LibJS: Handle empty named export

This is an export which looks like `export {} from "module"`, and
although it doesn't have any real export entries it should still add
"module" to the required modules to load.

.prettierignore

@@ -1,3 +1,4 @@
 Base/home/anon/Source/js
 Userland/Libraries/LibJS/Tests/invalid-lhs-in-assignment.js
 Userland/Libraries/LibJS/Tests/unicode-identifier-escape.js
+Userland/Libraries/LibJS/Tests/modules/failing.mjs

Userland/Libraries/LibJS/AST.cpp

@@ -4497,6 +4497,9 @@ void ImportStatement::dump(int indent) const
 bool ExportStatement::has_export(FlyString const& export_name) const
 {
  return any_of(m_entries.begin(), m_entries.end(), [&](auto& entry) {
+ // Make sure that empty exported names does not overlap with anything
+ if (entry.kind == ExportEntry::Kind::EmptyNamedExport)
+ return false;
  return entry.export_name == export_name;
  });
 }

Userland/Libraries/LibJS/AST.h

@@ -360,6 +360,11 @@ class ExportStatement final : public Statement {
  NamedExport,
  ModuleRequestAll,
  ModuleRequestAllButDefault,
+ // EmptyNamedExport is a special type for export {} from "module",
+ // which should import the module without getting any of the exports
+ // however we don't want give it a fake export name which may get
+ // duplicates
+ EmptyNamedExport,
  } kind;
 
  FlyString export_name; // [[ExportName]]
@@ -409,6 +414,11 @@ class ExportStatement final : public Statement {
  {
  return ExportEntry { Kind::ModuleRequestAll, move(export_name), {} };
  }
+
+ static ExportEntry empty_named_export()
+ {
+ return ExportEntry { Kind::EmptyNamedExport, {}, {} };
+ }
  };
 
  ExportStatement(SourceRange source_range, RefPtr<ASTNode> statement, Vector<ExportEntry> entries, bool is_default_export, ModuleRequest module_request)

Userland/Libraries/LibJS/Parser.cpp

@@ -550,7 +550,7 @@ void Parser::parse_module(Program& program)
  if (export_statement.has_statement())
  continue;
  for (auto& entry : export_statement.entries()) {
- if (entry.is_module_request())
+ if (entry.is_module_request() || entry.kind == ExportStatement::ExportEntry::Kind::EmptyNamedExport)
  return;
 
  auto const& exported_name = entry.local_or_import_name;
@@ -4489,6 +4489,7 @@ NonnullRefPtr<ExportStatement> Parser::parse_export_statement(Program& program)
  consume(TokenType::CurlyOpen);
  check_for_from = FromSpecifier::Optional;
 
+ // FIXME: Even when empty should add module to requiredModules!
  while (!done() && !match(TokenType::CurlyClose)) {
  auto identifier_position = position();
  auto identifier = parse_module_export_name(true);
@@ -4508,6 +4509,12 @@ NonnullRefPtr<ExportStatement> Parser::parse_export_statement(Program& program)
  consume(TokenType::Comma);
  }
 
+ if (entries_with_location.is_empty()) {
+ // export {} from "module"; Since this will never be a
+ // duplicate we can give a slightly wrong location.
+ entries_with_location.append({ ExportEntry::empty_named_export(), position() });
+ }
+
  consume(TokenType::CurlyClose);
 
  } else {
@@ -4535,7 +4542,7 @@ NonnullRefPtr<ExportStatement> Parser::parse_export_statement(Program& program)
  }
 
  for (auto& new_entry : entries) {
- if (new_entry.export_name == entry.entry.export_name)
+ if (new_entry.kind != ExportStatement::ExportEntry::Kind::EmptyNamedExport && new_entry.export_name == entry.entry.export_name)
  syntax_error(String::formatted("Duplicate export with name: '{}'", entry.entry.export_name), entry.position);
  }
 

Userland/Libraries/LibJS/SourceTextModule.cpp

@@ -174,6 +174,13 @@ Result<NonnullRefPtr<SourceTextModule>, Vector<Parser::Error>> SourceTextModule:
 
  for (auto const& export_entry : export_statement.entries()) {
 
+ // Special case, export {} from "module" should add "module" to
+ // required_modules but not any import or export so skip here.
+ if (export_entry.kind == ExportStatement::ExportEntry::Kind::EmptyNamedExport) {
+ VERIFY(export_statement.entries().size() == 1);
+ break;
+ }
+
  // a. If ee.[[ModuleRequest]] is null, then
  if (!export_entry.is_module_request()) {
 

Userland/Libraries/LibJS/Tests/modules/basic-modules.js

@@ -193,3 +193,25 @@ describe("loops", () => {
  expectModulePassed("./loop-entry.mjs");
  });
 });
+
+describe("failing modules cascade", () => {
+ let failingModuleError = "Left-hand side of postfix";
+ test("importing a file with a SyntaxError results in a SyntaxError", () => {
+ expectedModuleToThrowSyntaxError("./failing.mjs", failingModuleError);
+ });
+
+ test("importing a file without a syntax error which imports a file with a syntax error fails", () => {
+ expectedModuleToThrowSyntaxError("./importing-failing-module.mjs", failingModuleError);
+ });
+
+ test("importing a file which re exports a file with a syntax error fails", () => {
+ expectedModuleToThrowSyntaxError("./exporting-from-failing.mjs", failingModuleError);
+ });
+
+ test("importing a file re exports nothing from a file with a syntax error fails", () => {
+ expectedModuleToThrowSyntaxError(
+ "./exporting-nothing-from-failing.mjs",
+ failingModuleError
+ );
+ });
+});

Userland/Libraries/LibJS/Tests/modules/exporting-from-failing.mjs

@@ -0,0 +1 @@
+export * as shouldFail from "./failing.mjs";

Userland/Libraries/LibJS/Tests/modules/exporting-nothing-from-failing.mjs

@@ -0,0 +1,4 @@
+export {} from "./failing.mjs";
+export {};
+// This should not be a duplicate!
+export {} from "./failing.mjs";

Userland/Libraries/LibJS/Tests/modules/failing.mjs

@@ -0,0 +1,2 @@
+// Should produce a SyntaxError!
+0++;

Userland/Libraries/LibJS/Tests/modules/importing-failing-module.mjs

@@ -0,0 +1 @@
+import "./failing.mjs";