fix(parse): permit unbraced initializer after requires

regression-tests/pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp2

@@ -0,0 +1,2 @@
+f: <T> () requires std::regular<T> = g(T());
+main: ()                           = { }

regression-tests/test-results/gcc-13/gcc-version.output

@@ -0,0 +1,5 @@
+c++ (GCC) 13.1.1 20230429
+Copyright (C) 2023 Free Software Foundation, Inc.
+This is free software; see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+

regression-tests/test-results/pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp

@@ -0,0 +1,26 @@
+
+#define CPP2_USE_MODULES         Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp2"
+template<typename T> auto f() -> void;
+auto main() -> int;
+
+
+//=== Cpp2 function definitions =================================================
+
+#line 1 "pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp2"
+template<typename T> auto f() -> void
+requires (std::regular<T>)
+#line 1 "pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp2"
+ { g(T());  }
+auto main() -> int                 {}
+

regression-tests/test-results/pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp2.output

@@ -0,0 +1,2 @@
+pure2-bugfix-for-requires-clause-unbraced-function-initializer.cpp2... ok (all Cpp2, passes safety checks)
+

source/parse.h

@@ -1988,7 +1988,7 @@ struct declaration_node
     std::vector<std::unique_ptr<id_expression_node>> meta_functions;
     std::unique_ptr<parameter_declaration_list_node> template_parameters;
     source_position                                  requires_pos = {};
-    std::unique_ptr<expression_node>                 requires_clause_expression;
+    std::unique_ptr<logical_or_expression_node>      requires_clause_expression;
 
     source_position                 equal_sign = {};
     std::unique_ptr<statement_node> initializer;
@@ -5865,7 +5865,7 @@ class parser
     //G     meta-functions-list '@' id-expression
     //G
     //G requires-clause:
-    //G     'requires' expression
+    //G     'requires' logical-or-expression
     //G
     //G template-parameter-declaration-list
     //G     '<' parameter-declaration-seq '>'
@@ -6112,7 +6112,7 @@ class parser
         if (curr() == "requires") {
             n->requires_pos = curr().position();
             next();
-            auto e = expression();
+            auto e = logical_or_expression();
             if (!e) {
                 error("'requires' must be followed by an expression");
                 return {};