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//! Parsing of module `import` / `export` declarations. Methods on
//! [`Parser`](super::Parser).
//!
//! Dynamic `import(…)` and `import.meta` are expression-level and handled
//! elsewhere (a later increment); this module covers the static declarations.
use super::{Parser, cook};
use crate::ast::{
ExportDecl, ExportSpecifier, Ident, ImportDecl, ImportSpecifier, ModuleExportName, Stmt,
};
use crate::error::Result;
use crate::lexer::{Keyword as Kw, TokenKind};
use alloc::boxed::Box;
use alloc::format;
use alloc::vec::Vec;
impl<'src> Parser<'src> {
/// Whether the current token is an `Identifier` whose name is exactly `word`
/// (used for the contextual `defer` phase keyword, which is not a reserved
/// word in the lexer).
fn at_contextual_ident(&self, word: &str) -> bool {
self.peek() == TokenKind::Identifier && self.ident_name(self.peek_tok()) == word
}
// --- import ---------------------------------------------------------
/// Parses an `import` declaration (the cursor is at `import`).
pub(super) fn parse_import(&mut self) -> Result<Stmt> {
// An `import` declaration is a `ModuleItem`: legal only at the module top
// level. (Dynamic `import(…)` / `import.meta` are expressions, dispatched
// separately and allowed anywhere.)
if !self.module_top_level {
return Err(self.err("`import` is only allowed at the top level of a module"));
}
let start = self.bump().span; // `import`
// Bare side-effect import: `import "mod";`.
if self.at(TokenKind::String) {
let source = self.parse_module_specifier()?;
self.semicolon()?;
return Ok(Stmt::Import(ImportDecl {
specifiers: Vec::new(),
source,
deferred: false,
span: start.to(self.prev_span()),
}));
}
let mut specifiers = Vec::new();
// `import defer * as ns from "mod";` (import-defer proposal). `defer` is
// contextual: it is the *defer phase* only when immediately followed by a
// `*` namespace clause; everywhere else (`import defer from …`,
// `import defer, {x} from …`) it is an ordinary identifier (a default
// binding named `defer`). A `\u`-escaped spelling is not the keyword.
let deferred = self.at_contextual_ident("defer")
&& !self.peek_tok().had_escape
&& self.nth_kind(1) == TokenKind::Star;
if deferred {
self.bump(); // `defer`
self.parse_import_tail(&mut specifiers)?; // requires `* as ns`
} else if self.at_binding_ident() {
// Default binding, optionally followed by `, namespace|named`.
let local = self.parse_binding_ident()?;
specifiers.push(ImportSpecifier::Default(local));
if self.eat(TokenKind::Comma) {
self.parse_import_tail(&mut specifiers)?;
}
} else {
self.parse_import_tail(&mut specifiers)?;
}
self.expect_contextual(Kw::From, "from")?;
let source = self.parse_module_specifier()?;
self.semicolon()?;
Ok(Stmt::Import(ImportDecl {
specifiers,
source,
deferred,
span: start.to(self.prev_span()),
}))
}
/// Parses the namespace (`* as ns`) or named (`{ … }`) part of an import
/// clause.
fn parse_import_tail(&mut self, specifiers: &mut Vec<ImportSpecifier>) -> Result<()> {
if self.eat(TokenKind::Star) {
self.expect_contextual(Kw::As, "as")?;
let local = self.parse_binding_ident()?;
specifiers.push(ImportSpecifier::Namespace(local));
} else if self.at(TokenKind::LBrace) {
self.bump();
while !self.at(TokenKind::RBrace) {
let imported = self.parse_module_export_name()?;
let local = if self.eat(TokenKind::Keyword(Kw::As)) {
self.parse_binding_ident()?
} else {
match &imported {
ModuleExportName::Ident(name) => Ident::new(name.clone(), self.prev_span()),
ModuleExportName::Str(_) => {
return Err(self.err("a string-named import must be bound with `as`"));
}
}
};
specifiers.push(ImportSpecifier::Named { imported, local });
if !self.eat(TokenKind::Comma) {
break;
}
}
self.expect(TokenKind::RBrace)?;
} else {
return Err(self.err("expected an import clause"));
}
Ok(())
}
// --- export ---------------------------------------------------------
/// Parses an `export` declaration (the cursor is at `export`).
pub(super) fn parse_export(&mut self) -> Result<Stmt> {
// An `export` declaration is a `ModuleItem`: legal only at the module top
// level, never nested in a block, function, control body, or `switch`.
if !self.module_top_level {
return Err(self.err("`export` is only allowed at the top level of a module"));
}
let start = self.bump().span; // `export`
// `export * [as name] from "mod";`
if self.eat(TokenKind::Star) {
let exported = if self.eat(TokenKind::Keyword(Kw::As)) {
Some(self.parse_module_export_name()?)
} else {
None
};
self.expect_contextual(Kw::From, "from")?;
let source = self.parse_module_specifier()?;
self.semicolon()?;
return Ok(Stmt::Export(ExportDecl::All {
exported,
source,
span: start.to(self.prev_span()),
}));
}
// `export default …`
if self.eat(TokenKind::Keyword(Kw::Default)) {
let declaration = if self.at(TokenKind::Keyword(Kw::Function))
|| (self.at(TokenKind::Keyword(Kw::Async))
&& self.nth_kind(1) == TokenKind::Keyword(Kw::Function)
&& !self.nth_newline(1))
{
self.parse_default_function()?
} else if self.at(TokenKind::Keyword(Kw::Class)) {
self.parse_default_class()?
} else {
let expr = self.parse_assignment()?;
let espan = expr.span();
self.semicolon()?;
Stmt::Expr {
expression: Box::new(expr),
span: espan,
}
};
return Ok(Stmt::Export(ExportDecl::Default {
declaration: Box::new(declaration),
span: start.to(self.prev_span()),
}));
}
// `export { … } [from "mod"];`
if self.at(TokenKind::LBrace) {
let specifiers = self.parse_export_specifiers()?;
let source = if self.eat(TokenKind::Keyword(Kw::From)) {
Some(self.parse_module_specifier()?)
} else {
None
};
self.semicolon()?;
return Ok(Stmt::Export(ExportDecl::Named {
specifiers,
source,
span: start.to(self.prev_span()),
}));
}
// `export <declaration>` — only a `HoistableDeclaration`
// (function/generator/async/async-generator), a `ClassDeclaration`, a
// `VariableStatement` (`var`), or a `LexicalDeclaration` (`let`/`const`)
// may follow. Any other statement (`if`, `for`, `while`, `try`, a block,
// a labeled statement, a bare expression, a method/getter shorthand, …)
// is a SyntaxError at this position. Guard *before* parsing so we reject
// at the right place rather than accepting an arbitrary statement.
let decl_ok = matches!(
self.peek(),
TokenKind::Keyword(Kw::Function | Kw::Class | Kw::Var | Kw::Let | Kw::Const)
) || (self.at(TokenKind::Keyword(Kw::Async))
&& self.nth_kind(1) == TokenKind::Keyword(Kw::Function)
&& !self.nth_newline(1));
if !decl_ok {
return Err(
self.err("`export` must be followed by a declaration, `default`, `*`, or `{ … }`")
);
}
// This is a declaration position, so a leading `let` is a
// `LexicalDeclaration` (parse it as a `StatementListItem`).
let declaration = self.parse_statement_item()?;
Ok(Stmt::Export(ExportDecl::Decl {
span: start.to(declaration.span()),
declaration: Box::new(declaration),
}))
}
fn parse_export_specifiers(&mut self) -> Result<Vec<ExportSpecifier>> {
self.expect(TokenKind::LBrace)?;
let mut specifiers = Vec::new();
while !self.at(TokenKind::RBrace) {
let start = self.cur_span();
let local = self.parse_module_export_name()?;
let exported = if self.eat(TokenKind::Keyword(Kw::As)) {
self.parse_module_export_name()?
} else {
local.clone()
};
specifiers.push(ExportSpecifier {
local,
exported,
span: start.to(self.prev_span()),
});
if !self.eat(TokenKind::Comma) {
break;
}
}
self.expect(TokenKind::RBrace)?;
Ok(specifiers)
}
// --- shared ---------------------------------------------------------
/// A module specifier string literal (e.g. `"./mod.js"`).
fn parse_module_specifier(&mut self) -> Result<Box<str>> {
let tok = self.expect(TokenKind::String)?;
Ok(cook::string_key(tok.text(self.source), tok.span)?.into())
}
/// An import/export name — an identifier name or a string literal.
fn parse_module_export_name(&mut self) -> Result<ModuleExportName> {
let tok = self.peek_tok();
match tok.kind {
TokenKind::String => {
self.bump();
// A `ModuleExportName : StringLiteral` must be well-formed Unicode
// (no lone UTF-16 surrogate). Check the WTF-8 cooked bytes, which
// preserve surrogates, before the lossy `string_key` collapses them.
let bytes = cook::string(tok.text(self.source), tok.span)?;
if !crate::wtf8::is_well_formed_utf16(&bytes) {
return Err(self.err_at(
tok.span,
"a module export name string literal may not contain a lone surrogate",
));
}
Ok(ModuleExportName::Str(
crate::wtf8::to_string_lossy(&bytes).into(),
))
}
TokenKind::Identifier => {
self.bump();
Ok(ModuleExportName::Ident(self.ident_name(tok).into()))
}
TokenKind::Keyword(kw) => {
self.bump();
Ok(ModuleExportName::Ident(kw.as_str().into()))
}
_ => Err(self.err(format!("expected a module name, found {:?}", tok.kind))),
}
}
/// Consumes a contextual keyword (`from` / `as`), reporting `what` if it is
/// missing.
fn expect_contextual(&mut self, kw: Kw, what: &str) -> Result<()> {
if self.eat(TokenKind::Keyword(kw)) {
Ok(())
} else {
Err(self.err(format!("expected `{what}`, found {:?}", self.peek())))
}
}
}