do not delete files from the logs that still exist on disk

This is to keep the possibility of maybe having a tool that deletes
old files in the future, or for having a tool which exposes this
information to generators so they can do that.

See https://github.com/martine/ninja/pull/697#issuecomment-37140762
and the discussion on #762.

Idea from @maximuska!

1 files changed, 3 insertions, 1 deletions

diff --git a/src/ninja.cc b/src/ninja.cc
index e555df4..15e265b 100644
--- a/src/ninja.cc
+++ b/src/ninja.cc
@@ -147,7 +147,9 @@ struct NinjaMain : public BuildLogUser {
     // edge is rare, and the first recompaction will delete all old outputs from
     // the deps log, and then a second recompaction will clear the build log,
     // which seems good enough for this corner case.)
-    return !n || !n->in_edge();
+    // Do keep entries around for files which still exist on disk, for
+    // generators that want to use this information.
+    return (!n || !n->in_edge()) && disk_interface_.Stat(s.AsString()) == 0;
   }
 };