extra-files: Write a metadata file enumerating extra files

Introduces a new metadata file to track arbitrary files added during the
extra-files phase. This file is placed in the root of each tree and is
called ``extra_files.json``. It is a JSON file containing a single
object, which contains a "header" key with an object describing the
metadata, and a "data" key, which is an array of objects, where each
object represents a file. Each object contains the "file", "checksums",
and "size" keys. "file" is the relative path from the tree root to the
extra file. "checksums" is an object containing one or more checksums,
where the key is the digest type and the value of that key is the hex
digest. Finally, the size is the size of the file in bytes.

For example:
{
  "header": {"version": "1.0},
  "data": [
    {
      "file": "GPL",
      "checksums": {
        "sha256": "8177f97513213526df2cf6184d8ff986c675afb514d4e68a404010521b880643"
      },
      "size": 18092
    },
    {
      "file": "release-notes/notes.html",
      "checksums": {
        "sha256": "82b1ba8db522aadf101dca6404235fba179e559b95ea24ff39ee1e5d9a53bdcb"
      },
      "size": 1120
    }
  ]
}

Signed-off-by: Jeremy Cline <jeremy@jcline.org>
Fixes: #295

pungi/util.py

@@ -506,7 +506,24 @@ def get_format_substs(compose, **kwargs):
 
 
 def copy_all(src, dest):
-    """This function is equivalent to running `cp src/* dest`."""
+    """
+    Copy all files and directories within ``src`` to the ``dest`` directory.
+
+    This is equivalent to running ``cp -r src/* dest``.
+
+    :param src:
+        Source directory to copy from.
+
+    :param dest:
+        Destination directory to copy to.
+
+    :return:
+        A list of relative paths to the files copied.
+
+    Example:
+        >>> _copy_all('/tmp/src/', '/tmp/dest/')
+        ['file1', 'dir1/file2', 'dir1/subdir/file3']
+    """
     contents = os.listdir(src)
     if not contents:
         raise RuntimeError('Source directory %s is empty.' % src)
@@ -519,6 +536,26 @@ def copy_all(src, dest):
         else:
             shutil.copy2(source, destination)
 
+    return recursive_file_list(src)
+
+
+def recursive_file_list(directory):
+    """Return a list of files contained in ``directory``.
+
+    The files are paths relative to ``directory``
+
+    :param directory:
+        Path to the directory to list.
+
+    Example:
+        >>> recursive_file_list('/some/dir')
+        ['file1', 'subdir/file2']
+    """
+    file_list = []
+    for root, dirs, files in os.walk(directory):
+        file_list += [os.path.relpath(os.path.join(root, f), directory) for f in files]
+    return file_list
+
 
 def levenshtein(a, b):
     """Compute Levenshtein edit distance between two strings."""