From be57ba464fae756d5eb44cf4faf192536dec43ec Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 2 Dec 2021 10:16:00 +0200
Subject: Add $root_directory(<path>) function

---
 libbuild2/functions-path.cxx   | 43 +++++++++++++++++++++++++++++++++++++++++-
 tests/function/path/testscript | 22 +++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/libbuild2/functions-path.cxx b/libbuild2/functions-path.cxx
index 2953067..8362d2e 100644
--- a/libbuild2/functions-path.cxx
+++ b/libbuild2/functions-path.cxx
@@ -312,7 +312,11 @@ namespace build2
       return ns;
     };
 
-    // directory
+    // $directory(<path>)
+    // $directory(<paths>)
+    //
+    // Return the directory part of the path or empty path if there is no
+    // directory. Directory of a root directory is an empty path.
     //
     f["directory"] += &path::directory;
 
@@ -346,6 +350,43 @@ namespace build2
       return ns;
     };
 
+    // $root_directory(<path>)
+    // $root_directory(<paths>)
+    //
+    // Return the root directory of the path or empty path if the directory is
+    // not absolute.
+    //
+    f["root_directory"] += &path::root_directory;
+
+    f["root_directory"] += [](paths v)
+    {
+      dir_paths r;
+      for (const path& p: v)
+        r.push_back (p.root_directory ());
+      return r;
+    };
+
+    f["root_directory"] += [](dir_paths v)
+    {
+      for (dir_path& p: v)
+        p = p.root_directory ();
+      return v;
+    };
+
+    f[".root_directory"] += [](names ns)
+    {
+      // For each path decide based on the presence of a trailing slash
+      // whether it is a directory. Return as list of directory names.
+      //
+      for (name& n: ns)
+      {
+        if (n.directory ())
+          n.dir = n.dir.root_directory ();
+        else
+          n = convert<path> (move (n)).root_directory ();
+      }
+      return ns;
+    };
 
     // $leaf(<path>)
     //
diff --git a/tests/function/path/testscript b/tests/function/path/testscript
index b0c97c9..142c866 100644
--- a/tests/function/path/testscript
+++ b/tests/function/path/testscript
@@ -49,6 +49,28 @@ if! $posix
   $* <'print $path.directory(a/b c/d/)'        >"a/ c/" : dir-names
 }
 
+: root_directory
+:
+{
+  : posix
+  :
+  if $posix
+  {
+    $* <'print $root_directory([path] /a/b)' >'/' : basics
+    $* <'print $root_directory([path] /)' >'/'    : root
+  }
+
+  : windows
+  :
+  if $windows
+  {
+    $* <'print $root_directory([path] "c:\\a\\b")' >'c:\' : basics
+    $* <'print $root_directory([path] "c:")'       >'c:\' : root
+  }
+
+  $* <'print $root_directory([path] a/b)' >'' : relative
+}
+
 : base
 :
 {
-- 
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