Conditional rendering

.changes/unreleased/Fixes-20230817-164722.yaml

@@ -0,0 +1,6 @@
+kind: Fixes
+body: Render sql_header before prepending for 'dbt show'
+time: 2023-08-17T16:47:22.030206+02:00
+custom:
+  Author: jtcohen6
+  Issue: "8417"

core/dbt/task/show.py

@@ -11,6 +11,9 @@ from dbt.exceptions import DbtRuntimeError
 from dbt.task.compile import CompileTask, CompileRunner
 from dbt.task.seed import SeedRunner
 
+from dbt.context.providers import generate_runtime_model_context
+from dbt.clients.jinja import get_rendered, _HAS_RENDER_CHARS_PAT
+
 
 class ShowRunner(CompileRunner):
     def __init__(self, config, adapter, node, node_index, num_nodes):
@@ -24,12 +27,20 @@ class ShowRunner(CompileRunner):
         limit = None if self.config.args.limit < 0 else self.config.args.limit
 
         if "sql_header" in compiled_node.unrendered_config:
-            compiled_node.compiled_code = (
+            sql_header = compiled_node.unrendered_config["sql_header"]
-                compiled_node.unrendered_config["sql_header"] + compiled_node.compiled_code
+            # Does the sql_header contain Jinja and need to be rendered?
-            )
+            # Generating the context will be slower if we don't actually need to render the sql_header (if it contains no Jinja)
+            if _HAS_RENDER_CHARS_PAT.search(sql_header):
+                # Currently, we only render sql_header at *parse* time while *running* models
+                # See dbt-core issues #2793, #3264, #7151
+                # For simplicity, we will use "generate_runtime_model_context" instead of "generate_parser_model_context"
+                context = generate_runtime_model_context(compiled_node, self.config, manifest)
+                import ipdb; ipdb.set_trace()
+                sql_header = get_rendered(compiled_node.unrendered_config["sql_header"], context)
+            compiled_code = sql_header + compiled_code
 
-        adapter_response, execute_result = self.adapter.execute(
+        adapter_response, execute_result = self.adapter.execute_macro(
-            compiled_node.compiled_code, fetch=True, limit=limit
+            compiled_code, fetch=True, limit=limit
         )
         end_time = time.time()
 

tests/functional/show/fixtures.py

@@ -35,13 +35,20 @@ select
 from {{ ref('sample_model') }}
 """
 
-models__sql_header = """
+models__sql_header_no_rendering = """
 {% call set_sql_header(config) %}
 set session time zone 'Asia/Kolkata';
 {%- endcall %}
 select current_setting('timezone') as timezone
 """
 
+models__sql_header_yes_rendering = """
+{% call set_sql_header(config) %}
+set session time zone '{{ var("timezone", "Asia/Kolkata") }}';
+{%- endcall %}
+select current_setting('timezone') as timezone
+"""
+
 private_model_yml = """
 groups:
   - name: my_cool_group

tests/functional/show/test_show.py

@@ -11,7 +11,8 @@ from tests.functional.show.fixtures import (
     models__second_model,
     models__ephemeral_model,
     schema_yml,
-    models__sql_header,
+    models__sql_header_no_rendering,
+    models__sql_header_yes_rendering,
     private_model_yml,
 )
 
@@ -25,7 +26,8 @@ class ShowBase:
             "sample_number_model_with_nulls.sql": models__sample_number_model_with_nulls,
             "second_model.sql": models__second_model,
             "ephemeral_model.sql": models__ephemeral_model,
-            "sql_header.sql": models__sql_header,
+            "sql_header_no_rendering.sql": models__sql_header_no_rendering,
+            "sql_header_yes_rendering.sql": models__sql_header_yes_rendering,
         }
 
     @pytest.fixture(scope="class")
@@ -164,13 +166,16 @@ class TestShowSeed(ShowBase):
         (_, log_output) = run_dbt_and_capture(["show", "--select", "sample_seed"])
         assert "Previewing node 'sample_seed'" in log_output
 
-
+    def test_sql_header_no_rendering(self, project):
-class TestShowSqlHeader(ShowBase):
+        (_, log_output) = run_dbt_and_capture(["show", "--select", "sql_header_no_rendering"])
-    def test_sql_header(self, project):
-        run_dbt(["build"])
-        (_, log_output) = run_dbt_and_capture(["show", "--select", "sql_header"])
         assert "Asia/Kolkata" in log_output
 
+    def test_sql_header_yes_rendering(self, project):
+        (_, log_output) = run_dbt_and_capture(
+            ["show", "--select", "sql_header_yes_rendering", "--vars", "timezone: Europe/Paris"]
+        )
+        assert "Europe/Paris" in log_output
+
 
 class TestShowModelVersions:
     @pytest.fixture(scope="class")