[clang] [Clang] Fix dependency computation for pack indexing expression (PR #91933)

[via cfe-commits]

https://github.com/cor3ntin updated https://github.com/llvm/llvm-project/pull/91933

>From 4cadff527e02ae03aa5850ee713fe57aee663a52 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Mon, 13 May 2024 10:00:19 +0200
Subject: [PATCH 1/2] [Clang] Fix dependency computation for pack indexing
 expression

Given `foo...[idx]` if idx is value dependent, the expression
is type dependent.

Fixes #91885
Fixes #91884
---
 clang/lib/AST/ComputeDependence.cpp        |  3 +++
 clang/test/SemaCXX/cxx2c-pack-indexing.cpp | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/clang/lib/AST/ComputeDependence.cpp b/clang/lib/AST/ComputeDependence.cpp
index bad8e75b2f878..ee56c50d76512 100644
--- a/clang/lib/AST/ComputeDependence.cpp
+++ b/clang/lib/AST/ComputeDependence.cpp
@@ -376,6 +376,9 @@ ExprDependence clang::computeDependence(PackExpansionExpr *E) {
 
 ExprDependence clang::computeDependence(PackIndexingExpr *E) {
   ExprDependence D = E->getIndexExpr()->getDependence();
+  if (D & ExprDependence::Value)
+    D |= ExprDependence::TypeInstantiation;
+
   ArrayRef<Expr *> Exprs = E->getExpressions();
   if (Exprs.empty())
     D |= (E->getPackIdExpression()->getDependence() |
diff --git a/clang/test/SemaCXX/cxx2c-pack-indexing.cpp b/clang/test/SemaCXX/cxx2c-pack-indexing.cpp
index a3e5a0931491b..764f6163710bd 100644
--- a/clang/test/SemaCXX/cxx2c-pack-indexing.cpp
+++ b/clang/test/SemaCXX/cxx2c-pack-indexing.cpp
@@ -194,3 +194,17 @@ void h() {
   // expected-note-re at -2 {{function template specialization '{{.*}}' requested here}}
 }
 }
+
+namespace GH91885 {
+
+void test(auto...args){
+    [&]<int idx>(){
+        using R = decltype( args...[idx] ) ;
+    }.template operator()<0>();
+}
+
+void f( ) {
+    test(1);
+}
+
+}

>From 7c9192cffe099fe4a35e8cb9a88ec56b4480daa1 Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Mon, 13 May 2024 14:24:34 +0200
Subject: [PATCH 2/2] address review feedback

---
 clang/lib/AST/ComputeDependence.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/AST/ComputeDependence.cpp b/clang/lib/AST/ComputeDependence.cpp
index ee56c50d76512..bd0519a1787cc 100644
--- a/clang/lib/AST/ComputeDependence.cpp
+++ b/clang/lib/AST/ComputeDependence.cpp
@@ -377,7 +377,7 @@ ExprDependence clang::computeDependence(PackExpansionExpr *E) {
 ExprDependence clang::computeDependence(PackIndexingExpr *E) {
   ExprDependence D = E->getIndexExpr()->getDependence();
   if (D & ExprDependence::Value)
-    D |= ExprDependence::TypeInstantiation;
+    D |= E->getPackIdExpression()->getDependence() & ExprDependence::Type;
 
   ArrayRef<Expr *> Exprs = E->getExpressions();
   if (Exprs.empty())