[clang] [Clang] Fix a crash when dumping a pack indexing type. (PR #80439)

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https://github.com/cor3ntin created https://github.com/llvm/llvm-project/pull/80439

Fix a crash caused by incorrect assumptions
Reported here https://github.com/llvm/llvm-project/pull/72644#discussion_r1469525524

>From 5999b51171d5ac2abcc10a222d6307399b949008 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Fri, 2 Feb 2024 15:45:02 +0100
Subject: [PATCH] [Clang] Fix a crash when dumping a pack indexing type.

Fix a crash caused by incorrect assumptions
Reported here https://github.com/llvm/llvm-project/pull/72644#discussion_r1469525524
---
 clang/lib/AST/TypePrinter.cpp                 |  6 ++---
 .../test/AST/ast-dump-pack-indexing-crash.cpp | 24 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/AST/ast-dump-pack-indexing-crash.cpp

diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp
index 63e56a8296db3..281f529ee1f75 100644
--- a/clang/lib/AST/TypePrinter.cpp
+++ b/clang/lib/AST/TypePrinter.cpp
@@ -1195,10 +1195,10 @@ void TypePrinter::printDecltypeBefore(const DecltypeType *T, raw_ostream &OS) {
 
 void TypePrinter::printPackIndexingBefore(const PackIndexingType *T,
                                           raw_ostream &OS) {
-  if (T->isInstantiationDependentType())
-    OS << T->getPattern() << "...[" << T->getIndexExpr() << "]";
-  else
+  if (T->hasSelectedType())
     OS << T->getSelectedType();
+  else
+    OS << T->getPattern() << "...[" << T->getIndexExpr() << "]";
   spaceBeforePlaceHolder(OS);
 }
 
diff --git a/clang/test/AST/ast-dump-pack-indexing-crash.cpp b/clang/test/AST/ast-dump-pack-indexing-crash.cpp
new file mode 100644
index 0000000000000..1e4e38e2f7378
--- /dev/null
+++ b/clang/test/AST/ast-dump-pack-indexing-crash.cpp
@@ -0,0 +1,24 @@
+// RUN: not %clang_cc1 -std=c++2c -ast-dump %s | FileCheck  %s
+
+namespace InvalidPacksShouldNotCrash {
+
+struct NotAPack;
+template <typename T, auto V, template<typename> typename Tp>
+void not_pack() {
+    int i = 0;
+    i...[0]; // expected-error {{i does not refer to the name of a parameter pack}}
+    V...[0]; // expected-error {{V does not refer to the name of a parameter pack}}
+    NotAPack...[0] a; // expected-error{{'NotAPack' does not refer to the name of a parameter pack}}
+    T...[0] b;   // expected-error{{'T' does not refer to the name of a parameter pack}}
+    Tp...[0] c; // expected-error{{'Tp' does not refer to the name of a parameter pack}}
+}
+
+// CHECK:      -FunctionDecl {{.*}} not_pack 'void ()'
+// CHECK:           |-DeclStmt {{.*}}
+// CHECK:           | `-VarDecl {{.*}} a 'NotAPack...{{.*}}'
+// CHECK:           |-DeclStmt {{.*}}
+// CHECK:           | `-VarDecl {{.*}} 'T...{{.*}}'
+// CHECK:           `-DeclStmt {{.*}}
+// CHECK:             `-VarDecl {{.*}} c 'Tp...{{.*}}'
+
+}