From ec08b369ec1b348d8eeeffd3d48cb7138a918437 Mon Sep 17 00:00:00 2001
From: Akim Demaille <akim.demaille@gmail.com>
Date: Sun, 20 Jan 2019 08:23:41 +0100
Subject: [PATCH] c++: address -Wweak-vtables warnings

Reported by Derek Clegg
http://lists.gnu.org/archive/html/bug-bison/2019-01/msg00021.html

    aux/parser-internal.h:429:12: error: 'syntax_error' has no out-of-line virtual
         method definitions; its vtable will be emitted in every translation unit
         [-Werror,-Wweak-vtables]
       struct syntax_error : std::runtime_error

To avoid this warning, we need syntax_error to have a virtual function
defined in a compilation unit.  Let it be the destructor.  To comply
with C++98, this dtor should be 'throw()'.  Merely making YY_NOEXCEPT
be 'throw()' in C++98 triggers
errors (http://lists.gnu.org/archive/html/bug-bison/2019-01/msg00022.html),
so let's introduce YY_NOTHROW and flag only ~syntax_error with it.

Also, since we now have an explicit dtor, we need to provide an copy
ctor.

* configure.ac (warn_cxx): Add -Wweak-vtables.
* data/skeletons/c++.m4 (YY_NOTHROW): New.
(syntax_error): Declare the dtor, and define the copy ctor.
* data/skeletons/glr.cc, data/skeletons/lalr1.cc (~syntax_error):
Define.
---
 configure.ac            |  2 +-
 data/skeletons/c++.m4   | 11 ++++++++++-
 data/skeletons/glr.cc   |  3 +++
 data/skeletons/lalr1.cc |  2 ++
 tests/headers.at        |  1 +
 5 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index a3a471af..1b5343e7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -100,7 +100,7 @@ if test "$enable_gcc_warnings" = yes; then
     -Wpointer-arith -Wshadow
     -Wwrite-strings'
   warn_c='-Wbad-function-cast -Wstrict-prototypes'
-  warn_cxx='-Wextra-semi -Wnoexcept -Wundefined-func-template'
+  warn_cxx='-Wextra-semi -Wnoexcept -Wundefined-func-template -Wweak-vtables'
   # Warnings for the test suite only.
   #
   # -fno-color-diagnostics: Clang's use of colors in the error
diff --git a/data/skeletons/c++.m4 b/data/skeletons/c++.m4
index f6f95c4c..acc35b62 100644
--- a/data/skeletons/c++.m4
+++ b/data/skeletons/c++.m4
@@ -77,8 +77,10 @@ m4_define([b4_cxx_portability],
 // Support noexcept when possible.
 #if 201103L <= YY_CPLUSPLUS
 # define YY_NOEXCEPT noexcept
+# define YY_NOTHROW
 #else
 # define YY_NOEXCEPT
+# define YY_NOTHROW throw ()
 #endif
 
 // Support noexcept when possible.
@@ -217,7 +219,14 @@ m4_define([b4_public_types_declare],
       syntax_error (]b4_locations_if([const location_type& l, ])[const std::string& m)
         : std::runtime_error (m)]b4_locations_if([
         , location (l)])[
-      {}]b4_locations_if([
+      {}
+
+      syntax_error (const syntax_error& s)
+        : std::runtime_error (s.what ())]b4_locations_if([
+        , location (s.location)])[
+      {}
+
+      ~syntax_error () YY_NOEXCEPT YY_NOTHROW;]b4_locations_if([
 
       location_type location;])[
     };
diff --git a/data/skeletons/glr.cc b/data/skeletons/glr.cc
index 778c65b8..56217341 100644
--- a/data/skeletons/glr.cc
+++ b/data/skeletons/glr.cc
@@ -160,6 +160,9 @@ m4_pushdef([b4_parse_param], m4_defn([b4_parse_param_orig]))dnl
   ]b4_parser_class::~b4_parser_class[ ()
   {}
 
+  ]b4_parser_class[::syntax_error::~syntax_error () YY_NOEXCEPT YY_NOTHROW
+  {}
+
   int
   ]b4_parser_class[::operator() ()
   {
diff --git a/data/skeletons/lalr1.cc b/data/skeletons/lalr1.cc
index 053ba3be..1dc2851d 100644
--- a/data/skeletons/lalr1.cc
+++ b/data/skeletons/lalr1.cc
@@ -562,6 +562,8 @@ m4_if(b4_prefix, [yy], [],
   ]b4_parser_class::~b4_parser_class[ ()
   {}
 
+  ]b4_parser_class[::syntax_error::~syntax_error () YY_NOEXCEPT YY_NOTHROW
+  {}
 
   /*---------------.
   | Symbol types.  |
diff --git a/tests/headers.at b/tests/headers.at
index 87b765dd..bcf8525f 100644
--- a/tests/headers.at
+++ b/tests/headers.at
@@ -330,6 +330,7 @@ AT_CHECK([[$PERL -n -0777 -e '
       |YY_MOVE_OR_COPY
       |YY_MOVE_REF
       |YY_NOEXCEPT
+      |YY_NOTHROW
       |YY_NULLPTR
       |YY_RVREF
       |YY_\w+_INCLUDED