[clang] [Clang][Sema] Use the correct injected template arguments for partial specializations when collecting multi-level template argument lists (PR #112381)

[Krystian Stasiowski via cfe-commits]

https://github.com/sdkrystian created https://github.com/llvm/llvm-project/pull/112381

After #111852 refactored multi-level template argument list collection, the following results in a crash:
```cpp
template<typename T, bool B>
struct A;

template<bool B>
struct A<int, B>
{
    void f() requires B;
};

template<bool B>
void A<int, B>::f() requires B { } // crash here
```

This happens because when collecting template arguments for constraint normalization from a partial specialization, we incorrectly use the template argument list of the partial specialization. We should be using the template argument list of the _template-head_ (as defined in [[temp.arg.general] p2](http://eel.is/c++draft/temp.arg.general#2)). Fixes #112222.

>From 146b209c90a5ced513ec886882ed57ce09ca2f56 Mon Sep 17 00:00:00 2001
From: Krystian Stasiowski <sdkrystian at gmail.com>
Date: Tue, 15 Oct 2024 09:52:43 -0400
Subject: [PATCH] [Clang][Sema] Use the correct injected template arguments for
 partial specializations when collecting multi-level template argument lists

---
 clang/include/clang/AST/DeclTemplate.h     | 14 ++++++++++-
 clang/lib/AST/DeclTemplate.cpp             | 28 ++++++++++++++++++++++
 clang/lib/Sema/SemaTemplateInstantiate.cpp |  4 ++--
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/clang/include/clang/AST/DeclTemplate.h b/clang/include/clang/AST/DeclTemplate.h
index 141f58c4600af0..6c7f47cd5204c2 100644
--- a/clang/include/clang/AST/DeclTemplate.h
+++ b/clang/include/clang/AST/DeclTemplate.h
@@ -2085,7 +2085,9 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
 class ClassTemplatePartialSpecializationDecl
   : public ClassTemplateSpecializationDecl {
   /// The list of template parameters
-  TemplateParameterList* TemplateParams = nullptr;
+  TemplateParameterList *TemplateParams = nullptr;
+
+  TemplateArgument *InjectedArgs = nullptr;
 
   /// The class template partial specialization from which this
   /// class template partial specialization was instantiated.
@@ -2132,6 +2134,10 @@ class ClassTemplatePartialSpecializationDecl
     return TemplateParams;
   }
 
+  /// Retrieve the template arguments list of the template parameter list
+  /// of this template.
+  ArrayRef<TemplateArgument> getInjectedTemplateArgs();
+
   /// \brief All associated constraints of this partial specialization,
   /// including the requires clause and any constraints derived from
   /// constrained-parameters.
@@ -2856,6 +2862,8 @@ class VarTemplatePartialSpecializationDecl
   /// The list of template parameters
   TemplateParameterList *TemplateParams = nullptr;
 
+  TemplateArgument *InjectedArgs = nullptr;
+
   /// The variable template partial specialization from which this
   /// variable template partial specialization was instantiated.
   ///
@@ -2902,6 +2910,10 @@ class VarTemplatePartialSpecializationDecl
     return TemplateParams;
   }
 
+  /// Retrieve the template arguments list of the template parameter list
+  /// of this template.
+  ArrayRef<TemplateArgument> getInjectedTemplateArgs();
+
   /// \brief All associated constraints of this partial specialization,
   /// including the requires clause and any constraints derived from
   /// constrained-parameters.
diff --git a/clang/lib/AST/DeclTemplate.cpp b/clang/lib/AST/DeclTemplate.cpp
index d9b67b7bedf5a5..d2d8907b884ec8 100644
--- a/clang/lib/AST/DeclTemplate.cpp
+++ b/clang/lib/AST/DeclTemplate.cpp
@@ -1185,6 +1185,20 @@ SourceRange ClassTemplatePartialSpecializationDecl::getSourceRange() const {
   return Range;
 }
 
+ArrayRef<TemplateArgument>
+ClassTemplatePartialSpecializationDecl::getInjectedTemplateArgs() {
+  TemplateParameterList *Params = getTemplateParameters();
+  auto *First = cast<ClassTemplatePartialSpecializationDecl>(getFirstDecl());
+  if (!First->InjectedArgs) {
+    auto &Context = getASTContext();
+    SmallVector<TemplateArgument, 16> TemplateArgs;
+    Context.getInjectedTemplateArgs(Params, TemplateArgs);
+    First->InjectedArgs = new (Context) TemplateArgument[TemplateArgs.size()];
+    std::copy(TemplateArgs.begin(), TemplateArgs.end(), First->InjectedArgs);
+  }
+  return llvm::ArrayRef(First->InjectedArgs, Params->size());
+}
+
 //===----------------------------------------------------------------------===//
 // FriendTemplateDecl Implementation
 //===----------------------------------------------------------------------===//
@@ -1535,6 +1549,20 @@ SourceRange VarTemplatePartialSpecializationDecl::getSourceRange() const {
   return Range;
 }
 
+ArrayRef<TemplateArgument>
+VarTemplatePartialSpecializationDecl::getInjectedTemplateArgs() {
+  TemplateParameterList *Params = getTemplateParameters();
+  auto *First = cast<VarTemplatePartialSpecializationDecl>(getFirstDecl());
+  if (!First->InjectedArgs) {
+    auto &Context = getASTContext();
+    SmallVector<TemplateArgument, 16> TemplateArgs;
+    Context.getInjectedTemplateArgs(Params, TemplateArgs);
+    First->InjectedArgs = new (Context) TemplateArgument[TemplateArgs.size()];
+    std::copy(TemplateArgs.begin(), TemplateArgs.end(), First->InjectedArgs);
+  }
+  return llvm::ArrayRef(First->InjectedArgs, Params->size());
+}
+
 static TemplateParameterList *
 createMakeIntegerSeqParameterList(const ASTContext &C, DeclContext *DC) {
   // typename T
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 8c7f694c09042e..8665c099903dc3 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -237,7 +237,7 @@ struct TemplateInstantiationArgumentCollecter
     if (Innermost)
       AddInnermostTemplateArguments(VTPSD);
     else if (ForConstraintInstantiation)
-      AddOuterTemplateArguments(VTPSD, VTPSD->getTemplateArgs().asArray(),
+      AddOuterTemplateArguments(VTPSD, VTPSD->getInjectedTemplateArgs(),
                                 /*Final=*/false);
 
     if (VTPSD->isMemberSpecialization())
@@ -274,7 +274,7 @@ struct TemplateInstantiationArgumentCollecter
     if (Innermost)
       AddInnermostTemplateArguments(CTPSD);
     else if (ForConstraintInstantiation)
-      AddOuterTemplateArguments(CTPSD, CTPSD->getTemplateArgs().asArray(),
+      AddOuterTemplateArguments(CTPSD, CTPSD->getInjectedTemplateArgs(),
                                 /*Final=*/false);
 
     if (CTPSD->isMemberSpecialization())