aminghadersohi commented on code in PR #39922:
URL: https://github.com/apache/superset/pull/39922#discussion_r3482250501


##########
superset/mcp_service/chart/plugins/big_number.py:
##########
@@ -0,0 +1,247 @@
+# 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.
+
+"""Big number chart type plugin."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from superset.mcp_service.chart.chart_utils import (
+    _big_number_chart_what,
+    _summarize_filters,
+    is_column_truly_temporal,
+    map_big_number_config,
+)
+from superset.mcp_service.chart.plugin import BaseChartPlugin
+from superset.mcp_service.chart.schemas import BigNumberChartConfig, ColumnRef
+from superset.mcp_service.chart.validation.dataset_validator import 
DatasetValidator
+from superset.mcp_service.common.error_schemas import ChartGenerationError
+
+
+class BigNumberChartPlugin(BaseChartPlugin):
+    """Plugin for big_number chart type."""
+
+    chart_type = "big_number"
+    display_name = "Big Number"
+    native_viz_types = {
+        "big_number": "Big Number with Trendline",
+        "big_number_total": "Big Number",
+    }
+
+    def pre_validate(
+        self,
+        config: dict[str, Any],
+    ) -> ChartGenerationError | None:
+        if "metric" not in config:
+            return ChartGenerationError(
+                error_type="missing_metric",
+                message="Big Number chart missing required field: metric",
+                details=(
+                    "Big Number charts require a 'metric' field "
+                    "specifying the value to display"
+                ),
+                suggestions=[
+                    "Add 'metric' with name and aggregate: "
+                    "{'name': 'revenue', 'aggregate': 'SUM'}",
+                    "The aggregate function is required (SUM, COUNT, AVG, MIN, 
MAX)",
+                    "Example: {'chart_type': 'big_number', "
+                    "'metric': {'name': 'sales', 'aggregate': 'SUM'}}",
+                ],
+                error_code="MISSING_BIG_NUMBER_METRIC",
+            )
+
+        metric = config.get("metric", {})
+        if not isinstance(metric, dict):
+            return ChartGenerationError(
+                error_type="invalid_metric_type",
+                message="Big Number metric must be a dict with 'name' and 
'aggregate'",
+                details=(
+                    f"The 'metric' field must be an object, got 
{type(metric).__name__}"
+                ),
+                suggestions=[
+                    "Use a dict: {'name': 'col', 'aggregate': 'SUM'}",
+                    "Valid aggregates: SUM, COUNT, AVG, MIN, MAX",
+                ],
+                error_code="INVALID_BIG_NUMBER_METRIC_TYPE",
+            )
+        if metric.get("sql_expression"):
+            label = metric.get("label")
+            if not isinstance(label, str) or not label.strip():
+                return ChartGenerationError(
+                    error_type="missing_sql_metric_label",
+                    message="SQL expression metrics require a non-empty 
'label'",
+                    details=(
+                        "When using a custom SQL expression as the Big Number 
metric, "
+                        "a human-readable 'label' string is required so 
Superset can "
+                        "display the metric name."
+                    ),
+                    suggestions=[
+                        "Add 'label': e.g. {'sql_expression': 'SUM(a)/SUM(b)', 
"
+                        "'label': 'Conversion Rate'}",
+                        "The label must be a non-empty string",
+                    ],
+                    error_code="MISSING_SQL_METRIC_LABEL",
+                )
+        elif not metric.get("aggregate") and not metric.get("saved_metric"):
+            return ChartGenerationError(
+                error_type="missing_metric_aggregate",
+                message=(
+                    "Big Number metric must include an aggregate function "
+                    "or reference a saved metric"
+                ),
+                details=(
+                    "The metric must have an 'aggregate' field or 
'saved_metric': true"
+                ),
+                suggestions=[
+                    "Add 'aggregate': {'name': 'col', 'aggregate': 'SUM'}",
+                    "Or use a saved metric: {'name': 'metric', 'saved_metric': 
true}",
+                    "Valid aggregates: SUM, COUNT, AVG, MIN, MAX",
+                ],
+                error_code="MISSING_BIG_NUMBER_AGGREGATE",
+            )
+
+        show_trendline = config.get("show_trendline", False)
+        temporal_column = config.get("temporal_column")
+        if show_trendline and not temporal_column:
+            return ChartGenerationError(
+                error_type="missing_temporal_column",
+                message="Trendline requires a temporal column",
+                details=(
+                    "When 'show_trendline' is True, "
+                    "a 'temporal_column' must be specified"
+                ),
+                suggestions=[
+                    "Add 'temporal_column': 'date_column_name'",
+                    "Or set 'show_trendline': false for number only",
+                    "Use get_dataset_info to find temporal columns",
+                ],
+                error_code="MISSING_TEMPORAL_COLUMN",
+            )
+
+        return None
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:
+        if not isinstance(config, BigNumberChartConfig):
+            return []
+        refs: list[ColumnRef] = [config.metric]
+        # temporal_column is a str field, not a ColumnRef — validate it exists
+        if config.temporal_column:
+            refs.append(ColumnRef(name=config.temporal_column))
+        if config.filters:
+            for f in config.filters:
+                refs.append(ColumnRef(name=f.column))
+        return refs
+
+    def to_form_data(
+        self, config: Any, dataset_id: int | str | None = None
+    ) -> dict[str, Any]:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
superset/mcp_service/chart/plugins/big_number.py:
##########
@@ -0,0 +1,247 @@
+# 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.
+
+"""Big number chart type plugin."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from superset.mcp_service.chart.chart_utils import (
+    _big_number_chart_what,
+    _summarize_filters,
+    is_column_truly_temporal,
+    map_big_number_config,
+)
+from superset.mcp_service.chart.plugin import BaseChartPlugin
+from superset.mcp_service.chart.schemas import BigNumberChartConfig, ColumnRef
+from superset.mcp_service.chart.validation.dataset_validator import 
DatasetValidator
+from superset.mcp_service.common.error_schemas import ChartGenerationError
+
+
+class BigNumberChartPlugin(BaseChartPlugin):
+    """Plugin for big_number chart type."""
+
+    chart_type = "big_number"
+    display_name = "Big Number"
+    native_viz_types = {
+        "big_number": "Big Number with Trendline",
+        "big_number_total": "Big Number",
+    }
+
+    def pre_validate(
+        self,
+        config: dict[str, Any],
+    ) -> ChartGenerationError | None:
+        if "metric" not in config:
+            return ChartGenerationError(
+                error_type="missing_metric",
+                message="Big Number chart missing required field: metric",
+                details=(
+                    "Big Number charts require a 'metric' field "
+                    "specifying the value to display"
+                ),
+                suggestions=[
+                    "Add 'metric' with name and aggregate: "
+                    "{'name': 'revenue', 'aggregate': 'SUM'}",
+                    "The aggregate function is required (SUM, COUNT, AVG, MIN, 
MAX)",
+                    "Example: {'chart_type': 'big_number', "
+                    "'metric': {'name': 'sales', 'aggregate': 'SUM'}}",
+                ],
+                error_code="MISSING_BIG_NUMBER_METRIC",
+            )
+
+        metric = config.get("metric", {})
+        if not isinstance(metric, dict):
+            return ChartGenerationError(
+                error_type="invalid_metric_type",
+                message="Big Number metric must be a dict with 'name' and 
'aggregate'",
+                details=(
+                    f"The 'metric' field must be an object, got 
{type(metric).__name__}"
+                ),
+                suggestions=[
+                    "Use a dict: {'name': 'col', 'aggregate': 'SUM'}",
+                    "Valid aggregates: SUM, COUNT, AVG, MIN, MAX",
+                ],
+                error_code="INVALID_BIG_NUMBER_METRIC_TYPE",
+            )
+        if metric.get("sql_expression"):
+            label = metric.get("label")
+            if not isinstance(label, str) or not label.strip():
+                return ChartGenerationError(
+                    error_type="missing_sql_metric_label",
+                    message="SQL expression metrics require a non-empty 
'label'",
+                    details=(
+                        "When using a custom SQL expression as the Big Number 
metric, "
+                        "a human-readable 'label' string is required so 
Superset can "
+                        "display the metric name."
+                    ),
+                    suggestions=[
+                        "Add 'label': e.g. {'sql_expression': 'SUM(a)/SUM(b)', 
"
+                        "'label': 'Conversion Rate'}",
+                        "The label must be a non-empty string",
+                    ],
+                    error_code="MISSING_SQL_METRIC_LABEL",
+                )
+        elif not metric.get("aggregate") and not metric.get("saved_metric"):
+            return ChartGenerationError(
+                error_type="missing_metric_aggregate",
+                message=(
+                    "Big Number metric must include an aggregate function "
+                    "or reference a saved metric"
+                ),
+                details=(
+                    "The metric must have an 'aggregate' field or 
'saved_metric': true"
+                ),
+                suggestions=[
+                    "Add 'aggregate': {'name': 'col', 'aggregate': 'SUM'}",
+                    "Or use a saved metric: {'name': 'metric', 'saved_metric': 
true}",
+                    "Valid aggregates: SUM, COUNT, AVG, MIN, MAX",
+                ],
+                error_code="MISSING_BIG_NUMBER_AGGREGATE",
+            )
+
+        show_trendline = config.get("show_trendline", False)
+        temporal_column = config.get("temporal_column")
+        if show_trendline and not temporal_column:
+            return ChartGenerationError(
+                error_type="missing_temporal_column",
+                message="Trendline requires a temporal column",
+                details=(
+                    "When 'show_trendline' is True, "
+                    "a 'temporal_column' must be specified"
+                ),
+                suggestions=[
+                    "Add 'temporal_column': 'date_column_name'",
+                    "Or set 'show_trendline': false for number only",
+                    "Use get_dataset_info to find temporal columns",
+                ],
+                error_code="MISSING_TEMPORAL_COLUMN",
+            )
+
+        return None
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:
+        if not isinstance(config, BigNumberChartConfig):
+            return []
+        refs: list[ColumnRef] = [config.metric]
+        # temporal_column is a str field, not a ColumnRef — validate it exists
+        if config.temporal_column:
+            refs.append(ColumnRef(name=config.temporal_column))
+        if config.filters:
+            for f in config.filters:
+                refs.append(ColumnRef(name=f.column))
+        return refs
+
+    def to_form_data(
+        self, config: Any, dataset_id: int | str | None = None
+    ) -> dict[str, Any]:
+        return map_big_number_config(config)
+
+    def post_map_validate(
+        self,
+        config: Any,
+        form_data: dict[str, Any],
+        dataset_id: int | str | None = None,
+    ) -> ChartGenerationError | None:
+        """Verify the trendline temporal column is a real temporal SQL type.
+
+        This check was previously baked into map_config_to_form_data() in
+        chart_utils.py as a special case. Moving it here keeps the dispatcher
+        clean and makes the constraint explicit and discoverable.
+        """
+        if not isinstance(config, BigNumberChartConfig):
+            return None
+        if not (config.show_trendline and config.temporal_column):
+            return None
+
+        if not is_column_truly_temporal(config.temporal_column, dataset_id):
+            return ChartGenerationError(
+                error_type="non_temporal_trendline_column",
+                message=(
+                    f"Big Number trendline requires a temporal SQL column; "
+                    f"'{config.temporal_column}' is not temporal."
+                ),
+                details=(
+                    f"Column '{config.temporal_column}' does not have a 
temporal "
+                    f"SQL type (DATE, DATETIME, TIMESTAMP). The trendline 
requires "
+                    f"a true temporal column for DATE_TRUNC to work."
+                ),
+                suggestions=[
+                    "Use get_dataset_info to find columns with temporal SQL 
types",
+                    "Set 'show_trendline': false to use any column as the 
metric",
+                    "If the column contains dates stored as integers, "
+                    "consider casting it in a virtual dataset",
+                ],
+                error_code="NON_TEMPORAL_TRENDLINE_COLUMN",
+            )
+
+        return None
+
+    def generate_name(self, config: Any, dataset_name: str | None = None) -> 
str:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
superset/mcp_service/chart/plugins/big_number.py:
##########
@@ -0,0 +1,247 @@
+# 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.
+
+"""Big number chart type plugin."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from superset.mcp_service.chart.chart_utils import (
+    _big_number_chart_what,
+    _summarize_filters,
+    is_column_truly_temporal,
+    map_big_number_config,
+)
+from superset.mcp_service.chart.plugin import BaseChartPlugin
+from superset.mcp_service.chart.schemas import BigNumberChartConfig, ColumnRef
+from superset.mcp_service.chart.validation.dataset_validator import 
DatasetValidator
+from superset.mcp_service.common.error_schemas import ChartGenerationError
+
+
+class BigNumberChartPlugin(BaseChartPlugin):
+    """Plugin for big_number chart type."""
+
+    chart_type = "big_number"
+    display_name = "Big Number"
+    native_viz_types = {
+        "big_number": "Big Number with Trendline",
+        "big_number_total": "Big Number",
+    }
+
+    def pre_validate(
+        self,
+        config: dict[str, Any],
+    ) -> ChartGenerationError | None:
+        if "metric" not in config:
+            return ChartGenerationError(
+                error_type="missing_metric",
+                message="Big Number chart missing required field: metric",
+                details=(
+                    "Big Number charts require a 'metric' field "
+                    "specifying the value to display"
+                ),
+                suggestions=[
+                    "Add 'metric' with name and aggregate: "
+                    "{'name': 'revenue', 'aggregate': 'SUM'}",
+                    "The aggregate function is required (SUM, COUNT, AVG, MIN, 
MAX)",
+                    "Example: {'chart_type': 'big_number', "
+                    "'metric': {'name': 'sales', 'aggregate': 'SUM'}}",
+                ],
+                error_code="MISSING_BIG_NUMBER_METRIC",
+            )
+
+        metric = config.get("metric", {})
+        if not isinstance(metric, dict):
+            return ChartGenerationError(
+                error_type="invalid_metric_type",
+                message="Big Number metric must be a dict with 'name' and 
'aggregate'",
+                details=(
+                    f"The 'metric' field must be an object, got 
{type(metric).__name__}"
+                ),
+                suggestions=[
+                    "Use a dict: {'name': 'col', 'aggregate': 'SUM'}",
+                    "Valid aggregates: SUM, COUNT, AVG, MIN, MAX",
+                ],
+                error_code="INVALID_BIG_NUMBER_METRIC_TYPE",
+            )
+        if metric.get("sql_expression"):
+            label = metric.get("label")
+            if not isinstance(label, str) or not label.strip():
+                return ChartGenerationError(
+                    error_type="missing_sql_metric_label",
+                    message="SQL expression metrics require a non-empty 
'label'",
+                    details=(
+                        "When using a custom SQL expression as the Big Number 
metric, "
+                        "a human-readable 'label' string is required so 
Superset can "
+                        "display the metric name."
+                    ),
+                    suggestions=[
+                        "Add 'label': e.g. {'sql_expression': 'SUM(a)/SUM(b)', 
"
+                        "'label': 'Conversion Rate'}",
+                        "The label must be a non-empty string",
+                    ],
+                    error_code="MISSING_SQL_METRIC_LABEL",
+                )
+        elif not metric.get("aggregate") and not metric.get("saved_metric"):
+            return ChartGenerationError(
+                error_type="missing_metric_aggregate",
+                message=(
+                    "Big Number metric must include an aggregate function "
+                    "or reference a saved metric"
+                ),
+                details=(
+                    "The metric must have an 'aggregate' field or 
'saved_metric': true"
+                ),
+                suggestions=[
+                    "Add 'aggregate': {'name': 'col', 'aggregate': 'SUM'}",
+                    "Or use a saved metric: {'name': 'metric', 'saved_metric': 
true}",
+                    "Valid aggregates: SUM, COUNT, AVG, MIN, MAX",
+                ],
+                error_code="MISSING_BIG_NUMBER_AGGREGATE",
+            )
+
+        show_trendline = config.get("show_trendline", False)
+        temporal_column = config.get("temporal_column")
+        if show_trendline and not temporal_column:
+            return ChartGenerationError(
+                error_type="missing_temporal_column",
+                message="Trendline requires a temporal column",
+                details=(
+                    "When 'show_trendline' is True, "
+                    "a 'temporal_column' must be specified"
+                ),
+                suggestions=[
+                    "Add 'temporal_column': 'date_column_name'",
+                    "Or set 'show_trendline': false for number only",
+                    "Use get_dataset_info to find temporal columns",
+                ],
+                error_code="MISSING_TEMPORAL_COLUMN",
+            )
+
+        return None
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:
+        if not isinstance(config, BigNumberChartConfig):
+            return []
+        refs: list[ColumnRef] = [config.metric]
+        # temporal_column is a str field, not a ColumnRef — validate it exists
+        if config.temporal_column:
+            refs.append(ColumnRef(name=config.temporal_column))
+        if config.filters:
+            for f in config.filters:
+                refs.append(ColumnRef(name=f.column))
+        return refs
+
+    def to_form_data(
+        self, config: Any, dataset_id: int | str | None = None
+    ) -> dict[str, Any]:
+        return map_big_number_config(config)
+
+    def post_map_validate(
+        self,
+        config: Any,
+        form_data: dict[str, Any],
+        dataset_id: int | str | None = None,
+    ) -> ChartGenerationError | None:
+        """Verify the trendline temporal column is a real temporal SQL type.
+
+        This check was previously baked into map_config_to_form_data() in
+        chart_utils.py as a special case. Moving it here keeps the dispatcher
+        clean and makes the constraint explicit and discoverable.
+        """
+        if not isinstance(config, BigNumberChartConfig):
+            return None
+        if not (config.show_trendline and config.temporal_column):
+            return None
+
+        if not is_column_truly_temporal(config.temporal_column, dataset_id):
+            return ChartGenerationError(
+                error_type="non_temporal_trendline_column",
+                message=(
+                    f"Big Number trendline requires a temporal SQL column; "
+                    f"'{config.temporal_column}' is not temporal."
+                ),
+                details=(
+                    f"Column '{config.temporal_column}' does not have a 
temporal "
+                    f"SQL type (DATE, DATETIME, TIMESTAMP). The trendline 
requires "
+                    f"a true temporal column for DATE_TRUNC to work."
+                ),
+                suggestions=[
+                    "Use get_dataset_info to find columns with temporal SQL 
types",
+                    "Set 'show_trendline': false to use any column as the 
metric",
+                    "If the column contains dates stored as integers, "
+                    "consider casting it in a virtual dataset",
+                ],
+                error_code="NON_TEMPORAL_TRENDLINE_COLUMN",
+            )
+
+        return None
+
+    def generate_name(self, config: Any, dataset_name: str | None = None) -> 
str:
+        what = _big_number_chart_what(config)
+        context = _summarize_filters(getattr(config, "filters", None))
+        return self._with_context(what, context)
+
+    def resolve_viz_type(self, config: Any) -> str:
+        show_trendline = getattr(config, "show_trendline", False)
+        temporal_column = getattr(config, "temporal_column", None)
+        if show_trendline and temporal_column:
+            return "big_number"
+        return "big_number_total"
+
+    def normalize_column_refs(self, config: Any, dataset_context: Any) -> Any:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
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:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
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
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
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
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:
+        if not isinstance(config, HandlebarsChartConfig):
+            return []
+        refs: list[ColumnRef] = []
+        if config.columns:
+            refs.extend(config.columns)
+        if config.metrics:
+            refs.extend(config.metrics)
+        if config.groupby:
+            refs.extend(config.groupby)
+        if config.filters:
+            for f in config.filters:
+                refs.append(ColumnRef(name=f.column))
+        return refs
+
+    def to_form_data(
+        self, config: Any, dataset_id: int | str | None = None
+    ) -> dict[str, Any]:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
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
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:
+        if not isinstance(config, HandlebarsChartConfig):
+            return []
+        refs: list[ColumnRef] = []
+        if config.columns:
+            refs.extend(config.columns)
+        if config.metrics:
+            refs.extend(config.metrics)
+        if config.groupby:
+            refs.extend(config.groupby)
+        if config.filters:
+            for f in config.filters:
+                refs.append(ColumnRef(name=f.column))
+        return refs
+
+    def to_form_data(
+        self, config: Any, dataset_id: int | str | None = None
+    ) -> dict[str, Any]:
+        return map_handlebars_config(config)
+
+    def generate_name(self, config: Any, dataset_name: str | None = None) -> 
str:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



##########
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
+
+    def extract_column_refs(self, config: Any) -> list[ColumnRef]:
+        if not isinstance(config, HandlebarsChartConfig):
+            return []
+        refs: list[ColumnRef] = []
+        if config.columns:
+            refs.extend(config.columns)
+        if config.metrics:
+            refs.extend(config.metrics)
+        if config.groupby:
+            refs.extend(config.groupby)
+        if config.filters:
+            for f in config.filters:
+                refs.append(ColumnRef(name=f.column))
+        return refs
+
+    def to_form_data(
+        self, config: Any, dataset_id: int | str | None = None
+    ) -> dict[str, Any]:
+        return map_handlebars_config(config)
+
+    def generate_name(self, config: Any, dataset_name: str | None = None) -> 
str:
+        what = _handlebars_chart_what(config)
+        context = _summarize_filters(getattr(config, "filters", None))
+        return self._with_context(what, context)
+
+    def resolve_viz_type(self, config: Any) -> str:
+        return "handlebars"
+
+    def normalize_column_refs(self, config: Any, dataset_context: Any) -> Any:

Review Comment:
   Thank you for the suggestion. The plugin methods follow Superset's internal 
convention for implementation code: the class-level docstring names the chart 
type and the Protocol declaration in `plugin.py` documents each method's 
contract (parameter types, return type, and invariants) for the whole family. 
Adding per-method prose docstrings to ~40 implementation methods across 7 
plugins would add noise without proportionate readability gain for contributors 
already reading the Protocol. Happy to revisit if there's a project-wide policy 
requiring them.



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