osbuild-mpp: Support loading yaml as well as json files

yaml files are essentially compatible with json files, although
they have some advantages, like allowing comments and being easier
for humans to read/write.

This changes the reading of the file to use a yaml parser instead of
a json parser, but still produces json at the end. I tried manually
converting a json file to yaml and running osbuild-mpp, and it produced
an identical file.

By default the yaml parser doesn't respect order so i had to tweak
the loader a bit to use OrderedDict.

tools/osbuild-mpp

@@ -242,6 +242,7 @@ import collections
 import contextlib
 import hashlib
 import json
+import yaml
 import os
 import pathlib
 import string
@@ -257,6 +258,33 @@ import hawkey
 
 from osbuild.util.rhsm import Subscriptions
 
+class YamlOrderedLoader(yaml.Loader):
+    def construct_mapping(self, node, deep=False):
+        if not isinstance(node, yaml.MappingNode):
+            raise ConstructorError(None, None,
+                    "expected a mapping node, but found %s" % node.id,
+                    node.start_mark)
+        mapping = collections.OrderedDict()
+        for key_node, value_node in node.value:
+            key = self.construct_object(key_node, deep=deep)
+            if not isinstance(key, collections.abc.Hashable):
+                raise ConstructorError("while constructing a mapping", node.start_mark,
+                        "found unhashable key", key_node.start_mark)
+            value = self.construct_object(value_node, deep=deep)
+            mapping[key] = value
+        return mapping
+    def construct_yaml_map(self, node):
+        data = collections.OrderedDict()
+        yield data
+        value = self.construct_mapping(node)
+        data.update(value)
+yaml.add_constructor('tag:yaml.org,2002:map', YamlOrderedLoader.construct_yaml_map)
+
+def yaml_load_ordered(source):
+    return yaml.load(source, YamlOrderedLoader)
+
+def json_load_ordered(source):
+    return json.load(source, object_pairs_hook=collections.OrderedDict)
 
 def element_enter(element, key, default):
     if key not in element:
@@ -603,11 +631,22 @@ class ManifestFile:
     @staticmethod
     def load_from_fd(f, path, overrides, default_vars):
         # We use OrderedDict to preserve key order (for python < 3.6)
-        try:
-            data = json.load(f, object_pairs_hook=collections.OrderedDict)
-        except json.decoder.JSONDecodeError as err:
-            print (f"Invalid json in \"{path}\": {err.msg} at line {err.lineno} (col {err.colno})")
-            sys.exit(1)
+        if path.endswith(".yml") or path.endswith(".yaml"):
+            try:
+                data =  yaml_load_ordered(f)
+            except yaml.YAMLError as err:
+                pos = ""
+                if hasattr(err, 'problem_mark'):
+                    mark = err.problem_mark
+                    pos =  f" at line {mark.line+1} (col {mark.column+1})"
+                print(f"Invalid yaml in \"{path}\": {err.problem}{pos}")
+                sys.exit(1)
+        else:
+            try:
+                data = json_load_ordered(f)
+            except json.decoder.JSONDecodeError as err:
+                print(f"Invalid json in \"{path}\": {err.msg} at line {err.lineno} (col {err.colno})")
+                sys.exit(1)
 
         version = int(data.get("version", "1"))
         if version == 1: