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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: cor3ntin (cor3ntin)

<details>
<summary>Changes</summary>

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

Fixes #<!-- -->91885
Fixes #<!-- -->91884

---
Full diff: https://github.com/llvm/llvm-project/pull/91933.diff


2 Files Affected:

- (modified) clang/lib/AST/ComputeDependence.cpp (+3) 
- (modified) clang/test/SemaCXX/cxx2c-pack-indexing.cpp (+14) 


``````````diff
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);
+}
+
+}

``````````

</details>


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