[Clang] Destructors should not be immediate-escalating

[cor3ntin]

We allow destructors to become immediate functions, which makes little sense as the standard disallow
consteval destructors

Related CWG issue cplusplus/CWG#780

Fixes #109096

[llvmbot]

@llvm/pr-subscribers-clang

Author: Corentin Jabot (cor3ntin)

Changes

We allow destructors to become immediate functions, which makes little sense as the standard disallow
consteval destructors

Related CWG issue cplusplus/CWG#780

Fixes #109096

---

Full diff: https://github.com/llvm/llvm-project/pull/163390.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/AST/Decl.cpp (+4)
• (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+1-1)
• (modified) clang/test/SemaCXX/cxx2b-consteval-propagate.cpp (+17)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 65b086caf3652..15bcfec1ba2cf 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -429,6 +429,7 @@ Bug Fixes to C++ Support
 - Suppress ``-Wdeprecated-declarations`` in implicitly generated functions. (#GH147293)
 - Fix a crash when deleting a pointer to an incomplete array (#GH150359).
 - Fixed a mismatched lambda scope bug when propagating up ``consteval`` within nested lambdas. (#GH145776)
+- Disallow immediate escalation in destructors. (#GH109096)
 - Fix an assertion failure when expression in assumption attribute
   (``[[assume(expr)]]``) creates temporary objects.
 - Fix the dynamic_cast to final class optimization to correctly handle
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index c7341552be365..69cbf6e21c7f7 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -3316,6 +3316,10 @@ bool FunctionDecl::isImmediateEscalating() const {
       CD && CD->isInheritingConstructor())
     return CD->getInheritedConstructor().getConstructor();
 
+  // Destructors are not immediate escalating.
+  if (isa<CXXDestructorDecl>(this))
+    return false;
+
   // - a function that results from the instantiation of a templated entity
   // defined with the constexpr specifier.
   TemplatedKind TK = getTemplatedKind();
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 3819f775811e5..720a276614fc9 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5727,7 +5727,7 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
   Function->setDeclarationNameLoc(NameLocPointsToPattern());
 
   EnterExpressionEvaluationContextForFunction EvalContext(
-      *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+      *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, Function);
 
   Qualifiers ThisTypeQuals;
   CXXRecordDecl *ThisContext = nullptr;
diff --git a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
index 6cf0e0251ab62..331fe8387e1c7 100644
--- a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
+++ b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
@@ -626,3 +626,20 @@ void fn() {
 }
 
 }
+
+
+namespace GH109096 {
+consteval void undefined();
+template <typename T>
+struct scope_exit {
+    T t;
+    constexpr ~scope_exit() { t(); }
+    // expected-error@-1 {{call to immediate function 'GH109096::(anonymous class)::operator()' is not a constant expression}} \
+    // expected-note@-1 {{implicit use of 'this' pointer is only allowed within the evaluation}}
+};
+
+scope_exit guard( // expected-note {{in instantiation of member function}}
+    []() { undefined(); }
+);
+
+}