[Clang] Add captures to the instantiation scope of lambda call operators

Like concepts checking, a trailing return type of a lambda
in a dependent context may refer to captures in which case
they may need to be rebuilt, so the map of local decl
should include captures.

This patch reveal a pre-existing issue.
`this` is always recomputed by TreeTransform.

`*this` (like all captures) only become `const`
after the parameter list.

However, if try to recompute the value of `this` (in a parameter)
during template instantiation while determining the type of the call operator,
we will determine  it to be const (unless the lambda is mutable).

There is no good way to know at that point that we are in a parameter
or not, the easiest/best solution is to transform the type of this.

Note that doing so break a handful of HLSL tests.
So this is a prototype at this point.

Fixes #65067
Fixes #63675

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D159126

clang/docs/ReleaseNotes.rst

@@ -270,6 +270,11 @@ Bug Fixes to C++ Support
 - Fix crash when parsing the requires clause of some generic lambdas.
   (`#64689 <https://github.com/llvm/llvm-project/issues/64689>`_)
 
+- Fix crash when the trailing return type of a generic and dependent
+  lambda refers to an init-capture.
+  (`#65067 <https://github.com/llvm/llvm-project/issues/65067>`_` and
+   `#63675 <https://github.com/llvm/llvm-project/issues/63675>`_`)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.

clang/include/clang/Sema/Sema.h

@@ -7365,6 +7365,14 @@ public:
 
   sema::LambdaScopeInfo *RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator);
 
+  class LambdaScopeForCallOperatorInstantiationRAII
+      : private FunctionScopeRAII {
+  public:
+    LambdaScopeForCallOperatorInstantiationRAII(
+        Sema &SemasRef, FunctionDecl *FD, MultiLevelTemplateArgumentList MLTAL,
+        LocalInstantiationScope &Scope);
+  };
+
   /// Check whether the given expression is a valid constraint expression.
   /// A diagnostic is emitted if it is not, false is returned, and
   /// PossibleNonPrimary will be set to true if the failure might be due to a

clang/lib/Sema/SemaConcept.cpp

@@ -600,11 +600,6 @@ bool Sema::SetupConstraintScope(
       if (addInstantiatedParametersToScope(FD, FromMemTempl->getTemplatedDecl(),
                                            Scope, MLTAL))
         return true;
-      // Make sure the captures are also added to the instantiation scope.
-      if (isLambdaCallOperator(FD) &&
-          addInstantiatedCapturesToScope(FD, FromMemTempl->getTemplatedDecl(),
-                                         Scope, MLTAL))
-        return true;
     }
 
     return false;
@@ -629,11 +624,6 @@ bool Sema::SetupConstraintScope(
     // child-function.
     if (addInstantiatedParametersToScope(FD, InstantiatedFrom, Scope, MLTAL))
       return true;
-
-    // Make sure the captures are also added to the instantiation scope.
-    if (isLambdaCallOperator(FD) &&
-        addInstantiatedCapturesToScope(FD, InstantiatedFrom, Scope, MLTAL))
-      return true;
   }
 
   return false;
@@ -712,20 +702,8 @@ bool Sema::CheckFunctionConstraints(const FunctionDecl *FD,
   }
   CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
 
-  // When checking the constraints of a lambda, we need to restore a
-  // LambdaScopeInfo populated with correct capture information so that the type
-  // of a variable referring to a capture is correctly const-adjusted.
-  FunctionScopeRAII FuncScope(*this);
-  if (isLambdaCallOperator(FD)) {
-    LambdaScopeInfo *LSI = RebuildLambdaScopeInfo(
-        const_cast<CXXMethodDecl *>(cast<CXXMethodDecl>(FD)));
-    // Constraints are checked from the parent context of the lambda, so we set
-    // AfterParameterList to false, so that `tryCaptureVariable` finds
-    // explicit captures in the appropriate context.
-    LSI->AfterParameterList = false;
-  } else {
-    FuncScope.disable();
-  }
+  LambdaScopeForCallOperatorInstantiationRAII LambdaScope(
+      *this, const_cast<FunctionDecl *>(FD), *MLTAL, Scope);
 
   return CheckConstraintSatisfaction(
       FD, {FD->getTrailingRequiresClause()}, *MLTAL,
@@ -913,15 +891,10 @@ bool Sema::CheckInstantiatedFunctionTemplateConstraints(
     ThisQuals = Method->getMethodQualifiers();
     Record = Method->getParent();
   }
-  CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
-  FunctionScopeRAII FuncScope(*this);
 
-  if (isLambdaCallOperator(Decl)) {
-    LambdaScopeInfo *LSI = RebuildLambdaScopeInfo(cast<CXXMethodDecl>(Decl));
-    LSI->AfterParameterList = false;
-  } else {
-    FuncScope.disable();
-  }
+  CXXThisScopeRAII ThisScope(*this, Record, ThisQuals, Record != nullptr);
+  LambdaScopeForCallOperatorInstantiationRAII LambdaScope(
+      *this, const_cast<FunctionDecl *>(Decl), *MLTAL, Scope);
 
   llvm::SmallVector<Expr *, 1> Converted;
   return CheckConstraintSatisfaction(Template, TemplateAC, Converted, *MLTAL,

clang/lib/Sema/SemaDecl.cpp

@@ -15382,6 +15382,10 @@ LambdaScopeInfo *Sema::RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator) {
   LSI->CallOperator = CallOperator;
   LSI->Lambda = LambdaClass;
   LSI->ReturnType = CallOperator->getReturnType();
+  // This function in calls in situation where the context of the call operator
+  // is not entered, so we set AfterParameterList to false, so that
+  // `tryCaptureVariable` finds explicit captures in the appropriate context.
+  LSI->AfterParameterList = false;
   const LambdaCaptureDefault LCD = LambdaClass->getLambdaCaptureDefault();
 
   if (LCD == LCD_None)

clang/lib/Sema/SemaLambda.cpp

@@ -20,6 +20,7 @@
 #include "clang/Sema/ScopeInfo.h"
 #include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/SemaLambda.h"
+#include "clang/Sema/Template.h"
 #include "llvm/ADT/STLExtras.h"
 #include <optional>
 using namespace clang;
@@ -2254,3 +2255,34 @@ ExprResult Sema::BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
 
   return BuildBlock;
 }
+
+Sema::LambdaScopeForCallOperatorInstantiationRAII::
+    LambdaScopeForCallOperatorInstantiationRAII(
+        Sema &SemasRef, FunctionDecl *FD, MultiLevelTemplateArgumentList MLTAL,
+        LocalInstantiationScope &Scope)
+    : FunctionScopeRAII(SemasRef) {
+  if (!isLambdaCallOperator(FD)) {
+    FunctionScopeRAII::disable();
+    return;
+  }
+
+  if (FD->isTemplateInstantiation() && FD->getPrimaryTemplate()) {
+    FunctionTemplateDecl *PrimaryTemplate = FD->getPrimaryTemplate();
+    if (const auto *FromMemTempl =
+            PrimaryTemplate->getInstantiatedFromMemberTemplate()) {
+      SemasRef.addInstantiatedCapturesToScope(
+          FD, FromMemTempl->getTemplatedDecl(), Scope, MLTAL);
+    }
+  }
+
+  else if (FD->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization ||
+           FD->getTemplatedKind() == FunctionDecl::TK_DependentNonTemplate) {
+    FunctionDecl *InstantiatedFrom =
+        FD->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization
+            ? FD->getInstantiatedFromMemberFunction()
+            : FD->getInstantiatedFromDecl();
+    SemasRef.addInstantiatedCapturesToScope(FD, InstantiatedFrom, Scope, MLTAL);
+  }
+
+  SemasRef.RebuildLambdaScopeInfo(cast<CXXMethodDecl>(FD));
+}

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -2426,6 +2426,9 @@ Decl *TemplateDeclInstantiator::VisitCXXMethodDecl(
       cast<Decl>(Owner)->isDefinedOutsideFunctionOrMethod());
   LocalInstantiationScope Scope(SemaRef, MergeWithParentScope);
 
+  Sema::LambdaScopeForCallOperatorInstantiationRAII LambdaScope(
+      SemaRef, const_cast<CXXMethodDecl *>(D), TemplateArgs, Scope);
+
   // Instantiate enclosing template arguments for friends.
   SmallVector<TemplateParameterList *, 4> TempParamLists;
   unsigned NumTempParamLists = 0;

clang/lib/Sema/TreeTransform.h

@@ -12325,7 +12325,16 @@ TreeTransform<Derived>::TransformCXXNullPtrLiteralExpr(
 template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformCXXThisExpr(CXXThisExpr *E) {
-  QualType T = getSema().getCurrentThisType();
+
+  // In lambdas, the qualifiers of the type depends of where in
+  // the call operator `this` appear, and we do not have a good way to
+  // rebuild this information, so we transform the type.
+  //
+  // In other contexts, the type of `this` may be overrided
+  // for type deduction, so we need to recompute it.
+  QualType T = getSema().getCurLambda() ?
+                   getDerived().TransformType(E->getType())
+                 : getSema().getCurrentThisType();
 
   if (!getDerived().AlwaysRebuild() && T == E->getType()) {
     // Mark it referenced in the new context regardless.

clang/test/SemaCXX/lambda-capture-type-deduction.cpp

@@ -260,3 +260,40 @@ void f(int) {
 void test() { f<int>(0);  }
 
 }
+
+namespace GH65067 {
+
+template <typename> class a {
+public:
+  template <typename b> void c(b f) { d<int>(f)(0); }
+  template <typename, typename b> auto d(b f) {
+    return [f = f](auto arg) -> a<decltype(f(arg))> { return {}; };
+  }
+};
+a<void> e;
+auto fn1() {
+  e.c([](int) {});
+}
+
+}
+
+namespace GH63675 {
+
+template <class _Tp> _Tp __declval();
+struct __get_tag {
+  template <class _Tag> void operator()(_Tag);
+};
+template <class _ImplFn> struct __basic_sender {
+  using __tag_t = decltype(__declval<_ImplFn>()(__declval<__get_tag>()));
+  _ImplFn __impl_;
+};
+auto __make_basic_sender = []<class... _Children>(
+                               _Children... __children) {
+  return __basic_sender{[... __children = __children]<class _Fun>(
+                     _Fun __fun) -> decltype(__fun(__children...)) {}};
+};
+void __trans_tmp_1() {
+  __make_basic_sender(__trans_tmp_1);
+}
+
+}

clang/test/SemaCXX/this-type-deduction-concept.cpp

@@ -0,0 +1,54 @@
+
+// This test case came up in the review of
+// https://reviews.llvm.org/D159126
+// when transforming `this` within a
+// requires expression, we need to make sure
+// the type of this (and its qualifiers) is respected.
+namespace D159126 {
+
+template <class _Tp>
+concept __member_begin = requires(_Tp __t) {
+  __t.begin();
+};
+
+struct {
+  template <class _Tp>
+  requires __member_begin<_Tp>
+  auto operator()(_Tp &&) {}
+} inline begin;
+
+template <class>
+concept range = requires {
+  begin;
+};
+
+template <class _Tp>
+concept __can_compare_begin = requires(_Tp __t) {
+  begin(__t);
+};
+
+struct {
+  template <__can_compare_begin _Tp> void operator()(_Tp &&);
+} empty;
+
+template <range _Rp> struct owning_view {
+  _Rp __r_;
+public:
+  void empty() const requires requires { empty(__r_); };
+};
+
+template <class T>
+concept HasEmpty = requires(T t) {
+  t.empty();
+};
+
+struct ComparableIters {
+    void begin();
+};
+
+static_assert(HasEmpty<owning_view<ComparableIters&>>);
+static_assert(HasEmpty<owning_view<ComparableIters&&>>);
+static_assert(!HasEmpty<owning_view<const ComparableIters&>>);
+static_assert(!HasEmpty<owning_view<const ComparableIters&&>>);
+
+}