[PATCH] D137172: [Clang] Implement CWG2358 Explicit capture of value

[Corentin Jabot via Phabricator via cfe-commits]

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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137172

Files:
  clang/docs/ReleaseNotes.rst
  clang/lib/Sema/SemaDeclCXX.cpp
  clang/test/CXX/drs/dr23xx.cpp
  clang/test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
  clang/www/cxx_dr_status.html


Index: clang/www/cxx_dr_status.html
===================================================================
--- clang/www/cxx_dr_status.html
+++ clang/www/cxx_dr_status.html
@@ -13956,7 +13956,7 @@
     <td><a href="https://wg21.link/cwg2358">2358</a></td>
     <td>CD5</td>
     <td>Explicit capture of value</td>
-    <td class="none" align="center">Unknown</td>
+    <td class="unreleased" align="center">Clang 16</td>
   </tr>
   <tr id="2359">
     <td><a href="https://wg21.link/cwg2359">2359</a></td>
Index: clang/test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
===================================================================
--- clang/test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
+++ clang/test/CXX/expr/expr.prim/expr.prim.lambda/p13.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -std=c++11 %s -Wunused -Wno-unused-lambda-capture -verify
 
+const int global = 0;
 void f2() {
   int i = 1;
   void g1(int = ([i]{ return i; })()); // expected-error{{lambda expression in default argument cannot capture any entity}}
@@ -7,6 +8,8 @@
   void g3(int = ([=]{ return i; })()); // expected-error{{lambda expression in default argument cannot capture any entity}}
   void g4(int = ([=]{ return 0; })());
   void g5(int = ([]{ return sizeof i; })());
+  void g6(int = ([x=1, y = global, &z = global]{ return x; })());
+  void g7(int = ([x=i, &y=i]{ return x; })()); // expected-error 2{{default argument references local variable 'i' of enclosing function}}
 }
 
 namespace lambda_in_default_args {
Index: clang/test/CXX/drs/dr23xx.cpp
===================================================================
--- clang/test/CXX/drs/dr23xx.cpp
+++ clang/test/CXX/drs/dr23xx.cpp
@@ -89,6 +89,16 @@
 #pragma clang __debug dump not_use_2
 }
 
+#if __cplusplus >= 201402L
+namespace dr2358 { // dr2358: 16
+  void f2() {
+    int i = 1;
+    void g1(int = ([x=1] { return x; }))();  // OK
+    void g2(int = ([x=i] { return x; }))();  // expected-error {{default argument references local variable 'i' of enclosing function}}
+  }
+}
+#endif
+
 #if __cplusplus >= 201707L
 // Otherwise, if the qualified-id std::tuple_size<E> names a complete class
 // type **with a member value**, the expression std::tuple_size<E>::value shall
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -149,13 +149,19 @@
 }
 
 bool CheckDefaultArgumentVisitor::VisitLambdaExpr(const LambdaExpr *Lambda) {
-  // C++11 [expr.lambda.prim]p13:
-  //   A lambda-expression appearing in a default argument shall not
-  //   implicitly or explicitly capture any entity.
-  if (Lambda->capture_begin() == Lambda->capture_end())
-    return false;
-
-  return S.Diag(Lambda->getBeginLoc(), diag::err_lambda_capture_default_arg);
+  // [expr.prim.lambda.capture]/p9
+  // a lambda-expression appearing in a default argument cannot implicitly or explicitly capture any local entity.
+  // Such a lambda-expression can still have an init-capture if any full-expression in its initializer
+  // satisfies the constraints of an expression appearing in a default argument.
+  bool Invalid = false;
+  for(const LambdaCapture& LC : Lambda->captures()) {
+    if(!Lambda->isInitCapture(&LC))
+      return S.Diag(LC.getLocation(), diag::err_lambda_capture_default_arg);
+    // Init captures are always VarDecl.
+    auto *D = cast<VarDecl>(LC.getCapturedVar());
+    Invalid |= Visit(D->getInit());
+  }
+  return Invalid;
 }
 } // namespace
 
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -507,6 +507,7 @@
   This means Clang will by default accept code using features from C++17 and
   conforming GNU extensions. Projects incompatible with C++17 can add
   ``-std=gnu++14`` to their build settings to restore the previous behaviour.
+- Implemented DR2358 allowing init captures in lambdas in default arguments.
 
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^


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