core/packages/compiler-core/src/codegen.ts

import type { CodegenOptions } from './options'
import {
  type ArrayExpression,
  type AssignmentExpression,
  type CacheExpression,
  type CallExpression,
  type CommentNode,
  type CompoundExpressionNode,
  type ConditionalExpression,
  type ExpressionNode,
  type FunctionExpression,
  type IfStatement,
  type InterpolationNode,
  type JSChildNode,
  NodeTypes,
  type ObjectExpression,
  type Position,
  type ReturnStatement,
  type RootNode,
  type SSRCodegenNode,
  type SequenceExpression,
  type SimpleExpressionNode,
  type TemplateChildNode,
  type TemplateLiteral,
  type TextNode,
  type VNodeCall,
  getVNodeBlockHelper,
  getVNodeHelper,
  locStub,
} from './ast'
import { SourceMapGenerator } from 'source-map-js'
import {
  advancePositionWithMutation,
  assert,
  isSimpleIdentifier,
  toValidAssetId,
} from './utils'
import {
  PatchFlagNames,
  type PatchFlags,
  isArray,
  isString,
  isSymbol,
} from '@vue/shared'
import {
  CREATE_COMMENT,
  CREATE_ELEMENT_VNODE,
  CREATE_STATIC,
  CREATE_TEXT,
  CREATE_VNODE,
  OPEN_BLOCK,
  RESOLVE_COMPONENT,
  RESOLVE_DIRECTIVE,
  RESOLVE_FILTER,
  SET_BLOCK_TRACKING,
  TO_DISPLAY_STRING,
  WITH_CTX,
  WITH_DIRECTIVES,
  helperNameMap,
} from './runtimeHelpers'
import type { ImportItem } from './transform'

/**
 * The `SourceMapGenerator` type from `source-map-js` is a bit incomplete as it
 * misses `toJSON()`. We also need to add types for internal properties which we
 * need to access for better performance.
 *
 * Since TS 5.3, dts generation starts to strangely include broken triple slash
 * references for source-map-js, so we are inlining all source map related types
 * here to to workaround that.
 */
export interface CodegenSourceMapGenerator {
  setSourceContent(sourceFile: string, sourceContent: string): void
  // SourceMapGenerator has this method but the types do not include it
  toJSON(): RawSourceMap
  _sources: Set<string>
  _names: Set<string>
  _mappings: {
    add(mapping: MappingItem): void
  }
}

export interface RawSourceMap {
  file?: string
  sourceRoot?: string
  version: string
  sources: string[]
  names: string[]
  sourcesContent?: string[]
  mappings: string
}

interface MappingItem {
  source: string
  generatedLine: number
  generatedColumn: number
  originalLine: number
  originalColumn: number
  name: string | null
}

const PURE_ANNOTATION = `/*@__PURE__*/`

const aliasHelper = (s: symbol) => `${helperNameMap[s]}: _${helperNameMap[s]}`

type CodegenNode = TemplateChildNode | JSChildNode | SSRCodegenNode

export interface BaseCodegenResult {
  code: string
  preamble: string
  ast: unknown
  map?: RawSourceMap
  helpers?: Set<string> | Set<symbol>
}

export interface CodegenResult extends BaseCodegenResult {
  ast: RootNode
  helpers: Set<symbol>
}

export enum NewlineType {
  /** Start with `\n` */
  Start = 0,
  /** Ends with `\n` */
  End = -1,
  /** No `\n` included */
  None = -2,
  /** Don't know, calc it */
  Unknown = -3,
}

export interface CodegenContext
  extends Omit<
    Required<CodegenOptions>,
    | 'bindingMetadata'
    | 'inline'
    | 'vaporRuntimeModuleName'
    | 'expressionPlugins'
  > {
  source: string
  code: string
  line: number
  column: number
  offset: number
  indentLevel: number
  pure: boolean
  map?: CodegenSourceMapGenerator
  helper(key: symbol): string
  push(code: string, newlineIndex?: number, node?: CodegenNode): void
  indent(): void
  deindent(withoutNewLine?: boolean): void
  newline(): void
}

function createCodegenContext(
  ast: RootNode,
  {
    mode = 'function',
    prefixIdentifiers = mode === 'module',
    sourceMap = false,
    filename = `template.vue.html`,
    scopeId = null,
    optimizeImports = false,
    runtimeGlobalName = `Vue`,
    runtimeModuleName = `vue`,
    ssrRuntimeModuleName = 'vue/server-renderer',
    ssr = false,
    isTS = false,
    inSSR = false,
  }: CodegenOptions,
): CodegenContext {
  const context: CodegenContext = {
    mode,
    prefixIdentifiers,
    sourceMap,
    filename,
    scopeId,
    optimizeImports,
    runtimeGlobalName,
    runtimeModuleName,
    ssrRuntimeModuleName,
    ssr,
    isTS,
    inSSR,
    source: ast.source,
    code: ``,
    column: 1,
    line: 1,
    offset: 0,
    indentLevel: 0,
    pure: false,
    map: undefined,
    helper(key) {
      return `_${helperNameMap[key]}`
    },
    push(code, newlineIndex = NewlineType.None, node) {
      context.code += code
      if (!__BROWSER__ && context.map) {
        if (node) {
          let name
          if (node.type === NodeTypes.SIMPLE_EXPRESSION && !node.isStatic) {
            const content = node.content.replace(/^_ctx\./, '')
            if (content !== node.content && isSimpleIdentifier(content)) {
              name = content
            }
          }
          if (node.loc.source) {
            addMapping(node.loc.start, name)
          }
        }
        if (newlineIndex === NewlineType.Unknown) {
          // multiple newlines, full iteration
          advancePositionWithMutation(context, code)
        } else {
          // fast paths
          context.offset += code.length
          if (newlineIndex === NewlineType.None) {
            // no newlines; fast path to avoid newline detection
            if (__TEST__ && code.includes('\n')) {
              throw new Error(
                `CodegenContext.push() called newlineIndex: none, but contains` +
                  `newlines: ${code.replace(/\n/g, '\\n')}`,
              )
            }
            context.column += code.length
          } else {
            // single newline at known index
            if (newlineIndex === NewlineType.End) {
              newlineIndex = code.length - 1
            }
            if (
              __TEST__ &&
              (code.charAt(newlineIndex) !== '\n' ||
                code.slice(0, newlineIndex).includes('\n') ||
                code.slice(newlineIndex + 1).includes('\n'))
            ) {
              throw new Error(
                `CodegenContext.push() called with newlineIndex: ${newlineIndex} ` +
                  `but does not conform: ${code.replace(/\n/g, '\\n')}`,
              )
            }
            context.line++
            context.column = code.length - newlineIndex
          }
        }
        if (node && node.loc !== locStub && node.loc.source) {
          addMapping(node.loc.end)
        }
      }
    },
    indent() {
      newline(++context.indentLevel)
    },
    deindent(withoutNewLine = false) {
      if (withoutNewLine) {
        --context.indentLevel
      } else {
        newline(--context.indentLevel)
      }
    },
    newline() {
      newline(context.indentLevel)
    },
  }

  function newline(n: number) {
    context.push('\n' + `  `.repeat(n), NewlineType.Start)
  }

  function addMapping(loc: Position, name: string | null = null) {
    // we use the private property to directly add the mapping
    // because the addMapping() implementation in source-map-js has a bunch of
    // unnecessary arg and validation checks that are pure overhead in our case.
    const { _names, _mappings } = context.map!
    if (name !== null && !_names.has(name)) _names.add(name)
    _mappings.add({
      originalLine: loc.line,
      originalColumn: loc.column - 1, // source-map column is 0 based
      generatedLine: context.line,
      generatedColumn: context.column - 1,
      source: filename,
      name,
    })
  }

  if (!__BROWSER__ && sourceMap) {
    // lazy require source-map implementation, only in non-browser builds
    context.map =
      new SourceMapGenerator() as unknown as CodegenSourceMapGenerator
    context.map.setSourceContent(filename, context.source)
    context.map._sources.add(filename)
  }

  return context
}

export function generate(
  ast: RootNode,
  options: CodegenOptions & {
    onContextCreated?: (context: CodegenContext) => void
  } = {},
): CodegenResult {
  const context = createCodegenContext(ast, options)
  if (options.onContextCreated) options.onContextCreated(context)
  const {
    mode,
    push,
    prefixIdentifiers,
    indent,
    deindent,
    newline,
    scopeId,
    ssr,
  } = context

  const helpers = Array.from(ast.helpers)
  const hasHelpers = helpers.length > 0
  const useWithBlock = !prefixIdentifiers && mode !== 'module'
  const genScopeId = !__BROWSER__ && scopeId != null && mode === 'module'
  const isSetupInlined = !__BROWSER__ && !!options.inline

  // preambles
  // in setup() inline mode, the preamble is generated in a sub context
  // and returned separately.
  const preambleContext = isSetupInlined
    ? createCodegenContext(ast, options)
    : context
  if (!__BROWSER__ && mode === 'module') {
    genModulePreamble(ast, preambleContext, genScopeId, isSetupInlined)
  } else {
    genFunctionPreamble(ast, preambleContext)
  }
  // enter render function
  const functionName = ssr ? `ssrRender` : `render`
  const args = ssr ? ['_ctx', '_push', '_parent', '_attrs'] : ['_ctx', '_cache']
  if (!__BROWSER__ && options.bindingMetadata && !options.inline) {
    // binding optimization args
    args.push('$props', '$setup', '$data', '$options')
  }
  const signature =
    !__BROWSER__ && options.isTS
      ? args.map(arg => `${arg}: any`).join(',')
      : args.join(', ')

  if (isSetupInlined) {
    push(`(${signature}) => {`)
  } else {
    push(`function ${functionName}(${signature}) {`)
  }
  indent()

  if (useWithBlock) {
    push(`with (_ctx) {`)
    indent()
    // function mode const declarations should be inside with block
    // also they should be renamed to avoid collision with user properties
    if (hasHelpers) {
      push(
        `const { ${helpers.map(aliasHelper).join(', ')} } = _Vue\n`,
        NewlineType.End,
      )
      newline()
    }
  }

  // generate asset resolution statements
  if (ast.components.length) {
    genAssets(ast.components, 'component', context)
    if (ast.directives.length || ast.temps > 0) {
      newline()
    }
  }
  if (ast.directives.length) {
    genAssets(ast.directives, 'directive', context)
    if (ast.temps > 0) {
      newline()
    }
  }
  if (__COMPAT__ && ast.filters && ast.filters.length) {
    newline()
    genAssets(ast.filters, 'filter', context)
    newline()
  }

  if (ast.temps > 0) {
    push(`let `)
    for (let i = 0; i < ast.temps; i++) {
      push(`${i > 0 ? `, ` : ``}_temp${i}`)
    }
  }
  if (ast.components.length || ast.directives.length || ast.temps) {
    push(`\n`, NewlineType.Start)
    newline()
  }

  // generate the VNode tree expression
  if (!ssr) {
    push(`return `)
  }
  if (ast.codegenNode) {
    genNode(ast.codegenNode, context)
  } else {
    push(`null`)
  }

  if (useWithBlock) {
    deindent()
    push(`}`)
  }

  deindent()
  push(`}`)

  return {
    ast,
    code: context.code,
    preamble: isSetupInlined ? preambleContext.code : ``,
    map: context.map ? context.map.toJSON() : undefined,
    helpers: ast.helpers,
  }
}

function genFunctionPreamble(ast: RootNode, context: CodegenContext) {
  const {
    ssr,
    prefixIdentifiers,
    push,
    newline,
    runtimeModuleName,
    runtimeGlobalName,
    ssrRuntimeModuleName,
  } = context
  const VueBinding =
    !__BROWSER__ && ssr
      ? `require(${JSON.stringify(runtimeModuleName)})`
      : runtimeGlobalName
  // Generate const declaration for helpers
  // In prefix mode, we place the const declaration at top so it's done
  // only once; But if we not prefixing, we place the declaration inside the
  // with block so it doesn't incur the `in` check cost for every helper access.
  const helpers = Array.from(ast.helpers)
  if (helpers.length > 0) {
    if (!__BROWSER__ && prefixIdentifiers) {
      push(
        `const { ${helpers.map(aliasHelper).join(', ')} } = ${VueBinding}\n`,
        NewlineType.End,
      )
    } else {
      // "with" mode.
      // save Vue in a separate variable to avoid collision
      push(`const _Vue = ${VueBinding}\n`, NewlineType.End)
      // in "with" mode, helpers are declared inside the with block to avoid
      // has check cost, but hoists are lifted out of the function - we need
      // to provide the helper here.
      if (ast.hoists.length) {
        const staticHelpers = [
          CREATE_VNODE,
          CREATE_ELEMENT_VNODE,
          CREATE_COMMENT,
          CREATE_TEXT,
          CREATE_STATIC,
        ]
          .filter(helper => helpers.includes(helper))
          .map(aliasHelper)
          .join(', ')
        push(`const { ${staticHelpers} } = _Vue\n`, NewlineType.End)
      }
    }
  }
  // generate variables for ssr helpers
  if (!__BROWSER__ && ast.ssrHelpers && ast.ssrHelpers.length) {
    // ssr guarantees prefixIdentifier: true
    push(
      `const { ${ast.ssrHelpers
        .map(aliasHelper)
        .join(', ')} } = require("${ssrRuntimeModuleName}")\n`,
      NewlineType.End,
    )
  }
  genHoists(ast.hoists, context)
  newline()
  push(`return `)
}

function genModulePreamble(
  ast: RootNode,
  context: CodegenContext,
  genScopeId: boolean,
  inline?: boolean,
) {
  const {
    push,
    newline,
    optimizeImports,
    runtimeModuleName,
    ssrRuntimeModuleName,
  } = context

  // generate import statements for helpers
  if (ast.helpers.size) {
    const helpers = Array.from(ast.helpers)
    if (optimizeImports) {
      // when bundled with webpack with code-split, calling an import binding
      // as a function leads to it being wrapped with `Object(a.b)` or `(0,a.b)`,
      // incurring both payload size increase and potential perf overhead.
      // therefore we assign the imports to variables (which is a constant ~50b
      // cost per-component instead of scaling with template size)
      push(
        `import { ${helpers
          .map(s => helperNameMap[s])
          .join(', ')} } from ${JSON.stringify(runtimeModuleName)}\n`,
        NewlineType.End,
      )
      push(
        `\n// Binding optimization for webpack code-split\nconst ${helpers
          .map(s => `_${helperNameMap[s]} = ${helperNameMap[s]}`)
          .join(', ')}\n`,
        NewlineType.End,
      )
    } else {
      push(
        `import { ${helpers
          .map(s => `${helperNameMap[s]} as _${helperNameMap[s]}`)
          .join(', ')} } from ${JSON.stringify(runtimeModuleName)}\n`,
        NewlineType.End,
      )
    }
  }

  if (ast.ssrHelpers && ast.ssrHelpers.length) {
    push(
      `import { ${ast.ssrHelpers
        .map(s => `${helperNameMap[s]} as _${helperNameMap[s]}`)
        .join(', ')} } from "${ssrRuntimeModuleName}"\n`,
      NewlineType.End,
    )
  }

  if (ast.imports.length) {
    genImports(ast.imports, context)
    newline()
  }

  genHoists(ast.hoists, context)
  newline()

  if (!inline) {
    push(`export `)
  }
}

function genAssets(
  assets: string[],
  type: 'component' | 'directive' | 'filter',
  { helper, push, newline, isTS }: CodegenContext,
) {
  const resolver = helper(
    __COMPAT__ && type === 'filter'
      ? RESOLVE_FILTER
      : type === 'component'
        ? RESOLVE_COMPONENT
        : RESOLVE_DIRECTIVE,
  )
  for (let i = 0; i < assets.length; i++) {
    let id = assets[i]
    // potential component implicit self-reference inferred from SFC filename
    const maybeSelfReference = id.endsWith('__self')
    if (maybeSelfReference) {
      id = id.slice(0, -6)
    }
    push(
      `const ${toValidAssetId(id, type)} = ${resolver}(${JSON.stringify(id)}${
        maybeSelfReference ? `, true` : ``
      })${isTS ? `!` : ``}`,
    )
    if (i < assets.length - 1) {
      newline()
    }
  }
}

function genHoists(hoists: (JSChildNode | null)[], context: CodegenContext) {
  if (!hoists.length) {
    return
  }
  context.pure = true
  const { push, newline } = context
  newline()

  for (let i = 0; i < hoists.length; i++) {
    const exp = hoists[i]
    if (exp) {
      push(`const _hoisted_${i + 1} = `)
      genNode(exp, context)
      newline()
    }
  }

  context.pure = false
}

function genImports(importsOptions: ImportItem[], context: CodegenContext) {
  if (!importsOptions.length) {
    return
  }
  importsOptions.forEach(imports => {
    context.push(`import `)
    genNode(imports.exp, context)
    context.push(` from '${imports.path}'`)
    context.newline()
  })
}

function isText(n: string | CodegenNode) {
  return (
    isString(n) ||
    n.type === NodeTypes.SIMPLE_EXPRESSION ||
    n.type === NodeTypes.TEXT ||
    n.type === NodeTypes.INTERPOLATION ||
    n.type === NodeTypes.COMPOUND_EXPRESSION
  )
}

function genNodeListAsArray(
  nodes: (string | CodegenNode | TemplateChildNode[])[],
  context: CodegenContext,
) {
  const multilines =
    nodes.length > 3 ||
    ((!__BROWSER__ || __DEV__) && nodes.some(n => isArray(n) || !isText(n)))
  context.push(`[`)
  multilines && context.indent()
  genNodeList(nodes, context, multilines)
  multilines && context.deindent()
  context.push(`]`)
}

function genNodeList(
  nodes: (string | symbol | CodegenNode | TemplateChildNode[])[],
  context: CodegenContext,
  multilines: boolean = false,
  comma: boolean = true,
) {
  const { push, newline } = context
  for (let i = 0; i < nodes.length; i++) {
    const node = nodes[i]
    if (isString(node)) {
      push(node, NewlineType.Unknown)
    } else if (isArray(node)) {
      genNodeListAsArray(node, context)
    } else {
      genNode(node, context)
    }
    if (i < nodes.length - 1) {
      if (multilines) {
        comma && push(',')
        newline()
      } else {
        comma && push(', ')
      }
    }
  }
}

function genNode(node: CodegenNode | symbol | string, context: CodegenContext) {
  if (isString(node)) {
    context.push(node, NewlineType.Unknown)
    return
  }
  if (isSymbol(node)) {
    context.push(context.helper(node))
    return
  }
  switch (node.type) {
    case NodeTypes.ELEMENT:
    case NodeTypes.IF:
    case NodeTypes.FOR:
      __DEV__ &&
        assert(
          node.codegenNode != null,
          `Codegen node is missing for element/if/for node. ` +
            `Apply appropriate transforms first.`,
        )
      genNode(node.codegenNode!, context)
      break
    case NodeTypes.TEXT:
      genText(node, context)
      break
    case NodeTypes.SIMPLE_EXPRESSION:
      genExpression(node, context)
      break
    case NodeTypes.INTERPOLATION:
      genInterpolation(node, context)
      break
    case NodeTypes.TEXT_CALL:
      genNode(node.codegenNode, context)
      break
    case NodeTypes.COMPOUND_EXPRESSION:
      genCompoundExpression(node, context)
      break
    case NodeTypes.COMMENT:
      genComment(node, context)
      break
    case NodeTypes.VNODE_CALL:
      genVNodeCall(node, context)
      break

    case NodeTypes.JS_CALL_EXPRESSION:
      genCallExpression(node, context)
      break
    case NodeTypes.JS_OBJECT_EXPRESSION:
      genObjectExpression(node, context)
      break
    case NodeTypes.JS_ARRAY_EXPRESSION:
      genArrayExpression(node, context)
      break
    case NodeTypes.JS_FUNCTION_EXPRESSION:
      genFunctionExpression(node, context)
      break
    case NodeTypes.JS_CONDITIONAL_EXPRESSION:
      genConditionalExpression(node, context)
      break
    case NodeTypes.JS_CACHE_EXPRESSION:
      genCacheExpression(node, context)
      break
    case NodeTypes.JS_BLOCK_STATEMENT:
      genNodeList(node.body, context, true, false)
      break

    // SSR only types
    case NodeTypes.JS_TEMPLATE_LITERAL:
      !__BROWSER__ && genTemplateLiteral(node, context)
      break
    case NodeTypes.JS_IF_STATEMENT:
      !__BROWSER__ && genIfStatement(node, context)
      break
    case NodeTypes.JS_ASSIGNMENT_EXPRESSION:
      !__BROWSER__ && genAssignmentExpression(node, context)
      break
    case NodeTypes.JS_SEQUENCE_EXPRESSION:
      !__BROWSER__ && genSequenceExpression(node, context)
      break
    case NodeTypes.JS_RETURN_STATEMENT:
      !__BROWSER__ && genReturnStatement(node, context)
      break

    /* v8 ignore start */
    case NodeTypes.IF_BRANCH:
      // noop
      break
    default:
      if (__DEV__) {
        assert(false, `unhandled codegen node type: ${(node as any).type}`)
        // make sure we exhaust all possible types
        const exhaustiveCheck: never = node
        return exhaustiveCheck
      }
    /* v8 ignore stop */
  }
}

function genText(
  node: TextNode | SimpleExpressionNode,
  context: CodegenContext,
) {
  context.push(JSON.stringify(node.content), NewlineType.Unknown, node)
}

function genExpression(node: SimpleExpressionNode, context: CodegenContext) {
  const { content, isStatic } = node
  context.push(
    isStatic ? JSON.stringify(content) : content,
    NewlineType.Unknown,
    node,
  )
}

function genInterpolation(node: InterpolationNode, context: CodegenContext) {
  const { push, helper, pure } = context
  if (pure) push(PURE_ANNOTATION)
  push(`${helper(TO_DISPLAY_STRING)}(`)
  genNode(node.content, context)
  push(`)`)
}

function genCompoundExpression(
  node: CompoundExpressionNode,
  context: CodegenContext,
) {
  for (let i = 0; i < node.children!.length; i++) {
    const child = node.children![i]
    if (isString(child)) {
      context.push(child, NewlineType.Unknown)
    } else {
      genNode(child, context)
    }
  }
}

function genExpressionAsPropertyKey(
  node: ExpressionNode,
  context: CodegenContext,
) {
  const { push } = context
  if (node.type === NodeTypes.COMPOUND_EXPRESSION) {
    push(`[`)
    genCompoundExpression(node, context)
    push(`]`)
  } else if (node.isStatic) {
    // only quote keys if necessary
    const text = isSimpleIdentifier(node.content)
      ? node.content
      : JSON.stringify(node.content)
    push(text, NewlineType.None, node)
  } else {
    push(`[${node.content}]`, NewlineType.Unknown, node)
  }
}

function genComment(node: CommentNode, context: CodegenContext) {
  const { push, helper, pure } = context
  if (pure) {
    push(PURE_ANNOTATION)
  }
  push(
    `${helper(CREATE_COMMENT)}(${JSON.stringify(node.content)})`,
    NewlineType.Unknown,
    node,
  )
}

function genVNodeCall(node: VNodeCall, context: CodegenContext) {
  const { push, helper, pure } = context
  const {
    tag,
    props,
    children,
    patchFlag,
    dynamicProps,
    directives,
    isBlock,
    disableTracking,
    isComponent,
  } = node

  // add dev annotations to patch flags
  let patchFlagString
  if (patchFlag) {
    if (__DEV__) {
      if (patchFlag < 0) {
        // special flags (negative and mutually exclusive)
        patchFlagString = patchFlag + ` /* ${PatchFlagNames[patchFlag]} */`
      } else {
        // bitwise flags
        const flagNames = Object.keys(PatchFlagNames)
          .map(Number)
          .filter(n => n > 0 && patchFlag & n)
          .map(n => PatchFlagNames[n as PatchFlags])
          .join(`, `)
        patchFlagString = patchFlag + ` /* ${flagNames} */`
      }
    } else {
      patchFlagString = String(patchFlag)
    }
  }

  if (directives) {
    push(helper(WITH_DIRECTIVES) + `(`)
  }
  if (isBlock) {
    push(`(${helper(OPEN_BLOCK)}(${disableTracking ? `true` : ``}), `)
  }
  if (pure) {
    push(PURE_ANNOTATION)
  }
  const callHelper: symbol = isBlock
    ? getVNodeBlockHelper(context.inSSR, isComponent)
    : getVNodeHelper(context.inSSR, isComponent)
  push(helper(callHelper) + `(`, NewlineType.None, node)
  genNodeList(
    genNullableArgs([tag, props, children, patchFlagString, dynamicProps]),
    context,
  )
  push(`)`)
  if (isBlock) {
    push(`)`)
  }
  if (directives) {
    push(`, `)
    genNode(directives, context)
    push(`)`)
  }
}

function genNullableArgs(args: any[]): CallExpression['arguments'] {
  let i = args.length
  while (i--) {
    if (args[i] != null) break
  }
  return args.slice(0, i + 1).map(arg => arg || `null`)
}

// JavaScript
function genCallExpression(node: CallExpression, context: CodegenContext) {
  const { push, helper, pure } = context
  const callee = isString(node.callee) ? node.callee : helper(node.callee)
  if (pure) {
    push(PURE_ANNOTATION)
  }
  push(callee + `(`, NewlineType.None, node)
  genNodeList(node.arguments, context)
  push(`)`)
}

function genObjectExpression(node: ObjectExpression, context: CodegenContext) {
  const { push, indent, deindent, newline } = context
  const { properties } = node
  if (!properties.length) {
    push(`{}`, NewlineType.None, node)
    return
  }
  const multilines =
    properties.length > 1 ||
    ((!__BROWSER__ || __DEV__) &&
      properties.some(p => p.value.type !== NodeTypes.SIMPLE_EXPRESSION))
  push(multilines ? `{` : `{ `)
  multilines && indent()
  for (let i = 0; i < properties.length; i++) {
    const { key, value } = properties[i]
    // key
    genExpressionAsPropertyKey(key, context)
    push(`: `)
    // value
    genNode(value, context)
    if (i < properties.length - 1) {
      // will only reach this if it's multilines
      push(`,`)
      newline()
    }
  }
  multilines && deindent()
  push(multilines ? `}` : ` }`)
}

function genArrayExpression(node: ArrayExpression, context: CodegenContext) {
  genNodeListAsArray(node.elements as CodegenNode[], context)
}

function genFunctionExpression(
  node: FunctionExpression,
  context: CodegenContext,
) {
  const { push, indent, deindent } = context
  const { params, returns, body, newline, isSlot } = node
  if (isSlot) {
    // wrap slot functions with owner context
    push(`_${helperNameMap[WITH_CTX]}(`)
  }
  push(`(`, NewlineType.None, node)
  if (isArray(params)) {
    genNodeList(params, context)
  } else if (params) {
    genNode(params, context)
  }
  push(`) => `)
  if (newline || body) {
    push(`{`)
    indent()
  }
  if (returns) {
    if (newline) {
      push(`return `)
    }
    if (isArray(returns)) {
      genNodeListAsArray(returns, context)
    } else {
      genNode(returns, context)
    }
  } else if (body) {
    genNode(body, context)
  }
  if (newline || body) {
    deindent()
    push(`}`)
  }
  if (isSlot) {
    if (__COMPAT__ && node.isNonScopedSlot) {
      push(`, undefined, true`)
    }
    push(`)`)
  }
}

function genConditionalExpression(
  node: ConditionalExpression,
  context: CodegenContext,
) {
  const { test, consequent, alternate, newline: needNewline } = node
  const { push, indent, deindent, newline } = context
  if (test.type === NodeTypes.SIMPLE_EXPRESSION) {
    const needsParens = !isSimpleIdentifier(test.content)
    needsParens && push(`(`)
    genExpression(test, context)
    needsParens && push(`)`)
  } else {
    push(`(`)
    genNode(test, context)
    push(`)`)
  }
  needNewline && indent()
  context.indentLevel++
  needNewline || push(` `)
  push(`? `)
  genNode(consequent, context)
  context.indentLevel--
  needNewline && newline()
  needNewline || push(` `)
  push(`: `)
  const isNested = alternate.type === NodeTypes.JS_CONDITIONAL_EXPRESSION
  if (!isNested) {
    context.indentLevel++
  }
  genNode(alternate, context)
  if (!isNested) {
    context.indentLevel--
  }
  needNewline && deindent(true /* without newline */)
}

function genCacheExpression(node: CacheExpression, context: CodegenContext) {
  const { push, helper, indent, deindent, newline } = context
  const { needPauseTracking, needArraySpread } = node
  if (needArraySpread) {
    push(`[...(`)
  }
  push(`_cache[${node.index}] || (`)
  if (needPauseTracking) {
    indent()
    push(`${helper(SET_BLOCK_TRACKING)}(-1`)
    if (node.inVOnce) push(`, true`)
    push(`),`)
    newline()
    push(`(`)
  }
  push(`_cache[${node.index}] = `)
  genNode(node.value, context)
  if (needPauseTracking) {
    push(`).cacheIndex = ${node.index},`)
    newline()
    push(`${helper(SET_BLOCK_TRACKING)}(1),`)
    newline()
    push(`_cache[${node.index}]`)
    deindent()
  }
  push(`)`)
  if (needArraySpread) {
    push(`)]`)
  }
}

function genTemplateLiteral(node: TemplateLiteral, context: CodegenContext) {
  const { push, indent, deindent } = context
  push('`')
  const l = node.elements.length
  const multilines = l > 3
  for (let i = 0; i < l; i++) {
    const e = node.elements[i]
    if (isString(e)) {
      push(e.replace(/(`|\$|\\)/g, '\\$1'), NewlineType.Unknown)
    } else {
      push('${')
      if (multilines) indent()
      genNode(e, context)
      if (multilines) deindent()
      push('}')
    }
  }
  push('`')
}

function genIfStatement(node: IfStatement, context: CodegenContext) {
  const { push, indent, deindent } = context
  const { test, consequent, alternate } = node
  push(`if (`)
  genNode(test, context)
  push(`) {`)
  indent()
  genNode(consequent, context)
  deindent()
  push(`}`)
  if (alternate) {
    push(` else `)
    if (alternate.type === NodeTypes.JS_IF_STATEMENT) {
      genIfStatement(alternate, context)
    } else {
      push(`{`)
      indent()
      genNode(alternate, context)
      deindent()
      push(`}`)
    }
  }
}

function genAssignmentExpression(
  node: AssignmentExpression,
  context: CodegenContext,
) {
  genNode(node.left, context)
  context.push(` = `)
  genNode(node.right, context)
}

function genSequenceExpression(
  node: SequenceExpression,
  context: CodegenContext,
) {
  context.push(`(`)
  genNodeList(node.expressions, context)
  context.push(`)`)
}

function genReturnStatement(
  { returns }: ReturnStatement,
  context: CodegenContext,
) {
  context.push(`return `)
  if (isArray(returns)) {
    genNodeListAsArray(returns, context)
  } else {
    genNode(returns, context)
  }
}