interface IconLine {
  x1: number;
  y1: number;
  x2: number;
  y2: number;
  opacity?: number;
}

const CENTER = 7; // Center of 14x14 viewbox

const collapsed: IconLine = {
  x1: CENTER,
  y1: CENTER,
  x2: CENTER,
  y2: CENTER,
  opacity: 0,
};

interface IconDefinition {
  lines: [IconLine, IconLine, IconLine];
  rotation?: number;
  group?: string;
}

// These rotate smoothly between each other
{ lines: plusLines, rotation: 0, group: "plus-cross" }   // plus
{ lines: plusLines, rotation: 45, group: "plus-cross" }  // cross

// These rotate smoothly between each other
{ lines: arrowLines, rotation: 0, group: "arrow" }       // arrow-right
{ lines: arrowLines, rotation: 90, group: "arrow" }      // arrow-down
{ lines: arrowLines, rotation: 180, group: "arrow" }     // arrow-left
{ lines: arrowLines, rotation: -90, group: "arrow" }     // arrow-up

const checkIcon = {
  lines: [
    { x1: 2, y1: 7.5, x2: 5.5, y2: 11 },
    { x1: 5.5, y1: 11, x2: 12, y2: 3 },
  ], // Only 2 lines
};

const checkIcon = {
  lines: [
    { x1: 2, y1: 7.5, x2: 5.5, y2: 11 },
    { x1: 5.5, y1: 11, x2: 12, y2: 3 },
    collapsed, // Third line collapsed
  ],
};

const minusIcon = {
  lines: [
    { x1: 2, y1: 7, x2: 12, y2: 7 },
    null,
    null,
  ],
};

const minusIcon = {
  lines: [
    { x1: 2, y1: 7, x2: 12, y2: 7 },
    collapsed,
    collapsed,
  ],
};

// Mixing viewbox scales
const icon1 = { lines: [{ x1: 2, y1: 7, x2: 12, y2: 7 }, ...] }; // 14x14
const icon2 = { lines: [{ x1: 4, y1: 14, x2: 24, y2: 14 }, ...] }; // 28x28

const VIEWBOX_SIZE = 14;
const CENTER = 7;
// All coordinates within 0-14 range

// Different line definitions for arrows
const arrowRight = { lines: [{ x1: 2, y1: 7, x2: 12, y2: 7 }, ...] };
const arrowDown = { lines: [{ x1: 7, y1: 2, x2: 7, y2: 12 }, ...] }; // Different!

const arrowLines: [IconLine, IconLine, IconLine] = [
  { x1: 2, y1: 7, x2: 12, y2: 7 },
  { x1: 7.5, y1: 2.5, x2: 12, y2: 7 },
  { x1: 7.5, y1: 11.5, x2: 12, y2: 7 },
];

const icons = {
  "arrow-right": { lines: arrowLines, rotation: 0, group: "arrow" },
  "arrow-down": { lines: arrowLines, rotation: 90, group: "arrow" },
  "arrow-left": { lines: arrowLines, rotation: 180, group: "arrow" },
  "arrow-up": { lines: arrowLines, rotation: -90, group: "arrow" },
};

<motion.g animate={{ rotate: rotation }} transition={{ duration: 0.3 }} />

const rotation = useSpring(definition.rotation ?? 0, activeTransition);

<motion.g style={{ rotate: rotation, transformOrigin: "center" }} />

function MorphingIcon({ icon }: Props) {
  return <motion.line animate={...} transition={{ duration: 0.4 }} />;
}

function MorphingIcon({ icon }: Props) {
  const reducedMotion = useReducedMotion() ?? false;
  const activeTransition = reducedMotion ? { duration: 0 } : transition;
  
  return <motion.line animate={...} transition={activeTransition} />;
}

// Always animating rotation regardless of group
useEffect(() => {
  rotation.set(definition.rotation ?? 0);
}, [definition]);

useEffect(() => {
  if (shouldRotate) {
    rotation.set(definition.rotation ?? 0); // Animate
  } else {
    rotation.jump(definition.rotation ?? 0); // Instant
  }
}, [definition, shouldRotate]);

<motion.line strokeLinecap="butt" />

<motion.line strokeLinecap="round" />

<svg width={size} height={size}>...</svg>

<svg width={size} height={size} aria-hidden="true">...</svg>

const check = {
  lines: [
    { x1: 2, y1: 7.5, x2: 5.5, y2: 11 },
    { x1: 5.5, y1: 11, x2: 12, y2: 3 },
    collapsed,
  ],
};

const menu = {
  lines: [
    { x1: 2, y1: 3.5, x2: 12, y2: 3.5 },
    { x1: 2, y1: 7, x2: 12, y2: 7 },
    { x1: 2, y1: 10.5, x2: 12, y2: 10.5 },
  ],
};

const more = {
  lines: [
    { x1: 3, y1: 7, x2: 3, y2: 7 },
    { x1: 7, y1: 7, x2: 7, y2: 7 },
    { x1: 11, y1: 7, x2: 11, y2: 7 },
  ],
};

const defaultTransition: Transition = {
  ease: [0.19, 1, 0.22, 1],
  duration: 0.4,
};

file:line - [rule-id] description of issue

Example:
components/icon/index.tsx:45 - [morphing-three-lines] Icon "check" has only 2 lines, needs collapsed third
components/icon/index.tsx:78 - [morphing-group-variants] arrow-down uses different line definitions than arrow-right