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Re: [patch, c++] Add a warning flag for the enum bit-field declaration warning in bug #61414.

..I just realised that the clang flag is -Wbitfield-enum-conversion, not
-Wenum-bitfield-conversion. Please apply the patch below instead, which
has replaced the two words to remove the inconsistency.

2017-10-16  Sam van Kampen  <>

        * c-family/c.opt: Add a warning flag for struct bit-fields
        being too small to hold enumerated types.
        * cp/class.c: Likewise.
        * doc/invoke.texi: Add documentation for said warning flag.

Index: gcc/c-family/c.opt
--- gcc/c-family/c.opt	(revision 253784)
+++ gcc/c-family/c.opt	(working copy)
@@ -346,6 +346,10 @@ Wframe-address
 C ObjC C++ ObjC++ Var(warn_frame_address) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
 Warn when __builtin_frame_address or __builtin_return_address is used unsafely.
+C++ Var(warn_bitfield_enum_conversion) Init(1) Warning
+Warn about struct bit-fields being too small to hold enumerated types.
 C ObjC C++ ObjC++ Var(warn_builtin_declaraion_mismatch) Init(1) Warning
 Warn when a built-in function is declared with the wrong signature.
Index: gcc/cp/class.c
--- gcc/cp/class.c	(revision 253784)
+++ gcc/cp/class.c	(working copy)
@@ -3278,10 +3278,11 @@ check_bitfield_decl (tree field)
 		   && tree_int_cst_lt (TYPE_SIZE (type), w)))
 	warning_at (DECL_SOURCE_LOCATION (field), 0,
 		    "width of %qD exceeds its type", field);
-      else if (TREE_CODE (type) == ENUMERAL_TYPE
+      else if (warn_bitfield_enum_conversion
+	       && TREE_CODE (type) == ENUMERAL_TYPE
 	       && (0 > (compare_tree_int
-	warning_at (DECL_SOURCE_LOCATION (field), 0,
+	warning_at (DECL_SOURCE_LOCATION (field), OPT_Wbitfield_enum_conversion,
 		    "%qD is too small to hold all values of %q#T",
 		    field, type);
Index: gcc/doc/invoke.texi
--- gcc/doc/invoke.texi	(revision 253784)
+++ gcc/doc/invoke.texi	(working copy)
@@ -264,7 +264,7 @@ Objective-C and Objective-C++ Dialects}.
 -Walloca  -Walloca-larger-than=@var{n} @gol
 -Wno-aggressive-loop-optimizations  -Warray-bounds  -Warray-bounds=@var{n} @gol
 -Wno-attributes  -Wbool-compare  -Wbool-operation @gol
--Wno-builtin-declaration-mismatch @gol
+-Wbitfield-enum-conversion -Wno-builtin-declaration-mismatch @gol
 -Wno-builtin-macro-redefined  -Wc90-c99-compat  -Wc99-c11-compat @gol
 -Wc++-compat  -Wc++11-compat  -Wc++14-compat  @gol
 -Wcast-align  -Wcast-align=strict  -Wcast-qual  @gol
@@ -5431,6 +5431,12 @@ Incrementing a boolean is invalid in C++17, and de
 This warning is enabled by @option{-Wall}.
+@item -Wbitfield-enum-conversion
+@opindex Wbitfield-enum-conversion
+@opindex Wno-bitfield-enum-conversion
+Warn about a bit-field potentially being too small to hold all values
+of an enumerated type. This warning is enabled by default.
 @item -Wduplicated-branches
 @opindex Wno-duplicated-branches
 @opindex Wduplicated-branches

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