Re: clang++ 11 compilation issues

[Paul Eggert <eggert@cs.ucla.edu>]

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On 1/12/21 12:19 PM, Bruno Haible wrote:
>> Those macros check for
>> __cpp_static_assert to assume something about _Static_assert, which
>> seems dubious.
> Paul can tell more about this one.

I agree it's dubious.

Also, looking over the current verify.h, it's a little complicated and I 
doubt whether the complexity is worth it nowadays. How about if we 
simplify the C++ case, by simply relying on __cpp_static_assert there? 
Although this could miss opportunities for generating diagnostics via 
older C++ compilers, I doubt whether they're worth the trouble any more.

Proposed Gnulib patch attached (I haven't installed it).

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From ce90a689fc388c4c612861054adcb09bd3658b1c Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Wed, 13 Jan 2021 15:46:33 -0800
Subject: [PATCH] verify: rely more on __cpp_static_assert

* lib/verify.h (_GL_HAVE__STATIC_ASSERT, _GL_HAVE__STATIC_ASSERT1):
Simplify for the C++ case, by relying only on __cpp_static_assert.
That should be good enough nowadays for C++.
(_GL_HAVE_STATIC_ASSERT_CXX11, _GL_HAVE_STATIC_ASSERT_CXX17):
Remove.  All uses replaced by simply checking __cpp_static_assert.
---
 ChangeLog    |  9 +++++++++
 lib/verify.h | 53 ++++++++++++----------------------------------------
 2 files changed, 21 insertions(+), 41 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 2123974c8..8991d6a35 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2021-01-13  Paul Eggert  <eggert@cs.ucla.edu>
+
+	verify: simplify static_assert configuration
+	* lib/verify.h (_GL_HAVE__STATIC_ASSERT, _GL_HAVE__STATIC_ASSERT1):
+	Do not define for C++.  This should be good enough nowadays,
+	since recent-enough C++ compilers have static_assert.
+	(_GL_HAVE_STATIC_ASSERT_CXX11, _GL_HAVE_STATIC_ASSERT_CXX17):
+	Remove.  All uses replaced by simply checking __cpp_static_assert.
+
 2021-01-13  Simon Josefsson  <simon@josefsson.org>
 
 	lib-msvc-compat: Update libtool usage recommendation.
diff --git a/lib/verify.h b/lib/verify.h
index a9e75890f..a62a47087 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -22,52 +22,23 @@
 
 
 /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert (R, DIAGNOSTIC)
-   works as per C11.  This is supported by GCC 4.6.0 and later, in C
-   mode, and by clang (also in C++ mode).
+   works as per C11.  This is supported by GCC 4.6.0+ and by clang 4+.
 
    Define _GL_HAVE__STATIC_ASSERT1 to 1 if _Static_assert (R) works as
-   per C2X.  This is supported by GCC 9.1 and later, and by clang in
-   C++1z mode.
-
-   Define _GL_HAVE_STATIC_ASSERT_CXX11 if static_assert (R, DIAGNOSTIC)
-   works as per C++11.  This is supported by GCC 6.1 and later, and by
-   clang in C++11 mode.
-
-   Define _GL_HAVE_STATIC_ASSERT_CXX17 if static_assert (R) works as per
-   C++17.  This is supported by GCC 9.1 and later, and by clang in
-   C++1z mode.
+   per C2X.  This is supported by GCC 9.1+.
 
    Support compilers claiming conformance to the relevant standard,
    and also support GCC when not pedantic.  If we were willing to slow
    'configure' down we could also use it with other compilers, but
    since this affects only the quality of diagnostics, why bother?  */
-#ifndef __cplusplus
-# if (201112L <= __STDC_VERSION__ \
-      || (!defined __STRICT_ANSI__ \
-          && (4 < __GNUC__ + (6 <= __GNUC_MINOR__) || 4 <= __clang_major__)))
-#  define _GL_HAVE__STATIC_ASSERT 1
-# endif
-# if (202000L <= __STDC_VERSION__ \
-      || (!defined __STRICT_ANSI__ && 9 <= __GNUC__))
-#  define _GL_HAVE__STATIC_ASSERT1 1
-# endif
-#else
-# if 4 <= __clang_major__
-#  define _GL_HAVE__STATIC_ASSERT 1
-# endif
-# if 4 <= __clang_major__ && 201411 <= __cpp_static_assert
-#  define _GL_HAVE__STATIC_ASSERT1 1
-# endif
-# if 201103L <= __cplusplus \
-     || 6 <= __GNUC__ \
-     || (4 <= __clang_major__ && 200410 <= __cpp_static_assert)
-#  define _GL_HAVE_STATIC_ASSERT_CXX11 1
-# endif
-# if 201703L <= __cplusplus \
-     || 9 <= __GNUC__ \
-     || (4 <= __clang_major__ && 201411 <= __cpp_static_assert)
-#  define _GL_HAVE_STATIC_ASSERT_CXX17 1
-# endif
+#if (201112L <= __STDC_VERSION__ \
+     || (!defined __STRICT_ANSI__ \
+         && (4 < __GNUC__ + (6 <= __GNUC_MINOR__) || 4 <= __clang_major__)))
+# define _GL_HAVE__STATIC_ASSERT 1
+#endif
+#if (202000L <= __STDC_VERSION__ \
+     || (!defined __STRICT_ANSI__ && 9 <= __GNUC__))
+# define _GL_HAVE__STATIC_ASSERT1 1
 #endif
 
 /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
@@ -234,7 +205,7 @@ template <int w>
    Unfortunately, unlike C11, this implementation must appear as an
    ordinary declaration, and cannot appear inside struct { ... }.  */
 
-#if defined _GL_HAVE_STATIC_ASSERT_CXX11
+#if 200410 <= __cpp_static_assert
 # define _GL_VERIFY(R, DIAGNOSTIC, ...) static_assert (R, DIAGNOSTIC)
 #elif defined _GL_HAVE__STATIC_ASSERT
 # define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC)
@@ -250,7 +221,7 @@ template <int w>
 #  define _Static_assert(...) \
      _GL_VERIFY (__VA_ARGS__, "static assertion failed", -)
 # endif
-# if !defined _GL_HAVE_STATIC_ASSERT_CXX17 && !defined static_assert
+# if __cpp_static_assert < 201411 && !defined static_assert
 #  define static_assert _Static_assert /* C11 requires this #define.  */
 # endif
 #endif
-- 
2.27.0