Re: [PATCH RFA] libstdc++: add experimental Contracts support

[Jonathan Wakely <jwakely@redhat.com>]

On 03/11/22 15:57 -0400, Jason Merrill wrote:
>Tested x86_64-pc-linux-gnu.  OK for trunk?
>
>-- >8 --
>
>This patch adds the library support for the experimental C++ Contracts
>implementation.  This now consists only of a default definition of the
>violation handler, which users can override through defining their own
>version.  To avoid ABI stability problems with libstdc++.so this is added to
>a separate -lstdc++exp static library, which the driver knows to add when it
>sees -fcontracts.
>
>libstdc++-v3/ChangeLog:
>
>	* acinclude.m4 (glibcxx_SUBDIRS): Add src/experimental.
>	* include/Makefile.am (experimental_headers): Add contract.
>	* include/Makefile.in: Regenerate.
>	* src/Makefile.am (SUBDIRS): Add experimental.
>	* src/Makefile.in: Regenerate.
>	* configure: Regenerate.
>	* src/experimental/contract.cc: New file.
>	* src/experimental/Makefile.am: New file.
>	* src/experimental/Makefile.in: New file.
>	* include/experimental/contract: New file.
>---
> libstdc++-v3/src/experimental/contract.cc  |  41 ++
> libstdc++-v3/acinclude.m4                  |   2 +-
> libstdc++-v3/include/Makefile.am           |   1 +
> libstdc++-v3/include/Makefile.in           |   1 +
> libstdc++-v3/src/Makefile.am               |   3 +-
> libstdc++-v3/src/Makefile.in               |   6 +-
> libstdc++-v3/src/experimental/Makefile.am  |  96 +++
> libstdc++-v3/src/experimental/Makefile.in  | 796 +++++++++++++++++++++
> libstdc++-v3/include/experimental/contract |  84 +++
> 9 files changed, 1026 insertions(+), 4 deletions(-)
> create mode 100644 libstdc++-v3/src/experimental/contract.cc
> create mode 100644 libstdc++-v3/src/experimental/Makefile.am
> create mode 100644 libstdc++-v3/src/experimental/Makefile.in
> create mode 100644 libstdc++-v3/include/experimental/contract
>
>
>base-commit: a4cd2389276a30c39034a83d640ce68fa407bac1
>prerequisite-patch-id: 329bc16a88dc9a3b13cd3fcecb3678826cc592dc
>
>diff --git a/libstdc++-v3/src/experimental/contract.cc b/libstdc++-v3/src/experimental/contract.cc
>new file mode 100644
>index 00000000000..b9b72cd7df0
>--- /dev/null
>+++ b/libstdc++-v3/src/experimental/contract.cc
>@@ -0,0 +1,41 @@
>+// -*- C++ -*- std::experimental::contract_violation and friends
>+// Copyright (C) 1994-2022 Free Software Foundation, Inc.

Copy&paste from an old file? I don't think this uses anything
existing, should be just 2022.

>+//
>+// This file is part of GCC.
>+//
>+// GCC is free software; you can redistribute it and/or modify
>+// it under the terms of the GNU General Public License as published by
>+// the Free Software Foundation; either version 3, or (at your option)
>+// any later version.
>+//
>+// GCC is distributed in the hope that it will be useful,
>+// but WITHOUT ANY WARRANTY; without even the implied warranty of
>+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>+// GNU General Public License for more details.
>+//
>+// Under Section 7 of GPL version 3, you are granted additional
>+// permissions described in the GCC Runtime Library Exception, version
>+// 3.1, as published by the Free Software Foundation.
>+
>+// You should have received a copy of the GNU General Public License and
>+// a copy of the GCC Runtime Library Exception along with this program;
>+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
>+// <http://www.gnu.org/licenses/>.
>+
>+#include <experimental/contract>
>+#include <iostream>
>+
>+__attribute__ ((weak)) void
>+handle_contract_violation (const std::experimental::contract_violation &violation)
>+{
>+  std::cerr << "default std::handle_contract_violation called: " << std::endl

No need for flushing with endl here, just \n please.

>+    << " " << violation.file_name()
>+    << " " << violation.line_number()
>+    << " " << violation.function_name()
>+    << " " << violation.comment()
>+    << " " << violation.assertion_level()
>+    << " " << violation.assertion_role()
>+    << " " << (int)violation.continuation_mode()
>+    << std::endl;

And this will flush too, which typically isn't needed for stderr
because it's unbuffered. But somebody could have fiddled with cerr, so
doing this final flush seems OK.

>+}
>+
>diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
>index 6f672924a73..baf01913a90 100644
>--- a/libstdc++-v3/acinclude.m4
>+++ b/libstdc++-v3/acinclude.m4
>@@ -49,7 +49,7 @@ AC_DEFUN([GLIBCXX_CONFIGURE], [
>   # Keep these sync'd with the list in Makefile.am.  The first provides an
>   # expandable list at autoconf time; the second provides an expandable list
>   # (i.e., shell variable) at configure time.
>-  m4_define([glibcxx_SUBDIRS],[include libsupc++ src src/c++98 src/c++11 src/c++17 src/c++20 src/filesystem src/libbacktrace doc po testsuite python])
>+  m4_define([glibcxx_SUBDIRS],[include libsupc++ src src/c++98 src/c++11 src/c++17 src/c++20 src/filesystem src/libbacktrace src/experimental doc po testsuite python])
>   SUBDIRS='glibcxx_SUBDIRS'
>
>   # These need to be absolute paths, yet at the same time need to
>diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
>index 96137a6621a..a6f9912cb9b 100644
>--- a/libstdc++-v3/include/Makefile.am
>+++ b/libstdc++-v3/include/Makefile.am
>@@ -769,6 +769,7 @@ experimental_headers = \
> 	${experimental_srcdir}/array \
> 	${experimental_srcdir}/buffer \
> 	${experimental_srcdir}/chrono \
>+	${experimental_srcdir}/contract \
> 	${experimental_srcdir}/deque \
> 	${experimental_srcdir}/executor \
> 	${experimental_srcdir}/forward_list \
>diff --git a/libstdc++-v3/src/Makefile.am b/libstdc++-v3/src/Makefile.am
>index b83c222d51d..6f08068326d 100644
>--- a/libstdc++-v3/src/Makefile.am
>+++ b/libstdc++-v3/src/Makefile.am
>@@ -37,7 +37,7 @@ backtrace_supported_h =
> endif
>
> ## Keep this list sync'd with acinclude.m4:GLIBCXX_CONFIGURE.
>-SUBDIRS = c++98 c++11 c++17 c++20 $(filesystem_dir) $(backtrace_dir)
>+SUBDIRS = c++98 c++11 c++17 c++20 $(filesystem_dir) $(backtrace_dir) experimental
>
> # Cross compiler support.
> if VTV_CYGMIN
>@@ -75,6 +75,7 @@ endif
> if ENABLE_BACKTRACE
> vpath % $(top_srcdir)/src/libbacktrace
> endif
>+vpath % $(top_srcdir)/src/experimental
>
> if GLIBCXX_LDBL_COMPAT
> ldbl_compat_sources = compatibility-ldbl.cc
>diff --git a/libstdc++-v3/src/experimental/Makefile.am b/libstdc++-v3/src/experimental/Makefile.am
>new file mode 100644
>index 00000000000..a1c2f62a518
>--- /dev/null
>+++ b/libstdc++-v3/src/experimental/Makefile.am
>@@ -0,0 +1,96 @@
>+## Makefile for experimental additions to the GNU C++ Standard library.
>+##
>+## Copyright (C) 2014-2022 Free Software Foundation, Inc.
>+##
>+## Process this file with automake to produce Makefile.in.
>+##
>+## This file is part of GCC.
>+##
>+## GCC is free software; you can redistribute it and/or modify
>+## it under the terms of the GNU General Public License as published by
>+## the Free Software Foundation; either version 3, or (at your option)
>+## any later version.
>+##
>+## GCC is distributed in the hope that it will be useful,
>+## but WITHOUT ANY WARRANTY; without even the implied warranty of
>+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>+## GNU General Public License for more details.
>+##
>+## You should have received a copy of the GNU General Public License
>+## along with GCC; see the file COPYING3.  If not see
>+## <http://www.gnu.org/licenses/>.
>+
>+include $(top_srcdir)/fragment.am
>+
>+toolexeclib_LTLIBRARIES = libstdc++exp.la
>+
>+headers =
>+
>+sources = \
>+	contract.cc
>+
>+# vpath % $(top_srcdir)/src/experimental
>+
>+libstdc__exp_la_SOURCES = $(sources)
>+
>+# AM_CXXFLAGS needs to be in each subdirectory so that it can be
>+# modified in a per-library or per-sub-library way.  Need to manually
>+# set this option because CONFIG_CXXFLAGS has to be after
>+# OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
>+# as the occasion calls for it.
>+AM_CXXFLAGS = \
>+	-std=gnu++17 -nostdinc++ \
>+	$(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
>+	$(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
>+	$(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \
>+	-fimplicit-templates
>+
>+AM_MAKEFLAGS = \
>+	"gxx_include_dir=$(gxx_include_dir)"
>+
>+# Libtool notes
>+
>+# 1) In general, libtool expects an argument such as `--tag=CXX' when
>+# using the C++ compiler, because that will enable the settings
>+# detected when C++ support was being configured.  However, when no
>+# such flag is given in the command line, libtool attempts to figure
>+# it out by matching the compiler name in each configuration section
>+# against a prefix of the command line.  The problem is that, if the
>+# compiler name and its initial flags stored in the libtool
>+# configuration file don't match those in the command line, libtool
>+# can't decide which configuration to use, and it gives up.  The
>+# correct solution is to add `--tag CXX' to LTCXXCOMPILE and maybe
>+# CXXLINK, just after $(LIBTOOL), so that libtool doesn't have to
>+# attempt to infer which configuration to use.
>+#
>+# The second tag argument, `--tag disable-shared` means that libtool
>+# only compiles each source once, for static objects. In actuality,
>+# glibcxx_lt_pic_flag and glibcxx_compiler_shared_flag are added to
>+# the libtool command that is used create the object, which is
>+# suitable for shared libraries.  The `--tag disable-shared` must be
>+# placed after --tag CXX lest things CXX undo the affect of
>+# disable-shared.
>+
>+# 2) Need to explicitly set LTCXXCOMPILE so that EXTRA_CXX_FLAGS is
>+# last. (That way, things like -O2 passed down from the toplevel can
>+# be overridden by --enable-debug.)
>+LTCXXCOMPILE = \
>+	$(LIBTOOL) --tag CXX --tag disable-shared \
>+	$(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
>+	--mode=compile $(CXX) $(TOPLEVEL_INCLUDES) \
>+	$(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS) $(EXTRA_CXX_FLAGS)
>+
>+LTLDFLAGS = $(shell $(SHELL) $(top_srcdir)/../libtool-ldflags $(LDFLAGS))
>+
>+# 3) We'd have a problem when building the shared libstdc++ object if
>+# the rules automake generates would be used.  We cannot allow g++ to
>+# be used since this would add -lstdc++ to the link line which of
>+# course is problematic at this point.  So, we get the top-level
>+# directory to configure libstdc++-v3 to use gcc as the C++
>+# compilation driver.
>+CXXLINK = \
>+	$(LIBTOOL) --tag CXX --tag disable-shared \
>+	$(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
>+	--mode=link $(CXX) \
>+	$(VTV_CXXLINKFLAGS) \
>+	$(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) $(LTLDFLAGS) -o $@
>diff --git a/libstdc++-v3/include/experimental/contract b/libstdc++-v3/include/experimental/contract
>new file mode 100644
>index 00000000000..16f3fd5fd5a
>--- /dev/null
>+++ b/libstdc++-v3/include/experimental/contract
>@@ -0,0 +1,82 @@
>+// Contracts support header for -*- C++ -*-
>+
>+// Copyright (C) 1995-2022 Free Software Foundation, Inc.

Just 2022 again (or earlier if this is based on Lock3 code contributed
earilier? but not 1995 I think!)

>+// This file is part of GCC.
>+//
>+// GCC is free software; you can redistribute it and/or modify
>+// it under the terms of the GNU General Public License as published by
>+// the Free Software Foundation; either version 3, or (at your option)
>+// any later version.
>+//
>+// GCC is distributed in the hope that it will be useful,
>+// but WITHOUT ANY WARRANTY; without even the implied warranty of
>+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>+// GNU General Public License for more details.
>+//
>+// Under Section 7 of GPL version 3, you are granted additional
>+// permissions described in the GCC Runtime Library Exception, version
>+// 3.1, as published by the Free Software Foundation.
>+
>+// You should have received a copy of the GNU General Public License and
>+// a copy of the GCC Runtime Library Exception along with this program;
>+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
>+// <http://www.gnu.org/licenses/>.
>+
>+/** @file contract
>+ *  This is a Standard C++ Library header.
>+ */
>+
>+#ifndef _GLIBCXX_CONTRACT
>+#define _GLIBCXX_CONTRACT 1
>+
>+#pragma GCC system_header
>+
>+#if __cplusplus >= 201703L
>+
>+#include <bits/c++config.h>

This is included by <string_view> so not needed here.

OK for trunk with those tweaks, thanks.



>+#include <string_view>
>+#include <cstdint>
>+
>+namespace std _GLIBCXX_VISIBILITY(default)
>+{
>+_GLIBCXX_BEGIN_NAMESPACE_VERSION
>+
>+namespace experimental
>+{
>+  // From P1332
>+  enum class contract_violation_continuation_mode {
>+    NEVER_CONTINUE, MAYBE_CONTINUE
>+  };
>+
>+  class contract_violation {
>+    const char* _M_file;
>+    const char* _M_function;
>+    const char* _M_comment;
>+    const char* _M_level;
>+    const char* _M_role;
>+    uint_least32_t _M_line;
>+    signed char _M_continue;
>+  public:
>+    // From N4820
>+    uint_least32_t line_number() const noexcept { return _M_line; }
>+    string_view file_name() const noexcept { return _M_file; }
>+    string_view function_name() const noexcept { return _M_function; }
>+    string_view comment() const noexcept { return _M_comment; }
>+    string_view assertion_level() const noexcept { return _M_level; }
>+    // From P1332
>+    string_view assertion_role() const noexcept { return _M_role; }
>+    contract_violation_continuation_mode continuation_mode() const noexcept
>+    { return static_cast<contract_violation_continuation_mode>(_M_continue); }
>+  };
>+
>+} // namespace experimental
>+
>+_GLIBCXX_END_NAMESPACE_VERSION
>+} // namespace std
>+
>+// To override the contract violation handler, define
>+//void ::handle_contract_violation (const std::experimental::contract_violation &);
>+
>+#endif // C++17
>+#endif // _GLIBCXX_CONTRACT