Fix export name leak from nested function bodies

`export const a = t => { const o = ...; }` registered the arrow-local
`o` as an exported name: the nameDeclaredCallback installed while
parsing an exported declaration stayed active while nested function
bodies were parsed. A second exported arrow declaring `o` then failed
the whole module with "duplicate export name 'o'" -- make-plural's
cardinals module (which openstreetmap.org loads for localization) is
exactly this shape.

A single occurrence did not collide, so the module parsed but still
leaked the body-local into the namespace (Object.keys gained the extra
name); the duplicate-name parse error was just the loud case.

Both nested-body parse paths saved the callback but never cleared it
(the expression-body arrow path didn't even restore its dead saved
copy); null it during the nested parse and restore afterwards.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Joonhyung Hwang <jh1984.hwang@samsung.com>

Author: 2 people

src/parser/esprima_cpp/esprima.cpp

@@ -3407,12 +3407,18 @@ class Parser {
                 if (this->match(LeftBrace)) {
                     this->parseFunctionSourceElements(newBuilder);
                 } else {
+                    // names declared while parsing the arrow body belong to
+                    // the arrow's scope; they must not reach an outer
+                    // collector (e.g. `export const a = () => ...` collecting
+                    // exported names)
                     auto oldNameCallback = this->nameDeclaredCallback;
+                    this->nameDeclaredCallback = nullptr;
 #if defined(ESCARGOT_SMALL_CONFIG)
                     this->isolateCoverGrammar(newBuilder, &Parser::parseAssignmentExpression<ASTBuilder, false>);
 #else
                     this->isolateCoverGrammar(newBuilder, &Parser::parseAssignmentExpression<SyntaxChecker, false>);
 #endif
+                    this->nameDeclaredCallback = oldNameCallback;
 
                     this->currentScopeContext->m_bodyEndLOC.index = this->lastMarker.index;
 #if !(defined NDEBUG) || defined ESCARGOT_DEBUGGER
@@ -5224,6 +5230,11 @@ class Parser {
 
         bool oldAllowLexicalDeclaration = this->context->allowLexicalDeclaration;
         auto oldNameCallback = this->nameDeclaredCallback;
+        // names declared inside a nested function body belong to that
+        // function; without this, `export const a = t => { const o = ...; }`
+        // reported the arrow-local `o` as an exported name ("duplicate
+        // export name" once a second arrow declared `o` too)
+        this->nameDeclaredCallback = nullptr;
         this->context->allowLexicalDeclaration = true;
 
         bool oldInCatchClause = this->context->inCatchClause;