From a50652b3e3323a9492c32d2ca6e97befd7d9755b Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sun, 28 Nov 2021 09:40:25 +0200
Subject: Generalize depdb::touch functionality to support custom timestamp

---
 libbuild2/adhoc-rule-buildscript.cxx |  2 +-
 libbuild2/cc/compile-rule.cxx        |  2 +-
 libbuild2/depdb.cxx                  | 27 ++++++++++++++++++++++-----
 libbuild2/depdb.hxx                  | 13 ++++++++++---
 4 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/libbuild2/adhoc-rule-buildscript.cxx b/libbuild2/adhoc-rule-buildscript.cxx
index 78f87ae..e8bc20d 100644
--- a/libbuild2/adhoc-rule-buildscript.cxx
+++ b/libbuild2/adhoc-rule-buildscript.cxx
@@ -503,7 +503,7 @@ namespace build2
     }
 
     if (update && dd.reading () && !ctx.dry_run)
-      dd.touch = true;
+      dd.touch = timestamp_unknown;
 
     dd.close ();
     md->dd = move (dd.path);
diff --git a/libbuild2/cc/compile-rule.cxx b/libbuild2/cc/compile-rule.cxx
index 525821f..3c77ad3 100644
--- a/libbuild2/cc/compile-rule.cxx
+++ b/libbuild2/cc/compile-rule.cxx
@@ -1422,7 +1422,7 @@ namespace build2
         // on the real run).
         //
         if (u && dd.reading () && !ctx.dry_run)
-          dd.touch = true;
+          dd.touch = timestamp_unknown;
 
         dd.close ();
         md.dd = move (dd.path);
diff --git a/libbuild2/depdb.cxx b/libbuild2/depdb.cxx
index 657c772..1215e78 100644
--- a/libbuild2/depdb.cxx
+++ b/libbuild2/depdb.cxx
@@ -72,8 +72,7 @@ namespace build2
   depdb (path_type&& p, timestamp mt)
       : depdb_base (p, mt),
         path (move (p)),
-        mtime (mt != timestamp_nonexistent ? mt : timestamp_unknown),
-        touch (false)
+        mtime (mt != timestamp_nonexistent ? mt : timestamp_unknown)
   {
     // Read/write the database format version.
     //
@@ -290,6 +289,10 @@ namespace build2
     // the rest, and then add the "end marker" (we cannot have anything in the
     // write mode since we truncate in change()).
     //
+    // Note that we handle touch with timestamp_unknown specially by making a
+    // modification to the file (which happens naturally in the write mode)
+    // and letting the filesystem update its mtime.
+    //
     if (state_ == state::read_eof)
     {
       if (!touch)
@@ -314,8 +317,11 @@ namespace build2
       // Note also that utime() on Windows is a bad idea (see touch_file() for
       // details).
       //
-      pos_ = buf_->tellg ();         // The last line is accepted.
-      change (false /* truncate */); // Write end marker below.
+      if (*touch == timestamp_unknown)
+      {
+        pos_ = buf_->tellg ();         // The last line is accepted.
+        change (false /* truncate */); // Write end marker below.
+      }
     }
     else if (state_ != state::write)
     {
@@ -326,6 +332,7 @@ namespace build2
     if (mtime_check ())
       start_ = system_clock::now ();
 
+    if (state_ == state::write)
     try
     {
       os_.put ('\0'); // The "end marker".
@@ -333,7 +340,17 @@ namespace build2
     }
     catch (const io_error& e)
     {
-      fail << "unable to flush " << path << ": " << e;
+      fail << "unable to flush file " << path << ": " << e;
+    }
+
+    if (touch && *touch != timestamp_unknown)
+    try
+    {
+      file_mtime (path, *touch);
+    }
+    catch (const system_error& e)
+    {
+      fail << "unable to touch file " << path << ": " << e;
     }
 
     // On some platforms (currently confirmed on FreeBSD running as VMs) one
diff --git a/libbuild2/depdb.hxx b/libbuild2/depdb.hxx
index c3e60a2..9cff281 100644
--- a/libbuild2/depdb.hxx
+++ b/libbuild2/depdb.hxx
@@ -90,9 +90,16 @@ namespace build2
     // close() even if otherwise no modifications are necessary (i.e., the
     // database is in the read mode and is at eof).
     //
-    path_type path;
-    timestamp mtime;
-    bool      touch;
+    // If touch is present then update the database modification time in
+    // close() even if otherwise no modifications are necessary (i.e., the
+    // database is in the read mode and is at eof). Specifically, if touch is
+    // timestamp_unknown, then set mtime to the current (filesystem) time.
+    // Otherwise, set it to the specified time (which should be sourced from
+    // the filesystem, see touch_file() for details).
+    //
+    path_type           path;
+    timestamp           mtime;
+    optional<timestamp> touch;
 
     // Open the database for reading. Note that if the file does not exist,
     // has wrong format version, or is corrupt, then the database will be
-- 
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