next-ssg-transform.ts

import {
  NodePath,
  PluginObj,
  types as BabelTypes,
} from 'next/dist/compiled/babel/core'
import { SERVER_PROPS_SSG_CONFLICT } from '../../../lib/constants'
import {
  SERVER_PROPS_ID,
  STATIC_PROPS_ID,
} from '../../../next-server/lib/constants'

export const EXPORT_NAME_GET_STATIC_PROPS = 'getStaticProps'
export const EXPORT_NAME_GET_STATIC_PATHS = 'getStaticPaths'
export const EXPORT_NAME_GET_SERVER_PROPS = 'getServerSideProps'

const ssgExports = new Set([
  EXPORT_NAME_GET_STATIC_PROPS,
  EXPORT_NAME_GET_STATIC_PATHS,
  EXPORT_NAME_GET_SERVER_PROPS,

  // legacy methods added so build doesn't fail from importing
  // server-side only methods
  `unstable_getStaticProps`,
  `unstable_getStaticPaths`,
  `unstable_getServerProps`,
  `unstable_getServerSideProps`,
])

type PluginState = {
  refs: Set<NodePath<BabelTypes.Identifier>>
  isPrerender: boolean
  isServerProps: boolean
  done: boolean
}

function decorateSsgExport(
  t: typeof BabelTypes,
  path: NodePath<BabelTypes.Program>,
  state: PluginState
): void {
  const gsspName = state.isPrerender ? STATIC_PROPS_ID : SERVER_PROPS_ID
  const gsspId = t.identifier(gsspName)

  const addGsspExport = (
    exportPath:
      | NodePath<BabelTypes.ExportDefaultDeclaration>
      | NodePath<BabelTypes.ExportNamedDeclaration>
  ): void => {
    if (state.done) {
      return
    }
    state.done = true

    const [pageCompPath] = exportPath.replaceWithMultiple([
      t.exportNamedDeclaration(
        t.variableDeclaration(
          // We use 'var' instead of 'let' or 'const' for ES5 support. Since
          // this runs in `Program#exit`, no ES2015 transforms (preset env)
          // will be ran against this code.
          'var',
          [t.variableDeclarator(gsspId, t.booleanLiteral(true))]
        ),
        [t.exportSpecifier(gsspId, gsspId)]
      ),
      exportPath.node,
    ])
    exportPath.scope.registerDeclaration(
      pageCompPath as NodePath<BabelTypes.Node>
    )
  }

  path.traverse({
    ExportDefaultDeclaration(exportDefaultPath) {
      addGsspExport(exportDefaultPath)
    },
    ExportNamedDeclaration(exportNamedPath) {
      addGsspExport(exportNamedPath)
    },
  })
}

const isDataIdentifier = (name: string, state: PluginState): boolean => {
  if (ssgExports.has(name)) {
    if (name === EXPORT_NAME_GET_SERVER_PROPS) {
      if (state.isPrerender) {
        throw new Error(SERVER_PROPS_SSG_CONFLICT)
      }
      state.isServerProps = true
    } else {
      if (state.isServerProps) {
        throw new Error(SERVER_PROPS_SSG_CONFLICT)
      }
      state.isPrerender = true
    }
    return true
  }
  return false
}

export default function nextTransformSsg({
  types: t,
}: {
  types: typeof BabelTypes
}): PluginObj<PluginState> {
  function getIdentifier(
    path:
      | NodePath<BabelTypes.FunctionDeclaration>
      | NodePath<BabelTypes.FunctionExpression>
      | NodePath<BabelTypes.ArrowFunctionExpression>
  ): NodePath<BabelTypes.Identifier> | null {
    const parentPath = path.parentPath
    if (parentPath.type === 'VariableDeclarator') {
      const pp = parentPath as NodePath<BabelTypes.VariableDeclarator>
      const name = pp.get('id')
      return name.node.type === 'Identifier'
        ? (name as NodePath<BabelTypes.Identifier>)
        : null
    }

    if (parentPath.type === 'AssignmentExpression') {
      const pp = parentPath as NodePath<BabelTypes.AssignmentExpression>
      const name = pp.get('left')
      return name.node.type === 'Identifier'
        ? (name as NodePath<BabelTypes.Identifier>)
        : null
    }

    if (path.node.type === 'ArrowFunctionExpression') {
      return null
    }

    return path.node.id && path.node.id.type === 'Identifier'
      ? (path.get('id') as NodePath<BabelTypes.Identifier>)
      : null
  }

  function isIdentifierReferenced(
    ident: NodePath<BabelTypes.Identifier>
  ): boolean {
    const b = ident.scope.getBinding(ident.node.name)
    if (b?.referenced) {
      // Functions can reference themselves, so we need to check if there's a
      // binding outside the function scope or not.
      if (b.path.type === 'FunctionDeclaration') {
        return !b.constantViolations
          .concat(b.referencePaths)
          // Check that every reference is contained within the function:
          .every((ref) => ref.findParent((p) => p === b.path))
      }

      return true
    }
    return false
  }

  function markFunction(
    path:
      | NodePath<BabelTypes.FunctionDeclaration>
      | NodePath<BabelTypes.FunctionExpression>
      | NodePath<BabelTypes.ArrowFunctionExpression>,
    state: PluginState
  ): void {
    const ident = getIdentifier(path)
    if (ident?.node && isIdentifierReferenced(ident)) {
      state.refs.add(ident)
    }
  }

  function markImport(
    path:
      | NodePath<BabelTypes.ImportSpecifier>
      | NodePath<BabelTypes.ImportDefaultSpecifier>
      | NodePath<BabelTypes.ImportNamespaceSpecifier>,
    state: PluginState
  ): void {
    const local = path.get('local') as NodePath<BabelTypes.Identifier>
    if (isIdentifierReferenced(local)) {
      state.refs.add(local)
    }
  }

  return {
    visitor: {
      Program: {
        enter(path, state) {
          state.refs = new Set<NodePath<BabelTypes.Identifier>>()
          state.isPrerender = false
          state.isServerProps = false
          state.done = false

          path.traverse(
            {
              VariableDeclarator(variablePath, variableState) {
                if (variablePath.node.id.type === 'Identifier') {
                  const local = variablePath.get('id') as NodePath<
                    BabelTypes.Identifier
                  >
                  if (isIdentifierReferenced(local)) {
                    variableState.refs.add(local)
                  }
                } else if (variablePath.node.id.type === 'ObjectPattern') {
                  const pattern = variablePath.get('id') as NodePath<
                    BabelTypes.ObjectPattern
                  >

                  const properties = pattern.get('properties')
                  properties.forEach((p) => {
                    const local = p.get(
                      p.node.type === 'ObjectProperty'
                        ? 'value'
                        : p.node.type === 'RestElement'
                        ? 'argument'
                        : (function () {
                            throw new Error('invariant')
                          })()
                    ) as NodePath<BabelTypes.Identifier>
                    if (isIdentifierReferenced(local)) {
                      variableState.refs.add(local)
                    }
                  })
                } else if (variablePath.node.id.type === 'ArrayPattern') {
                  const pattern = variablePath.get('id') as NodePath<
                    BabelTypes.ArrayPattern
                  >

                  const elements = pattern.get('elements')
                  elements.forEach((e) => {
                    let local: NodePath<BabelTypes.Identifier>
                    if (e.node?.type === 'Identifier') {
                      local = e as NodePath<BabelTypes.Identifier>
                    } else if (e.node?.type === 'RestElement') {
                      local = e.get('argument') as NodePath<
                        BabelTypes.Identifier
                      >
                    } else {
                      return
                    }

                    if (isIdentifierReferenced(local)) {
                      variableState.refs.add(local)
                    }
                  })
                }
              },
              FunctionDeclaration: markFunction,
              FunctionExpression: markFunction,
              ArrowFunctionExpression: markFunction,
              ImportSpecifier: markImport,
              ImportDefaultSpecifier: markImport,
              ImportNamespaceSpecifier: markImport,
              ExportNamedDeclaration(exportNamedPath, exportNamedState) {
                const specifiers = exportNamedPath.get('specifiers')
                if (specifiers.length) {
                  specifiers.forEach((s) => {
                    if (
                      isDataIdentifier(
                        t.isIdentifier(s.node.exported)
                          ? s.node.exported.name
                          : s.node.exported.value,
                        exportNamedState
                      )
                    ) {
                      s.remove()
                    }
                  })

                  if (exportNamedPath.node.specifiers.length < 1) {
                    exportNamedPath.remove()
                  }
                  return
                }

                const decl = exportNamedPath.get('declaration') as NodePath<
                  | BabelTypes.FunctionDeclaration
                  | BabelTypes.VariableDeclaration
                >
                if (decl == null || decl.node == null) {
                  return
                }

                switch (decl.node.type) {
                  case 'FunctionDeclaration': {
                    const name = decl.node.id!.name
                    if (isDataIdentifier(name, exportNamedState)) {
                      exportNamedPath.remove()
                    }
                    break
                  }
                  case 'VariableDeclaration': {
                    const inner = decl.get('declarations') as NodePath<
                      BabelTypes.VariableDeclarator
                    >[]
                    inner.forEach((d) => {
                      if (d.node.id.type !== 'Identifier') {
                        return
                      }
                      const name = d.node.id.name
                      if (isDataIdentifier(name, exportNamedState)) {
                        d.remove()
                      }
                    })
                    break
                  }
                  default: {
                    break
                  }
                }
              },
            },
            state
          )

          if (!state.isPrerender && !state.isServerProps) {
            return
          }

          const refs = state.refs
          let count: number

          function sweepFunction(
            sweepPath:
              | NodePath<BabelTypes.FunctionDeclaration>
              | NodePath<BabelTypes.FunctionExpression>
              | NodePath<BabelTypes.ArrowFunctionExpression>
          ): void {
            const ident = getIdentifier(sweepPath)
            if (
              ident?.node &&
              refs.has(ident) &&
              !isIdentifierReferenced(ident)
            ) {
              ++count

              if (
                t.isAssignmentExpression(sweepPath.parentPath) ||
                t.isVariableDeclarator(sweepPath.parentPath)
              ) {
                sweepPath.parentPath.remove()
              } else {
                sweepPath.remove()
              }
            }
          }

          function sweepImport(
            sweepPath:
              | NodePath<BabelTypes.ImportSpecifier>
              | NodePath<BabelTypes.ImportDefaultSpecifier>
              | NodePath<BabelTypes.ImportNamespaceSpecifier>
          ): void {
            const local = sweepPath.get('local') as NodePath<
              BabelTypes.Identifier
            >
            if (refs.has(local) && !isIdentifierReferenced(local)) {
              ++count
              sweepPath.remove()
              if (
                (sweepPath.parent as BabelTypes.ImportDeclaration).specifiers
                  .length === 0
              ) {
                sweepPath.parentPath.remove()
              }
            }
          }

          do {
            ;(path.scope as any).crawl()
            count = 0

            path.traverse({
              // eslint-disable-next-line no-loop-func
              VariableDeclarator(variablePath) {
                if (variablePath.node.id.type === 'Identifier') {
                  const local = variablePath.get('id') as NodePath<
                    BabelTypes.Identifier
                  >
                  if (refs.has(local) && !isIdentifierReferenced(local)) {
                    ++count
                    variablePath.remove()
                  }
                } else if (variablePath.node.id.type === 'ObjectPattern') {
                  const pattern = variablePath.get('id') as NodePath<
                    BabelTypes.ObjectPattern
                  >

                  const beforeCount = count
                  const properties = pattern.get('properties')
                  properties.forEach((p) => {
                    const local = p.get(
                      p.node.type === 'ObjectProperty'
                        ? 'value'
                        : p.node.type === 'RestElement'
                        ? 'argument'
                        : (function () {
                            throw new Error('invariant')
                          })()
                    ) as NodePath<BabelTypes.Identifier>

                    if (refs.has(local) && !isIdentifierReferenced(local)) {
                      ++count
                      p.remove()
                    }
                  })

                  if (
                    beforeCount !== count &&
                    pattern.get('properties').length < 1
                  ) {
                    variablePath.remove()
                  }
                } else if (variablePath.node.id.type === 'ArrayPattern') {
                  const pattern = variablePath.get('id') as NodePath<
                    BabelTypes.ArrayPattern
                  >

                  const beforeCount = count
                  const elements = pattern.get('elements')
                  elements.forEach((e) => {
                    let local: NodePath<BabelTypes.Identifier>
                    if (e.node?.type === 'Identifier') {
                      local = e as NodePath<BabelTypes.Identifier>
                    } else if (e.node?.type === 'RestElement') {
                      local = e.get('argument') as NodePath<
                        BabelTypes.Identifier
                      >
                    } else {
                      return
                    }

                    if (refs.has(local) && !isIdentifierReferenced(local)) {
                      ++count
                      e.remove()
                    }
                  })

                  if (
                    beforeCount !== count &&
                    pattern.get('elements').length < 1
                  ) {
                    variablePath.remove()
                  }
                }
              },
              FunctionDeclaration: sweepFunction,
              FunctionExpression: sweepFunction,
              ArrowFunctionExpression: sweepFunction,
              ImportSpecifier: sweepImport,
              ImportDefaultSpecifier: sweepImport,
              ImportNamespaceSpecifier: sweepImport,
            })
          } while (count)

          decorateSsgExport(t, path, state)
        },
      },
    },
  }
}