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 @@ public:
             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 @@ public:
         {
             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";