Run postconditions before the 'return'

So they correctly see the pre-moved named return value(s)

The following example now works correctly - before this commit, the postconditions would fail because the moved-from strings were zero length because of the automatic move-from-definite-last-use of the named return values

    make_string: () -> (ret: std::string = "xyzzy")
        post (ret.length() == ret.length()$ + 5)
    = {
        ret += " and ";
    }

    make_strings: ()
    -> (
        a: std::string = "xyzzy",
        b: std::string = "plugh"
        )
        post (a.length() == b.length() == 5)
    = { }

    main: () = {
        std::cout << make_string() + "plugh\n";
        std::cout << make_strings().a + make_strings().b + "\n";
    }

Author: hsutter

include/cpp2util.h

@@ -242,6 +242,7 @@
     #if defined(__cpp_lib_format) || (defined(_MSC_VER) && _MSC_VER >= 1929)
         #include <format>
     #endif
+    #include <functional>
     #include <iostream>
     #include <iterator>
     #include <limits>
@@ -1576,6 +1577,11 @@ constexpr auto as( X const& x ) -> decltype(auto)
 //  finally_success ensures something is run at the end of a scope
 //      if no exception is thrown
 //
+//  finally_presuccess ensures a group of add'd operations are run
+//      immediately before (not after) the return if no exception is
+//      thrown - right now this is used only for postconditions, so
+//      they can inspect named return values before they're moved from
+//
 //-----------------------------------------------------------------------
 //
 
@@ -1631,6 +1637,39 @@ class finally
 };
 
 
+class finally_presuccess
+{
+public:
+    finally_presuccess() = default;
+
+    auto add(const auto& f) { fs.push_back(f); }
+
+    //  In compiled Cpp2 code, this function will be called
+    //  immediately before 'return' (both explicit and implicit)
+    auto run() {
+        if (invoke && ecount == std::uncaught_exceptions()) {
+            for (auto const& f : fs) {
+                f();
+            }
+        }
+        invoke = false;
+    }
+
+    ~finally_presuccess() noexcept {
+        run();
+    }
+
+    finally_presuccess(finally_presuccess const&) = delete;
+    void operator=    (finally_presuccess const&) = delete;
+    void operator=    (finally_presuccess &&)     = delete;
+
+private:
+    std::vector<std::function<void()>> fs;
+    int  ecount = std::uncaught_exceptions();
+    bool invoke = true;
+};
+
+
 //-----------------------------------------------------------------------
 //
 //  args: see main() arguments as vector<string_view>

regression-tests/mixed-postexpression-with-capture.cpp2

@@ -7,6 +7,8 @@
 
 main: () -> int = {
     insert_at( 0, 42 );
+    std::cout << make_string() + "plugh\n";
+    std::cout << make_strings().a + make_strings().b + "\n";
 }
 
 vec: std::vector<int> = ();
@@ -17,3 +19,20 @@ insert_at: (where: int, val: int)
 = {
     vec.push_back(val);
 }
+
+make_string: () -> (ret: std::string = "xyzzy")
+    post (ret.length() == ret.length()$ + 5)
+= {
+    ret += " and ";
+}
+
+make_strings: ()
+-> (
+    a: std::string = "xyzzy",
+    b: std::string = "plugh"
+    )
+    post (a.length() == b.length() == 5)
+= {
+    // 'return' is generated when omitted like this
+}
+

regression-tests/test-results/clang-12/mixed-postexpression-with-capture.cpp.execution

@@ -0,0 +1,2 @@
+xyzzy and plugh
+xyzzyplugh

regression-tests/test-results/gcc-10/mixed-postexpression-with-capture.cpp.execution

@@ -0,0 +1,2 @@
+xyzzy and plugh
+xyzzyplugh

regression-tests/test-results/gcc-10/pure2-bugfix-for-requires-clause-in-forward-declaration.cpp.output

@@ -6,12 +6,12 @@ pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:46: error: expect
 In file included from pure2-bugfix-for-requires-clause-in-forward-declaration.cpp:7:
 ../../../include/cpp2util.h:10005:47: error: static assertion failed: GCC 11 or higher is required to support variables and type-scope functions that have a 'requires' clause. This includes a type-scope 'forward' parameter of non-wildcard type, such as 'func: (this, forward s: std::string)', which relies on being able to add a 'requires' clause - in that case, use 'forward s: _' instead if you need the result to compile with GCC 10.
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:4:1: note: in expansion of macro ‘CPP2_REQUIRES_’
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:3: error: no declaration matches ‘element::element(auto:90&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::__ct ::n)>::type>::type, std::__cxx11::string>’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:3: error: no declaration matches ‘element::element(auto:91&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::__ct ::n)>::type>::type, std::__cxx11::string>’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:5:11: note: candidates are: ‘element::element(const element&)’
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:20: note:                 ‘template<class auto:88> element::element(auto:88&&)’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:20: note:                 ‘template<class auto:89> element::element(auto:89&&)’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:1:7: note: ‘class element’ defined here
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:5:78: error: expected unqualified-id before ‘{’ token
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:8: error: no declaration matches ‘element& element::operator=(auto:91&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::operator=::n)>::type>::type, std::__cxx11::string>’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:8: error: no declaration matches ‘element& element::operator=(auto:92&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::operator=::n)>::type>::type, std::__cxx11::string>’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:6:16: note: candidates are: ‘void element::operator=(const element&)’
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:16: note:                 ‘template<class auto:89> element& element::operator=(auto:89&&)’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:16: note:                 ‘template<class auto:90> element& element::operator=(auto:90&&)’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:1:7: note: ‘class element’ defined here

regression-tests/test-results/gcc-10/pure2-print.cpp.output

@@ -9,8 +9,8 @@ pure2-print.cpp2:66:1: note: in expansion of macro ‘CPP2_REQUIRES_’
 pure2-print.cpp2:94:1: note: in expansion of macro ‘CPP2_REQUIRES_’
 pure2-print.cpp2:7:41: error: ‘constexpr const T outer::object_alias’ is not a static data member of ‘class outer’
 pure2-print.cpp2:7:48: error: template definition of non-template ‘constexpr const T outer::object_alias’
-pure2-print.cpp2:65:14: error: no declaration matches ‘void outer::mytype::variadic(const auto:97& ...) requires (is_convertible_v<typename std::remove_cv<typename std::remove_reference<decltype(outer::mytype::variadic::x)>::type>::type, int> && ...)’
-pure2-print.cpp2:65:29: note: candidate is: ‘template<class ... auto:88> static void outer::mytype::variadic(const auto:88& ...)’
+pure2-print.cpp2:65:14: error: no declaration matches ‘void outer::mytype::variadic(const auto:98& ...) requires (is_convertible_v<typename std::remove_cv<typename std::remove_reference<decltype(outer::mytype::variadic::x)>::type>::type, int> && ...)’
+pure2-print.cpp2:65:29: note: candidate is: ‘template<class ... auto:89> static void outer::mytype::variadic(const auto:89& ...)’
 pure2-print.cpp2:8:19: note: ‘class outer::mytype’ defined here
 pure2-print.cpp2:93:37: error: no declaration matches ‘void outer::print(std::ostream&, const Args& ...) requires  cpp2::cmp_greater_eq(sizeof (Args)..., 0)’
 pure2-print.cpp2:93:37: note: no functions named ‘void outer::print(std::ostream&, const Args& ...) requires  cpp2::cmp_greater_eq(sizeof (Args)..., 0)’

regression-tests/test-results/gcc-13/mixed-postexpression-with-capture.cpp.execution

@@ -0,0 +1,2 @@
+xyzzy and plugh
+xyzzyplugh

regression-tests/test-results/mixed-captures-in-expressions-and-postconditions.cpp

@@ -46,8 +46,9 @@ auto insert_at(cpp2::in<int> where, cpp2::in<int> val) -> void
 
 #line 22 "mixed-captures-in-expressions-and-postconditions.cpp2"
 {
+    cpp2::finally_presuccess cpp2_finally_presuccess;
     cpp2::Default.expects(cpp2::cmp_less_eq(0,where) && cpp2::cmp_less_eq(where,CPP2_UFCS_0(ssize, vec)), "");
-    auto post_21_5 = cpp2::finally_success([&, _1 = CPP2_UFCS_0(ssize, vec)]{cpp2::Default.expects(CPP2_UFCS_0(ssize, vec) == _1 + 1, "");} );
+    cpp2_finally_presuccess.add([&, _1 = CPP2_UFCS_0(ssize, vec)]{cpp2::Default.expects(CPP2_UFCS_0(ssize, vec) == _1 + 1, "");} );
 #line 23 "mixed-captures-in-expressions-and-postconditions.cpp2"
     static_cast<void>(CPP2_UFCS(insert, vec, CPP2_UFCS_0(begin, vec) + where, val));
 }

regression-tests/test-results/mixed-postexpression-with-capture.cpp

@@ -21,10 +21,24 @@
 #line 8 "mixed-postexpression-with-capture.cpp2"
 [[nodiscard]] auto main() -> int;
 
-#line 12 "mixed-postexpression-with-capture.cpp2"
+#line 14 "mixed-postexpression-with-capture.cpp2"
 extern std::vector<int> vec;
 
 auto insert_at(cpp2::in<int> where, cpp2::in<int> val) -> void;
+using make_string_ret = std::string;
+
+
+#line 23 "mixed-postexpression-with-capture.cpp2"
+[[nodiscard]] auto make_string() -> make_string_ret;
+struct make_strings_ret { std::string a; std::string b; };
+
+
+
+#line 29 "mixed-postexpression-with-capture.cpp2"
+[[nodiscard]] auto make_strings() -> make_strings_ret;
+#line 38 "mixed-postexpression-with-capture.cpp2"
+
+#line 1 "mixed-postexpression-with-capture.cpp2"
 
 //=== Cpp2 function definitions =================================================
 
@@ -33,17 +47,45 @@ auto insert_at(cpp2::in<int> where, cpp2::in<int> val) -> void;
 #line 8 "mixed-postexpression-with-capture.cpp2"
 [[nodiscard]] auto main() -> int{
     insert_at(0, 42);
+    std::cout << make_string() + "plugh\n";
+    std::cout << make_strings().a + make_strings().b + "\n";
 }
 
 std::vector<int> vec {}; 
 
 auto insert_at(cpp2::in<int> where, cpp2::in<int> val) -> void
 
-#line 17 "mixed-postexpression-with-capture.cpp2"
+#line 19 "mixed-postexpression-with-capture.cpp2"
 {
+    cpp2::finally_presuccess cpp2_finally_presuccess;
     cpp2::Default.expects(cpp2::cmp_less_eq(0,where) && cpp2::cmp_less_eq(where,CPP2_UFCS_0(ssize, vec)), "");
-    auto post_16_5 = cpp2::finally_success([&, _1 = CPP2_UFCS_0(size, vec)]{cpp2::Default.expects(CPP2_UFCS_0(size, vec) == _1 + 1, "");} );
-#line 18 "mixed-postexpression-with-capture.cpp2"
+    cpp2_finally_presuccess.add([&, _1 = CPP2_UFCS_0(size, vec)]{cpp2::Default.expects(CPP2_UFCS_0(size, vec) == _1 + 1, "");} );
+#line 20 "mixed-postexpression-with-capture.cpp2"
     CPP2_UFCS(push_back, vec, val);
 }
 
+[[nodiscard]] auto make_string() -> make_string_ret
+
+{
+    cpp2::finally_presuccess cpp2_finally_presuccess;
+    std::string ret {"xyzzy"};
+    cpp2_finally_presuccess.add([&, _1 = CPP2_UFCS_0(length, ret)]{cpp2::Default.expects(CPP2_UFCS_0(length, ret) == _1 + 5, "");} );
+#line 26 "mixed-postexpression-with-capture.cpp2"
+    ret += " and ";
+cpp2_finally_presuccess.run(); return std::move(ret); }
+
+[[nodiscard]] auto make_strings() -> make_strings_ret
+
+#line 35 "mixed-postexpression-with-capture.cpp2"
+{
+cpp2::finally_presuccess cpp2_finally_presuccess;
+std::string a {"xyzzy"};
+std::string b {"plugh"};
+cpp2_finally_presuccess.add([&]{cpp2::Default.expects([_0 = CPP2_UFCS_0(length, a), _1 = CPP2_UFCS_0(length, b), _2 = 5]{ return _0==_1 && _1==_2; }(), "");} );
+#line 30 "mixed-postexpression-with-capture.cpp2"
+cpp2_finally_presuccess.run(); return  { std::move(a), std::move(b) }; 
+
+#line 36 "mixed-postexpression-with-capture.cpp2"
+    // 'return' is generated when omitted like this
+}
+

regression-tests/test-results/msvc-2022/mixed-postexpression-with-capture.cpp.execution

@@ -0,0 +1,2 @@
+xyzzy and plugh
+xyzzyplugh

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.3.0   Build 8B16:1224
+cppfront compiler v0.3.0   Build 8B19:0904
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

source/build.info

@@ -1 +1 @@
-"8B16:1224"
+"8B19:0904"

source/parse.h

@@ -2190,6 +2190,9 @@ struct function_type_node
 
     //  API
     //
+    auto has_postconditions() const
+        -> bool;
+
     auto is_function_with_this() const
         -> bool;
 
@@ -3480,6 +3483,16 @@ auto function_type_node::nth_parameter_type_name(int n) const
 }
 
 
+auto function_type_node::has_postconditions() const
+    -> bool
+{
+    return
+        std::ranges::find_if(
+            contracts,
+            [](auto const& e){ return *e->kind == "post"; }
+        ) != contracts.end();
+}
+
 auto function_type_node::is_function_with_this() const
     -> bool
 {

source/to_cpp1.h

@@ -1050,15 +1050,18 @@ class cppfront
     struct function_info
     {
         declaration_node const*                    decl                         = {};
+        function_type_node const*                  func                         = {};
         declaration_node::declared_value_set_funcs declared_value_set_functions = {};
         function_prolog                            prolog                       = {};
         std::vector<std::string>                   epilog                       = {};
 
         function_info(
-            declaration_node const* decl_,
+            declaration_node const*                    decl_,
+            function_type_node const*                  func_,
             declaration_node::declared_value_set_funcs declared_value_set_functions_
         )
             : decl{decl_}
+            , func{func_}
             , declared_value_set_functions{declared_value_set_functions_}
         { }
     };
@@ -1067,10 +1070,11 @@ class cppfront
         std::deque<function_info> list = { {} };
     public:
         auto push(
-            declaration_node const*               decl,
+            declaration_node const*                    decl,
+            function_type_node const*                  func,
             declaration_node::declared_value_set_funcs thats
         ) {
-            list.emplace_back(decl, thats);
+            list.emplace_back(decl, func, thats);
         }
 
         auto pop() {
@@ -2261,6 +2265,11 @@ class cppfront
     auto emit(return_statement_node const& n)
         -> void
     {
+        assert (!current_functions.empty());
+        if (current_functions.back().func->has_postconditions()) {
+            printer.print_cpp2( "cpp2_finally_presuccess.run(); ", n.position() );
+        }
+
         assert(n.identifier);
         assert(*n.identifier == "return");
         printer.print_cpp2("return ", n.position());
@@ -4319,13 +4328,12 @@ class cppfront
     {
         assert (n.kind);
 
-        //  For a postcondition, we'll wrap it in a final_action_success lambda
+        //  For a postcondition, we'll wrap it in a lambda and register it
         //
         if (*n.kind == "post") {
             auto lambda_intro = build_capture_lambda_intro_for(n.captures, n.position(), true);
             printer.print_cpp2(
-                "auto post_" + std::to_string(n.position().lineno) + "_" +
-                    std::to_string(n.position().colno) + " = cpp2::finally_success(" +
+                "cpp2_finally_presuccess.add(" +
                     lambda_intro + "{",
                 n.position()
             );
@@ -4374,7 +4382,7 @@ class cppfront
         }
         printer.print_cpp2(");", n.position());
 
-        //  For a postcondition, close out the final_action_success lambda
+        //  For a postcondition, close out the lambda
         //
         if (*n.kind == "post") {
             printer.print_cpp2( "} );", n.position()
@@ -5747,6 +5755,7 @@ class cppfront
 
             current_functions.push(
                 &n,
+                func.get(),
                 n.find_parent_declared_value_set_functions()
                 );
             auto guard = finally([&]{ current_functions.pop(); });
@@ -6065,6 +6074,10 @@ class cppfront
                     function_returns.emplace_back(nullptr);        // no return type at all
                 }
 
+                if (func->has_postconditions()) {
+                    current_functions.back().prolog.statements.push_back("cpp2::finally_presuccess cpp2_finally_presuccess;");
+                }
+
                 if (func->returns.index() == function_type_node::list)
                 {
                     auto& r = std::get<function_type_node::list>(func->returns);