[C++17] Fix PR34970 - tweak overload resolution for class template deduction-guides in line with WG21's p0620r0.
In order to identify the copy deduction candidate, I considered two approaches:
- attempt to determine whether an implicit guide is a copy deduction candidate by checking certain properties of its subsituted parameter during overload-resolution.
- using one of the many bits (WillHaveBody) from FunctionDecl (that CXXDeductionGuideDecl inherits from) that are otherwise irrelevant for deduction guides
After some brittle gymnastics w the first strategy, I settled on the second, although to avoid confusion and to give that bit a better name, i turned it into a member of an anonymous union.
Given this identification 'bit', the tweak to overload resolution was a simple reordering of the deduction guide checks (in SemaOverload.cpp::isBetterOverloadCandidate), in-line with Jason Merrill's p0620r0 drafting which made it into the working paper. Concordant with that, I made sure the copy deduction candidate is always added.
References:
See https://bugs.llvm.org/show_bug.cgi?id=34970
See http://wg21.link/p0620r0
llvm-svn: 316292
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 186a618..d93fbd7 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1651,11 +1651,13 @@
}
FunctionDecl *Function;
- if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D))
+ if (auto *DGuide = dyn_cast<CXXDeductionGuideDecl>(D)) {
Function = CXXDeductionGuideDecl::Create(
- SemaRef.Context, DC, D->getInnerLocStart(), DGuide->isExplicit(),
- D->getNameInfo(), T, TInfo, D->getSourceRange().getEnd());
- else {
+ SemaRef.Context, DC, D->getInnerLocStart(), DGuide->isExplicit(),
+ D->getNameInfo(), T, TInfo, D->getSourceRange().getEnd());
+ if (DGuide->isCopyDeductionCandidate())
+ cast<CXXDeductionGuideDecl>(Function)->setIsCopyDeductionCandidate();
+ } else {
Function = FunctionDecl::Create(
SemaRef.Context, DC, D->getInnerLocStart(), D->getNameInfo(), T, TInfo,
D->getCanonicalDecl()->getStorageClass(), D->isInlineSpecified(),