Fix: add warning on duplicated yaml keys

.changes/unreleased/Fixes-20220428-100157.yaml

@@ -0,0 +1,7 @@
+kind: Fixes
+body: Add warning if yaml contains duplicate keys
+time: 2022-04-28T10:01:57.893956+12:00
+custom:
+  Author: jeremyyeo
+  Issue: "5114"
+  PR: "5146"

core/dbt/clients/yaml_helper.py

@@ -8,6 +8,7 @@
 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}
@@ -20,6 +21,26 @@
 """.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)
@@ -48,10 +69,10 @@ def contextualized_yaml_error(raw_contents, error):
 
 
 def safe_load(contents) -> Optional[Dict[str, Any]]:
-    return yaml.load(contents, Loader=SafeLoader)
+    return yaml.load(contents, Loader=UniqueKeyLoader)
 
 
-def load_yaml_text(contents):
+def load_yaml_text(contents, path=None):
     try:
         return safe_load(contents)
     except (yaml.scanner.ScannerError, yaml.YAMLError) as e:
@@ -61,3 +82,7 @@ def load_yaml_text(contents):
             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("{}"))

core/dbt/exceptions.py

@@ -436,6 +436,10 @@ def __init__(self, name: str):
         super().__init__(name)
 
 
+class DuplicateYamlKeyException(CompilationException):
+    pass
+
+
 def raise_compiler_error(msg, node=None) -> NoReturn:
     raise CompilationException(msg, node)
 
@@ -903,7 +907,8 @@ def raise_ambiguous_alias(node_1, node_2, duped_name=None):
 def raise_ambiguous_catalog_match(unique_id, match_1, match_2):
     def get_match_string(match):
         return "{}.{}".format(
-            match.get("metadata", {}).get("schema"), match.get("metadata", {}).get("name")
+            match.get("metadata", {}).get("schema"),
+            match.get("metadata", {}).get("name"),
         )
 
     raise_compiler_error(

core/dbt/parser/schemas.py

@@ -115,7 +115,7 @@ def yaml_from_file(source_file: SchemaSourceFile) -> Dict[str, Any]:
     """If loading the yaml fails, raise an exception."""
     path = source_file.path.relative_path
     try:
-        return load_yaml_text(source_file.contents)
+        return load_yaml_text(source_file.contents, source_file.path)
     except ValidationException as e:
         reason = validator_error_message(e)
         raise ParsingException(
@@ -548,7 +548,8 @@ def parse_file(self, block: FileBlock, dct: Dict = None) -> None:
 def check_format_version(file_path, yaml_dct) -> None:
     if "version" not in yaml_dct:
         raise_invalid_property_yml_version(
-            file_path, "the yml property file {} is missing a version tag".format(file_path)
+            file_path,
+            "the yml property file {} is missing a version tag".format(file_path),
         )
 
     version = yaml_dct["version"]
@@ -562,7 +563,8 @@ def check_format_version(file_path, yaml_dct) -> None:
         )
     if version != 2:
         raise_invalid_property_yml_version(
-            file_path, "its 'version:' tag is set to {}.  Only 2 is supported".format(version)
+            file_path,
+            "its 'version:' tag is set to {}.  Only 2 is supported".format(version),
         )
 
 

test/integration/006_simple_dependency_tests/local_dependency/models/schema.yml

@@ -4,7 +4,6 @@ sources:
     schema: invalid_schema
     tables:
       - name: my_table
-sources:
   - name: seed_source
     schema: "{{ var('schema_override', target.schema) }}"
     tables:

tests/functional/duplications/test_basic_duplications.py

@@ -0,0 +1,33 @@
+import pytest
+
+from dbt.tests.util import run_dbt_and_capture, run_dbt
+from dbt.exceptions import DuplicateYamlKeyException
+
+duplicate_key_schema__schema_yml = """
+version: 2
+models:
+  - name: my_model
+models:
+  - name: my_model
+"""
+
+my_model_sql = """
+  select 1 as fun
+"""
+
+
+class TestBasicDuplications:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "my_model.sql": my_model_sql,
+            "schema.yml": duplicate_key_schema__schema_yml,
+        }
+
+    def test_warning_in_stdout(self, project):
+        results, stdout = run_dbt_and_capture(["run"])
+        assert "Duplicate 'models' key found in yaml file models/schema.yml" in stdout
+
+    def test_exception_is_raised_with_warn_error_flag(self, project):
+        with pytest.raises(DuplicateYamlKeyException):
+            run_dbt(["--warn-error", "run"])