Add partial support for variadics (basic cases, only simple fold expressions)

Author: hsutter

regression-tests/pure2-variadics.cpp2

@@ -0,0 +1,17 @@
+
+x: <Ts...: type> type = {
+    tup: std::tuple<Ts...> = ();
+}
+
+make_string: <Args...: type> (forward args...: Args) -> _ = :std::string = args...;
+
+make: <T, Args...: type> (forward args...: Args) -> _ = :T = args...;
+
+main: ()
+= {
+    a: x<int, long, std::string> = ();
+
+    std::cout << std::string("xyzzy", 3) << "\n";
+    std::cout << make_string("plugh", :u8=3) << "\n";
+    std::cout << make<std::string>("abracadabra", :u8=3) << "\n";
+}

regression-tests/test-results/clang-12/pure2-variadics.cpp.execution

@@ -0,0 +1,3 @@
+xyz
+plu
+abr

regression-tests/test-results/clang-12/pure2-variadics.cpp.output

@@ -0,0 +1,3 @@
+xyz
+plu
+abr

regression-tests/test-results/gcc-10/pure2-variadics.cpp.execution

@@ -0,0 +1,3 @@
+xyz
+plu
+abr

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

@@ -0,0 +1,3 @@
+xyz
+plu
+abr

regression-tests/test-results/gcc-13/pure2-variadics.cpp.execution

@@ -0,0 +1 @@
+pure2-variadics.cpp

regression-tests/test-results/gcc-13/pure2-variadics.cpp.output

@@ -0,0 +1,50 @@
+
+#define CPP2_USE_MODULES         Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+
+#line 2 "pure2-variadics.cpp2"
+template<typename ...Ts> class x;
+    
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+
+#line 2 "pure2-variadics.cpp2"
+template<typename ...Ts> class x {
+    private: std::tuple<Ts...> tup {}; 
+    public: x() = default;
+    public: x(x const&) = delete; /* No 'that' constructor, suppress copy */
+    public: auto operator=(x const&) -> void = delete;
+
+#line 4 "pure2-variadics.cpp2"
+};
+
+template<typename ...Args> [[nodiscard]] auto make_string(Args&& ...args) -> auto;
+
+template<typename T, typename ...Args> [[nodiscard]] auto make(Args&& ...args) -> auto;
+
+auto main() -> int;
+
+
+//=== Cpp2 function definitions =================================================
+
+
+#line 6 "pure2-variadics.cpp2"
+template<typename ...Args> [[nodiscard]] auto make_string(Args&& ...args) -> auto { return std::string{CPP2_FORWARD(args)...};  }
+
+template<typename T, typename ...Args> [[nodiscard]] auto make(Args&& ...args) -> auto { return T{CPP2_FORWARD(args)...};  }
+
+auto main() -> int
+{
+    x<int,long,std::string> a {}; 
+
+    std::cout << std::string("xyzzy", 3) << "\n";
+    std::cout << make_string("plugh", cpp2::u8{3}) << "\n";
+    std::cout << make<std::string>("abracadabra", cpp2::u8{3}) << "\n";
+}
+

regression-tests/test-results/msvc-2022/pure2-variadics.cpp.execution

@@ -0,0 +1,2 @@
+pure2-variadics.cpp2... ok (all Cpp2, passes safety checks)
+

regression-tests/test-results/msvc-2022/pure2-variadics.cpp.output

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.2.1   Build 8911:1701
+cppfront compiler v0.2.1   Build 8912:1051
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

regression-tests/test-results/pure2-variadics.cpp

@@ -1 +1 @@
-"8911:1701"
+"8912:1051"

regression-tests/test-results/pure2-variadics.cpp2.output

@@ -2514,7 +2514,14 @@ class cppfront
                 emit(*type_id);
                 printer.print_cpp2("{", decl->position());
 
-                assert(decl->initializer);
+                if (!decl->initializer) {
+                    errors.emplace_back(
+                        decl->position(),
+                        "an anonymous object declaration must have '=' and an initializer"
+                    );
+                    return;
+                }
+
                 emit(*decl->initializer, false);
 
                 printer.print_cpp2("}", decl->position());
@@ -3888,8 +3895,6 @@ class cppfront
                 )
             {
                 pass = "&&";
-                //assert(emitting_move_that_function);    // this should already have been set
-                ////emitting_move_that_function = true;
             }
 
             auto func_name = get_enclosing_function_name();
@@ -3918,6 +3923,12 @@ class cppfront
 
         if (n.declaration->is_type()) {
             printer.print_cpp2("typename ", n.declaration->identifier->position());
+            if (n.declaration->is_variadic) {
+                printer.print_cpp2(
+                    "...",
+                    n.declaration->identifier->position()
+                );
+            }
             assert (n.declaration->identifier);
             emit(*n.declaration->identifier);
             return;
@@ -3999,6 +4010,7 @@ class cppfront
 
         if (
             !is_returns
+            && !n.declaration->is_variadic
             && !type_id.is_wildcard()
             && !is_dependent_parameter_type
             && !type_id.is_pointer_qualified()
@@ -4023,6 +4035,7 @@ class cppfront
         else if (
             type_id.is_wildcard()
             || is_dependent_parameter_type
+            || n.declaration->is_variadic
             )
         {
             auto name = std::string{"auto"};
@@ -4080,6 +4093,7 @@ class cppfront
             && !type_id.is_wildcard()
             && !is_dependent_parameter_type
             && !type_id.is_pointer_qualified()
+            && !n.declaration->is_variadic
             )
         {
             switch (n.pass) {
@@ -4097,7 +4111,23 @@ class cppfront
             printer.print_extra( " " + identifier);
         }
         else {
-            printer.print_cpp2( " " + identifier, n.declaration->identifier->position());
+            printer.print_cpp2( " ", n.declaration->identifier->position());
+            if (n.declaration->is_variadic)
+            {
+                if (n.direction() == passing_style::out) {
+                    errors.emplace_back(
+                        n.declaration->position(),
+                        "a variadic parameter cannot be 'out'"
+                    );
+                    return;
+                }
+
+                printer.print_cpp2(
+                    "...",
+                    n.declaration->identifier->position()
+                );
+            }
+            printer.print_cpp2( identifier, n.declaration->identifier->position());
         }
 
         if (
@@ -5167,7 +5197,7 @@ class cppfront
                 || n.is_object()
                 || (
                     n.is_function()
-                    && n.has_name()     // only if it is not unnambed function aka lambda
+                    && n.has_name()     // only if it is not unnamed function aka lambda
                     && n.initializer    // only if the function has a definition (is not abstract)
                     && printer.get_phase() == printer.phase2_func_defs
                     )

regression-tests/test-results/version

@@ -55,7 +55,7 @@ auto is_prefix_operator(token const& tok)
 
 
 //G postfix-operator:
-//G     one of  '++' '--' '*' '&' '~' '$'
+//G     one of  '++' '--' '*' '&' '~' '$' '...'
 //G
 auto is_postfix_operator(lexeme l)
     -> bool
@@ -67,6 +67,7 @@ auto is_postfix_operator(lexeme l)
           case lexeme::Ampersand:
           case lexeme::Tilde:
           case lexeme::Dollar:
+          case lexeme::Ellipsis:
         return true;
     break;default:
         return false;
@@ -2346,11 +2347,11 @@ struct declaration_node
 {
     //  The capture_group is declared first, because it should outlive
     //  any owned postfix_expressions that could refer to it
-    capture_group captures;
-
-    source_position pos;
+    capture_group                        captures;
+    source_position                      pos;
+    bool                                 is_variadic = false;
     std::unique_ptr<unqualified_id_node> identifier;
-    accessibility access = accessibility::default_;
+    accessibility                        access = accessibility::default_;
 
     enum active : std::uint8_t { a_function, an_object, a_type, a_namespace, an_alias };
     std::variant<
@@ -6224,7 +6225,7 @@ class parser
                     pos = start_pos;    // backtrack
                 }
                 else {
-                    error("expected , in parameter list", true, {}, true);
+                    error("expected ',' in parameter list", true, {}, true);
                 }
                 return {};
             }
@@ -6496,15 +6497,17 @@ class parser
         bool                                 is_parameter          = false,
         bool                                 is_template_parameter = false,
         std::unique_ptr<unqualified_id_node> id                    = {},
-        accessibility                        access                = {}
+        accessibility                        access                = {},
+        bool                                 is_variadic           = false
     )
         -> std::unique_ptr<declaration_node>
     {
         auto n = std::make_unique<declaration_node>( current_declarations.back() );
         n->pos = start;
 
-        n->identifier = std::move(id);
-        n->access     = access;
+        n->identifier  = std::move(id);
+        n->access      = access;
+        n->is_variadic = is_variadic;
 
         //  If we're in a type scope and the next token is ';', treat this as if
         //  ': _;' without an initializer.
@@ -7164,6 +7167,12 @@ class parser
                 return {};
             }
 
+            auto is_variadic = false;
+            if (curr().type() == lexeme::Ellipsis) {
+                is_variadic = true;
+                next();
+            }
+
             //  Provide some useful Cpp1->Cpp2 migration diagnostics for common mistakes
             //
             if (
@@ -7232,6 +7241,14 @@ class parser
                     return {};
                 }
 
+                if (is_variadic) {
+                    errors.emplace_back(
+                        curr().position(),
+                        "an alias declaration may not be variadic"
+                    );
+                    return {};
+                }
+
                 n->pos        = start_pos;
                 n->identifier = std::move(id);
                 n->access     = access;
@@ -7247,7 +7264,8 @@ class parser
                 is_parameter,
                 is_template_parameter,
                 std::move(id),
-                access
+                access,
+                is_variadic
             );
             if (!n) {
                 pos = start_pos;    // backtrack
@@ -7539,6 +7557,7 @@ class parse_tree_printer : printing_visitor
     {
         o << pre(indent) << "declaration [" << &n << "]\n";
         o << pre(indent+1) << "parent: [" << n.parent_declaration << "]\n";
+        o << pre(indent+1) << "is_variadic: [" << std::boolalpha << n.is_variadic << "]\n";
         switch (n.type.index()) {
         break;case declaration_node::a_function:
             o << pre(indent+1) << "function\n";