r343279 - [cxx2a] P0624R2: Lambdas with no capture-default are
David Blaikie via cfe-commits
cfe-commits at lists.llvm.org
Mon Oct 1 10:23:17 PDT 2018
Excellent, excellent - thanks!
On Mon, Oct 1, 2018 at 10:22 AM Richard Smith <richard at metafoo.co.uk> wrote:
> On Mon, 1 Oct 2018, 09:55 David Blaikie via cfe-commits, <
> cfe-commits at lists.llvm.org> wrote:
>
>> Awesome - should/does this mean stateless lambdas can be used in
>> uninitialized contexts?
>>
>> std::set<foo, decltype([](const foo& LHS, const foo& RHS) { return ...;
>> })> s;
>>
>> Would be kind of neat/handy (so you didn't have to pass in the comparator
>> on construction, etc)
>>
>
> Not quite: that also needs p0315r4, but that's coming in C++20 too.
>
> On Thu, Sep 27, 2018 at 3:48 PM Richard Smith via cfe-commits <
>> cfe-commits at lists.llvm.org> wrote:
>>
>>> Author: rsmith
>>> Date: Thu Sep 27 15:47:04 2018
>>> New Revision: 343279
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=343279&view=rev
>>> Log:
>>> [cxx2a] P0624R2: Lambdas with no capture-default are
>>> default-constructible and assignable.
>>>
>>> Added:
>>> cfe/trunk/test/SemaCXX/cxx2a-lambda-default-ctor-assign.cpp
>>> Modified:
>>> cfe/trunk/include/clang/AST/DeclCXX.h
>>> cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>>> cfe/trunk/lib/AST/DeclCXX.cpp
>>> cfe/trunk/lib/Sema/SemaDeclCXX.cpp
>>> cfe/trunk/lib/Sema/SemaExpr.cpp
>>> cfe/trunk/test/SemaCXX/cxx17-compat.cpp
>>> cfe/trunk/www/cxx_status.html
>>>
>>> Modified: cfe/trunk/include/clang/AST/DeclCXX.h
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/DeclCXX.h?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/include/clang/AST/DeclCXX.h (original)
>>> +++ cfe/trunk/include/clang/AST/DeclCXX.h Thu Sep 27 15:47:04 2018
>>> @@ -974,10 +974,7 @@ public:
>>> bool needsImplicitDefaultConstructor() const {
>>> return !data().UserDeclaredConstructor &&
>>> !(data().DeclaredSpecialMembers & SMF_DefaultConstructor) &&
>>> - // C++14 [expr.prim.lambda]p20:
>>> - // The closure type associated with a lambda-expression
>>> has no
>>> - // default constructor.
>>> - !isLambda();
>>> + (!isLambda() || lambdaIsDefaultConstructibleAndAssignable());
>>> }
>>>
>>> /// Determine whether this class has any user-declared constructors.
>>> @@ -1167,10 +1164,7 @@ public:
>>> !hasUserDeclaredCopyAssignment() &&
>>> !hasUserDeclaredMoveConstructor() &&
>>> !hasUserDeclaredDestructor() &&
>>> - // C++1z [expr.prim.lambda]p21: "the closure type has a
>>> deleted copy
>>> - // assignment operator". The intent is that this counts as a
>>> user
>>> - // declared copy assignment, but we do not model it that way.
>>> - !isLambda();
>>> + (!isLambda() || lambdaIsDefaultConstructibleAndAssignable());
>>> }
>>>
>>> /// Determine whether we need to eagerly declare a move assignment
>>> @@ -1210,6 +1204,10 @@ public:
>>> /// a template).
>>> bool isGenericLambda() const;
>>>
>>> + /// Determine whether this lambda should have an implicit default
>>> constructor
>>> + /// and copy and move assignment operators.
>>> + bool lambdaIsDefaultConstructibleAndAssignable() const;
>>> +
>>> /// Retrieve the lambda call operator of the closure type
>>> /// if this is a closure type.
>>> CXXMethodDecl *getLambdaCallOperator() const;
>>>
>>> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
>>> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Thu Sep 27
>>> 15:47:04 2018
>>> @@ -6633,6 +6633,11 @@ let CategoryName = "Lambda Issue" in {
>>> InGroup<DeprecatedThisCapture>, DefaultIgnore;
>>> def note_deprecated_this_capture : Note<
>>> "add an explicit capture of 'this' to capture '*this' by
>>> reference">;
>>> +
>>> + // C++2a default constructible / assignable lambdas.
>>> + def warn_cxx17_compat_lambda_def_ctor_assign : Warning<
>>> + "%select{default construction|assignment}0 of lambda is
>>> incompatible with "
>>> + "C++ standards before C++2a">, InGroup<CXXPre2aCompat>,
>>> DefaultIgnore;
>>> }
>>>
>>> def err_return_in_captured_stmt : Error<
>>>
>>> Modified: cfe/trunk/lib/AST/DeclCXX.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/DeclCXX.cpp?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/AST/DeclCXX.cpp (original)
>>> +++ cfe/trunk/lib/AST/DeclCXX.cpp Thu Sep 27 15:47:04 2018
>>> @@ -628,6 +628,24 @@ bool CXXRecordDecl::hasSubobjectAtOffset
>>> return false;
>>> }
>>>
>>> +bool CXXRecordDecl::lambdaIsDefaultConstructibleAndAssignable() const {
>>> + assert(isLambda() && "not a lambda");
>>> +
>>> + // C++2a [expr.prim.lambda.capture]p11:
>>> + // The closure type associated with a lambda-expression has no
>>> default
>>> + // constructor if the lambda-expression has a lambda-capture and a
>>> + // defaulted default constructor otherwise. It has a deleted copy
>>> + // assignment operator if the lambda-expression has a
>>> lambda-capture and
>>> + // defaulted copy and move assignment operators otherwise.
>>> + //
>>> + // C++17 [expr.prim.lambda]p21:
>>> + // The closure type associated with a lambda-expression has no
>>> default
>>> + // constructor and a deleted copy assignment operator.
>>> + if (getLambdaCaptureDefault() != LCD_None)
>>> + return false;
>>> + return getASTContext().getLangOpts().CPlusPlus2a;
>>> +}
>>> +
>>> void CXXRecordDecl::addedMember(Decl *D) {
>>> if (!D->isImplicit() &&
>>> !isa<FieldDecl>(D) &&
>>>
>>> Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
>>> +++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Thu Sep 27 15:47:04 2018
>>> @@ -7088,7 +7088,8 @@ bool Sema::ShouldDeleteSpecialMember(CXX
>>> // The closure type associated with a lambda-expression has a
>>> // deleted (8.4.3) default constructor and a deleted copy
>>> // assignment operator.
>>> - if (RD->isLambda() &&
>>> + // C++2a adds back these operators if the lambda has no
>>> capture-default.
>>> + if (RD->isLambda() &&
>>> !RD->lambdaIsDefaultConstructibleAndAssignable() &&
>>> (CSM == CXXDefaultConstructor || CSM == CXXCopyAssignment)) {
>>> if (Diagnose)
>>> Diag(RD->getLocation(), diag::note_lambda_decl);
>>>
>>> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
>>> +++ cfe/trunk/lib/Sema/SemaExpr.cpp Thu Sep 27 15:47:04 2018
>>> @@ -266,6 +266,17 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *
>>> return true;
>>> }
>>>
>>> + if (auto *MD = dyn_cast<CXXMethodDecl>(D)) {
>>> + // Lambdas are only default-constructible or assignable in C++2a
>>> onwards.
>>> + if (MD->getParent()->isLambda() &&
>>> + ((isa<CXXConstructorDecl>(MD) &&
>>> + cast<CXXConstructorDecl>(MD)->isDefaultConstructor()) ||
>>> + MD->isCopyAssignmentOperator() ||
>>> MD->isMoveAssignmentOperator())) {
>>> + Diag(Loc, diag::warn_cxx17_compat_lambda_def_ctor_assign)
>>> + << !isa<CXXConstructorDecl>(MD);
>>> + }
>>> + }
>>> +
>>> auto getReferencedObjCProp = [](const NamedDecl *D) ->
>>> const ObjCPropertyDecl * {
>>> if (const auto *MD = dyn_cast<ObjCMethodDecl>(D))
>>>
>>> Modified: cfe/trunk/test/SemaCXX/cxx17-compat.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/cxx17-compat.cpp?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/test/SemaCXX/cxx17-compat.cpp (original)
>>> +++ cfe/trunk/test/SemaCXX/cxx17-compat.cpp Thu Sep 27 15:47:04 2018
>>> @@ -27,3 +27,18 @@ struct B {
>>> // expected-warning at -4 {{default member initializer for bit-field
>>> is incompatible with C++ standards before C++2a}}
>>> #endif
>>> };
>>> +
>>> +auto Lambda = []{};
>>> +decltype(Lambda) AnotherLambda;
>>> +#if __cplusplus <= 201703L
>>> + // expected-error at -2 {{no matching constructor}} expected-note at -3
>>> 2{{candidate}}
>>> +#else
>>> + // expected-warning at -4 {{default construction of lambda is
>>> incompatible with C++ standards before C++2a}}
>>> +#endif
>>> +
>>> +void copy_lambda() { Lambda = Lambda; }
>>> +#if __cplusplus <= 201703L
>>> + // expected-error at -2 {{deleted}} expected-note at -10 {{lambda}}
>>> +#else
>>> + // expected-warning at -4 {{assignment of lambda is incompatible with
>>> C++ standards before C++2a}}
>>> +#endif
>>>
>>> Added: cfe/trunk/test/SemaCXX/cxx2a-lambda-default-ctor-assign.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/cxx2a-lambda-default-ctor-assign.cpp?rev=343279&view=auto
>>>
>>> ==============================================================================
>>> --- cfe/trunk/test/SemaCXX/cxx2a-lambda-default-ctor-assign.cpp (added)
>>> +++ cfe/trunk/test/SemaCXX/cxx2a-lambda-default-ctor-assign.cpp Thu Sep
>>> 27 15:47:04 2018
>>> @@ -0,0 +1,37 @@
>>> +// RUN: %clang_cc1 -std=c++2a -verify %s
>>> +
>>> +auto a = []{};
>>> +decltype(a) a2;
>>> +void f(decltype(a) x, decltype(a) y) {
>>> + x = y;
>>> + x = static_cast<decltype(a)&&>(y);
>>> +}
>>> +
>>> +template<typename T>
>>> +struct X {
>>> + constexpr X() { T::error; } // expected-error {{'::'}}
>>> + X(const X&);
>>> + constexpr X &operator=(const X&) { T::error; } // expected-error
>>> {{'::'}}
>>> + constexpr X &operator=(X&&) { T::error; } // expected-error {{'::'}}
>>> +};
>>> +extern X<int> x;
>>> +auto b = [x = x]{}; // expected-note 3{{in instantiation of}}
>>> +decltype(b) b2; // expected-note {{in implicit default constructor}}
>>> +void f(decltype(b) x, decltype(b) y) {
>>> + x = y; // expected-note {{in implicit copy assignment}}
>>> + x = static_cast<decltype(b)&&>(y); // expected-note {{in implicit
>>> move assignment}}
>>> +}
>>> +
>>> +struct Y {
>>> + Y() = delete; // expected-note {{deleted}}
>>> + Y(const Y&);
>>> + Y &operator=(const Y&) = delete; // expected-note 2{{deleted}}
>>> + Y &operator=(Y&&) = delete;
>>> +};
>>> +extern Y y;
>>> +auto c = [y = y]{}; // expected-note 3{{deleted because}}
>>> +decltype(c) c2; // expected-error {{deleted}}
>>> +void f(decltype(c) x, decltype(c) y) {
>>> + x = y; // expected-error {{deleted}}
>>> + x = static_cast<decltype(c)&&>(y); // expected-error {{deleted}}
>>> +}
>>>
>>> Modified: cfe/trunk/www/cxx_status.html
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/www/cxx_status.html?rev=343279&r1=343278&r2=343279&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/www/cxx_status.html (original)
>>> +++ cfe/trunk/www/cxx_status.html Thu Sep 27 15:47:04 2018
>>> @@ -905,7 +905,7 @@ as the draft C++2a standard evolves.
>>> <tr>
>>> <td>Default constructible and assignable stateless lambdas</td>
>>> <td><a href="http://wg21.link/p0624r2">P0624R2</a></td>
>>> - <td class="none" align="center">No</td>
>>> + <td class="svn" align="center">SVN</td>
>>> </tr>
>>> <tr>
>>> <td>Lambdas in unevaluated contexts</td>
>>>
>>>
>>> _______________________________________________
>>> cfe-commits mailing list
>>> cfe-commits at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>>
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