Model contracts: raise warning for numeric types without specified scale

.changes/unreleased/Features-20230926-134728.yaml

@@ -0,0 +1,6 @@
+kind: Features
+body: Raise a warning when a contracted model has a numeric field without scale defined
+time: 2023-09-26T13:47:28.645383-05:00
+custom:
+  Author: emmyoop
+  Issue: "8183"

core/dbt/include/global_project/macros/adapters/columns.sql

@@ -36,24 +36,29 @@
     limit 0
 {% endmacro %}
 
-
 {% macro get_empty_schema_sql(columns) -%}
   {{ return(adapter.dispatch('get_empty_schema_sql', 'dbt')(columns)) }}
 {% endmacro %}
 
 {% macro default__get_empty_schema_sql(columns) %}
     {%- set col_err = [] -%}
+    {%- set col_naked_numeric = [] -%}
     select
     {% for i in columns %}
       {%- set col = columns[i] -%}
       {%- if col['data_type'] is not defined -%}
-        {{ col_err.append(col['name']) }}
+        {%- do col_err.append(col['name']) -%}
+      {#-- If this column's type is just 'numeric' then it is missing precision/scale, raise a warning --#}
+      {%- elif col['data_type'].strip().lower() in ('numeric', 'decimal', 'number') -%}
+        {%- do col_naked_numeric.append(col['name']) -%}
       {%- endif -%}
       {% set col_name = adapter.quote(col['name']) if col.get('quote') else col['name'] %}
       cast(null as {{ col['data_type'] }}) as {{ col_name }}{{ ", " if not loop.last }}
     {%- endfor -%}
     {%- if (col_err | length) > 0 -%}
       {{ exceptions.column_type_missing(column_names=col_err) }}
+    {%- elif (col_naked_numeric | length) > 0 -%}
+      {{ exceptions.warn("Detected columns with numeric type and unspecified precision/scale, this can lead to unintended rounding: " ~ col_naked_numeric ~ "`") }}
     {%- endif -%}
 {% endmacro %}
 

tests/functional/contracts/test_contract_precision.py

@@ -0,0 +1,63 @@
+import pytest
+from dbt.tests.util import run_dbt_and_capture
+
+
+my_numeric_model_sql = """
+select
+  1.234 as non_integer
+"""
+
+model_schema_numerics_yml = """
+version: 2
+models:
+  - name: my_numeric_model
+    config:
+      contract:
+        enforced: true
+    columns:
+      - name: non_integer
+        data_type: numeric
+"""
+
+model_schema_numerics_precision_yml = """
+version: 2
+models:
+  - name: my_numeric_model
+    config:
+      contract:
+        enforced: true
+    columns:
+      - name: non_integer
+        data_type: numeric(38,3)
+"""
+
+
+class TestModelContractNumericNoPrecision:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "my_numeric_model.sql": my_numeric_model_sql,
+            "schema.yml": model_schema_numerics_yml,
+        }
+
+    def test_contracted_numeric_without_precision(self, project):
+        expected_msg = "Detected columns with numeric type and unspecified precision/scale, this can lead to unintended rounding: ['non_integer']"
+        _, logs = run_dbt_and_capture(["run"], expect_pass=True)
+        assert expected_msg in logs
+        _, logs = run_dbt_and_capture(["--warn-error", "run"], expect_pass=False)
+        assert "Compilation Error in model my_numeric_model" in logs
+        assert expected_msg in logs
+
+
+class TestModelContractNumericPrecision:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "my_numeric_model.sql": my_numeric_model_sql,
+            "schema.yml": model_schema_numerics_precision_yml,
+        }
+
+    def test_contracted_numeric_with_precision(self, project):
+        expected_msg = "Detected columns with numeric type and unspecified precision/scale, this can lead to unintended rounding: ['non_integer']"
+        _, logs = run_dbt_and_capture(["run"], expect_pass=True)
+        assert expected_msg not in logs