[clang] [Clang] Fix spurious "satisfaction of constraint ... depends on itself" from nested synthesized comparisons (PR #223289)

via cfe-commits cfe-commits at lists.llvm.org
Sun Sep 13 19:44:45 PDT 2026


llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Hsin (GEJXD)

<details>
<summary>Changes</summary>

Fixes #<!-- -->223220

This re-lands #<!-- -->221707 with a minimal fix for the regression it introduced,
which made comparing two `std::map` objects fail with:

```text
error: satisfaction of constraint 'requires { { __t < __u } -> __boolean_testable; { __u < __t } -> __boolean_testable; }' depends on itself
```

## Root cause

`TemplateInstantiator::instantiateMissingDeclsToScopeForConcepts` (added by
#<!-- -->221707) resolves a missing declaration by walking the
`LocalInstantiationScope` chain. After #<!-- -->221707 this walk returns mappings for
*all* declaration kinds, including function parameters.

When the constraint of one specialization of a function template is checked
while another specialization of the *same* template is still being checked
(`std::__detail::__synth3way_t` reached from `std::pair`'s rewritten
`operator<=>` inside `std::map`'s), the parameters of the inner
specialization are looked up through the outer scope chain and find the outer
specialization's parameter mapping. The inner constraint expression then
substitutes the outer (pair-typed) parameters, so the check re-enters an
identical constraint check and is reported as "depends on itself" (the
constraint-satisfaction stack contains the same constraint ID twice).

## Fix

In the outer-scope walk, skip `ParmVarDecl`s and fall through to on-demand
instantiation (CWG2770), which always builds a parameter bound to the
*current* specialization. Non-parameter declarations (e.g. the typedefs that
#<!-- -->221707 intended to make visible in the current scope; see #GH198052,
#GH209632) still reuse outer-scope mappings as before.

This matches the intent stated in the original change ("we don't want clashes
of instantiated function parameters").

## Regression test

`clang/test/SemaTemplate/concepts-nested-synth.cpp` reproduces the
`std::__detail::__synth3way_t` structure instantiated from the `operator<=>`
of `std::map` and `std::pair` with no standard library, exercising the exact
nested-constraint path:

- `Map::operator<=>` returns `synth_t<Pair<const K, V>>` → outer
  `Synth::operator()<Pair,...>` constraint check active
- inside its requirement, `lhs < rhs` resolves through `Pair`'s rewritten
  `operator<=>` whose return type instantiates `synth_t<K, K>` → inner
  `Synth::operator()<K, K>` check nested in the outer one

## Validation

- Fails on the re-landed commit ("depends on itself"), passes with the fix
- `check-clang` (full clang test suite): 0 failures
- `git clang-format` and `git diff --check`: clean

---

Patch is 28.26 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/223289.diff


8 Files Affected:

- (modified) clang/docs/ReleaseNotes.md (+9) 
- (modified) clang/include/clang/Sema/Sema.h (+7-19) 
- (modified) clang/include/clang/Sema/Template.h (+2) 
- (modified) clang/lib/Sema/SemaConcept.cpp (+32-144) 
- (modified) clang/lib/Sema/SemaTemplateInstantiate.cpp (+87-35) 
- (modified) clang/test/SemaCXX/cxx2c-fold-exprs.cpp (+25) 
- (modified) clang/test/SemaTemplate/concepts-lambda.cpp (+16) 
- (added) clang/test/SemaTemplate/concepts-nested-synth.cpp (+82) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 043a0ddae2a6c..f55d5570da375 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -589,6 +589,15 @@ features cannot lower the translation-unit ABI level;
 - Fixed a crash when module directive export module foo not following a
   semicolon and there are no rest pp-tokens in current module file. (#GH187771)
 
+- Fixed concept evaluation bugs where some declarations were not added to
+  the current instantiation scope. (#GH198052), (#GH209632)
+
+- Fixed a regression where the constraint of one specialization of a function
+  template could reuse the function parameters of an outer (still active)
+  specialization of the same template, causing a spurious
+  "satisfaction of constraint ... depends on itself" error for synthesized
+  three-way comparisons such as ``std::map``'s ``operator<=>``. (#GH223220)
+
 - Fixed a crash when a lambda parameter pack was given a default argument that
   is a pack expansion referencing an enclosing function's parameter pack (e.g.
   `[](Types... = args...) {}`). Clang now diagnoses the illegal default
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 4ff4c669a6b70..fc8da0ed56005 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -15129,11 +15129,17 @@ class Sema final : public SemaBase {
       const NamedDecl *D1, ArrayRef<AssociatedConstraint> AC1,
       const NamedDecl *D2, ArrayRef<AssociatedConstraint> AC2);
 
+private:
+  friend class ConstraintSatisfactionChecker;
+  friend class SubstituteParameterMappings;
+
+  UnsignedOrNone EvaluateFoldExpandedConstraintSize(
+      const Expr *Pattern, const MultiLevelTemplateArgumentList &MLTAL);
+
   /// Cache the satisfaction of an atomic constraint.
   /// The key is based on the unsubstituted expression and the parameter
   /// mapping. This lets us not substituting the mapping more than once,
   /// which is (very!) expensive.
-  /// FIXME: this should be private.
   llvm::DenseMap<llvm::FoldingSetNodeID,
                  UnsubstitutedConstraintSatisfactionCacheResult>
       UnsubstitutedConstraintSatisfactionCache;
@@ -15145,7 +15151,6 @@ class Sema final : public SemaBase {
   llvm::DenseMap<llvm::FoldingSetNodeID, TemplateArgumentLoc>
       *CurrentCachedTemplateArgs = nullptr;
 
-private:
   /// Caches pairs of template-like decls whose associated constraints were
   /// checked for subsumption and whether or not the first's constraints did in
   /// fact subsume the second's.
@@ -15166,23 +15171,6 @@ class Sema final : public SemaBase {
   // The current stack of constraint satisfactions, so we can exit-early.
   llvm::SmallVector<SatisfactionStackEntryTy, 10> SatisfactionStack;
 
-  /// Used by SetupConstraintCheckingTemplateArgumentsAndScope to set up the
-  /// LocalInstantiationScope of the current non-lambda function. For lambdas,
-  /// use LambdaScopeForCallOperatorInstantiationRAII.
-  bool
-  SetupConstraintScope(FunctionDecl *FD,
-                       std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
-                       const MultiLevelTemplateArgumentList &MLTAL,
-                       LocalInstantiationScope &Scope);
-
-  /// Used during constraint checking, sets up the constraint template argument
-  /// lists, and calls SetupConstraintScope to set up the
-  /// LocalInstantiationScope to have the proper set of ParVarDecls configured.
-  std::optional<MultiLevelTemplateArgumentList>
-  SetupConstraintCheckingTemplateArgumentsAndScope(
-      FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
-      LocalInstantiationScope &Scope);
-
   ///@}
 
   //
diff --git a/clang/include/clang/Sema/Template.h b/clang/include/clang/Sema/Template.h
index 50e950e56c6ca..818528744511d 100644
--- a/clang/include/clang/Sema/Template.h
+++ b/clang/include/clang/Sema/Template.h
@@ -540,6 +540,8 @@ enum class TemplateSubstitutionKind : char {
     llvm::PointerUnion<Decl *, DeclArgumentPack *> *
     getInstantiationOfIfExists(const Decl *D);
 
+    LocalInstantiationScope *getOuterScope() const { return Outer; }
+
     void InstantiatedLocal(const Decl *D, Decl *Inst);
     void InstantiatedLocalPackArg(const Decl *D, VarDecl *Inst);
     void MakeInstantiatedLocalArgPack(const Decl *D);
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index ee17f826dc32c..0122e920e5d89 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -549,7 +549,9 @@ class HashParameterMapping : public RecursiveASTVisitor<HashParameterMapping> {
     }
   }
 };
+} // namespace
 
+namespace clang {
 class ConstraintSatisfactionChecker {
   Sema &S;
   const NamedDecl *Template;
@@ -652,10 +654,6 @@ class ConstraintSatisfactionChecker {
   EvaluateAtomicConstraint(const Expr *AtomicExpr,
                            const MultiLevelTemplateArgumentList &MLTAL);
 
-  UnsignedOrNone EvaluateFoldExpandedConstraintSize(
-      const FoldExpandedConstraint &FE,
-      const MultiLevelTemplateArgumentList &MLTAL);
-
   // XXX: It is SLOW! Use it very carefully.
   std::optional<MultiLevelTemplateArgumentList> SubstitutionInTemplateArguments(
       const NormalizedConstraintWithParamMapping &Constraint,
@@ -700,7 +698,7 @@ class ConstraintSatisfactionChecker {
                       const MultiLevelTemplateArgumentList &MLTAL);
 };
 
-} // namespace
+} // namespace clang
 
 ExprResult ConstraintSatisfactionChecker::EvaluateAtomicConstraint(
     const Expr *AtomicExpr, const MultiLevelTemplateArgumentList &MLTAL) {
@@ -948,31 +946,6 @@ ExprResult ConstraintSatisfactionChecker::Evaluate(
   return PMCache.cache(EvaluateSlow(Constraint, MLTAL));
 }
 
-UnsignedOrNone
-ConstraintSatisfactionChecker::EvaluateFoldExpandedConstraintSize(
-    const FoldExpandedConstraint &FE,
-    const MultiLevelTemplateArgumentList &MLTAL) {
-
-  Expr *Pattern = const_cast<Expr *>(FE.getPattern());
-
-  SmallVector<UnexpandedParameterPack, 2> Unexpanded;
-  S.collectUnexpandedParameterPacks(Pattern, Unexpanded);
-  assert(!Unexpanded.empty() && "Pack expansion without parameter packs?");
-  bool Expand = true;
-  bool RetainExpansion = false;
-  UnsignedOrNone NumExpansions(std::nullopt);
-  if (S.CheckParameterPacksForExpansion(
-          Pattern->getExprLoc(), Pattern->getSourceRange(), Unexpanded, MLTAL,
-          /*FailOnPackProducingTemplates=*/false, Expand, RetainExpansion,
-          NumExpansions, /*Diagnose=*/false) ||
-      !Expand || RetainExpansion)
-    return std::nullopt;
-
-  if (NumExpansions && S.getLangOpts().BracketDepth < *NumExpansions)
-    return std::nullopt;
-  return NumExpansions;
-}
-
 ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
     const FoldExpandedConstraint &Constraint,
     const MultiLevelTemplateArgumentList &MLTAL) {
@@ -993,9 +966,15 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
     return ExprError();
   }
 
-  ExprResult Out;
-  UnsignedOrNone NumExpansions =
-      EvaluateFoldExpandedConstraintSize(Constraint, *SubstitutedArgs);
+  UnsignedOrNone NumExpansions(std::nullopt);
+  {
+    Sema::InstantiatingTemplate InstTemplate(
+        S, TemplateNameLoc,
+        Sema::InstantiatingTemplate::ConstraintSubstitution{},
+        const_cast<NamedDecl *>(Template), Constraint.getSourceRange());
+    NumExpansions = S.EvaluateFoldExpandedConstraintSize(
+        Constraint.getPattern(), *SubstitutedArgs);
+  }
   if (!NumExpansions)
     return ExprEmpty();
 
@@ -1004,6 +983,7 @@ ExprResult ConstraintSatisfactionChecker::EvaluateSlow(
     return ExprEmpty();
   }
 
+  ExprResult Out;
   for (unsigned I = 0; I < *NumExpansions; I++) {
     Sema::ArgPackSubstIndexRAII SubstIndex(S, I);
     Satisfaction.IsSatisfied = false;
@@ -1412,98 +1392,6 @@ SubstituteConceptsInConstraintExpression(Sema &S, const NamedDecl *D,
                                          MLTAL);
 }
 
-bool Sema::SetupConstraintScope(
-    FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
-    const MultiLevelTemplateArgumentList &MLTAL,
-    LocalInstantiationScope &Scope) {
-  assert(!isLambdaCallOperator(FD) &&
-         "Use LambdaScopeForCallOperatorInstantiationRAII to handle lambda "
-         "instantiations");
-  if (FD->isTemplateInstantiation() && FD->getPrimaryTemplate()) {
-    FunctionTemplateDecl *PrimaryTemplate = FD->getPrimaryTemplate();
-    InstantiatingTemplate Inst(
-        *this, FD->getPointOfInstantiation(),
-        Sema::InstantiatingTemplate::ConstraintsCheck{}, PrimaryTemplate,
-        TemplateArgs ? *TemplateArgs : ArrayRef<TemplateArgument>{},
-        SourceRange());
-    if (Inst.isInvalid())
-      return true;
-
-    // addInstantiatedParametersToScope creates a map of 'uninstantiated' to
-    // 'instantiated' parameters and adds it to the context. For the case where
-    // this function is a template being instantiated NOW, we also need to add
-    // the list of current template arguments to the list so that they also can
-    // be picked out of the map.
-    if (auto *SpecArgs = FD->getTemplateSpecializationArgs()) {
-      MultiLevelTemplateArgumentList JustTemplArgs(FD, SpecArgs->asArray(),
-                                                   /*Final=*/false);
-      if (addInstantiatedParametersToScope(
-              FD, PrimaryTemplate->getTemplatedDecl(), Scope, JustTemplArgs))
-        return true;
-    }
-
-    // If this is a member function, make sure we get the parameters that
-    // reference the original primary template.
-    if (FunctionTemplateDecl *FromMemTempl =
-            PrimaryTemplate->getInstantiatedFromMemberTemplate()) {
-      if (addInstantiatedParametersToScope(FD, FromMemTempl->getTemplatedDecl(),
-                                           Scope, MLTAL))
-        return true;
-    }
-
-    return false;
-  }
-
-  if (FD->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization ||
-      FD->getTemplatedKind() == FunctionDecl::TK_DependentNonTemplate) {
-    FunctionDecl *InstantiatedFrom =
-        FD->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization
-            ? FD->getInstantiatedFromMemberFunction()
-            : FD->getInstantiatedFromDecl();
-
-    InstantiatingTemplate Inst(
-        *this, FD->getPointOfInstantiation(),
-        Sema::InstantiatingTemplate::ConstraintsCheck{}, InstantiatedFrom,
-        TemplateArgs ? *TemplateArgs : ArrayRef<TemplateArgument>{},
-        SourceRange());
-    if (Inst.isInvalid())
-      return true;
-
-    // Case where this was not a template, but instantiated as a
-    // child-function.
-    if (addInstantiatedParametersToScope(FD, InstantiatedFrom, Scope, MLTAL))
-      return true;
-  }
-
-  return false;
-}
-
-// This function collects all of the template arguments for the purposes of
-// constraint-instantiation and checking.
-std::optional<MultiLevelTemplateArgumentList>
-Sema::SetupConstraintCheckingTemplateArgumentsAndScope(
-    FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
-    LocalInstantiationScope &Scope) {
-  MultiLevelTemplateArgumentList MLTAL;
-
-  // Collect the list of template arguments relative to the 'primary' template.
-  // We need the entire list, since the constraint is completely uninstantiated
-  // at this point.
-  MLTAL =
-      getTemplateInstantiationArgs(FD, FD->getLexicalDeclContext(),
-                                   /*Final=*/false, /*Innermost=*/std::nullopt,
-                                   /*RelativeToPrimary=*/true,
-                                   /*Pattern=*/nullptr,
-                                   /*ForConstraintInstantiation=*/true);
-  // Lambdas are handled by LambdaScopeForCallOperatorInstantiationRAII.
-  if (isLambdaCallOperator(FD))
-    return MLTAL;
-  if (SetupConstraintScope(FD, TemplateArgs, MLTAL, Scope))
-    return std::nullopt;
-
-  return MLTAL;
-}
-
 bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
                                     ConstraintSatisfaction &Satisfaction,
                                     SourceLocation UsageLoc,
@@ -1543,12 +1431,12 @@ bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
 
   ContextRAII SavedContext{*this, CtxToSave};
   LocalInstantiationScope Scope(*this, !ForOverloadResolution);
-  std::optional<MultiLevelTemplateArgumentList> MLTAL =
-      SetupConstraintCheckingTemplateArgumentsAndScope(
-          const_cast<FunctionDecl *>(FD), {}, Scope);
-
-  if (!MLTAL)
-    return true;
+  MultiLevelTemplateArgumentList MLTAL =
+      getTemplateInstantiationArgs(FD, FD->getLexicalDeclContext(),
+                                   /*Final=*/false, /*Innermost=*/std::nullopt,
+                                   /*RelativeToPrimary=*/true,
+                                   /*Pattern=*/nullptr,
+                                   /*ForConstraintInstantiation=*/true);
 
   Qualifiers ThisQuals;
   CXXRecordDecl *Record = nullptr;
@@ -1559,11 +1447,11 @@ bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
   CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
 
   LambdaScopeForCallOperatorInstantiationRAII LambdaScope(
-      *this, const_cast<FunctionDecl *>(FD), *MLTAL, Scope,
+      *this, const_cast<FunctionDecl *>(FD), MLTAL, Scope,
       ForOverloadResolution);
 
   return CheckConstraintSatisfaction(
-      FD, FD->getTrailingRequiresClause(), *MLTAL,
+      FD, FD->getTrailingRequiresClause(), MLTAL,
       SourceRange(UsageLoc.isValid() ? UsageLoc : FD->getLocation()),
       Satisfaction);
 }
@@ -1796,12 +1684,12 @@ bool Sema::CheckFunctionTemplateConstraints(
   Sema::ContextRAII savedContext(*this, Decl);
   LocalInstantiationScope Scope(*this);
 
-  std::optional<MultiLevelTemplateArgumentList> MLTAL =
-      SetupConstraintCheckingTemplateArgumentsAndScope(Decl, TemplateArgs,
-                                                       Scope);
-
-  if (!MLTAL)
-    return true;
+  MultiLevelTemplateArgumentList MLTAL =
+      getTemplateInstantiationArgs(Decl, Decl->getLexicalDeclContext(),
+                                   /*Final=*/false, /*Innermost=*/std::nullopt,
+                                   /*RelativeToPrimary=*/true,
+                                   /*Pattern=*/nullptr,
+                                   /*ForConstraintInstantiation=*/true);
 
   Qualifiers ThisQuals;
   CXXRecordDecl *Record = nullptr;
@@ -1811,10 +1699,10 @@ bool Sema::CheckFunctionTemplateConstraints(
   }
 
   CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
-  LambdaScopeForCallOperatorInstantiationRAII LambdaScope(*this, Decl, *MLTAL,
+  LambdaScopeForCallOperatorInstantiationRAII LambdaScope(*this, Decl, MLTAL,
                                                           Scope);
 
-  return CheckConstraintSatisfaction(Template, TemplateAC, *MLTAL,
+  return CheckConstraintSatisfaction(Template, TemplateAC, MLTAL,
                                      PointOfInstantiation, Satisfaction);
 }
 
@@ -2087,7 +1975,7 @@ void Sema::DiagnoseUnsatisfiedConstraint(
                                   ConstraintExpr->getBeginLoc(), First);
 }
 
-namespace {
+namespace clang {
 
 class SubstituteParameterMappings {
   Sema &SemaRef;
@@ -2125,6 +2013,8 @@ class SubstituteParameterMappings {
   bool substitute(NormalizedConstraint &N);
 };
 
+} // namespace clang
+
 void SubstituteParameterMappings::buildParameterMapping(
     NormalizedConstraintWithParamMapping &N) {
   TemplateParameterList *TemplateParams =
@@ -2418,8 +2308,6 @@ bool SubstituteParameterMappings::substitute(NormalizedConstraint &N) {
   llvm_unreachable("Unknown ConstraintKind enum");
 }
 
-} // namespace
-
 NormalizedConstraint *NormalizedConstraint::fromAssociatedConstraints(
     Sema &S, const NamedDecl *D, ArrayRef<AssociatedConstraint> ACs) {
   assert(ACs.size() != 0);
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index ffbe8bb0506bc..fe27b9ea1f323 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1324,11 +1324,10 @@ namespace {
     bool BailOutOnIncomplete;
 
     std::optional<llvm::FoldingSetNodeID> TemplateArgsHashValue;
+    llvm::DenseMap<llvm::FoldingSetNodeID, TemplateArgumentLoc>
+        *CurrentCachedTemplateArgs = nullptr;
 
-    // CWG2770: Function parameters should be instantiated when they are
-    // needed by a satisfaction check of an atomic constraint or
-    // (recursively) by another function parameter.
-    bool maybeInstantiateFunctionParameterToScope(ParmVarDecl *OldParm);
+    bool instantiateMissingDeclsToScopeForConcepts(Decl *D);
 
   public:
     typedef TreeTransform<TemplateInstantiator> inherited;
@@ -1358,12 +1357,14 @@ namespace {
     inline static struct ForConstraintSubstitution_t {
     } ForConstraintSubstitution;
 
-    TemplateInstantiator(ForParameterMappingSubstitution_t, Sema &SemaRef,
-                         SourceLocation Loc,
-                         const MultiLevelTemplateArgumentList &TemplateArgs)
+    TemplateInstantiator(
+        ForParameterMappingSubstitution_t, Sema &SemaRef, SourceLocation Loc,
+        const MultiLevelTemplateArgumentList &TemplateArgs,
+        llvm::DenseMap<llvm::FoldingSetNodeID, TemplateArgumentLoc> *Cache)
         : inherited(SemaRef), TemplateArgs(TemplateArgs), Loc(Loc),
-          EvaluateLambdaConstraint(true), BailOutOnIncomplete(false) {
-      if (!SemaRef.CurrentCachedTemplateArgs)
+          EvaluateLambdaConstraint(true), BailOutOnIncomplete(false),
+          CurrentCachedTemplateArgs(Cache) {
+      if (!Cache)
         return;
       auto &V = TemplateArgsHashValue.emplace();
       for (auto &Level : TemplateArgs)
@@ -1410,22 +1411,18 @@ namespace {
                                  ArrayRef<UnexpandedParameterPack> Unexpanded,
                                  bool FailOnPackProducingTemplates,
                                  bool &ShouldExpand, bool &RetainExpansion,
-                                 UnsignedOrNone &NumExpansions) {
-      if (SemaRef.CurrentInstantiationScope &&
-          (SemaRef.inConstraintSubstitution() ||
-           SemaRef.inParameterMappingSubstitution())) {
-        for (UnexpandedParameterPack ParmPack : Unexpanded) {
-          NamedDecl *VD = ParmPack.first.dyn_cast<NamedDecl *>();
-          if (auto *PVD = dyn_cast_if_present<ParmVarDecl>(VD);
-              PVD && maybeInstantiateFunctionParameterToScope(PVD))
-            return true;
-        }
+                                 UnsignedOrNone &NumExpansions,
+                                 bool Diagnose = true) {
+      for (UnexpandedParameterPack ParmPack : Unexpanded) {
+        if (instantiateMissingDeclsToScopeForConcepts(
+                dyn_cast<NamedDecl *>(ParmPack.first)))
+          return true;
       }
 
       return getSema().CheckParameterPacksForExpansion(
           EllipsisLoc, PatternRange, Unexpanded, TemplateArgs,
           FailOnPackProducingTemplates, ShouldExpand, RetainExpansion,
-          NumExpansions);
+          NumExpansions, Diagnose);
     }
 
     void ExpandingFunctionParameterPack(ParmVarDecl *Pack) {
@@ -1637,7 +1634,7 @@ namespace {
                                    TemplateArgumentLoc &Output,
                                    bool Uneval = false) {
       const TemplateArgument &Arg = Input.getArgument();
-      if (auto *Cache = SemaRef.CurrentCachedTemplateArgs;
+      if (auto *Cache = CurrentCachedTemplateArgs;
           Cache && TemplateArgsHashValue) {
         llvm::FoldingSetNodeID ID = *TemplateArgsHashValue;
         ID.AddInteger(SemaRef.ArgPackSubstIndex.toInternalRepresentation());
@@ -1980,11 +1977,7 @@ Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
     // template parameter.
   }
 
-  if (ParmVarDecl *PVD = dyn_cast<ParmVarDecl>(D);
-      PVD && SemaRef.CurrentInstantiationScope &&
-      (SemaRef.inConstraintSubstitution() ||
-       SemaRef.inParameterMappingSubstitution()) &&
-      maybeInstantiateFunctionParameterToScope(PVD))
+  if (instantiateMissingDeclsToScopeForConcepts(D))
     return nullptr;
 
   if (isa<CXXExpansionStmtDecl>(D)) {
@@ -1996,9 +1989,47 @@ Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
   return SemaRef.FindInstantiatedDecl(Loc, cast<NamedDecl>(D), TemplateArgs);
 }
 
-bool TemplateInstantiator::mayb...
[truncated]

``````````

</details>


https://github.com/llvm/llvm-project/pull/223289


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