[PATCH] D147909: [clang] Implement CWG 2397

[Younan Zhang via Phabricator via cfe-commits]

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Note GCC had implemented such feature since GCC 12 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100975>.


This patch implements CWG 2397, allowing array of placeholder type
to be valid.

See also https://wg21.cmeerw.net/cwg/issue2397.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D147909

Files:
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/lib/Sema/SemaType.cpp
  clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/cwg2397.cpp
  clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/p1-cxx0x.cpp


Index: clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/p1-cxx0x.cpp
===================================================================
--- clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/p1-cxx0x.cpp
+++ clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/p1-cxx0x.cpp
@@ -2,6 +2,6 @@
 
 void f() {
   int b[5];
-  auto a[5] = b; // expected-error{{'a' declared as array of 'auto'}}
-  auto *c[5] = b; // expected-error{{'c' declared as array of 'auto *'}}
+  auto a[5] = b; // expected-error{{variable 'a' with type 'auto[5]' has incompatible initializer of type 'int[5]'}}
+  auto *c[5] = b; // expected-error{{variable 'c' with type 'auto *[5]' has incompatible initializer of type 'int[5]'}}
 }
Index: clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/cwg2397.cpp
===================================================================
--- /dev/null
+++ clang/test/CXX/dcl.decl/dcl.meaning/dcl.array/cwg2397.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11
+
+void foo() {
+  int a[5];
+
+  auto (&b)[5] = a;
+  auto (*c)[5] = &a;
+
+  auto d[] = {0}; // expected-error{{cannot deduce actual type for variable 'd' with type 'auto[]' from initializer list}}
+}
+
+void g() {
+  int a[5];
+  auto (*b)[5] = &a;
+  auto (&c)[5] = a;
+  auto (&&d)[5] = static_cast<int(&&)[5]>(a);
+  static_assert(__is_same(decltype(b), int (*)[5]), "");
+  static_assert(__is_same(decltype(c), int (&)[5]), "");
+  static_assert(__is_same(decltype(d), int (&&)[5]), "");
+}
Index: clang/lib/Sema/SemaType.cpp
===================================================================
--- clang/lib/Sema/SemaType.cpp
+++ clang/lib/Sema/SemaType.cpp
@@ -5130,17 +5130,6 @@
           D.setInvalidType(true);
         }
       }
-      const AutoType *AT = T->getContainedAutoType();
-      // Allow arrays of auto if we are a generic lambda parameter.
-      // i.e. [](auto (&array)[5]) { return array[0]; }; OK
-      if (AT && D.getContext() != DeclaratorContext::LambdaExprParameter) {
-        // We've already diagnosed this for decltype(auto).
-        if (!AT->isDecltypeAuto())
-          S.Diag(DeclType.Loc, diag::err_illegal_decl_array_of_auto)
-              << getPrintableNameForEntity(Name) << T;
-        T = QualType();
-        break;
-      }
 
       // Array parameters can be marked nullable as well, although it's not
       // necessary if they're marked 'static'.
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2314,8 +2314,6 @@
 def err_binding_cannot_appear_in_own_initializer : Error<
   "binding %0 cannot appear in the initializer of its own "
   "decomposition declaration">;
-def err_illegal_decl_array_of_auto : Error<
-  "'%0' declared as array of %1">;
 def err_new_array_of_auto : Error<
   "cannot allocate array of 'auto'">;
 def err_auto_not_allowed : Error<


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