[Fix]: remove duplicate key checking (#5403)

* remove duplicate key checking

* add changelog

.changes/unreleased/Fixes-20220623-082431.yaml

@@ -0,0 +1,7 @@
+kind: Fixes
+body: Remove duplicate key checking introduced in 1.2.0a1
+time: 2022-06-23T08:24:31.900647+12:00
+custom:
+  Author: jeremyyeo
+  Issue: "5331"
+  PR: "5403"

core/dbt/clients/yaml_helper.py

@@ -8,7 +8,6 @@
 except ImportError:
     from yaml import Loader, SafeLoader, Dumper  # type: ignore  # noqa: F401
 
-from dbt.ui import warning_tag
 
 YAML_ERROR_MESSAGE = """
 Syntax error near line {line_number}
@@ -21,26 +20,6 @@
 """.strip()
 
 
-class UniqueKeyLoader(SafeLoader):
-    """A subclass that checks for unique yaml mapping nodes.
-
-    This class extends `SafeLoader` from the `yaml` library to check for
-    unique top level keys (mapping nodes). See issue (https://github.com/yaml/pyyaml/issues/165)
-    and solution (https://gist.github.com/pypt/94d747fe5180851196eb?permalink_comment_id=4015118).
-    """
-
-    def construct_mapping(self, node, deep=False):
-        mapping = set()
-        for key_node, value_node in node.value:
-            key = self.construct_object(key_node, deep=deep)
-            if key in mapping:
-                raise dbt.exceptions.DuplicateYamlKeyException(
-                    f"Duplicate {key!r} key found in yaml file"
-                )
-            mapping.add(key)
-        return super().construct_mapping(node, deep)
-
-
 def line_no(i, line, width=3):
     line_number = str(i).ljust(width)
     return "{}| {}".format(line_number, line)
@@ -69,7 +48,7 @@ def contextualized_yaml_error(raw_contents, error):
 
 
 def safe_load(contents) -> Optional[Dict[str, Any]]:
-    return yaml.load(contents, Loader=UniqueKeyLoader)
+    return yaml.load(contents, Loader=SafeLoader)
 
 
 def load_yaml_text(contents, path=None):
@@ -82,7 +61,3 @@ def load_yaml_text(contents, path=None):
             error = str(e)
 
         raise dbt.exceptions.ValidationException(error)
-    except dbt.exceptions.DuplicateYamlKeyException as e:
-        # TODO: We may want to raise an exception instead of a warning in the future.
-        e.msg = f"{e} {path.searched_path}/{path.relative_path}."
-        dbt.exceptions.warn_or_raise(e, log_fmt=warning_tag("{}"))