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

After #111852 refactored multi-level template argument list collection,
the following results in a crash:
```
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). Fixes #112222.

Author: sdkrystian

clang/include/clang/AST/DeclTemplate.h

@@ -2085,7 +2085,11 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
 class ClassTemplatePartialSpecializationDecl
   : public ClassTemplateSpecializationDecl {
   /// The list of template parameters
-  TemplateParameterList* TemplateParams = nullptr;
+  TemplateParameterList *TemplateParams = nullptr;
+
+  /// The set of "injected" template arguments used within this
+  /// partial specialization.
+  TemplateArgument *InjectedArgs = nullptr;
 
   /// The class template partial specialization from which this
   /// class template partial specialization was instantiated.
@@ -2132,6 +2136,10 @@ 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 +2864,10 @@ class VarTemplatePartialSpecializationDecl
   /// The list of template parameters
   TemplateParameterList *TemplateParams = nullptr;
 
+  /// The set of "injected" template arguments used within this
+  /// partial specialization.
+  TemplateArgument *InjectedArgs = nullptr;
+
   /// The variable template partial specialization from which this
   /// variable template partial specialization was instantiated.
   ///
@@ -2902,6 +2914,10 @@ 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.

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

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())