export function isEmptyDeclarator (node: t.Node) {
  if (
    t.isVariableDeclarator(node) &&
    (node.init === null ||
    t.isNullLiteral(node.init))
  ) {
    return true
  }
  return false
}

// Remove null args at the end of method or constructor calls.
// This may conflict in some situations when comparing null to undefined, see #231,
// but if disabled can cause problems with some APIs that use options to represent optional
// arguments like CanvasRenderingContext2D.fill: ?fillRule: string -> unit (fails if passed null).
function removeNullTailArgs<T>(path: traverse.NodePath<types.NewExpression | types.CallExpression>) {
  if (Array.isArray(path.node.arguments)) {
    for (var i = path.node.arguments.length - 1; i >= 0; i--) {
      if (types.isNullLiteral(path.node.arguments[i]))
        path.node.arguments.splice(i, 1);
      else
        break;
    }
  }
}

export function getArgumentName (arg) {
  if (t.isThisExpression(arg)) {
    return 'this'
  } else if (t.isNullLiteral(arg)) {
    return 'null'
  } else if (t.isStringLiteral(arg) || t.isNumericLiteral(arg)) {
    return arg.value
  } else if (t.isIdentifier(arg)) {
    return arg.name
  } else {
    return generate(arg).code
  }
  throw new Error(`bind 不支持传入该参数: ${arg}`)
}

//.........这里部分代码省略.........
     ) {
       return options.constants[expression.name];
     }
   }
   if (b.isLogicalExpression(expression)) {
     const left = toConstant(expression.left);
     const right = toConstant(expression.right);
     if (constant && expression.operator === '&&') {
       return left && right;
     }
     if (constant && expression.operator === '||') {
       return left || right;
     }
   }
   if (b.isMemberExpression(expression)) {
     const object = toConstant(expression.object);
     if (!object || !constant) {
       constant = false;
       return;
     }
     const member = expression.computed
       ? toConstant(expression.property)
       : b.isIdentifier(expression.property)
         ? expression.property.name
         : undefined;
     if (member === undefined && !expression.computed) {
       constant = false;
     }
     if (!constant) return;
     if ({}.hasOwnProperty.call(object, '' + member) && member[0] !== '_') {
       return object[member];
     }
   }
   if (b.isNullLiteral(expression)) {
     return null;
   }
   if (b.isNumericLiteral(expression)) {
     return expression.value;
   }
   if (b.isObjectExpression(expression)) {
     const result: any = {};
     for (let i = 0; constant && i < expression.properties.length; i++) {
       const property = expression.properties[i];
       if (b.isObjectProperty(property)) {
         if (property.shorthand) {
           constant = false;
           return;
         }
         const key = property.computed
           ? toConstant(property.key)
           : b.isIdentifier(property.key)
             ? property.key.name
             : b.isStringLiteral(property.key)
               ? property.key.value
               : undefined;
         if (!key || key[0] === '_') {
           constant = false;
         }
         if (!constant) return;
         const value = toConstant(property.value);
         if (!constant) return;
         result[key] = value;
       } else if (b.isObjectMethod(property)) {
         constant = false;
       } else if (b.isSpreadProperty(property)) {
         const argument = toConstant(property.argument);

export function parseLoopBody (
  body: NodePath<t.BlockStatement>,
  jsxDeclarations: Set<NodePath<t.Node>>,
  // @TODO
  // 把 templates 换成 Map 可以支持 shalow variables declared
  // 现在先用 ESLint 的 no-shalow 顶着
  templates: Map<string, t.JSXElement>,
  loopScopes: Set<string>,
  finalReturnElement: t.JSXElement,
  returnedPaths: NodePath<t.Node>[]
) {
  const bodyScope = body.scope
  body.traverse({
    JSXElement (jsxElementPath) {
      const parentNode = jsxElementPath.parent
      const parentPath = jsxElementPath.parentPath
      const isFinalReturn = jsxElementPath.getFunctionParent().isClassMethod()
      const isJSXChildren = t.isJSXElement(parentNode)
      if (!isJSXChildren) {
        let statementParent = jsxElementPath.getStatementParent()
        if (
          !(
            statementParent.isVariableDeclaration() ||
            statementParent.isExpressionStatement()
          )
        ) {
          statementParent = statementParent.findParent(
            s => s.isVariableDeclaration() || s.isExpressionStatement()
          ) as NodePath<t.Statement>
        }
        jsxDeclarations.add(statementParent)
        if (t.isVariableDeclarator(parentNode)) {
          if (statementParent) {
            const name = findIdentifierFromStatement(statementParent.node as t.VariableDeclaration)
            // setTemplate(name, path, templates)
            name && templates.set(name, jsxElementPath.node)
          }
        } else if (t.isLogicalExpression(parentNode)) {
          const { left, operator } = parentNode
          if (operator === '&&') {
            if (t.isExpression(left)) {
              newJSXIfAttr(jsxElementPath.node, left)
              parentPath.replaceWith(jsxElementPath.node)
              if (statementParent) {
                const name = findIdentifierFromStatement(statementParent.node as t.VariableDeclaration)
                setTemplate(name, jsxElementPath, templates)
                // name && templates.set(name, path.node)
              }
            }
          }
        } else if (t.isConditionalExpression(parentNode)) {
          const { test, consequent, alternate } = parentNode
          const block = buildBlockElement()
          if (t.isJSXElement(consequent) && t.isLiteral(alternate)) {
            const { value, confident } = parentPath.get('alternate').evaluate()
            if (confident && !value) {
              newJSXIfAttr(block, test)
              block.children = [ jsxElementPath.node ]
              // newJSXIfAttr(jsxElementPath.node, test)
              parentPath.replaceWith(block)
              if (statementParent) {
                const name = findIdentifierFromStatement(
                  statementParent.node as t.VariableDeclaration
                )
                setTemplate(name, jsxElementPath, templates)
                // name && templates.set(name, path.node)
              }
            }
          } else if (t.isLiteral(consequent) && t.isJSXElement(consequent)) {
            if (t.isNullLiteral(consequent)) {
              newJSXIfAttr(block, reverseBoolean(test))
              // newJSXIfAttr(jsxElementPath.node, reverseBoolean(test))
              parentPath.replaceWith(block)
              if (statementParent) {
                const name = findIdentifierFromStatement(
                  statementParent.node as t.VariableDeclaration
                )
                setTemplate(name, jsxElementPath, templates)
                // name && templates.set(name, path.node)
              }
            }
          } else if (t.isJSXElement(consequent) && t.isJSXElement(alternate)) {
            const block2 = buildBlockElement()
            block.children = [consequent]
            newJSXIfAttr(block, test)
            setJSXAttr(block2, Adapter.else)
            block2.children = [alternate]
            const parentBlock = buildBlockElement()
            parentBlock.children = [block, block2]
            parentPath.replaceWith(parentBlock)
            if (statementParent) {
              const name = findIdentifierFromStatement(
                statementParent.node as t.VariableDeclaration
              )
              setTemplate(name, jsxElementPath, templates)
            }
          } else {
            // console.log('todo')
          }
        } else if (t.isReturnStatement(parentNode)) {
//.........这里部分代码省略.........

 ExpressionStatement: function(path: traverse.NodePath<types.ExpressionStatement>) {
   if (types.isNullLiteral(path.node.expression))
     path.remove();
 }