[c++17] P0490R0, NB comment FI 20: allow direct-initialization of decomposition declarations.

llvm-svn: 289286

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -398,8 +398,6 @@ def err_decomp_decl_not_alone : Error<
   "decomposition declaration must be the only declaration in its group">;
 def err_decomp_decl_requires_init : Error<
   "decomposition declaration %0 requires an initializer">;
-def err_decomp_decl_paren_init : Error<
-  "decomposition declaration %0 cannot have a parenthesized initializer">;
 def err_decomp_decl_wrong_number_bindings : Error<
   "type %0 decomposes into %2 elements, but %select{only |}3%1 "
   "names were provided">;

clang/lib/Sema/SemaDecl.cpp

@@ -9625,6 +9625,20 @@ namespace {
   }
 } // end anonymous namespace
 
+namespace {
+  // Simple wrapper to add the name of a variable or (if no variable is
+  // available) a DeclarationName into a diagnostic.
+  struct VarDeclOrName {
+    VarDecl *VDecl;
+    DeclarationName Name;
+
+    friend const Sema::SemaDiagnosticBuilder &
+    operator<<(const Sema::SemaDiagnosticBuilder &Diag, VarDeclOrName VN) {
+      return VN.VDecl ? Diag << VN.VDecl : Diag << VN.Name;
+    }
+  };
+} // end anonymous namespace
+
 QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
                                             DeclarationName Name, QualType Type,
                                             TypeSourceInfo *TSI,
@@ -9634,6 +9648,8 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
   assert((!VDecl || !VDecl->isInitCapture()) &&
          "init captures are expected to be deduced prior to initialization");
 
+  VarDeclOrName VN{VDecl, Name};
+
   // FIXME: Deduction for a decomposition declaration does weird things if the
   // initializer is an array.
 
@@ -9652,7 +9668,7 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
     Diag(Init->getLocStart(), IsInitCapture
                                   ? diag::err_init_capture_no_expression
                                   : diag::err_auto_var_init_no_expression)
-        << Name << Type << Range;
+        << VN << Type << Range;
     return QualType();
   }
 
@@ -9660,7 +9676,7 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
     Diag(DeduceInits[1]->getLocStart(),
          IsInitCapture ? diag::err_init_capture_multiple_expressions
                        : diag::err_auto_var_init_multiple_expressions)
-        << Name << Type << Range;
+        << VN << Type << Range;
     return QualType();
   }
 
@@ -9669,7 +9685,7 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
     Diag(Init->getLocStart(), IsInitCapture
                                   ? diag::err_init_capture_paren_braces
                                   : diag::err_auto_var_init_paren_braces)
-        << isa<InitListExpr>(Init) << Name << Type << Range;
+        << isa<InitListExpr>(Init) << VN << Type << Range;
     return QualType();
   }
 
@@ -9692,13 +9708,13 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
     else if (isa<InitListExpr>(Init))
       Diag(Range.getBegin(),
            diag::err_init_capture_deduction_failure_from_init_list)
-          << Name
+          << VN
           << (DeduceInit->getType().isNull() ? TSI->getType()
                                              : DeduceInit->getType())
           << DeduceInit->getSourceRange();
     else
       Diag(Range.getBegin(), diag::err_init_capture_deduction_failure)
-          << Name << TSI->getType()
+          << VN << TSI->getType()
           << (DeduceInit->getType().isNull() ? TSI->getType()
                                              : DeduceInit->getType())
           << DeduceInit->getSourceRange();
@@ -9712,7 +9728,7 @@ QualType Sema::deduceVarTypeFromInitializer(VarDecl *VDecl,
   if (ActiveTemplateInstantiations.empty() && !DefaultedAnyToId &&
       !IsInitCapture && !DeducedType.isNull() && DeducedType->isObjCIdType()) {
     SourceLocation Loc = TSI->getTypeLoc().getBeginLoc();
-    Diag(Loc, diag::warn_auto_var_is_id) << Name << Range;
+    Diag(Loc, diag::warn_auto_var_is_id) << VN << Range;
   }
 
   return DeducedType;
@@ -9746,11 +9762,6 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init,
     return;
   }
 
-  // C++1z [dcl.dcl]p1 grammar implies that a parenthesized initializer is not
-  // permitted.
-  if (isa<DecompositionDecl>(VDecl) && DirectInit && isa<ParenListExpr>(Init))
-    Diag(VDecl->getLocation(), diag::err_decomp_decl_paren_init) << VDecl;
-
   // C++11 [decl.spec.auto]p6. Deduce the type which 'auto' stands in for.
   if (TypeMayContainAuto && VDecl->getType()->isUndeducedType()) {
     // Attempt typo correction early so that the type of the init expression can

clang/test/Parser/cxx1z-decomposition.cpp

@@ -139,9 +139,11 @@ namespace Init {
     int arr[1];
     struct S { int n; };
     auto &[bad1]; // expected-error {{decomposition declaration '[bad1]' requires an initializer}}
-    const auto &[bad2](S{}); // expected-error {{decomposition declaration '[bad2]' cannot have a parenthesized initializer}}
+    const auto &[bad2](S{}, S{}); // expected-error {{initializer for variable '[bad2]' with type 'const auto &' contains multiple expressions}}
+    const auto &[bad3](); // expected-error {{expected expression}}
     auto &[good1] = arr;
     auto &&[good2] = S{};
+    const auto &[good3](S{});
     S [goodish3] = { 4 }; // expected-error {{cannot be declared with type 'S'}}
     S [goodish4] { 4 }; // expected-error {{cannot be declared with type 'S'}}
   }