::LoadDepFile(Edge* edge, const string& path,
                                     string* err) {
   METRIC_RECORD("depfile load");
-  string content = disk_interface_->ReadFile(path, err);
-  if (!err->empty()) {
+  // Read depfile content.  Treat a missing depfile as empty.
+  string content;
+  switch (disk_interface_->ReadFile(path, &content, err)) {
+  case DiskInterface::Okay:
+    break;
+  case DiskInterface::NotFound:
+    err->clear();
+    break;
+  case DiskInterface::OtherError:
     *err = "loading '" + path + "': " + *err;
     return false;
   }