[clang] [clang][bytecode] Silently reject ctors of invalid decls (PR #128290)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/128290

The follow-up diagnostic would otherwise be:

array.cpp:111:33: note: undefined constructor '(unnamed struct at array.cpp:111:11)' cannot be used in a constant expression array.cpp:111:11: note: declared here
  111 | constexpr struct { Unknown U; } InvalidCtor;
      |           ^

... and complaining about the undefined constructor of a class that is invalid anyway doesn't make much sense.

>From 5128abac545f1e86042cf1aa72374df070e4dbc2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Sat, 22 Feb 2025 07:29:02 +0100
Subject: [PATCH] [clang][bytecode] Silently reject ctors of invalid decls

The follow-up diagnostic would otherwise be:

array.cpp:111:33: note: undefined constructor '(unnamed struct at array.cpp:111:11)' cannot be used in a constant expression array.cpp:111:11: note: declared here
  111 | constexpr struct { Unknown U; } InvalidCtor;
      |           ^

... and complaining about the undefined constructor of a class that is invalid anyway doesn't make much sense.
---
 clang/lib/AST/ByteCode/Interp.cpp   | 5 +++++
 clang/test/AST/ByteCode/records.cpp | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/clang/lib/AST/ByteCode/Interp.cpp b/clang/lib/AST/ByteCode/Interp.cpp
index c07690a3d941c..dfa59a50b2711 100644
--- a/clang/lib/AST/ByteCode/Interp.cpp
+++ b/clang/lib/AST/ByteCode/Interp.cpp
@@ -732,6 +732,11 @@ bool CheckCallable(InterpState &S, CodePtr OpPC, const Function *F) {
         DiagDecl = CD = Inherited;
     }
 
+    // Silently reject constructors of invalid classes. The invalid class
+    // has been rejected elsewhere before.
+    if (CD && CD->getParent()->isInvalidDecl())
+      return false;
+
     // FIXME: If DiagDecl is an implicitly-declared special member function
     // or an inheriting constructor, we should be much more explicit about why
     // it's not constexpr.
diff --git a/clang/test/AST/ByteCode/records.cpp b/clang/test/AST/ByteCode/records.cpp
index a13f30cd23119..608b94e55560a 100644
--- a/clang/test/AST/ByteCode/records.cpp
+++ b/clang/test/AST/ByteCode/records.cpp
@@ -1734,3 +1734,8 @@ namespace DeadUpcast {
   static_assert(foo(), "");
 }
 #endif
+
+namespace CtorOfInvalidClass {
+  constexpr struct { Unknown U; } InvalidCtor; // both-error {{unknown type name 'Unknown'}} \
+                                               // both-error {{must be initialized by a constant expression}}
+}