[PATCH] c++: CWG 2229, cv-qualified unnamed bit-fields [PR123935]

[Marek Polacek]

Bootstrapped/regtested on ppc64le-pc-linux-gnu, ok for 17.0?

-- >8 --
This implements [class.bit]/2: An unnamed bit-field shall not be
declared with a cv-qualified type.  This was clarified in DR 2229.

        DR 2229
        PR c++/123935

gcc/cp/ChangeLog:

        * decl2.cc (grokbitfield): Disallow cv-qualified unnamed bit-fields.

gcc/testsuite/ChangeLog:

        * g++.dg/DRs/dr2229.C: New test.
---
 gcc/cp/decl2.cc                   |  9 +++++++++
 gcc/testsuite/g++.dg/DRs/dr2229.C | 12 ++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/DRs/dr2229.C

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 20ee662eea2..eb2294fffd0 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -1635,6 +1635,15 @@ grokbitfield (const cp_declarator *declarator,
       return NULL_TREE;
     }
 
+  /* [class.bit]/2 "An unnamed bit-field shall not be declared with
+     a cv-qualified type."  */
+  if (!DECL_NAME (value) && TYPE_QUALS (type) != TYPE_UNQUALIFIED)
+    {
+      error_at (DECL_SOURCE_LOCATION (value),
+               "unnamed bit-field cannot be cv-qualified");
+      return NULL_TREE;
+    }
+
   int flags = LOOKUP_IMPLICIT;
   if (init && DIRECT_LIST_INIT_P (init))
     flags = LOOKUP_NORMAL;
diff --git a/gcc/testsuite/g++.dg/DRs/dr2229.C 
b/gcc/testsuite/g++.dg/DRs/dr2229.C
new file mode 100644
index 00000000000..32548071090
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2229.C
@@ -0,0 +1,12 @@
+// DR 2229, Volatile unnamed bit-fields
+// PR c++/123935
+
+struct S {
+  const unsigned : 1; // { dg-error "unnamed bit-field cannot be cv-qualified" 
}
+  volatile unsigned : 1; // { dg-error "unnamed bit-field cannot be 
cv-qualified" }
+  const volatile unsigned : 1; // { dg-error "unnamed bit-field cannot be 
cv-qualified" }
+  unsigned : 1;
+  const unsigned i1 : 1;
+  volatile unsigned i2 : 1;
+  const volatile unsigned i3 : 1;
+};

base-commit: 7197d0cce705254d0779a81bdad82d5a71b7f63b
-- 
2.52.0