[C++23] Fix infinite recursion (Clang 19.x regression)

[AaronBallman]

d469794 was fixing an issue with triggering vtable instantiations, but it accidentally introduced infinite recursion when the type to be checked is the same as the type used in a base specifier or field declaration.

Fixes #104802

[AaronBallman]

I intentionally did not add a release note as I would like to get this into the 19.x release.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

d469794 was fixing an issue with triggering vtable instantiations, but it accidentally introduced infinite recursion when the type to be checked is the same as the type used in a base specifier or field declaration.

Fixes #104802

---

Full diff: https://github.com/llvm/llvm-project/pull/104829.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaDeclCXX.cpp (+2-2)
• (modified) clang/test/SemaCXX/gh102293.cpp (+12-1)

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index e05595e565d54a..c1fc61c263791a 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -7057,10 +7057,10 @@ void Sema::CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record) {
           return false;
 
         for (const CXXBaseSpecifier &B : RD->bases())
-          if (!Check(B.getType(), Check))
+          if (B.getType() != T && !Check(B.getType(), Check))
             return false;
         for (const FieldDecl *FD : RD->fields())
-          if (!Check(FD->getType(), Check))
+          if (FD->getType() != T && !Check(FD->getType(), Check))
             return false;
         return true;
       };
diff --git a/clang/test/SemaCXX/gh102293.cpp b/clang/test/SemaCXX/gh102293.cpp
index 30629fc03bf6a9..ece9dfd21da11c 100644
--- a/clang/test/SemaCXX/gh102293.cpp
+++ b/clang/test/SemaCXX/gh102293.cpp
@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
-// expected-no-diagnostics
 
 template <typename T> static void destroy() {
     T t;
@@ -20,3 +19,15 @@ struct S : HasVT {
   HasD<> v;
 };
 
+// Ensure we don't get infinite recursion from the check, however. See GH104802
+namespace GH104802 {
+class foo {       // expected-note {{definition of 'GH104802::foo' is not complete until the closing '}'}}
+  foo a;          // expected-error {{field has incomplete type 'foo'}}
+  virtual int c();
+};
+
+class bar : bar { // expected-error {{base class has incomplete type}} \
+                     expected-note {{definition of 'GH104802::bar' is not complete until the closing '}'}}
+  virtual int c();
+};
+}

[shafik]

Should we also test an alias declaration?

[AaronBallman]

No need; typedefs already test type canonicalization.

[AaronBallman]

/cherry-pick 435cb0d

[llvmbot]

/pull-request #104858