EricWF created this revision.
EricWF added reviewers: rsmith, james.dennett, gromer.
Some style guides want to allow using CTAD only on types that "opt-in"; i.e. on
types that are designed to support it and not just types that *happen* to work
with it.
This patch implements the `-Wimplicit-ctad` warning, which is off by default,
which warns when CTAD is used on a type that does not define any deduction
guides.
Repository:
rC Clang
https://reviews.llvm.org/D56731
Files:
include/clang/Basic/DiagnosticGroups.td
include/clang/Basic/DiagnosticSemaKinds.td
lib/Sema/SemaInit.cpp
test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
Index: test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
===================================================================
--- test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
+++ test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
@@ -409,6 +409,35 @@
}
+#pragma clang diagnostic push
+#pragma clang diagnostic warning "-Wimplicit-ctad"
+namespace test_implicit_ctad_warning {
+
+template <class T>
+struct Tag {};
+
+template <class T>
+struct NoExplicit {
+ NoExplicit(T) {}
+ NoExplicit(T, int) {}
+};
+
+// expected-warning@+1 {{class template argument deduction for 'NoExplicit' that has no user defined deduction guides}}
+NoExplicit ne(42);
+
+template <class U>
+struct HasExplicit {
+ HasExplicit(U) {}
+ HasExplicit(U, int) {}
+};
+template <class U> HasExplicit(U, int) -> HasExplicit<Tag<U>>;
+
+HasExplicit he(42);
+
+
+}
+#pragma clang diagnostic pop
+
#else
// expected-no-diagnostics
Index: lib/Sema/SemaInit.cpp
===================================================================
--- lib/Sema/SemaInit.cpp
+++ lib/Sema/SemaInit.cpp
@@ -9264,9 +9264,15 @@
OverloadCandidateSet Candidates(Kind.getLocation(),
OverloadCandidateSet::CSK_Normal);
OverloadCandidateSet::iterator Best;
+
+ // Record if at least a user-declared deduction guide was considered
+ bool HasUserDeclaredDeductionGuideCandidate = false;
+
auto tryToResolveOverload =
[&](bool OnlyListConstructors) -> OverloadingResult {
Candidates.clear(OverloadCandidateSet::CSK_Normal);
+ HasUserDeclaredDeductionGuideCandidate = false;
+
for (auto I = Guides.begin(), E = Guides.end(); I != E; ++I) {
NamedDecl *D = (*I)->getUnderlyingDecl();
if (D->isInvalidDecl())
@@ -9278,6 +9284,8 @@
if (!GD)
continue;
+ HasUserDeclaredDeductionGuideCandidate |= !GD->isImplicit();
+
// C++ [over.match.ctor]p1: (non-list copy-initialization from non-class)
// For copy-initialization, the candidate functions are all the
// converting constructors (12.3.1) of that class.
@@ -9430,5 +9438,14 @@
Diag(TSInfo->getTypeLoc().getBeginLoc(),
diag::warn_cxx14_compat_class_template_argument_deduction)
<< TSInfo->getTypeLoc().getSourceRange() << 1 << DeducedType;
+
+
+ // -Wimplicit-ctad: Warn if CTAD was used on a
+ if (!HasUserDeclaredDeductionGuideCandidate) {
+ Diag(TSInfo->getTypeLoc().getBeginLoc(),
+ diag::warn_class_template_argument_deduction_no_user_defined_guides)
+ << TemplateName;
+ }
+
return DeducedType;
}
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -2125,6 +2125,9 @@
"class template argument deduction is incompatible with C++ standards "
"before C++17%select{|; for compatibility, use explicit type name %1}0">,
InGroup<CXXPre17Compat>, DefaultIgnore;
+def warn_class_template_argument_deduction_no_user_defined_guides : Warning<
+ "class template argument deduction for %0 that has no user defined deduction guides" >,
+ InGroup<ImplicitCTADUsage>, DefaultIgnore;
// C++14 deduced return types
def err_auto_fn_deduction_failure : Error<
Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -1050,3 +1050,5 @@
// A group for cross translation unit static analysis related warnings.
def CrossTU : DiagGroup<"ctu">;
+
+def ImplicitCTADUsage : DiagGroup<"implicit-ctad">;
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