1 files changed, 74 insertions, 0 deletions
diff --git a/libbutl/default-options.cxx b/libbutl/default-options.cxx
new file mode 100644
index 0000000..69b9c42
--- /dev/null
+++ b/libbutl/default-options.cxx
@@ -0,0 +1,74 @@
+// file      : libbutl/default-options.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef __cpp_modules_ts
+#include <libbutl/default-options.mxx>
+#endif
+
+#include <cassert>
+
+#ifndef __cpp_lib_modules_ts
+#include <vector>
+#endif
+
+// Other includes.
+
+#ifdef __cpp_modules_ts
+module butl.default_options;
+
+// Only imports additional to interface.
+#ifdef __clang__
+#ifdef __cpp_lib_modules_ts
+import std.core;
+#endif
+import butl.path;
+import butl.optional;
+import butl.small_vector;
+#endif
+
+#endif
+
+using namespace std;
+
+namespace butl
+{
+  optional<dir_path>
+  default_options_start (const optional<dir_path>& home,
+                         const vector<dir_path>& dirs)
+  {
+    if (home)
+      assert (home->absolute () && home->normalized ());
+
+    if (dirs.empty ())
+      return nullopt;
+
+    // Use the first directory as a start.
+    //
+    auto i (dirs.begin ());
+    dir_path d (*i);
+
+    // Try to find a common prefix for each subsequent directory.
+    //
+    for (++i; i != dirs.end (); ++i)
+    {
+      bool p (false);
+
+      for (;
+           !(d.root () || (home && d == *home));
+           d = d.directory ())
+      {
+        if (i->sub (d))
+        {
+          p = true;
+          break;
+        }
+      }
+
+      if (!p)
+        return nullopt;
+    }
+
+    return d;
+  }
+}