rZhBoYao created this revision.
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1. '-Wctad-copy-not-wrap' warns when copy deduction candidate is selected in
CTAD, and the initialization is a direct-initialization. The warning is
suppressed when the class template is in a system header and has at least one
explicit deduction guide.
2. Add a group '-Wctad' which incldues '-Wctad-copy-not-wrap' and
'-Wctad-maybe-unsupported'.
Fixes #63288
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D155475
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaInit.cpp
clang/test/SemaTemplate/ctad.cpp
Index: clang/test/SemaTemplate/ctad.cpp
===================================================================
--- clang/test/SemaTemplate/ctad.cpp
+++ clang/test/SemaTemplate/ctad.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++17 -verify %s
+// RUN: %clang_cc1 -std=c++23 -verify %s
namespace pr41427 {
template <typename T> class A {
@@ -44,3 +44,32 @@
};
D z = {Z(), {}};
}
+
+namespace warn_ctad_copy {
+#pragma clang diagnostic push
+#pragma clang diagnostic warning "-Wctad-copy-not-wrap"
+// like std::revrse_iterator, the motivating example
+template <typename T> struct CTAD {
+ template <typename From>
+ requires(!__is_same(From, T) && __is_convertible_to(From, T))
+ CTAD(const CTAD<From>&) {} // #1
+ CTAD(T) {}
+};
+CTAD(void) -> CTAD<void>; // does not suppress -Wctad-copy-not-wrap
+
+CTAD<int>& fc1();
+CTAD<double> fc2(),
+ c1 = fc1(); // uses #1
+CTAD c2 = fc2(), // OK, uses copy-initialization
+ c3 = CTAD(4.2), // OK, copy deduction candidate not selected
+ c4{fc2()}; // test prvalue expression
+// expected-warning@-1{{move-constructing not wrapping a 'CTAD<double>' \
+(aka 'warn_ctad_copy::CTAD<double>'), use copy-list-initialization to suppress this warning}}
+CTAD c5 = CTAD{fc1()}, // test lvalue expression
+// expected-warning@-1{{copy-constructing not wrapping a 'CTAD<int>' \
+(aka 'warn_ctad_copy::CTAD<int>'), use copy-list-initialization to suppress this warning}}
+ c6 = CTAD((CTAD<int>&&)c5); // test xvalue expression
+// expected-warning@-1{{move-constructing not wrapping a 'CTAD<int>' \
+(aka 'warn_ctad_copy::CTAD<int>'), use copy-initialization to suppress this warning}}
+#pragma clang diagnostic pop
+} // namespace warn_ctad_copy
Index: clang/lib/Sema/SemaInit.cpp
===================================================================
--- clang/lib/Sema/SemaInit.cpp
+++ clang/lib/Sema/SemaInit.cpp
@@ -19,6 +19,7 @@
#include "clang/Basic/CharInfo.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
+#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/Designator.h"
#include "clang/Sema/EnterExpressionEvaluationContext.h"
#include "clang/Sema/Initialization.h"
@@ -10908,6 +10909,17 @@
diag::warn_cxx14_compat_class_template_argument_deduction)
<< TSInfo->getTypeLoc().getSourceRange() << 1 << DeducedType;
+ // Warn if the copy deduction candidate is selected in direct-initialization.
+ auto DiagnoseCTADCopy = [&] {
+ if (auto IK = Kind.getKind();
+ IK <= InitializationKind::IK_DirectList &&
+ cast<CXXDeductionGuideDecl>(Best->Function)
+ ->getDeductionCandidateKind() == DeductionCandidate::Copy) {
+ Diag(Kind.getLocation(), diag::warn_ctad_copy_not_wrap)
+ << Inits.front()->isLValue() << DeducedType << !ListInit;
+ }
+ };
+
// Warn if CTAD was used on a type that does not have any user-defined
// deduction guides.
if (!FoundDeductionGuide) {
@@ -10915,6 +10927,9 @@
diag::warn_ctad_maybe_unsupported)
<< TemplateName;
Diag(Template->getLocation(), diag::note_suppress_ctad_maybe_unsupported);
+ DiagnoseCTADCopy();
+ } else if (!PP.getSourceManager().isInSystemHeader(Template->getLocation())) {
+ DiagnoseCTADCopy();
}
return DeducedType;
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2488,6 +2488,10 @@
InGroup<CTADMaybeUnsupported>, DefaultIgnore;
def note_suppress_ctad_maybe_unsupported : Note<
"add a deduction guide to suppress this warning">;
+def warn_ctad_copy_not_wrap : Warning<
+ "%select{move|copy}0-constructing not wrapping a %1, "
+ "use copy-%select{list-|}2initialization to suppress this warning">,
+ InGroup<CTADCopyNotWrap>, DefaultIgnore;
// C++14 deduced return types
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -1380,6 +1380,9 @@
def CrossTU : DiagGroup<"ctu">;
def CTADMaybeUnsupported : DiagGroup<"ctad-maybe-unsupported">;
+def CTADCopyNotWrap : DiagGroup<"ctad-copy-not-wrap">;
+def CTAD : DiagGroup<"ctad", [CTADMaybeUnsupported,
+ CTADCopyNotWrap]>;
def FortifySource : DiagGroup<"fortify-source">;
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -421,6 +421,20 @@
- ``-Wformat`` will no longer suggest a no-op fix-it for fixing scoped enum format
warnings. Instead, it will suggest casting the enum object to the type specified
in the format string.
+- Clang now warns when the class template argument deduction deduces the type to be the same as the initializer
+ of a direct-initialization. Turn this on with ``-Wctad-copy-not-wrap``. If the class template is in a system header
+ and a reachable explicit deduction guide is present, the warning is suppressed.
+ (`#63288 <https://github.com/llvm/llvm-project/issues/63288>`_).
+
+ .. code-block:: c++
+
+ auto vec = std::vector{42};
+ auto v = std::vector{vec};
+ // no warning, user-defined deduction guides exist and the template is in a system header
+
+ std::reverse_iterator it1 = v.rbegin(); // no warning, copy-initialization
+ auto it2 = std::reverse_iterator{v.rbegin()}; // warns, the intent might be the next line
+ auto it3 = std::reverse_iterator<decltype(v.rbegin())>(v.rbegin()); // no warning, no CTAD
Bug Fixes in This Version
-------------------------
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