Re: [PATCH] c++: Refine enum direct-list-initialization [CWG2374]

[Jason Merrill via Gcc-patches]

On 4/22/21 10:49 AM, Patrick Palka wrote:

This implements the wording changes of CWG2374, which clarifies the
wording of P0138 to forbid e.g. direct-list-initialization of a scoped
enumeration from a different scoped enumeration.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?


OK.


gcc/cp/ChangeLog:

DR 2374
* decl.c (is_direct_enum_init): Check the implicit
convertibility requirement added by CWG 2374.

gcc/testsuite/ChangeLog:

DR 2374
* g++.dg/cpp1z/direct-enum-init2.C: New test.
---
  gcc/cp/decl.c  | 8 +++-
  gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C | 8 
  2 files changed, 15 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index b81de8ef934..60dc2bf182d 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6191,7 +6191,13 @@ is_direct_enum_init (tree type, tree init)
&& ENUM_FIXED_UNDERLYING_TYPE_P (type)
&& TREE_CODE (init) == CONSTRUCTOR
&& CONSTRUCTOR_IS_DIRECT_INIT (init)
-  && CONSTRUCTOR_NELTS (init) == 1)
+  && CONSTRUCTOR_NELTS (init) == 1
+  /* DR 2374: The single element needs to be implicitly
+convertible to the underlying type of the enum.  */
+  && can_convert_arg (ENUM_UNDERLYING_TYPE (type),
+ TREE_TYPE (CONSTRUCTOR_ELT (init, 0)->value),
+ CONSTRUCTOR_ELT (init, 0)->value,
+ LOOKUP_IMPLICIT, tf_none))
  return true;
return false;
  }
diff --git a/gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C 
b/gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C
new file mode 100644
index 000..5b94a8d00fe
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C
@@ -0,0 +1,8 @@
+// DR 2374
+// { dg-do compile { target c++17 } }
+
+enum class Orange;
+enum class Apple;
+
+extern Orange o;
+Apple a{o}; // { dg-error "cannot convert" }

[PATCH] c++: Refine enum direct-list-initialization [CWG2374]

[Patrick Palka via Gcc-patches]

This implements the wording changes of CWG2374, which clarifies the
wording of P0138 to forbid e.g. direct-list-initialization of a scoped
enumeration from a different scoped enumeration.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

gcc/cp/ChangeLog:

DR 2374
* decl.c (is_direct_enum_init): Check the implicit
convertibility requirement added by CWG 2374.

gcc/testsuite/ChangeLog:

DR 2374
* g++.dg/cpp1z/direct-enum-init2.C: New test.
---
 gcc/cp/decl.c  | 8 +++-
 gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C | 8 
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index b81de8ef934..60dc2bf182d 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6191,7 +6191,13 @@ is_direct_enum_init (tree type, tree init)
   && ENUM_FIXED_UNDERLYING_TYPE_P (type)
   && TREE_CODE (init) == CONSTRUCTOR
   && CONSTRUCTOR_IS_DIRECT_INIT (init)
-  && CONSTRUCTOR_NELTS (init) == 1)
+  && CONSTRUCTOR_NELTS (init) == 1
+  /* DR 2374: The single element needs to be implicitly
+convertible to the underlying type of the enum.  */
+  && can_convert_arg (ENUM_UNDERLYING_TYPE (type),
+ TREE_TYPE (CONSTRUCTOR_ELT (init, 0)->value),
+ CONSTRUCTOR_ELT (init, 0)->value,
+ LOOKUP_IMPLICIT, tf_none))
 return true;
   return false;
 }
diff --git a/gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C 
b/gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C
new file mode 100644
index 000..5b94a8d00fe
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/direct-enum-init2.C
@@ -0,0 +1,8 @@
+// DR 2374
+// { dg-do compile { target c++17 } }
+
+enum class Orange;
+enum class Apple;
+
+extern Orange o;
+Apple a{o}; // { dg-error "cannot convert" }
-- 
2.31.1.362.g311531c9de