class Ref {}

// the following makes use of the fact that branches that can be eliminated statically
// won't become compiled, hence the ERROR statement is never executed.

export function testTrue(a: Ref | null): void {
  if (a) {
    if (isNullable(a)) ERROR("should be non-nullable");
  }
}

export function testFalseElse(a: Ref | null): void {
  if (!a) return;
  else {
    if (isNullable(a)) ERROR("should be non-nullable");
  }
}

export function testFalseContinuation(a: Ref | null): void {
  if (!a) return;
  if (isNullable(a)) ERROR("should be non-nullable");
}

export function testNeNull(a: Ref | null): void {
  if (a != null) {
    if (isNullable(a)) ERROR("should be non-nullable");
  }
}

export function testEqNullElse(a: Ref | null): void {
  if (a == null) return;
  else {
    if (isNullable(a)) ERROR("should be non-nullable");
  }
}

export function testEqNullContinuation(a: Ref | null): void {
  if (a == null) return;
  if (isNullable(a)) ERROR("should be non-nullable");
}

export function testNotEqNull(a: Ref | null): void {
  if (!(a == null)) {
    if (isNullable(a)) ERROR("should be non-nullable");
  }
}

export function testNotNeNullElse(a: Ref | null): void {
  if (!(a != null)) return;
  else {
    if (isNullable(a)) ERROR("should be non-nullable");
  }
}

export function testNotNeNullContinuation(a: Ref | null): void {
  if (!(a != null)) return;
  if (isNullable(a)) ERROR("should be non-nullable");
}

export function testWhile(a: Ref | null): void {
  while (a) {
    if (isNullable(a)) ERROR("should be non-nullable");
    a = null;
    if (!isNullable(a)) ERROR("should be nullable again");
  }
}

export function testWhile2(a: Ref | null, b: Ref | null): void {
  while (a) {
    if (isNullable(a)) ERROR("should be non-nullable");
    a = b;
    if (!isNullable(a)) ERROR("should be nullable again");
  }
}

export function testWhile3(a: Ref | null, b: Ref | null): void {
  while (a) {
    if (isNullable(a)) ERROR("should be non-nullable");
    if (b) {
      a = b;
      if (isNullable(a)) ERROR("should be non-nullable still");
    }
  }
}

// TODO:

// function requireNonNull(a: Ref): Ref {
//   return a;
// }

// export function testLogicalAnd(a: Ref | null): void {
//   a && requireNonNull(a);
// }

// export function testLogicalOr(a: Ref | null): void {
//   !a || requireNonNull(a);
// }