r343279 - [cxx2a] P0624R2: Lambdas with no capture-default are
David Blaikie via cfe-commits
cfe-commits at lists.llvm.org
Mon Oct 1 09:55:23 PDT 2018
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)
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>
>
>
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>
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