stages/assemblers: add tree/untree assembler and stage

In the simplest case we don't need to make an image, a filesystem tree
will do. Also support using such a tree as input for further pipelines
through the untree stage.

Signed-off-by: Tom Gundersen <teg@jklm.no>

assemblers/io.weldr.tree

@@ -0,0 +1,24 @@
+#!/usr/bin/python3
+
+import json
+import os
+import shutil
+import subprocess
+import sys
+
+def main(tree, output_dir, options):
+    output_tree = os.path.join(output_dir, options["tree"])
+
+    shutil.rmtree(output_tree, ignore_errors=True)
+    os.makedirs(output_tree, mode=0o755)
+
+    # Copy the tree to the output directory
+    for name in os.listdir(tree):
+        srcname = os.path.join(tree, name)
+        dstname = os.path.join(output_tree, name)
+        subprocess.run(["cp", "-a", "-T", srcname, dstname], check=True)
+
+if __name__ == '__main__':
+    args = json.load(sys.stdin)
+    r = main(args["tree"], args["output_dir"], args["options"])
+    sys.exit(r)

stages/io.weldr.untree

@@ -0,0 +1,20 @@
+#!/usr/bin/python3
+
+import json
+import os
+import subprocess
+import sys
+
+def main(tree, input_dir, options):
+    input_tree = os.path.join(input_dir, options["tree"])
+
+    # Initialize the tree from the tree given in the input
+    for name in os.listdir(input_tree):
+        srcname = os.path.join(input_tree, name)
+        dstname = os.path.join(tree, name)
+        subprocess.run(["cp", "-a", "-T", srcname, dstname], check=True)
+
+if __name__ == '__main__':
+    args = json.load(sys.stdin)
+    r = main(args["tree"], args["input_dir"], args["options"])
+    sys.exit(r)