next-typescript.ts

/**
 * This is a TypeScript language service plugin for Next.js app directory,
 * it provides the following features:
 *
 * - Warns about disallowed React APIs in server components.
 * - Warns about disallowed layout and page exports.
 * - Autocompletion for entry configurations.
 * - Hover hint and docs for entry configurations.
 */

import path from 'path'

const DISALLOWED_SERVER_REACT_APIS: string[] = [
  'useState',
  'useEffect',
  'useLayoutEffect',
  'useDeferredValue',
  'useImperativeHandle',
  'useInsertionEffect',
  'useReducer',
  'useRef',
  'useSyncExternalStore',
  'useTransition',
  'Component',
  'PureComponent',
  'createContext',
  'createFactory',
]

const ALLOWED_EXPORTS = ['config', 'generateStaticParams']

const API_DOCS: Record<
  string,
  {
    description: string
    options: Record<string, string>
    type?: string
    isValid?: (value: string) => boolean
    getHint?: (value: any) => string
  }
> = {
  dynamic: {
    description:
      'The `dynamic` option provides a few ways to opt in or out of dynamic behavior.',
    options: {
      '"auto"':
        'Heuristic to cache as much as possible but doesn’t prevent any component to opt-in to dynamic behavior.',
      '"force-dynamic"':
        'This disables all caching of fetches and always revalidates. (This is equivalent to `getServerSideProps`.)',
      '"error"':
        'This errors if any dynamic Hooks or fetches are used. (This is equivalent to `getStaticProps`.)',
      '"force-static"':
        'This forces caching of all fetches and returns empty values from `useCookies`, `useHeaders` and `useSearchParams`.',
    },
  },
  fetchCache: {
    description:
      'The `fetchCache` option controls how Next.js statically caches fetches. By default it statically caches fetches reachable before any dynamic Hooks are used, and it doesn’t cache fetches that are discovered after that.',
    options: {
      '"force-no-store"':
        "This lets you intentionally opt-out of all caching of data. This option forces all fetches to be refetched every request even if the `cache: 'force-cache'` option is passed to `fetch()`.",
      '"only-no-store"':
        "This lets you enforce that all data opts out of caching. This option makes `fetch()` reject with an error if `cache: 'force-cache'` is provided. It also changes the default to `no-store`.",
      '"default-no-store"':
        "Allows any explicit `cache` option to be passed to `fetch()` but if `'default'`, or no option, is provided then it defaults to `'no-store'`. This means that even fetches before a dynamic Hook are considered dynamic.",
      '"auto"':
        'This is the default option. It caches any fetches with the default `cache` option provided, that happened before a dynamic Hook is used and don’t cache any such fetches if they’re issued after a dynamic Hook.',
      '"default-cache"':
        "Allows any explicit `cache` option to be passed to `fetch()` but if `'default'`, or no option, is provided then it defaults to `'force-cache'`. This means that even fetches before a dynamic Hook are considered dynamic.",
      '"only-cache"':
        "This lets you enforce that all data opts into caching. This option makes `fetch()` reject with an error if `cache: 'force-cache'` is provided. It also changes the default to `force-cache`. This error can be discovered early during static builds - or dynamically during Edge rendering.",
      '"force-cache"':
        "This lets you intentionally opt-in to all caching of data. This option forces all fetches to be cache even if the `cache: 'no-store'` option is passed to `fetch()`.",
    },
  },
  preferredRegion: {
    description:
      'Specify the perferred region that this layout or page should be deployed to. If the region option is not specified, it inherits the option from the nearest parent layout. The root defaults to `"auto"`.',
    options: {
      '"auto"':
        'Next.js will first deploy to the `"home"` region. Then if it doesn’t detect any waterfall requests after a few requests, it can upgrade that route, to be deployed globally to `"edge"`. If it detects any waterfall requests after that, it can eventually downgrade back to `"home`".',
      '"home"': 'Prefer deploying to the Home region.',
      '"edge"': 'Prefer deploying to the Edge globally.',
    },
  },
  revalidate: {
    description:
      'The `revalidate` option sets the default revalidation time for that layout or page. Note that it doesn’t override the value specify by each `fetch()`.',
    type: 'mixed',
    options: {
      false:
        'This is the default and changes the fetch cache to indefinitely cache anything that uses force-cache or is fetched before a dynamic Hook/fetch.',
      0: 'Specifying `0` implies that this layout or page should never be static.',
      30: 'Set the revalidation time to `30` seconds. The value can be `0` or any positive number.',
    },
    isValid: (value: string) => {
      return value === 'false' || Number(value) >= 0
    },
    getHint: (value: any) => {
      return `Set the default revalidation time to \`${value}\` seconds.`
    },
  },
  dynamicParams: {
    description:
      '`dynamicParams` replaces the `fallback` option of `getStaticPaths`. It controls whether we allow `dynamicParams` beyond the generated static params from `generateStaticParams`.',
    options: {
      true: 'Allow rendering dynamic params that are not generated by `generateStaticParams`.',
      false:
        'Disallow rendering dynamic params that are not generated by `generateStaticParams`.',
    },
  },
  runtime: {
    description:
      'The `runtime` option controls the preferred runtime to render this route.',
    options: {
      '"nodejs"': 'Prefer the Node.js runtime.',
      '"experimental-edge"': 'Prefer the experimental Edge runtime.',
    },
  },
}

function getAPIDescription(api: string): string {
  return (
    API_DOCS[api].description +
    '\n\n' +
    Object.entries(API_DOCS[api].options)
      .map(([key, value]) => `- \`${key}\`: ${value}`)
      .join('\n')
  )
}

function removeStringQuotes(str: string): string {
  return str.replace(/^['"`]|['"`]$/g, '')
}

export function createTSPlugin(modules: {
  typescript: typeof import('typescript/lib/tsserverlibrary')
}) {
  const ts = modules.typescript

  function createAutoCompletionOptionName(sort: number, name: string) {
    return {
      name,
      sortText: '' + sort,
      kind: ts.ScriptElementKind.unknown,
      kindModifiers: ts.ScriptElementKindModifier.exportedModifier,
      labelDetails: {
        description: `Next.js ${name} option`,
      },
      data: {
        exportName: name,
        moduleSpecifier: 'next/typescript/entry_option_name',
      },
    } as ts.CompletionEntry
  }

  function createAutoCompletionOptionValue(
    sort: number,
    name: string,
    apiName: string
  ) {
    const isString = name.startsWith('"')
    return {
      name,
      insertText: removeStringQuotes(name),
      sortText: '' + sort,
      kind: isString
        ? ts.ScriptElementKind.string
        : ts.ScriptElementKind.unknown,
      kindModifiers: ts.ScriptElementKindModifier.none,
      labelDetails: {
        description: `Next.js ${apiName} option`,
      },
      data: {
        exportName: apiName,
        moduleSpecifier: 'next/typescript/entry_option_value',
      },
    } as ts.CompletionEntry
  }

  function create(info: ts.server.PluginCreateInfo) {
    const appDir = path.join(info.project.getCurrentDirectory(), 'app')
    const isAppEntryFile = (filePath: string) => {
      return (
        filePath.startsWith(appDir) &&
        /(page|layout)\.(mjs|js|jsx|ts|tsx)$/.test(path.basename(filePath))
      )
    }

    function getIsClientEntry(
      fileName: string,
      throwOnInvalidDirective?: boolean
    ) {
      const source = info.languageService.getProgram()?.getSourceFile(fileName)
      if (source) {
        let isClientEntry = false
        let isDirective = true

        ts.forEachChild(source!, (node) => {
          if (
            ts.isExpressionStatement(node) &&
            ts.isStringLiteral(node.expression)
          ) {
            if (node.expression.text === 'use client') {
              if (isDirective) {
                isClientEntry = true
              } else {
                if (throwOnInvalidDirective) {
                  throw {
                    messageText:
                      'The `"use client"` directive must be put at the top of the file.',
                    start: node.expression.getStart(),
                    length:
                      node.expression.getEnd() - node.expression.getStart(),
                  }
                }
              }
            }
          } else {
            isDirective = false
          }
        })

        return isClientEntry
      }
      return false
    }

    function visitEntryConfig(
      fileName: string,
      position: number,
      callback: (entryEonfig: string, value: ts.VariableDeclaration) => void
    ) {
      const source = info.languageService.getProgram()?.getSourceFile(fileName)
      if (source) {
        ts.forEachChild(source, function visit(node) {
          // Covered by this node
          if (
            node.getFullStart() <= position &&
            position <= node.getFullStart() + node.getFullWidth()
          ) {
            // Export variable
            if (
              ts.isVariableStatement(node) &&
              node.modifiers?.some(
                (m) => m.kind === ts.SyntaxKind.ExportKeyword
              )
            ) {
              if (ts.isVariableDeclarationList(node.declarationList)) {
                for (const declarartion of node.declarationList.declarations) {
                  if (
                    declarartion.getFullStart() <= position &&
                    position <=
                      declarartion.getFullStart() + declarartion.getFullWidth()
                  ) {
                    // `export const ... = ...`
                    const text = declarartion.name.getText()
                    callback(text, declarartion)
                  }
                }
              }
            }
          }
        })
      }
    }

    function log(message: string) {
      info.project.projectService.logger.info(message)
    }

    log('Starting Next.js TypeScript plugin: ' + appDir)

    // Set up decorator object
    const proxy = Object.create(null)
    for (let k of Object.keys(info.languageService)) {
      const x = (info.languageService as any)[k]
      proxy[k] = (...args: Array<{}>) => x.apply(info.languageService, args)
    }

    // Auto completion
    proxy.getCompletionsAtPosition = (
      fileName: string,
      position: number,
      options: any
    ) => {
      let prior = info.languageService.getCompletionsAtPosition(
        fileName,
        position,
        options
      ) || {
        isGlobalCompletion: false,
        isMemberCompletion: false,
        isNewIdentifierLocation: false,
        entries: [],
      }
      if (!isAppEntryFile(fileName)) return prior

      // Remove specified entries from completion list if it's a server entry.
      if (!getIsClientEntry(fileName)) {
        prior.entries = prior.entries.filter((e: ts.CompletionEntry) => {
          // Remove disallowed React APIs.
          if (
            DISALLOWED_SERVER_REACT_APIS.includes(e.name) &&
            e.kindModifiers === 'declare'
          ) {
            return false
          }
          return true
        })
      }

      // Auto completion for entry exported configs.
      visitEntryConfig(fileName, position, (entryConfig, declarartion) => {
        if (!API_DOCS[entryConfig]) {
          if (
            declarartion.name.getFullStart() <= position &&
            position <=
              declarartion.name.getFullStart() +
                declarartion.name.getFullWidth()
          ) {
            prior.entries = [
              ...prior.entries,
              ...Object.keys(API_DOCS).map((name, index) => {
                return createAutoCompletionOptionName(index, name)
              }),
            ] as ts.CompletionEntry[]
          }
          return
        }

        prior.entries = [
          ...prior.entries,
          ...Object.keys(API_DOCS[entryConfig].options).map((name, index) => {
            return createAutoCompletionOptionValue(index, name, entryConfig)
          }),
        ] as ts.CompletionEntry[]
      })

      return prior
    }

    // Show auto completion details
    proxy.getCompletionEntryDetails = (
      fileName: string,
      position: number,
      entryName: string,
      formatOptions: ts.FormatCodeOptions,
      source: string,
      preferences: ts.UserPreferences,
      data: ts.CompletionEntryData
    ) => {
      if (
        data &&
        data.moduleSpecifier &&
        data.moduleSpecifier.startsWith('next/typescript')
      ) {
        let content = ''
        if (data.moduleSpecifier === 'next/typescript/entry_option_name') {
          content = getAPIDescription(entryName)
        } else {
          content = API_DOCS[data.exportName].options[entryName]
        }
        return {
          name: entryName,
          kind: ts.ScriptElementKind.enumElement,
          kindModifiers: ts.ScriptElementKindModifier.none,
          displayParts: [],
          documentation: [
            {
              kind: 'text',
              text: content,
            },
          ],
        }
      }

      const prior = info.languageService.getCompletionEntryDetails(
        fileName,
        position,
        entryName,
        formatOptions,
        source,
        preferences,
        data
      )

      return prior
    }

    // Quick info
    proxy.getQuickInfoAtPosition = (fileName: string, position: number) => {
      const prior = info.languageService.getQuickInfoAtPosition(
        fileName,
        position
      )
      if (!isAppEntryFile(fileName)) return prior

      // Remove type suggestions for disallowed APIs in server components.
      if (!getIsClientEntry(fileName)) {
        const definitions = info.languageService.getDefinitionAtPosition(
          fileName,
          position
        )
        if (
          definitions?.some(
            (d) =>
              DISALLOWED_SERVER_REACT_APIS.includes(d.name) &&
              d.containerName === 'React'
          )
        ) {
          return
        }
      }

      let overriden: ts.QuickInfo | undefined
      visitEntryConfig(fileName, position, (entryConfig, declarartion) => {
        if (!API_DOCS[entryConfig]) return

        const name = declarartion.name
        const value = declarartion.initializer

        if (
          value &&
          value.getFullStart() <= position &&
          value.getFullStart() + value.getFullWidth() >= position
        ) {
          // Hovers the value of the config
          const isString = ts.isStringLiteral(value)
          const text = removeStringQuotes(value.getText())
          const key = isString ? `"${text}"` : text

          const isValid = API_DOCS[entryConfig].isValid
            ? API_DOCS[entryConfig].isValid?.(key)
            : !!API_DOCS[entryConfig].options[key]

          if (isValid) {
            overriden = {
              kind: ts.ScriptElementKind.enumElement,
              kindModifiers: ts.ScriptElementKindModifier.none,
              textSpan: {
                start: value.getStart(),
                length: value.getWidth(),
              },
              displayParts: [],
              documentation: [
                {
                  kind: 'text',
                  text:
                    API_DOCS[entryConfig].options[key] ||
                    API_DOCS[entryConfig].getHint?.(key) ||
                    '',
                },
              ],
            }
          }
        } else {
          // Hovers the name of the config
          if (API_DOCS[entryConfig]) {
            overriden = {
              kind: ts.ScriptElementKind.enumElement,
              kindModifiers: ts.ScriptElementKindModifier.none,
              textSpan: {
                start: name.getStart(),
                length: name.getWidth(),
              },
              displayParts: [],
              documentation: [
                {
                  kind: 'text',
                  text: getAPIDescription(entryConfig),
                },
              ],
            }
          }
        }
      })
      if (overriden) return overriden

      return prior
    }

    // Show errors for disallowed imports
    proxy.getSemanticDiagnostics = (fileName: string) => {
      const prior = info.languageService.getSemanticDiagnostics(fileName)
      if (!isAppEntryFile(fileName)) return prior

      const source = info.languageService.getProgram()?.getSourceFile(fileName)
      if (source) {
        let isClientEntry = false

        try {
          isClientEntry = getIsClientEntry(fileName, true)
        } catch (e: any) {
          prior.push({
            file: source,
            category: ts.DiagnosticCategory.Error,
            code: 71004,
            ...e,
          })
          isClientEntry = false
        }

        ts.forEachChild(source!, (node) => {
          if (ts.isImportDeclaration(node)) {
            if (!isClientEntry) {
              const importPath = node.moduleSpecifier.getText(source!)
              if (importPath === "'react'" || importPath === '"react"') {
                // Check if it imports "useState"
                const importClause = node.importClause
                if (importClause) {
                  const namedBindings = importClause.namedBindings
                  if (namedBindings && ts.isNamedImports(namedBindings)) {
                    const elements = namedBindings.elements
                    for (const element of elements) {
                      const name = element.name.getText(source!)
                      if (DISALLOWED_SERVER_REACT_APIS.includes(name)) {
                        prior.push({
                          file: source,
                          category: ts.DiagnosticCategory.Error,
                          code: 71001,
                          messageText: `"${name}" is not allowed in Server Components.`,
                          start: element.name.getStart(),
                          length:
                            element.name.getEnd() - element.name.getStart(),
                        })
                      }
                    }
                  }
                }
              }
            }
          } else if (
            ts.isVariableStatement(node) &&
            node.modifiers?.some((m) => m.kind === ts.SyntaxKind.ExportKeyword)
          ) {
            if (ts.isVariableDeclarationList(node.declarationList)) {
              for (const declarartion of node.declarationList.declarations) {
                const name = declarartion.name
                if (ts.isIdentifier(name)) {
                  if (
                    !ALLOWED_EXPORTS.includes(name.text) &&
                    !API_DOCS[name.text]
                  ) {
                    prior.push({
                      file: source,
                      category: ts.DiagnosticCategory.Error,
                      code: 71002,
                      messageText: `"${name.text}" is not a valid Next.js entry export value.`,
                      start: name.getStart(),
                      length: name.getEnd() - name.getStart(),
                    })
                  } else if (API_DOCS[name.text]) {
                    // Check if the value is valid
                    const value = declarartion.initializer

                    if (value) {
                      let displayedValue = ''
                      let errorMessage = ''
                      let isInvalid = false

                      if (
                        ts.isStringLiteral(value) ||
                        ts.isNoSubstitutionTemplateLiteral(value)
                      ) {
                        const text = removeStringQuotes(value.getText())
                        const allowedValues = Object.keys(
                          API_DOCS[name.text].options
                        )
                          .filter((v) => /^['"]/.test(v))
                          .map(removeStringQuotes)

                        if (!allowedValues.includes(text)) {
                          isInvalid = true
                          displayedValue = `'${text}'`
                        }
                      } else if (
                        ts.isNumericLiteral(value) ||
                        (ts.isPrefixUnaryExpression(value) &&
                          ts.isMinusToken((value as any).operator) &&
                          (ts.isNumericLiteral((value as any).operand.kind) ||
                            (ts.isIdentifier((value as any).operand.kind) &&
                              (value as any).operand.kind.getText() ===
                                'Infinity'))) ||
                        (ts.isIdentifier(value) &&
                          value.getText() === 'Infinity')
                      ) {
                        const v = value.getText()
                        if (API_DOCS[name.text].isValid?.(v) === false) {
                          isInvalid = true
                          displayedValue = v
                        }
                      } else if (
                        value.kind === ts.SyntaxKind.TrueKeyword ||
                        value.kind === ts.SyntaxKind.FalseKeyword
                      ) {
                        const v = value.getText()
                        if (API_DOCS[name.text].isValid?.(v) === false) {
                          isInvalid = true
                          displayedValue = v
                        }
                      } else if (
                        // Other literals
                        ts.isBigIntLiteral(value) ||
                        ts.isArrayLiteralExpression(value) ||
                        ts.isObjectLiteralExpression(value) ||
                        ts.isRegularExpressionLiteral(value)
                      ) {
                        isInvalid = true
                        displayedValue = value.getText()
                      } else {
                        // Not a literal, error because it's not statically analyzable
                        isInvalid = true
                        displayedValue = value.getText()
                        errorMessage = `"${displayedValue}" is not a valid value for the "${name.text}" option. The configuration must be statically analyzable.`
                      }

                      if (isInvalid) {
                        prior.push({
                          file: source,
                          category: ts.DiagnosticCategory.Error,
                          code: 71003,
                          messageText:
                            errorMessage ||
                            `"${displayedValue}" is not a valid value for the "${name.text}" option.`,
                          start: value.getStart(),
                          length: value.getEnd() - value.getStart(),
                        })
                      }
                    }
                  }
                }
              }
            }
          }
        })
      }

      return prior
    }

    return proxy
  }

  return { create }
}