From 2880831f78dba2fca9ec72dd63d4fd7cfb9ac445 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 26 Jul 2017 13:46:19 +0200
Subject: Fix bug in precise change detection logic

---
 build2/cc/compile.cxx | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/build2/cc/compile.cxx b/build2/cc/compile.cxx
index c5ab236..b65cee7 100644
--- a/build2/cc/compile.cxx
+++ b/build2/cc/compile.cxx
@@ -755,6 +755,8 @@ namespace build2
         //
         timestamp mt;
         bool u (dd.writing () || dd.mtime () > (mt = file_mtime (tp)));
+        if (u)
+          mt = timestamp_nonexistent; // Treat as if it doesn't exist.
 
         // Update prerequisite targets (normally just the source file).
         //
@@ -827,11 +829,15 @@ namespace build2
               }
               else if (f) // Don't clear if it was forced.
               {
-                // Clear the update flag and set the touch flag. See also
-                // the md.mt logic below.
+                // Clear the update flag and set the touch flag. Unless there
+                // is no object file, of course. See also the md.mt logic
+                // below.
                 //
-                u = false;
-                md.touch = true;
+                if (mt != timestamp_nonexistent)
+                {
+                  u = false;
+                  md.touch = true;
+                }
               }
 
               tu = move (p.first);
-- 
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