add exceptions.warn to the dbt context (#1970)

core/dbt/exceptions.py

@@ -756,12 +756,19 @@ def warn_or_raise(exc, log_fmt=None):
         logger.warning(msg)
 
 
+def emit_warning(msg, node=None):
+    # there's no reason to expose log_fmt to macros - it's only useful for
+    # handling colors
+    return warn_or_error(msg, node=node)
+
+
 # Update this when a new function should be added to the
 # dbt context's `exceptions` key!
 CONTEXT_EXPORTS = {
     fn.__name__: fn
     for fn in
     [
+        emit_warning,
         missing_config,
         missing_materialization,
         missing_relation,

test/integration/013_context_var_tests/emit-warning-models/warnings.sql

@@ -0,0 +1,2 @@
+{% do exceptions.emit_warning('warning: everything is terrible but not that terrible') %}
+select 1 as id

test/integration/013_context_var_tests/test_context_vars.py

@@ -2,6 +2,10 @@
 
 import os
 
+import pytest
+
+import dbt.exceptions
+
 
 class TestContextVars(DBTIntegrationTest):
 
@@ -133,3 +137,19 @@ def test_postgres_env_vars_prod(self):
         self.assertEqual(ctx['target.user'], 'root')
         self.assertEqual(ctx['target.pass'], '')
         self.assertEqual(ctx['env_var'], '1')
+
+
+class TestEmitWarning(DBTIntegrationTest):
+    @property
+    def schema(self):
+        return "context_vars_013"
+
+    @property
+    def models(self):
+        return "emit-warning-models"
+
+    @use_profile('postgres')
+    def test_postgres_emit_warning(self):
+        with pytest.raises(dbt.exceptions.CompilationException):
+            self.run_dbt(['run'], strict=True)
+        self.run_dbt(['run'], strict=False, expect_pass=True)