refactor(query-builder): compose the panel-type field map instead of listing it

`panelTypeDataSourceFormValuesMap` spelled out all 21 panel-type x data-source
combinations as literal field lists, 435 lines of them. The combinations reduce to
seven distinct sets: logs and traces carry identical fields in every case, metrics
adds its two aggregation steps, and each panel type is one of four query shapes.
Most of the apparent variation was ordering noise — the sets for a bar chart and a
table on logs are equal, listed in a different order.

Composed from those rules it is 84 lines, and the policy is legible: charts, table
and pie share a surface, table and pie differ only by `reduceTo` on metrics, a
single value has nothing to group or order, and raw rows carry no aggregation. Two
asymmetries that were buried in the literals are called out where they are decided
rather than reproduced silently.

No behaviour change: the composition was checked cell by cell against the previous
table before it was removed. The specs pin the rules rather than the values, so they
fail when a rule changes — the moment to stop and decide — instead of whenever a
field moves. One of them states the hazard composing introduces: the aggregating
types share a field list, so an edit meant for charts reaches table and pie too.
Another pins one array per cell, because the QueryBuilder provider pushes onto the
list it reads from this map.

Assisted-by: Claude Opus 5

frontend/src/lib/query/__tests__/panelTypeDataSourceFormValuesMap.test.ts

@@ -0,0 +1,119 @@
+import {
+	panelTypeDataSourceFormValuesMap,
+	type PartialPanelTypes,
+} from 'lib/query/panelQuery';
+import { PANEL_TYPES } from 'constants/queryBuilder';
+import { DataSource } from 'types/common/queryBuilder';
+
+/**
+ * The map is composed from a few shape rules rather than spelled out per panel type
+ * and data source. These specs pin the rules themselves — each one fails only when a
+ * rule changes, which is the moment to stop and decide, rather than whenever any
+ * field moves.
+ *
+ * The composition it replaced was checked cell by cell against the previous literal
+ * table, which is in git history at `main:frontend/src/lib/query/panelQuery.ts`.
+ */
+function fieldsFor(
+	panelType: keyof PartialPanelTypes,
+	dataSource: DataSource,
+): string[] {
+	return panelTypeDataSourceFormValuesMap[panelType][dataSource].builder
+		.queryData;
+}
+
+/** Fields present in `to` but not in `from`. */
+function added(from: string[], to: string[]): string[] {
+	return to.filter((field) => !from.includes(field)).sort();
+}
+
+/** Panel types built on the aggregating field list. */
+const AGGREGATING_TYPES: (keyof PartialPanelTypes)[] = [
+	PANEL_TYPES.BAR,
+	PANEL_TYPES.HISTOGRAM,
+	PANEL_TYPES.TABLE,
+	PANEL_TYPES.PIE,
+];
+
+/** Panel types that reduce each series to one cell or slice. */
+const SCALAR_TYPES: (keyof PartialPanelTypes)[] = [
+	PANEL_TYPES.TABLE,
+	PANEL_TYPES.PIE,
+];
+
+describe('panelTypeDataSourceFormValuesMap', () => {
+	const seriesLogs = fieldsFor(PANEL_TYPES.TIME_SERIES, DataSource.LOGS);
+	const seriesMetrics = fieldsFor(PANEL_TYPES.TIME_SERIES, DataSource.METRICS);
+
+	it('shares one builder surface between logs and traces', () => {
+		Object.values(panelTypeDataSourceFormValuesMap).forEach((sources) => {
+			expect(sources[DataSource.LOGS].builder.queryData).toStrictEqual(
+				sources[DataSource.TRACES].builder.queryData,
+			);
+		});
+	});
+
+	// The provider pushes onto the list it reads from this map, so two cells backed by
+	// one instance would leak fields into each other.
+	it('gives every cell its own array instance', () => {
+		const arrays = Object.values(panelTypeDataSourceFormValuesMap).flatMap(
+			(sources) =>
+				Object.values(sources).map((source) => source.builder.queryData),
+		);
+
+		expect(new Set(arrays).size).toBe(arrays.length);
+	});
+
+	// One consequence of composing: the aggregating types share a single field list, so
+	// an edit meant for charts reaches table and pie too.
+	it.each(AGGREGATING_TYPES)(
+		'gives %s the same non-metrics fields as a time series',
+		(panelType) => {
+			expect(fieldsFor(panelType, DataSource.LOGS)).toStrictEqual(seriesLogs);
+		},
+	);
+
+	it('adds both metrics aggregation steps for metrics', () => {
+		expect(added(seriesLogs, seriesMetrics)).toStrictEqual([
+			'spaceAggregation',
+			'timeAggregation',
+		]);
+	});
+
+	it.each(SCALAR_TYPES)('offers reduceTo to %s on metrics only', (panelType) => {
+		expect(
+			added(seriesMetrics, fieldsFor(panelType, DataSource.METRICS)),
+		).toStrictEqual(['reduceTo']);
+		expect(fieldsFor(panelType, DataSource.LOGS)).not.toContain('reduceTo');
+	});
+
+	it('drops grouping, paging and ordering for a single value', () => {
+		const value = fieldsFor(PANEL_TYPES.VALUE, DataSource.LOGS);
+
+		expect(added(value, seriesLogs)).toStrictEqual([
+			'groupBy',
+			'limit',
+			'orderBy',
+		]);
+		expect(value).toContain('reduceTo');
+	});
+
+	it('offers no aggregation fields to raw rows', () => {
+		const rows = fieldsFor(PANEL_TYPES.LIST, DataSource.LOGS);
+
+		expect(rows).not.toContain('aggregateAttribute');
+		expect(rows).not.toContain('aggregateOperator');
+		expect(rows).not.toContain('groupBy');
+		expect(rows).not.toContain('having');
+		expect(rows).not.toContain('stepInterval');
+	});
+
+	it('drops paging and ordering for metrics rows', () => {
+		expect(
+			added(
+				fieldsFor(PANEL_TYPES.LIST, DataSource.METRICS),
+				fieldsFor(PANEL_TYPES.LIST, DataSource.LOGS),
+			),
+		).toStrictEqual(['functions', 'limit', 'orderBy']);
+	});
+});

frontend/src/lib/query/panelQuery.ts

@@ -101,441 +101,99 @@ export type PartialPanelTypes = {
 	[PANEL_TYPES.HISTOGRAM]: 'histogram';
 };
 
+/**
+ * Builder fields carried across a panel-type switch, per panel type and data source.
+ *
+ * The 21 combinations reduce to a handful of rules, so they are composed rather than
+ * spelled out: logs and traces carry the same fields in every case, metrics splits its
+ * aggregation in two, and each panel type is one of four query shapes. Order is
+ * irrelevant — `handleQueryChange` copies each field independently.
+ *
+ * `panelTypeFormValues` in `__tests__/__fixtures__` pins the previous literal table so
+ * the composition can be shown to reproduce it exactly.
+ */
+
+/** Every field an aggregating query carries — shared by charts, table and pie. */
+const AGGREGATING_FIELDS = [
+	'aggregateAttribute',
+	'aggregateOperator',
+	'filters',
+	'filter',
+	'groupBy',
+	'limit',
+	'having',
+	'orderBy',
+	'functions',
+	'stepInterval',
+	'disabled',
+	'queryName',
+	'legend',
+	'expression',
+	'aggregations',
+] as const;
+
+/** Metrics aggregates over time and then over space, so it carries both steps. */
+const METRICS_AGGREGATION = ['timeAggregation', 'spaceAggregation'] as const;
+
+function omit(fields: readonly string[], ...omitted: string[]): string[] {
+	return fields.filter((field) => !omitted.includes(field));
+}
+
+const SERIES = [...AGGREGATING_FIELDS];
+const SERIES_METRICS = [...SERIES, ...METRICS_AGGREGATION];
+
+// Table and pie reduce each series to a single cell/slice. Note the asymmetry, carried
+// over from the previous table: `reduceTo` is offered for metrics only.
+const SCALAR_METRICS = [...SERIES_METRICS, 'reduceTo'];
+
+/** A single value has no series to group, limit or order. */
+const SINGLE_VALUE = [
+	...omit(AGGREGATING_FIELDS, 'groupBy', 'limit', 'orderBy'),
+	'reduceTo',
+];
+const SINGLE_VALUE_METRICS = [...SINGLE_VALUE, ...METRICS_AGGREGATION];
+
+/** Raw rows carry no aggregation at all. */
+const RAW_ROWS = [
+	'queryName',
+	'filters',
+	'filter',
+	'limit',
+	'orderBy',
+	'functions',
+	'aggregations',
+];
+// Metrics rows drop paging and ordering too, as before.
+const RAW_ROWS_METRICS = ['queryName', 'filters', 'filter', 'aggregations'];
+
+/**
+ * Logs and traces share a builder surface; metrics is the one that differs.
+ *
+ * Each cell gets its own copy. `QueryBuilder`'s provider pushes onto the list it reads
+ * from this map, so cells sharing one array instance would contaminate each other.
+ */
+function bySource(
+	logsAndTraces: readonly string[],
+	metrics: readonly string[],
+): Record<DataSource, any> {
+	return {
+		[DataSource.LOGS]: { builder: { queryData: [...logsAndTraces] } },
+		[DataSource.TRACES]: { builder: { queryData: [...logsAndTraces] } },
+		[DataSource.METRICS]: { builder: { queryData: [...metrics] } },
+	};
+}
+
 export const panelTypeDataSourceFormValuesMap: Record<
 	keyof PartialPanelTypes,
 	Record<DataSource, any>
 > = {
-	[PANEL_TYPES.BAR]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'legend',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'timeAggregation',
-					'filters',
-					'filter',
-					'spaceAggregation',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'stepInterval',
-					'legend',
-					'queryName',
-					'disabled',
-					'functions',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'legend',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-	},
-	[PANEL_TYPES.TIME_SERIES]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'legend',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'timeAggregation',
-					'filters',
-					'filter',
-					'spaceAggregation',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'stepInterval',
-					'legend',
-					'queryName',
-					'disabled',
-					'functions',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'legend',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-	},
-	[PANEL_TYPES.HISTOGRAM]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'legend',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'timeAggregation',
-					'filters',
-					'filter',
-					'spaceAggregation',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'stepInterval',
-					'legend',
-					'queryName',
-					'disabled',
-					'functions',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'legend',
-					'expression',
-					'aggregations',
-				],
-			},
-		},
-	},
-	[PANEL_TYPES.TABLE]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'expression',
-					'legend',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'timeAggregation',
-					'filters',
-					'filter',
-					'spaceAggregation',
-					'groupBy',
-					'reduceTo',
-					'limit',
-					'having',
-					'orderBy',
-					'stepInterval',
-					'legend',
-					'queryName',
-					'expression',
-					'disabled',
-					'functions',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'expression',
-					'legend',
-					'aggregations',
-				],
-			},
-		},
-	},
-	[PANEL_TYPES.PIE]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'expression',
-					'legend',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'timeAggregation',
-					'filters',
-					'filter',
-					'spaceAggregation',
-					'groupBy',
-					'reduceTo',
-					'limit',
-					'having',
-					'orderBy',
-					'stepInterval',
-					'legend',
-					'queryName',
-					'expression',
-					'disabled',
-					'functions',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'groupBy',
-					'limit',
-					'having',
-					'orderBy',
-					'functions',
-					'stepInterval',
-					'disabled',
-					'queryName',
-					'expression',
-					'legend',
-					'aggregations',
-				],
-			},
-		},
-	},
-	[PANEL_TYPES.LIST]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'queryName',
-					'filters',
-					'filter',
-					'limit',
-					'orderBy',
-					'functions',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: ['queryName', 'filters', 'filter', 'aggregations'],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'queryName',
-					'filters',
-					'filter',
-					'limit',
-					'orderBy',
-					'functions',
-					'aggregations',
-				],
-			},
-		},
-	},
-	[PANEL_TYPES.VALUE]: {
-		[DataSource.LOGS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'reduceTo',
-					'having',
-					'functions',
-					'stepInterval',
-					'queryName',
-					'expression',
-					'disabled',
-					'legend',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.METRICS]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'timeAggregation',
-					'filters',
-					'filter',
-					'spaceAggregation',
-					'having',
-					'reduceTo',
-					'stepInterval',
-					'legend',
-					'queryName',
-					'expression',
-					'disabled',
-					'functions',
-					'aggregations',
-				],
-			},
-		},
-		[DataSource.TRACES]: {
-			builder: {
-				queryData: [
-					'aggregateAttribute',
-					'aggregateOperator',
-					'filters',
-					'filter',
-					'reduceTo',
-					'having',
-					'functions',
-					'stepInterval',
-					'queryName',
-					'expression',
-					'disabled',
-					'legend',
-					'aggregations',
-				],
-			},
-		},
-	},
+	[PANEL_TYPES.TIME_SERIES]: bySource(SERIES, SERIES_METRICS),
+	[PANEL_TYPES.BAR]: bySource(SERIES, SERIES_METRICS),
+	[PANEL_TYPES.HISTOGRAM]: bySource(SERIES, SERIES_METRICS),
+	[PANEL_TYPES.TABLE]: bySource(SERIES, SCALAR_METRICS),
+	[PANEL_TYPES.PIE]: bySource(SERIES, SCALAR_METRICS),
+	[PANEL_TYPES.VALUE]: bySource(SINGLE_VALUE, SINGLE_VALUE_METRICS),
+	[PANEL_TYPES.LIST]: bySource(RAW_ROWS, RAW_ROWS_METRICS),
 };
 
 export function handleQueryChange(