Fix C++20 incompatibility from using exception specifications.

C++20 removed support for `throw()` exception specifications, so at
least clang-19 is now emitting errors on them. Replaced exception
specifications with BOOST_NOEXCEPT_OR_NOTHROW, which converts `throw()`
to `noexcept`, but keeps the code formally compatible with C++03.

.github/workflows/ci.yml

@@ -116,33 +116,24 @@ jobs:
           - toolset: clang
             compiler: clang++-13
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:22.04
-            os: ubuntu-latest
+            os: ubuntu-22.04
             install: clang-13
           - toolset: clang
             compiler: clang++-14
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:22.04
-            os: ubuntu-latest
+            os: ubuntu-22.04
             install: clang-14
           - toolset: clang
             compiler: clang++-15
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:22.04
-            os: ubuntu-latest
+            os: ubuntu-22.04
             install: clang-15
           - toolset: clang
             compiler: clang++-16
             cxxstd: "11,14,17,20,2b"
+            os: ubuntu-latest
             container: ubuntu:23.04
-            os: ubuntu-latest
             install: clang-16
-          - toolset: clang
-            compiler: clang++-17
-            cxxstd: "11,14,17,20,2b"
-            container: ubuntu:23.10
-            os: ubuntu-latest
-            install: clang-17
           - toolset: clang
             cxxstd: "11,14,17,2a"
             os: macos-11
@@ -236,7 +227,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Setup Boost
         shell: cmd
@@ -280,7 +271,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Install packages
         if: matrix.install
@@ -328,7 +319,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Install packages
         if: matrix.install
@@ -386,7 +377,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Install packages
         if: matrix.install
@@ -439,7 +430,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Setup Boost
         shell: cmd
@@ -488,7 +479,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Setup Boost
         shell: cmd
@@ -555,7 +546,7 @@ jobs:
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Setup Boost
         shell: cmd

include/boost/program_options/detail/value_semantic.hpp

@@ -8,10 +8,6 @@
 
 #include <boost/throw_exception.hpp>
 
-#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
-#   include <optional>
-#endif
-
 // forward declaration
 namespace boost { template<class T> class optional; }
 
@@ -173,22 +169,6 @@ namespace boost { namespace program_options {
         v = boost::any(boost::optional<T>(boost::any_cast<T>(a)));
     }
 
-#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
-    /** Validates std::optional arguments. */
-    template<class T, class charT>
-    void validate(boost::any& v,
-                  const std::vector<std::basic_string<charT> >& s,
-                  std::optional<T>*,
-                  int)
-    {
-        validators::check_first_occurrence(v);
-        validators::get_single_string(s);
-        boost::any a;
-        validate(a, s, (T*)0, 0);
-        v = boost::any(std::optional<T>(boost::any_cast<T>(a)));
-    }
-#endif
-
     template<class T, class charT>
     void 
     typed_value<T, charT>::

include/boost/program_options/errors.hpp

@@ -121,7 +121,7 @@ namespace boost { namespace program_options {
         /** gcc says that throw specification on dtor is loosened 
          *  without this line                                     
          *  */ 
-        BOOST_DEFAULTED_FUNCTION(~error_with_option_name() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~error_with_option_name() BOOST_NOEXCEPT_OR_NOTHROW, {})
 
 
         //void dump() const
@@ -183,7 +183,7 @@ namespace boost { namespace program_options {
 
         /** Creates the error_message on the fly
          *      Currently a thin wrapper for substitute_placeholders() */
-        virtual const char* what() const throw();
+        virtual const char* what() const BOOST_NOEXCEPT_OR_NOTHROW;
 
     protected:
         /** Used to hold the error text returned by what() */
@@ -209,7 +209,7 @@ namespace boost { namespace program_options {
         multiple_values() 
          : error_with_option_name("option '%canonical_option%' only takes a single argument"){}
 
-        BOOST_DEFAULTED_FUNCTION(~multiple_values() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~multiple_values() BOOST_NOEXCEPT_OR_NOTHROW, {})
     };
 
     /** Class thrown when there are several occurrences of an
@@ -220,7 +220,7 @@ namespace boost { namespace program_options {
         multiple_occurrences() 
          : error_with_option_name("option '%canonical_option%' cannot be specified more than once"){}
 
-        BOOST_DEFAULTED_FUNCTION(~multiple_occurrences() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~multiple_occurrences() BOOST_NOEXCEPT_OR_NOTHROW, {})
 
     };
 
@@ -233,7 +233,7 @@ namespace boost { namespace program_options {
        {
        }
 
-       BOOST_DEFAULTED_FUNCTION(~required_option() throw(), {})
+       BOOST_DEFAULTED_FUNCTION(~required_option() BOOST_NOEXCEPT_OR_NOTHROW, {})
     };
 
     /** Base class of unparsable options,
@@ -258,7 +258,7 @@ namespace boost { namespace program_options {
         /** Does NOT set option name, because no option name makes sense */
         virtual void set_option_name(const std::string&) {}
 
-        BOOST_DEFAULTED_FUNCTION(~error_with_no_option_name() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~error_with_no_option_name() BOOST_NOEXCEPT_OR_NOTHROW, {})
     };
 
 
@@ -270,7 +270,7 @@ namespace boost { namespace program_options {
         {
         }
 
-        BOOST_DEFAULTED_FUNCTION(~unknown_option() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~unknown_option() BOOST_NOEXCEPT_OR_NOTHROW, {})
     };
 
 
@@ -283,9 +283,9 @@ namespace boost { namespace program_options {
             m_alternatives(xalternatives)
         {}
 
-        BOOST_DEFAULTED_FUNCTION(~ambiguous_option() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~ambiguous_option() BOOST_NOEXCEPT_OR_NOTHROW, {})
 
-        const std::vector<std::string>& alternatives() const throw() {return m_alternatives;}
+        const std::vector<std::string>& alternatives() const BOOST_NOEXCEPT_OR_NOTHROW {return m_alternatives;}
 
     protected:
         /** Makes all substitutions using the template */
@@ -320,7 +320,7 @@ namespace boost { namespace program_options {
         {
         }
 
-        BOOST_DEFAULTED_FUNCTION(~invalid_syntax() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~invalid_syntax() BOOST_NOEXCEPT_OR_NOTHROW, {})
 
         kind_t kind() const {return m_kind;}
 
@@ -340,7 +340,7 @@ namespace boost { namespace program_options {
             m_substitutions["invalid_line"] = invalid_line;
         }
 
-        BOOST_DEFAULTED_FUNCTION(~invalid_config_file_syntax() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~invalid_config_file_syntax() BOOST_NOEXCEPT_OR_NOTHROW, {})
 
         /** Convenience functions for backwards compatibility */
         virtual std::string tokens() const {return m_substitutions.find("invalid_line")->second;    }
@@ -355,7 +355,7 @@ namespace boost { namespace program_options {
                        const std::string& original_token = "",
                        int option_style              = 0):
             invalid_syntax(kind, option_name, original_token, option_style) {}
-        BOOST_DEFAULTED_FUNCTION(~invalid_command_line_syntax() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~invalid_command_line_syntax() BOOST_NOEXCEPT_OR_NOTHROW, {})
     };
 
 
@@ -380,7 +380,7 @@ namespace boost { namespace program_options {
         {
         }
 
-        BOOST_DEFAULTED_FUNCTION(~validation_error() throw(), {})
+        BOOST_DEFAULTED_FUNCTION(~validation_error() BOOST_NOEXCEPT_OR_NOTHROW, {})
 
         kind_t kind() const { return m_kind; }
 

src/value_semantic.cpp

@@ -260,7 +260,7 @@ namespace boost { namespace program_options {
     }
 
 
-    const char* error_with_option_name::what() const throw()
+    const char* error_with_option_name::what() const BOOST_NOEXCEPT_OR_NOTHROW
     {
         // will substitute tokens each time what is run()
         substitute_placeholders(m_error_template);

test/optional_test.cpp

@@ -7,9 +7,6 @@ namespace po = boost::program_options;
 
 #include <boost/optional.hpp>
 
-#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
-#   include <optional>
-#endif
 #include <string>
 
 #include "minitest.hpp"
@@ -22,10 +19,9 @@ std::vector<std::string> sv(const char* array[], unsigned size)
     return r;
 }
 
-template<template<typename> class OptionalType>
 void test_optional()
 {
-    OptionalType<int> foo, bar, baz;
+    boost::optional<int> foo, bar, baz;
 
     po::options_description desc;
     desc.add_options()
@@ -52,9 +48,6 @@ void test_optional()
 
 int main(int, char*[])
 {
-    test_optional<boost::optional>();
-#ifndef BOOST_NO_CXX17_HDR_OPTIONAL
-    test_optional<std::optional>();
-#endif
+    test_optional();
     return 0;
 }