[Clang] Make passing incomplete types to builtin type-traits a non-sfinae-friendly error #121333
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…inae-friendly error LWG3929 suggests that passing incomplete types to __is_base_of and other builtins supporting [meta.unary] should result in a non-sfinaeable error. This is consistent with GCC's behavior and avoid inconsistency when using a builtin instead of a standard trait in a concept-definition. Fixes llvm#121278
llvmbot
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@llvm/pr-subscribers-clang Author: cor3ntin (cor3ntin) ChangesLWG3929 suggests that passing incomplete types to __is_base_of and other builtins supporting [meta.unary] should result in a non-sfinaeable error. This is consistent with GCC's behavior and avoid inconsistency when using a builtin instead of a standard trait in a concept-definition. Fixes #121278 Full diff: https://github.com/llvm/llvm-project/pull/121333.diff 3 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b7da12bcf65818..e41d355ac424d6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -886,6 +886,9 @@ Bug Fixes to C++ Support
out of a module (which is the case e.g. in MSVC's implementation of ``std`` module). (#GH118218)
- Fixed a pack expansion issue in checking unexpanded parameter sizes. (#GH17042)
- Fixed a bug where captured structured bindings were modifiable inside non-mutable lambda (#GH95081)
+- Passing incomplete types to ``__is_base_of`` and other builtin type traits for which the corresponding
+ standard type trait mandates a complete type is now a hard (non-sfinae-friendly) error
+ (`LWG3929 <https://wg21.link/LWG3929>`__.) (#GH121278)
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 330ae045616aba..03fb7ca9bc3c3b 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -9361,7 +9361,7 @@ def note_inequality_comparison_to_or_assign : Note<
"use '|=' to turn this inequality comparison into an or-assignment">;
def err_incomplete_type_used_in_type_trait_expr : Error<
- "incomplete type %0 used in type trait expression">;
+ "incomplete type %0 used in type trait expression">, NoSFINAE;
// C++20 constinit and require_constant_initialization attribute
def warn_cxx20_compat_constinit : Warning<
diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp
index 91ef7786f11bb9..1b9e2ba6ff162f 100644
--- a/clang/test/SemaCXX/type-traits.cpp
+++ b/clang/test/SemaCXX/type-traits.cpp
@@ -5031,3 +5031,18 @@ void remove_all_extents() {
using SomeArray = int[1][2];
static_assert(__is_same(remove_all_extents_t<const SomeArray>, const int));
}
+
+namespace GH121278 {
+// https://cplusplus.github.io/LWG/lwg-active.html#3929
+#if __cplusplus >= 202002L
+template <typename B, typename D>
+concept C = __is_base_of(B, D);
+// expected-error@-1 {{incomplete type 'GH121278::S' used in type trait expression}}
+// expected-note@-2 {{while substituting template arguments into constraint expression here}}
+
+struct T;
+struct S;
+bool b = C<T, S>;
+// expected-note@-1 {{while checking the satisfaction of concept 'C<GH121278::T, GH121278::S>' requested here}}
+#endif
+}
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philnik777
approved these changes
Dec 31, 2024
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I confirmed this was the intent with LWG |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/51/builds/8555 Here is the relevant piece of the build log for the reference |
paulhuggett
pushed a commit
to paulhuggett/llvm-project
that referenced
this pull request
Jan 7, 2025
…inae-friendly error (llvm#121333) LWG3929 suggests that passing incomplete types to __is_base_of and other builtins supporting [meta.unary] should result in a non-sfinaeable error. This is consistent with GCC's behavior and avoid inconsistency when using a builtin instead of a standard trait in a concept-definition. Fixes llvm#121278
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LWG3929 suggests that passing incomplete types to __is_base_of and other builtins supporting [meta.unary] should result in a non-sfinaeable error.
This is consistent with GCC's behavior and avoid inconsistency when using a builtin instead of a standard trait in a concept-definition.
Fixes #121278