[clang][Interp] Handle PackIndexExprs

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2226,6 +2226,12 @@ bool ByteCodeExprGen<Emitter>::VisitPseudoObjectExpr(
   return true;
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitPackIndexingExpr(
+    const PackIndexingExpr *E) {
+  return this->delegate(E->getSelectedExpr());
+}
+
 template <class Emitter> bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   if (E->containsErrors())
     return false;

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -119,6 +119,7 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   bool VisitConceptSpecializationExpr(const ConceptSpecializationExpr *E);
   bool VisitCXXRewrittenBinaryOperator(const CXXRewrittenBinaryOperator *E);
   bool VisitPseudoObjectExpr(const PseudoObjectExpr *E);
+  bool VisitPackIndexingExpr(const PackIndexingExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;

clang/test/AST/Interp/cxx23.cpp

@@ -137,3 +137,12 @@ int test_in_lambdas() {
                            // all-note {{in call to}}
   return 0;
 }
+
+/// PackIndexExpr.
+template <auto... p>
+struct check_ice {
+    enum e {
+        x = p...[0] // all-warning {{is a C++2c extension}}
+    };
+};
+static_assert(check_ice<42>::x == 42);