fix(#749): handle negative step values

.changeset/proud-years-chew.md

@@ -0,0 +1,6 @@
+---
+'@getodk/xforms-engine': patch
+'@getodk/common': patch
+---
+
+Fixed handling of ranges with negative step values

packages/common/test-utils/xform-dsl/index.ts

@@ -126,6 +126,22 @@ export const select1 = (ref: string, ...children: XFormsElement[]): XFormsElemen
 	return t(`select1 ref="${ref}"`, ...children);
 };
 
+interface RangeAttributes {
+	start: number;
+	end: number;
+	step: number;
+}
+export const range = (
+	ref: string,
+	attributes: RangeAttributes,
+	...children: XFormsElement[]
+): XFormsElement => {
+	return t(
+		`range ref="${ref}" start="${attributes.start}" end="${attributes.end}" step="${attributes.step}"`,
+		...children
+	);
+};
+
 type Select1DynamicParameters =
 	// eslint-disable-next-line @typescript-eslint/sort-type-constituents
 	| readonly [ref: string, nodesetRef: string]

packages/xforms-engine/src/parse/body/control/RangeControlDefinition.ts

@@ -54,6 +54,16 @@ const parseNumericStringAttribute = (element: Element, localName: string): Numer
 	return value;
 };
 
+const abs = (value: string | null) => (value?.startsWith('-') ? value.substring(1) : value);
+
+const parseNumericStringAttributeAbs = (element: Element, localName: string): NumericString => {
+	const value = abs(element.getAttribute(localName));
+
+	assertNumericStringAttribute(localName, value);
+
+	return value;
+};
+
 /**
  * Per
  * {@link https://getodk.github.io/xforms-spec/#body-elements | ODK XForms spec},
@@ -69,15 +79,13 @@ const parseNumericStringAttribute = (element: Element, localName: string): Numer
  * checking only that they appear to be numeric values. We also preserve the
  * attributes' names here, for consistency with the spec.
  *
- * Downstream, we parse these to their appropriate numeric runtime types, and
- * alias them to their more conventional names (i.e. "start" -> "min", "end" ->
- * "max").
+ * Downstream, we parse these to their appropriate numeric runtime types.
  */
 export class RangeControlBoundsDefinition {
 	static from(element: Element) {
 		const start = parseNumericStringAttribute(element, 'start');
 		const end = parseNumericStringAttribute(element, 'end');
-		const step = parseNumericStringAttribute(element, 'step');
+		const step = parseNumericStringAttributeAbs(element, 'step');
 
 		return new this(start, end, step);
 	}

packages/xforms-engine/test/parse/body/control/RangeControlDefinition.test.ts

@@ -0,0 +1,70 @@
+import {
+	bind,
+	body,
+	head,
+	html,
+	mainInstance,
+	model,
+	range,
+	t,
+	title,
+} from '@getodk/common/test-utils/xform-dsl/index.ts';
+import { describe, expect, it } from 'vitest';
+import { RangeControlDefinition } from '../../../../src/parse/body/control/RangeControlDefinition.ts';
+import { XFormDefinition } from '../../../../src/parse/XFormDefinition.ts';
+import { XFormDOM } from '../../../../src/parse/XFormDOM.ts';
+
+describe('RangeControlDefinition', () => {
+	const create = (type: string, start: number, end: number, step: number) => {
+		const xform = html(
+			head(
+				title('Range definition'),
+				model(
+					mainInstance(t('root id="body-definition"', t('range'))),
+					bind('/root/range').type(type)
+				)
+			),
+			body(range('/root/range', { start, end, step }))
+		);
+
+		const xformDOM = XFormDOM.from(xform.asXml());
+		const xformDefinition = new XFormDefinition(xformDOM);
+		const rangeElement = xformDefinition.body.element.children[0];
+
+		return new RangeControlDefinition(xformDefinition, xformDefinition.body, rangeElement!);
+	};
+
+	describe('bounds', () => {
+		describe('int', () => {
+			it('parses', () => {
+				const definition = create('int', -2, 10, 2);
+				expect(definition.bounds.start).to.equal('-2');
+				expect(definition.bounds.step).to.equal('2');
+				expect(definition.bounds.end).to.equal('10');
+			});
+
+			it('takes the absolute value of step', () => {
+				const definition = create('int', 0, 10, -2);
+				expect(definition.bounds.start).to.equal('0');
+				expect(definition.bounds.step).to.equal('2');
+				expect(definition.bounds.end).to.equal('10');
+			});
+		});
+
+		describe('decimal', () => {
+			it('parses', () => {
+				const definition = create('decimal', -2.5, 10.5, 2.5);
+				expect(definition.bounds.start).to.equal('-2.5');
+				expect(definition.bounds.step).to.equal('2.5');
+				expect(definition.bounds.end).to.equal('10.5');
+			});
+
+			it('takes the absolute value of step', () => {
+				const definition = create('decimal', 0, 10, -2.5);
+				expect(definition.bounds.start).to.equal('0');
+				expect(definition.bounds.step).to.equal('2.5');
+				expect(definition.bounds.end).to.equal('10');
+			});
+		});
+	});
+});