@masknet/eslint-plugin/src/rules/no-redundant-variable.ts

eslint plugin for masknet

import type { TSESTree } from '@typescript-eslint/types'
import type { ReportFixFunction, SourceCode } from '@typescript-eslint/utils/ts-eslint'
import { closest, isAwait, isIdentifier, isSameIdentifier } from '../node.ts'
import { createRule } from '../rule.ts'
import { wrap } from '../utils.ts'

export default createRule({
  name: 'no-redundant-variable',
  meta: {
    type: 'problem',
    fixable: 'code',
    docs: {
      description: 'Disallow redundant variable',
      recommended: 'stylistic',
    },
    schema: [],
    messages: {
      invalid: 'Disallow Redundant Variable',
    },
  },
  defaultOptions: [],
  create(context) {
    return {
      BlockStatement({ body }) {
        const exit = body.find(isReturnStatement)
        if (!exit) return
        const previous = body[body.indexOf(exit) - 1]
        if (!isRedundantVariable(previous, exit)) return
        context.report({
          node: exit,
          messageId: 'invalid',
          fix: getFixer(context.sourceCode, previous, exit),
        })
      },
    }
  },
})

function isReturnStatement(node: TSESTree.Node): node is TSESTree.ReturnStatement {
  return node.type === 'ReturnStatement' && isIdentifier(node.argument)
}

function isRedundantVariable(
  node: TSESTree.Node | undefined,
  exit: TSESTree.ReturnStatement,
): node is TSESTree.VariableDeclaration {
  if (!node) return false
  return (
    node.type === 'VariableDeclaration' &&
    node.declarations.length === 1 &&
    node.declarations.some(({ init, id }) => init !== null && isSameIdentifier(exit.argument, id))
  )
}

function getFixer(
  source: Readonly<SourceCode>,
  variable: TSESTree.VariableDeclaration,
  exit: TSESTree.ReturnStatement,
): ReportFixFunction {
  return (fixer) => {
    const { init, id } = variable.declarations[0]
    if (!(init && id && exit.argument)) return null
    const replaced = getReturnExpression(init)
    const modified = wrap(source.getText(replaced), (input) => {
      if (!id.typeAnnotation) return input
      const annotation = source.getText(id.typeAnnotation.typeAnnotation)
      return `(${input}) as ${isAwait(init) ? `Promise<${annotation}>` : annotation}`
    })
    return [fixer.remove(variable), fixer.replaceText(exit.argument, modified)]
  }
}

export function getReturnExpression(node: TSESTree.Node) {
  if (!isAwait(node)) return node
  if (closest(node, 'TryStatement')) return node
  return node.argument
}