rnk created this revision.
rnk added a reviewer: rsmith.
Herald added a project: clang.
Allow implementations to provide complete definitions of
std::tuple_size<T>, but to omit the 'value' member to signal that T is
not tuple-like. The Microsoft standard library implements
std::tuple_size<const T> this way.
If the value member exists, clang still validates that it is an ICE, but
if it does not, then the type is considered to not be tuple-like.
Fixes PR33236
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D66040
Files:
clang/lib/Sema/SemaDeclCXX.cpp
clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
Index: clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
===================================================================
--- clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
+++ clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
@@ -12,7 +12,7 @@
struct Bad1 { int a, b; };
template<> struct std::tuple_size<Bad1> {};
-void no_tuple_size_3() { auto [x, y] = Bad1(); } // expected-error {{cannot
decompose this type; 'std::tuple_size<Bad1>::value' is not a valid integral
constant expression}}
+void no_tuple_size_3() { auto [x, y] = Bad1(); } // ok, omitting value is
valid after DR2386
struct Bad2 {};
template<> struct std::tuple_size<Bad2> { const int value = 5; };
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -1030,8 +1030,10 @@
TemplateArgumentListInfo Args(Loc, Loc);
Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
- // If there's no tuple_size specialization, it's not tuple-like.
- if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/0))
+ // If there's no tuple_size specialization or the lookup of 'value' is empty,
+ // it's not tuple-like.
+ if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/ 0) ||
+ R.empty())
return IsTupleLike::NotTupleLike;
// If we get this far, we've committed to the tuple interpretation, but
@@ -1048,11 +1050,6 @@
}
} Diagnoser(R, Args);
- if (R.empty()) {
- Diagnoser.diagnoseNotICE(S, Loc, SourceRange());
- return IsTupleLike::Error;
- }
-
ExprResult E =
S.BuildDeclarationNameExpr(CXXScopeSpec(), R, /*NeedsADL*/false);
if (E.isInvalid())
Index: clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
===================================================================
--- clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
+++ clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
@@ -12,7 +12,7 @@
struct Bad1 { int a, b; };
template<> struct std::tuple_size<Bad1> {};
-void no_tuple_size_3() { auto [x, y] = Bad1(); } // expected-error {{cannot decompose this type; 'std::tuple_size<Bad1>::value' is not a valid integral constant expression}}
+void no_tuple_size_3() { auto [x, y] = Bad1(); } // ok, omitting value is valid after DR2386
struct Bad2 {};
template<> struct std::tuple_size<Bad2> { const int value = 5; };
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -1030,8 +1030,10 @@
TemplateArgumentListInfo Args(Loc, Loc);
Args.addArgument(getTrivialTypeTemplateArgument(S, Loc, T));
- // If there's no tuple_size specialization, it's not tuple-like.
- if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/0))
+ // If there's no tuple_size specialization or the lookup of 'value' is empty,
+ // it's not tuple-like.
+ if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/ 0) ||
+ R.empty())
return IsTupleLike::NotTupleLike;
// If we get this far, we've committed to the tuple interpretation, but
@@ -1048,11 +1050,6 @@
}
} Diagnoser(R, Args);
- if (R.empty()) {
- Diagnoser.diagnoseNotICE(S, Loc, SourceRange());
- return IsTupleLike::Error;
- }
-
ExprResult E =
S.BuildDeclarationNameExpr(CXXScopeSpec(), R, /*NeedsADL*/false);
if (E.isInvalid())
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