#
#
# add_dir "tests/unchanged_options_preserves_mtime"
# 
# add_file "tests/unchanged_options_preserves_mtime/__driver__.lua"
#  content [468ac9c7ee9b602a21e0dfa4e35432da6acba0b4]
# 
# patch "paths.hh"
#  from [e92b013f510afba1da74ab8f47a8f2fa799b3b5c]
#    to [16f68fd413cd8c13bcb7756bdfbccfddb181215f]
# 
# patch "work.cc"
#  from [4a27d0c0133f6cc04b06944afe080400095676e2]
#    to [910fd95c745f3ffb0b5f337571e07c84f00a7ef8]
#
============================================================
--- tests/unchanged_options_preserves_mtime/__driver__.lua	468ac9c7ee9b602a21e0dfa4e35432da6acba0b4
+++ tests/unchanged_options_preserves_mtime/__driver__.lua	468ac9c7ee9b602a21e0dfa4e35432da6acba0b4
@@ -0,0 +1,67 @@
+mtn_setup()
+
+-- the sleep calls here are to ensure a change is visible even if
+-- the resolution of mtime is one second or more
+
+time1 = mtime("_MTN/options")
+
+-- commit doesn't change mtime
+
+sleep(1)
+writefile("foo", "foo")
+check(mtn("add", "foo"), 0, false, false)
+commit()
+check(time1 == mtime("_MTN/options"))
+
+r1 = base_revision()
+
+-- commit doesn't change mtime
+
+sleep(1)
+writefile("foo", "bar")
+commit()
+check(time1 == mtime("_MTN/options"))
+
+r2 = base_revision()
+
+-- status doesn't change mtime
+
+sleep(1)
+check(mtn("status"), 0, false, false)
+check(time1 == mtime("_MTN/options"))
+
+-- update on same branch doesn't change mtime
+
+sleep(1)
+check(mtn("update", "--revision", r1), 0, false, false)
+check(time1 == mtime("_MTN/options"))
+
+-- changing branch updates mtime of cached options
+
+sleep(1)
+writefile("foo", "baz")
+check(mtn("commit", "--branch", "baz", "--message", "baz"), 0, false, false)
+time2 = mtime("_MTN/options")
+check(time1 < time2)
+
+r3 = base_revision()
+
+-- update to different branch changes mtime
+
+sleep(1)
+check(mtn("update", "--revision", r1), 0, false, false)
+time3 = mtime("_MTN/options")
+check(time2 < time3)
+
+-- update to same branch doesn't change mtime
+
+sleep(1)
+check(mtn("update", "--revision", r2), 0, false, false)
+check(time3 == mtime("_MTN/options"))
+
+-- update to different branch changes mtime
+
+sleep(1)
+check(mtn("update", "--revision", r3), 0, false, false)
+time4 = mtime("_MTN/options")
+check(time3 < time4)
============================================================
--- paths.hh	e92b013f510afba1da74ab8f47a8f2fa799b3b5c
+++ paths.hh	16f68fd413cd8c13bcb7756bdfbccfddb181215f
@@ -378,8 +378,9 @@ public:
   explicit system_path(utf8 const & path);
 
   bool operator==(const system_path & other) const
-  { return data== other.data; }
-
+  { return data == other.data; }
+  bool operator!=(const system_path & other) const
+  { return data != other.data; }
   bool operator <(const system_path & other) const
   { return data < other.data; }
 
============================================================
--- work.cc	4a27d0c0133f6cc04b06944afe080400095676e2
+++ work.cc	910fd95c745f3ffb0b5f337571e07c84f00a7ef8
@@ -577,21 +577,43 @@ workspace::set_options(options const & o
   // file and if it contains the correct identifier, but these checks would
   // duplicate those in database.cc. At the time it is checked there, however,
   // the options file for the workspace is already written out...
+  bool options_changed = false;
+
   if (!opts.dbname.as_internal().empty() &&
-      get_path_status(opts.dbname.as_internal()) == path::file)
-    workspace_database = opts.dbname;
+      get_path_status(opts.dbname.as_internal()) == path::file &&
+      workspace_database != opts.dbname)
+    {
+      workspace_database = opts.dbname;
+      options_changed = true;
+    }
+
   if (!opts.key_dir.as_internal().empty() &&
-      get_path_status(opts.key_dir.as_internal()) == path::directory)
-    workspace_keydir = opts.key_dir;
-  if ((branch_is_sticky || workspace::branch_is_sticky)
-      && !opts.branch().empty())
-    workspace_branch = opts.branch;
-  if (opts.key_given)
-    workspace_key = opts.signing_key;
+      get_path_status(opts.key_dir.as_internal()) == path::directory &&
+      workspace_keydir != opts.key_dir)
+    {
+      workspace_keydir = opts.key_dir;
+      options_changed = true;
+    }
 
-  write_options_file(o_path,
-                     workspace_database, workspace_branch,
-                     workspace_key, workspace_keydir);
+  if ((branch_is_sticky || workspace::branch_is_sticky) &&
+      !opts.branch().empty() && 
+      workspace_branch != opts.branch)
+    {
+      workspace_branch = opts.branch;
+      options_changed = true;
+    }
+
+  if (opts.key_given && workspace_key != opts.signing_key)
+    {
+      workspace_key = opts.signing_key;
+      options_changed = true;
+    }
+
+  // only rewrite the options file if there are actual changes
+  if (options_changed)
+    write_options_file(o_path,
+                       workspace_database, workspace_branch,
+                       workspace_key, workspace_keydir);
 }
 
 void