src/vs/base/common/jsonEdit.ts/setProperty
export function setProperty(text: string, originalPath: JSONPath, value: any, formattingOptions: FormattingOptions, getInsertionIndex?: (properties: string[]) => number): Edit[] {
	const path = originalPath.slice();
	const errors: ParseError[] = [];
	const root = parseTree(text, errors);
	let parent: Node | undefined = undefined;

	let lastSegment: Segment | undefined = undefined;
	while (path.length > 0) {
		lastSegment = path.pop();
		parent = findNodeAtLocation(root, path);
		if (parent === undefined && value !== undefined) {
			if (typeof lastSegment === 'string') {
				value = { [lastSegment]: value };
			} else {
				value = [value];
			}
		} else {
			break;
		}
	}

	if (!parent) {
		// empty document
		if (value === undefined) { // delete
			throw new Error('Can not delete in empty document');
		}
		return withFormatting(text, { offset: root ? root.offset : 0, length: root ? root.length : 0, content: JSON.stringify(value) }, formattingOptions);
	} else if (parent.type === 'object' && typeof lastSegment === 'string' && Array.isArray(parent.children)) {
		const existing = findNodeAtLocation(parent, [lastSegment]);
		if (existing !== undefined) {
			if (value === undefined) { // delete
				if (!existing.parent) {
					throw new Error('Malformed AST');
				}
				const propertyIndex = parent.children.indexOf(existing.parent);
				let removeBegin: number;
				let removeEnd = existing.parent.offset + existing.parent.length;
				if (propertyIndex > 0) {
					// remove the comma of the previous node
					const previous = parent.children[propertyIndex - 1];
					removeBegin = previous.offset + previous.length;
				} else {
					removeBegin = parent.offset + 1;
					if (parent.children.length > 1) {
						// remove the comma of the next node
						const next = parent.children[1];
						removeEnd = next.offset;
					}
				}
				return withFormatting(text, { offset: removeBegin, length: removeEnd - removeBegin, content: '' }, formattingOptions);
			} else {
				// set value of existing property
				return withFormatting(text, { offset: existing.offset, length: existing.length, content: JSON.stringify(value) }, formattingOptions);
			}
		} else {
			if (value === undefined) { // delete
				return []; // property does not exist, nothing to do
			}
			const newProperty = `${JSON.stringify(lastSegment)}: ${JSON.stringify(value)}`;
			const index = getInsertionIndex ? getInsertionIndex(parent.children.map(p => p.children![0].value)) : parent.children.length;
			let edit: Edit;
			if (index > 0) {
				const previous = parent.children[index - 1];
				edit = { offset: previous.offset + previous.length, length: 0, content: ',' + newProperty };
			} else if (parent.children.length === 0) {
				edit = { offset: parent.offset + 1, length: 0, content: newProperty };
			} else {
				edit = { offset: parent.offset + 1, length: 0, content: newProperty + ',' };
			}
			return withFormatting(text, edit, formattingOptions);
		}
	} else if (parent.type === 'array' && typeof lastSegment === 'number' && Array.isArray(parent.children)) {
		if (value !== undefined) {
			// Insert
			const newProperty = `${JSON.stringify(value)}`;
			let edit: Edit;
			if (parent.children.length === 0 || lastSegment === 0) {
				edit = { offset: parent.offset + 1, length: 0, content: parent.children.length === 0 ? newProperty : newProperty + ',' };
			} else {
				const index = lastSegment === -1 || lastSegment > parent.children.length ? parent.children.length : lastSegment;
				const previous = parent.children[index - 1];
				edit = { offset: previous.offset + previous.length, length: 0, content: ',' + newProperty };
			}
			return withFormatting(text, edit, formattingOptions);
		} else {
			//Removal
			const removalIndex = lastSegment;
			const toRemove = parent.children[removalIndex];
			let edit: Edit;
			if (parent.children.length === 1) {
				// only item
				edit = { offset: parent.offset + 1, length: parent.length - 2, content: '' };
			} else if (parent.children.length - 1 === removalIndex) {
				// last item
				const previous = parent.children[removalIndex - 1];
				const offset = previous.offset + previous.length;
				const parentEndOffset = parent.offset + parent.length;
				edit = { offset, length: parentEndOffset - 2 - offset, content: '' };
			} else {
				edit = { offset: toRemove.offset, length: parent.children[removalIndex + 1].offset - toRemove.offset, content: '' };
			}
			return withFormatting(text, edit, formattingOptions);
		}
	} else {
		throw new Error(`Can not add ${typeof lastSegment !== 'number' ? 'index' : 'property'} to parent of type ${parent.type}`);
	}
}