sys-devel/gdb: fix build w/ clang 16 (-Wenum-constexpr-conversion)

Closes: https://bugs.gentoo.org/894174
Signed-off-by: Sam James <sam@gentoo.org>

2 files changed, 129 insertions, 0 deletions

diff --git a/sys-devel/gdb/files/gdb-13.1-Wenum-constexpr-conversion-clang16.patch b/sys-devel/gdb/files/gdb-13.1-Wenum-constexpr-conversion-clang16.patch
new file mode 100644
index 000000000000..adc09f83ea68
--- /dev/null
+++ b/sys-devel/gdb/files/gdb-13.1-Wenum-constexpr-conversion-clang16.patch
@@ -0,0 +1,128 @@
+https://bugs.gentoo.org/894174
+https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ae61525fcf456ab395d55c45492a106d1275873a
+
+From ae61525fcf456ab395d55c45492a106d1275873a Mon Sep 17 00:00:00 2001
+From: Simon Marchi <simon.marchi@efficios.com>
+Date: Thu, 23 Feb 2023 12:35:40 -0500
+Subject: [PATCH] gdbsupport: ignore -Wenum-constexpr-conversion in
+ enum-flags.h
+
+When building with clang 16, we get:
+
+      CXX    gdb.o
+    In file included from /home/smarchi/src/binutils-gdb/gdb/gdb.c:19:
+    In file included from /home/smarchi/src/binutils-gdb/gdb/defs.h:65:
+    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 15] for this enumeration type [-Wenum-constexpr-conversion]
+        integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
+                                                       ^
+
+The error message does not make it clear in the context of which enum
+flag this fails (i.e. what is T in this context), but it doesn't really
+matter, we have similar warning/errors for many of them, if we let the
+build go through.
+
+clang is right that the value -1 is invalid for the enum type we cast -1
+to.  However, we do need this expression in order to select an integer
+type with the appropriate signedness.  That is, with the same signedness
+as the underlying type of the enum.
+
+I first wondered if that was really needed, if we couldn't use
+std::underlying_type for that.  It turns out that the comment just above
+says:
+
+    /* Note that std::underlying_type<enum_type> is not what we want here,
+       since that returns unsigned int even when the enum decays to signed
+       int.  */
+
+I was surprised, because std::is_signed<std::underlying_type<enum_type>>
+returns the right thing.  So I tried replacing all this with
+std::underlying_type, see if that would work.  Doing so causes some
+build failures in unittests/enum-flags-selftests.c:
+
+      CXX    unittests/enum-flags-selftests.o
+    /home/smarchi/src/binutils-gdb/gdb/unittests/enum-flags-selftests.c:254:1: error: static assertion failed due to requirement 'gdb::is_same<selftests::enum_flags_tests::check_valid_expr254::archetype<enum_flags<s
+    elftests::enum_flags_tests::RE>, selftests::enum_flags_tests::RE, enum_flags<selftests::enum_flags_tests::RE2>, selftests::enum_flags_tests::RE2, enum_flags<selftests::enum_flags_tests::URE>, selftests::enum_fla
+    gs_tests::URE, int>, selftests::enum_flags_tests::check_valid_expr254::archetype<enum_flags<selftests::enum_flags_tests::RE>, selftests::enum_flags_tests::RE, enum_flags<selftests::enum_flags_tests::RE2>, selfte
+    sts::enum_flags_tests::RE2, enum_flags<selftests::enum_flags_tests::URE>, selftests::enum_flags_tests::URE, unsigned int>>::value == true':
+    CHECK_VALID (true,  int,  true ? EF () : EF2 ())
+    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    /home/smarchi/src/binutils-gdb/gdb/unittests/enum-flags-selftests.c:91:3: note: expanded from macro 'CHECK_VALID'
+      CHECK_VALID_EXPR_6 (EF, RE, EF2, RE2, UEF, URE, VALID, EXPR_TYPE, EXPR)
+      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/valid-expr.h:105:3: note: expanded from macro 'CHECK_VALID_EXPR_6'
+      CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2,           \
+      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/valid-expr.h:66:3: note: expanded from macro 'CHECK_VALID_EXPR_INT'
+      static_assert (gdb::is_detected_exact<archetype<TYPES, EXPR_TYPE>,    \
+      ^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is a bit hard to decode, but basically enumerations have the
+following funny property that they decay into a signed int, even if
+their implicit underlying type is unsigned.  This code:
+
+    enum A {};
+    enum B {};
+
+    int main() {
+      std::cout << std::is_signed<std::underlying_type<A>::type>::value
+                << std::endl;
+      std::cout << std::is_signed<std::underlying_type<B>::type>::value
+                << std::endl;
+      auto result = true ? A() : B();
+      std::cout << std::is_signed<decltype(result)>::value << std::endl;
+    }
+
+produces:
+
+    0
+    0
+    1
+
+So, the "CHECK_VALID" above checks that this property works for enum flags the
+same way as it would if you were using their underlying enum types.  And
+somehow, changing integer_for_size to use std::underlying_type breaks that.
+
+Since the current code does what we want, and I don't see any way of doing it
+differently, ignore -Wenum-constexpr-conversion around it.
+
+Change-Id: Ibc82ae7bbdb812102ae3f1dd099fc859dc6f3cc2
+--- a/gdbsupport/enum-flags.h
++++ b/gdbsupport/enum-flags.h
+@@ -91,9 +91,12 @@ template<> struct integer_for_size<8, 1> { typedef int64_t type; };
+ template<typename T>
+ struct enum_underlying_type
+ {
++  DIAGNOSTIC_PUSH
++  DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION
+   typedef typename
+     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
+     type;
++  DIAGNOSTIC_POP
+ };
+ 
+ namespace enum_flags_detail
+--- a/include/diagnostics.h
++++ b/include/diagnostics.h
+@@ -76,6 +76,11 @@
+ # define DIAGNOSTIC_ERROR_SWITCH \
+   DIAGNOSTIC_ERROR ("-Wswitch")
+ 
++# if __has_warning ("-Wenum-constexpr-conversion")
++#  define DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION \
++   DIAGNOSTIC_IGNORE ("-Wenum-constexpr-conversion")
++# endif
++
+ #elif defined (__GNUC__) /* GCC */
+ 
+ # define DIAGNOSTIC_IGNORE_DEPRECATED_DECLARATIONS \
+@@ -155,4 +160,8 @@
+ # define DIAGNOSTIC_ERROR_SWITCH
+ #endif
+ 
++#ifndef DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION
++# define DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION
++#endif
++
+ #endif /* DIAGNOSTICS_H */
+-- 
+2.31.1
diff --git a/sys-devel/gdb/gdb-13.1-r1.ebuild b/sys-devel/gdb/gdb-13.1-r1.ebuild
index bc86849c6276..60adac18680f 100644
--- a/sys-devel/gdb/gdb-13.1-r1.ebuild
+++ b/sys-devel/gdb/gdb-13.1-r1.ebuild
@@ -101,6 +101,7 @@ BDEPEND="
 
 PATCHES=(
 	"${FILESDIR}"/${PN}-8.3.1-verbose-build.patch
+	"${FILESDIR}"/${P}-Wenum-constexpr-conversion-clang16.patch
 )
 
 pkg_setup() {