ES6 feature: Modules: Tracking Issue

[mikesherov]

Syntax:

• imports:

ImportDeclaration :
  import ImportClause FromClause ;
  import ModuleSpecifier ;
ImportClause :
  ImportedDefaultBinding
  NameSpaceImport
  NamedImports
  ImportedDefaultBinding , NameSpaceImport
  ImportedDefaultBinding , NamedImports
ImportedDefaultBinding :
  ImportedBinding
NameSpaceImport :
  * as ImportedBinding
NamedImports :
  { }
  { ImportsList }
  { ImportsList , }
FromClause :
  from ModuleSpecifier
ImportsList :
  ImportSpecifier
  ImportsList , ImportSpecifier
ImportSpecifier :
  ImportedBinding
  IdentifierName as ImportedBinding
ModuleSpecifier :
  StringLiteral
ImportedBinding :
  BindingIdentifier

• exports:

ExportDeclaration :
  export * FromClause ;
  export ExportClause FromClause ;
  export ExportClause ;
  export VariableStatement
  export Declaration
  export default HoistableDeclaration[Default]
  export default ClassDeclaration[Default]
  export default [lookahead ∉ {function, class}] AssignmentExpression[In] ;
ExportClause :
  { }
  { ExportsList }
  { ExportsList , }
ExportsList :
  ExportSpecifier
  ExportsList , ExportSpecifier
ExportSpecifier :
  IdentifierName
  IdentifierName as IdentifierName

Spec:

• imports: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-imports
• exports: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-exports

Remaining Tasks:

• Land the Classes feature
• Review and Test Token Generation
• Review Error Messages
• Fix export default function() {} Should parse the function as a nameless FuncDecl #311
• Address Import Specifiers: slightly inconsistent between Acorn and Esprima estree/estree#11
• Address https://github.com/estree/estree/pulls/38
• Address https://github.com/estree/estree/pulls/39
• Fix Use Literal instead of ModuleSpecifier for ImportDeclaration's source field. #1077
• Fix export default (1 + 42); does not parse correctly #1087
• Fix data structure for export default AN_EXPRESSION #1088

[ikarienator]

We need to discuss in Wednesday meeting on whether we need to expose an API to parse using different start symbols and the details on it.

In ES5, the only start symbol is Script, so parse is unambiguous. In ES6, we have two symbols, Script and Module. Modules are parsed only in strict mode and imports/exports are only allowed in top level of Modules.

[ariya]

For now, Script vs Module can be handled just like in commit 85fc2f4 from the harmony branch.

[jeffmo]

FWIW We've found it useful already (at FB) to add a nonStrictModule source type for intermediary conversion-of-codebase purposes. I've been meaning to send this upstream, but wanted to try it downstream first to be sure it's worth it.

(@ariya feel free to say you told me so: #290 (comment))

Worth considering here too. We found it to be super convenient to be able to opt in to disabling implicit-strict in order to switch existing CJS (etc) modules over to ES6 before having a chance to go through and audit for strict-safety.

[caridy]

@jeffmo that's pretty interesting.

[caridy]

I plan to work on the modules, at least taking the bulk of the work.

[caridy]

implemented in #1149