aminghadersohi commented on code in PR #39922:
URL: https://github.com/apache/superset/pull/39922#discussion_r3305704451


##########
superset/mcp_service/chart/plugins/handlebars.py:
##########
@@ -0,0 +1,193 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+"""Handlebars chart type plugin."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from superset.mcp_service.chart.chart_utils import (
+    _handlebars_chart_what,
+    _summarize_filters,
+    map_handlebars_config,
+)
+from superset.mcp_service.chart.plugin import BaseChartPlugin
+from superset.mcp_service.chart.schemas import ColumnRef, HandlebarsChartConfig
+from superset.mcp_service.chart.validation.dataset_validator import 
DatasetValidator
+from superset.mcp_service.common.error_schemas import ChartGenerationError
+
+
+class HandlebarsChartPlugin(BaseChartPlugin):
+    """Plugin for handlebars chart type (custom HTML template charts)."""
+
+    chart_type = "handlebars"
+    display_name = "Handlebars (Custom Template)"
+    native_viz_types = {
+        "handlebars": "Custom Template Chart",
+    }
+
+    def pre_validate(
+        self,
+        config: dict[str, Any],
+    ) -> ChartGenerationError | None:
+        if "handlebars_template" not in config:
+            return ChartGenerationError(
+                error_type="missing_handlebars_template",
+                message="Handlebars chart missing required field: 
handlebars_template",
+                details=(
+                    "Handlebars charts require a 'handlebars_template' string "
+                    "containing Handlebars HTML template markup"
+                ),
+                suggestions=[
+                    "Add 'handlebars_template' with a Handlebars HTML 
template",
+                    "Data is available as {{data}} array in the template",
+                    "Example: '<ul>{{#each data}}<li>{{this.name}}: "
+                    "{{this.value}}</li>{{/each}}</ul>'",
+                ],
+                error_code="MISSING_HANDLEBARS_TEMPLATE",
+            )
+
+        template = config.get("handlebars_template")
+        if not isinstance(template, str) or not template.strip():
+            return ChartGenerationError(
+                error_type="invalid_handlebars_template",
+                message="Handlebars template must be a non-empty string",
+                details=(
+                    "The 'handlebars_template' field must be a non-empty 
string "
+                    "containing valid Handlebars HTML template markup"
+                ),
+                suggestions=[
+                    "Ensure handlebars_template is a non-empty string",
+                    "Example: '<ul>{{#each 
data}}<li>{{this.name}}</li>{{/each}}</ul>'",
+                ],
+                error_code="INVALID_HANDLEBARS_TEMPLATE",
+            )
+
+        query_mode = config.get("query_mode", "aggregate")
+        if query_mode not in ("aggregate", "raw"):
+            return ChartGenerationError(
+                error_type="invalid_query_mode",
+                message="Invalid query_mode for handlebars chart",
+                details="query_mode must be either 'aggregate' or 'raw'",
+                suggestions=[
+                    "Use 'aggregate' for aggregated data (default)",
+                    "Use 'raw' for individual rows",
+                ],
+                error_code="INVALID_QUERY_MODE",
+            )
+
+        if query_mode == "raw" and not config.get("columns"):
+            return ChartGenerationError(
+                error_type="missing_raw_columns",
+                message="Handlebars chart in 'raw' mode requires 'columns'",
+                details=(
+                    "When query_mode is 'raw', you must specify which columns "
+                    "to include in the query results"
+                ),
+                suggestions=[
+                    "Add 'columns': [{'name': 'column_name'}] for raw mode",
+                    "Or use query_mode='aggregate' with 'metrics' and optional 
'groupby'",  # noqa: E501
+                ],
+                error_code="MISSING_RAW_COLUMNS",
+            )
+
+        if query_mode == "aggregate" and not config.get("metrics"):
+            return ChartGenerationError(
+                error_type="missing_aggregate_metrics",
+                message="Handlebars chart in 'aggregate' mode requires 
'metrics'",
+                details=(
+                    "When query_mode is 'aggregate' (default), you must 
specify "
+                    "at least one metric with an aggregate function"
+                ),
+                suggestions=[
+                    "Add 'metrics': [{'name': 'column', 'aggregate': 'SUM'}]",
+                    "Or use query_mode='raw' with 'columns' for individual 
rows",
+                ],
+                error_code="MISSING_AGGREGATE_METRICS",
+            )
+
+        return None

Review Comment:
   Intentional. `pre_validate` runs on the raw dict before Pydantic parsing, 
providing LLM-readable early-exit errors for the most common mistakes (missing 
template, wrong mode, missing columns/metrics). The Pydantic schema validators 
fire later with generic Pydantic messages; having both allows the plugin to 
return structured, actionable `ChartGenerationError` objects at the cheapest 
possible point.



##########
tests/unit_tests/mcp_service/chart/validation/test_runtime_validator.py:
##########
@@ -226,28 +220,15 @@ def test_validate_table_chart_skips_xy_validations(self):
             ],
         )
 
-        # These should not be called for table charts
-        with (
-            patch(
-                
"superset.mcp_service.chart.validation.runtime.RuntimeValidator."
-                "_validate_format_compatibility"
-            ) as mock_format,
-            patch(
-                
"superset.mcp_service.chart.validation.runtime.RuntimeValidator."
-                "_validate_cardinality"
-            ) as mock_cardinality,
-            patch(
-                
"superset.mcp_service.chart.validation.runtime.RuntimeValidator."
-                "_validate_chart_type"
-            ) as mock_chart_type,
-        ):
-            # Mock chart type validator to return no warnings
+        # Plugin runtime dispatches to TableChartPlugin which returns no 
warnings.
+        # Chart type suggester is also stubbed to return no warnings.
+        with patch(
+            "superset.mcp_service.chart.validation.runtime.RuntimeValidator."
+            "_validate_chart_type"
+        ) as mock_chart_type:
             mock_chart_type.return_value = ([], [])
 
             is_valid, error = RuntimeValidator.validate_runtime_issues(config, 
1)
 
-            # Format and cardinality validation should not be called for table 
charts
-            mock_format.assert_not_called()
-            mock_cardinality.assert_not_called()
             assert is_valid is True
             assert error is None

Review Comment:
   The old `mock_format.assert_not_called()` and 
`mock_cardinality.assert_not_called()` assertions targeted internal helpers 
that were removed in the refactor. The refactored implementation dispatches 
through the plugin boundary, and `TableChartPlugin.get_runtime_warnings()` 
returns `[]` by base-class default. The behavioral invariant (table chart 
produces no XY-specific warnings) is still tested — just at the plugin boundary 
rather than the removed internal methods.



##########
superset/mcp_service/chart/validation/runtime/__init__.py:
##########
@@ -98,61 +85,28 @@ def validate_runtime_issues(
         return True, None
 
     @staticmethod
-    def _validate_format_compatibility(config: XYChartConfig) -> List[str]:
-        """Validate format-type compatibility."""
-        warnings: List[str] = []
-
-        try:
-            # Import here to avoid circular imports
-            from .format_validator import FormatTypeValidator
-
-            is_valid, format_warnings = (
-                FormatTypeValidator.validate_format_compatibility(config)
-            )
-            if format_warnings:
-                warnings.extend(format_warnings)
-        except ImportError:
-            logger.warning("Format validator not available")
-        except Exception as e:
-            logger.warning("Format validation failed: %s", e)
-
-        return warnings
-
-    @staticmethod
-    def _validate_cardinality(
-        config: XYChartConfig, dataset_id: int | str
-    ) -> Tuple[List[str], List[str]]:
-        """Validate cardinality issues."""
-        warnings: List[str] = []
-        suggestions: List[str] = []
+    def _validate_plugin_runtime(
+        config: ChartConfig, dataset_id: int | str
+    ) -> List[str]:
+        """Delegate per-chart-type runtime warnings to the plugin registry.
 
+        Each plugin's get_runtime_warnings() method returns chart-type-specific
+        warnings (e.g. format/cardinality for XY). The registry dispatch 
removes
+        the previous isinstance(config, XYChartConfig) hardcoding.
+        """
         try:
-            # Import here to avoid circular imports
-            from .cardinality_validator import CardinalityValidator
-
-            # Determine chart type for cardinality thresholds
-            chart_type = config.kind if hasattr(config, "kind") else "default"
-
-            # Check X-axis cardinality
-            if config.x is None:
-                return warnings, suggestions
-            is_ok, cardinality_info = CardinalityValidator.check_cardinality(
-                dataset_id=dataset_id,
-                x_column=config.x.name,
-                chart_type=chart_type,
-                group_by_column=config.group_by[0].name if config.group_by 
else None,
-            )
-
-            if not is_ok and cardinality_info:
-                warnings.extend(cardinality_info.get("warnings", []))
-                suggestions.extend(cardinality_info.get("suggestions", []))
-
-        except ImportError:
-            logger.warning("Cardinality validator not available")
-        except Exception as e:
-            logger.warning("Cardinality validation failed: %s", e)
-
-        return warnings, suggestions
+            from superset.mcp_service.chart.registry import get_registry
+
+            chart_type = getattr(config, "chart_type", None)
+            if chart_type is None:
+                return []
+            plugin = get_registry().get(chart_type)
+            if plugin is None:
+                return []
+            return plugin.get_runtime_warnings(config, dataset_id)
+        except Exception as exc:

Review Comment:
   Intentional broad catch. Plugin `get_runtime_warnings()` is 
third-party-extensible and can raise any exception type — `ValueError`, 
`TypeError`, `KeyError`, etc. — not just 
`ImportError`/`AttributeError`/`RuntimeError`. Runtime warnings are 
non-blocking (they never prevent chart generation), so any plugin exception 
should be swallowed and logged as a warning rather than surfaced to the user.



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