Reland "[clang] Fix CTAD for aggregates for nested template classes"

[antangelo]

Reland of #78387

Use the template pattern in determining whether to synthesize the aggregate deduction guide, and update DeclareImplicitDeductionGuideFromInitList to substitute outer template arguments.

The tests in the original patch made an assumption about the size of a pointer type, and this led to them failing on targets with 32-bit pointers. The tests have been updated to not depend on the size of any type. This only requires updates to the test file, no functionality has otherwise changed between this and the original patch.

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (antangelo)

Changes

Reland of #78387

Use the template pattern in determining whether to synthesize the aggregate deduction guide, and update DeclareImplicitDeductionGuideFromInitList to substitute outer template arguments.

The tests in the original patch made an assumption about the size of a pointer type, and this led to them failing on targets with 32-bit pointers. The tests have been updated to not depend on the size of any type. This only requires updates to the test file, no functionality has otherwise changed between this and the original patch.

---

Full diff: https://github.com/llvm/llvm-project/pull/78670.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+3)
• (modified) clang/lib/Sema/SemaInit.cpp (+8-1)
• (modified) clang/lib/Sema/SemaTemplate.cpp (+17-4)
• (modified) clang/test/SemaTemplate/nested-implicit-deduction-guides.cpp (+30-4)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b400d75095421c7..ee431587a7853dd 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -979,6 +979,9 @@ Bug Fixes to C++ Support
 - Clang now allows parenthesized initialization of arrays in `operator new[]`.
   Fixes: (`#68198 <https://github.com/llvm/llvm-project/issues/68198>`_)
 
+- Fixes CTAD for aggregates on nested template classes. Fixes:
+  (`#77599 <https://github.com/llvm/llvm-project/issues/77599>`_)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 18440a69e3a3d92..457fa377355a97c 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -10731,7 +10731,14 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
     bool HasAnyDeductionGuide = false;
 
     auto SynthesizeAggrGuide = [&](InitListExpr *ListInit) {
-      auto *RD = cast<CXXRecordDecl>(Template->getTemplatedDecl());
+      auto *Pattern = Template;
+      while (Pattern->getInstantiatedFromMemberTemplate()) {
+        if (Pattern->isMemberSpecialization())
+          break;
+        Pattern = Pattern->getInstantiatedFromMemberTemplate();
+      }
+
+      auto *RD = cast<CXXRecordDecl>(Pattern->getTemplatedDecl());
       if (!(RD->getDefinition() && RD->isAggregate()))
         return;
       QualType Ty = Context.getRecordType(RD);
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 0655d3633520676..839d508b911f063 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2418,6 +2418,9 @@ struct ConvertConstructorToDeductionGuideTransform {
     QualType Result = SemaRef.BuildFunctionType(DeducedType, ParamTypes, Loc,
                                                 DeductionGuideName, EPI);
     TypeSourceInfo *TSI = SemaRef.Context.getTrivialTypeSourceInfo(Result, Loc);
+    if (NestedPattern)
+      TSI = SemaRef.SubstType(TSI, OuterInstantiationArgs, Loc,
+                              DeductionGuideName);
 
     FunctionProtoTypeLoc FPTL =
         TSI->getTypeLoc().castAs<FunctionProtoTypeLoc>();
@@ -2425,9 +2428,13 @@ struct ConvertConstructorToDeductionGuideTransform {
     // Build the parameters, needed during deduction / substitution.
     SmallVector<ParmVarDecl*, 4> Params;
     for (auto T : ParamTypes) {
-      ParmVarDecl *NewParam = ParmVarDecl::Create(
-          SemaRef.Context, DC, Loc, Loc, nullptr, T,
-          SemaRef.Context.getTrivialTypeSourceInfo(T, Loc), SC_None, nullptr);
+      auto *TSI = SemaRef.Context.getTrivialTypeSourceInfo(T, Loc);
+      if (NestedPattern)
+        TSI = SemaRef.SubstType(TSI, OuterInstantiationArgs, Loc,
+                                DeclarationName());
+      ParmVarDecl *NewParam =
+          ParmVarDecl::Create(SemaRef.Context, DC, Loc, Loc, nullptr,
+                              TSI->getType(), TSI, SC_None, nullptr);
       NewParam->setScopeInfo(0, Params.size());
       FPTL.setParam(Params.size(), NewParam);
       Params.push_back(NewParam);
@@ -2670,8 +2677,14 @@ FunctionTemplateDecl *Sema::DeclareImplicitDeductionGuideFromInitList(
   if (BuildingDeductionGuides.isInvalid())
     return nullptr;
 
-  return cast<FunctionTemplateDecl>(
+  ClassTemplateDecl *Pattern =
+      Transform.NestedPattern ? Transform.NestedPattern : Transform.Template;
+  ContextRAII SavedContext(*this, Pattern->getTemplatedDecl());
+
+  auto *DG = cast<FunctionTemplateDecl>(
       Transform.buildSimpleDeductionGuide(ParamTypes));
+  SavedContext.pop();
+  return DG;
 }
 
 void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
diff --git a/clang/test/SemaTemplate/nested-implicit-deduction-guides.cpp b/clang/test/SemaTemplate/nested-implicit-deduction-guides.cpp
index c44ec6918c7afb1..38b6706595a1169 100644
--- a/clang/test/SemaTemplate/nested-implicit-deduction-guides.cpp
+++ b/clang/test/SemaTemplate/nested-implicit-deduction-guides.cpp
@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -std=c++20 -verify %s
-// expected-no-diagnostics
 
 template<class T> struct S {
     template<class U> struct N {
@@ -36,11 +35,14 @@ using NonTypeParam = decltype(ntp);
 using NonTypeParam = non_type_param<int>::B<int>;
 
 template<typename A, typename T>
-concept C = (sizeof(T) == sizeof(A));
+concept True = true;
+
+template<typename T>
+concept False = false;
 
 template<class X> struct concepts {
     template<class Y> struct B {
-        template<class K = X, C<K> Z> B(Y, Z);
+        template<class K = X, True<K> Z> B(Y, Z);
     };
 };
 
@@ -50,7 +52,7 @@ using Concepts = concepts<int>::B<int>;
 
 template<class X> struct requires_clause {
     template<class Y> struct B {
-        template<class Z> requires (sizeof(Z) == sizeof(X))
+        template<class Z> requires true
             B(Y, Z);
     };
 };
@@ -58,3 +60,27 @@ template<class X> struct requires_clause {
 requires_clause<int>::B req(1, 2);
 using RC = decltype(req);
 using RC = requires_clause<int>::B<int>;
+
+template<typename X> struct nested_init_list {
+    template<True<X> Y>
+    struct B {
+        X x;
+        Y y;
+    };
+
+    template<False F>
+    struct concept_fail { // #INIT_LIST_INNER_INVALID
+        X x;
+        F f;
+    };
+};
+
+nested_init_list<int>::B nil {1, 2};
+using NIL = decltype(nil);
+using NIL = nested_init_list<int>::B<int>;
+
+// expected-error@+1 {{no viable constructor or deduction guide for deduction of template arguments of 'concept_fail'}}
+nested_init_list<int>::concept_fail nil_invalid{1, ""};
+// expected-note@#INIT_LIST_INNER_INVALID {{candidate template ignored: substitution failure [with F = const char *]: constraints not satisfied for class template 'concept_fail' [with F = const char *]}}
+// expected-note@#INIT_LIST_INNER_INVALID {{candidate function template not viable: requires 1 argument, but 2 were provided}}
+// expected-note@#INIT_LIST_INNER_INVALID {{candidate function template not viable: requires 0 arguments, but 2 were provided}}

[cor3ntin]

@antangelo do you need me to merge this for you?

[antangelo]

Thanks for the review! Apologies for the delayed response but I'm available to merge this in now.