[clang] [Clang] Fix concept paramater mapping for SizeOfPackExpr (PR #161994)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 created https://github.com/llvm/llvm-project/pull/161994

This expression is not handled by default in RAV, so our parameter mapping and cache mechanism don't work when it appears in a template argument list.

There are a few other expressions, such as PackIndexingExpr and FunctionParmPackExpr, which are also no-ops by default. I don't have a test case for them now, so let's leave those until complain :/

There was also a bug in updating the parameter mapping, where the AssociatedDecl was not updated accordingly.

Relies on #161671

Fixes https://github.com/llvm/llvm-project/issues/161983
Fixes https://github.com/llvm/llvm-project/issues/161987

>From db646e20fe7acb1a88205dbf0821db02d17ed08d Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Sun, 5 Oct 2025 11:56:32 +0800
Subject: [PATCH] [Clang] Fix concept paramater mapping for SizeOfPackExpr

This expression is not handled by default in RAV, so our parameter
mapping and cache mechanism don't work when it appears in a
template argument list.

There are a few other expressions, such as PackIndexingExpr and
FunctionParmPackExpr, which are also no-ops by default.
I don't have a test case for them now, so let's leave those until
complain :/

There was also a bug in updating the parameter mapping, where the
AssociatedDecl was not updated accordingly.
---
 clang/lib/Sema/SemaConcept.cpp           | 20 +++++++----------
 clang/lib/Sema/SemaTemplateDeduction.cpp |  4 ++++
 clang/test/SemaTemplate/concepts.cpp     | 28 ++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 8413090e7ebd1..0b70f61028e49 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -264,14 +264,6 @@ class HashParameterMapping : public RecursiveASTVisitor<HashParameterMapping> {
 
   UnsignedOrNone OuterPackSubstIndex;
 
-  TemplateArgument getPackSubstitutedTemplateArgument(TemplateArgument Arg) {
-    assert(*SemaRef.ArgPackSubstIndex < Arg.pack_size());
-    Arg = Arg.pack_begin()[*SemaRef.ArgPackSubstIndex];
-    if (Arg.isPackExpansion())
-      Arg = Arg.getPackExpansionPattern();
-    return Arg;
-  }
-
   bool shouldVisitTemplateInstantiations() const { return true; }
 
 public:
@@ -294,7 +286,7 @@ class HashParameterMapping : public RecursiveASTVisitor<HashParameterMapping> {
       assert(Arg.getKind() == TemplateArgument::Pack &&
              "Missing argument pack");
 
-      Arg = getPackSubstitutedTemplateArgument(Arg);
+      Arg = SemaRef.getPackSubstitutedTemplateArgument(Arg);
     }
 
     UsedTemplateArgs.push_back(
@@ -312,7 +304,7 @@ class HashParameterMapping : public RecursiveASTVisitor<HashParameterMapping> {
     if (NTTP->isParameterPack() && SemaRef.ArgPackSubstIndex) {
       assert(Arg.getKind() == TemplateArgument::Pack &&
              "Missing argument pack");
-      Arg = getPackSubstitutedTemplateArgument(Arg);
+      Arg = SemaRef.getPackSubstitutedTemplateArgument(Arg);
     }
 
     UsedTemplateArgs.push_back(
@@ -363,6 +355,10 @@ class HashParameterMapping : public RecursiveASTVisitor<HashParameterMapping> {
     return inherited::TraverseTemplateArgument(Arg);
   }
 
+  bool TraverseSizeOfPackExpr(SizeOfPackExpr *SOPE) {
+    return TraverseDecl(SOPE->getPack());
+  }
+
   void VisitConstraint(const NormalizedConstraintWithParamMapping &Constraint) {
     if (!Constraint.hasParameterMapping()) {
       for (const auto &List : TemplateArgs)
@@ -2083,8 +2079,8 @@ bool SubstituteParameterMappings::substitute(ConceptIdConstraint &CC) {
                                         /*UpdateArgsWithConversions=*/false))
     return true;
   auto TemplateArgs = *MLTAL;
-  TemplateArgs.replaceOutermostTemplateArguments(
-      TemplateArgs.getAssociatedDecl(0).first, CTAI.SugaredConverted);
+  TemplateArgs.replaceOutermostTemplateArguments(CSE->getNamedConcept(),
+                                                 CTAI.SugaredConverted);
   return SubstituteParameterMappings(SemaRef, &TemplateArgs, ArgsAsWritten,
                                      InFoldExpr)
       .substitute(CC.getNormalizedConstraint());
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 6bba505ece07d..3baa9775a49e4 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -6718,6 +6718,10 @@ struct MarkUsedTemplateParameterVisitor : DynamicRecursiveASTVisitor {
     }
     return true;
   }
+
+  bool TraverseSizeOfPackExpr(SizeOfPackExpr *SOPE) override {
+    return TraverseDecl(SOPE->getPack());
+  }
 };
 }
 
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index 6d29f8b798e73..e3b9f9d26bfaf 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1333,4 +1333,32 @@ static_assert(__cpp17_iterator<not_move_constructible>); \
 // expected-note@#is_move_constructible_v {{because 'is_move_constructible_v<parameter_mapping_regressions::case3::not_move_constructible>' evaluated to false}}
 }
 
+namespace case4 {
+
+template<bool b>
+concept bool_ = b;
+
+template<typename... Ts>
+concept unary = bool_<sizeof...(Ts) == 1>;
+
+static_assert(!unary<>);
+static_assert(unary<void>);
+
+}
+
+namespace case5 {
+
+template<int size>
+concept true1 = size == size;
+
+template<typename... Ts>
+concept true2 = true1<sizeof...(Ts)>;
+
+template<typename... Ts>
+concept true3 = true2<Ts...>;
+
+static_assert(true3<void>);
+
+}
+
 }