fix(parse): permit unbraced function expression as index and to is/as

regression-tests/pure2-bugfix-for-unbraced-function-expression.cpp2

@@ -0,0 +1,7 @@
+t: type = {
+  operator[]: (this, f) = { }
+}
+main: () -> int = {
+  (x := t()) { x[:() -> _ = 0]; }
+  [[assert: !(:() = 0; is int) ]]
+}

regression-tests/test-results/pure2-bugfix-for-unbraced-function-expression.cpp

@@ -0,0 +1,42 @@
+
+#define CPP2_USE_MODULES         Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-bugfix-for-unbraced-function-expression.cpp2"
+class t;
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-bugfix-for-unbraced-function-expression.cpp2"
+class t {
+  public: auto operator[](auto const& f) const -> void;
+
+  public: t() = default;
+  public: t(t const&) = delete; /* No 'that' constructor, suppress copy */
+  public: auto operator=(t const&) -> void = delete;
+#line 3 "pure2-bugfix-for-unbraced-function-expression.cpp2"
+};
+[[nodiscard]] auto main() -> int;
+
+
+//=== Cpp2 function definitions =================================================
+
+
+#line 2 "pure2-bugfix-for-unbraced-function-expression.cpp2"
+  auto t::operator[](auto const& f) const -> void{}
+
+[[nodiscard]] auto main() -> int{
+{
+auto const& x = t();
+#line 5 "pure2-bugfix-for-unbraced-function-expression.cpp2"
+  {cpp2::assert_in_bounds(x, []() -> auto { return 0;  }); }
+}
+#line 6 "pure2-bugfix-for-unbraced-function-expression.cpp2"
+  cpp2::Default.expects(!((cpp2::is<int>([]() -> void { 0;  }))), "");
+}
+

regression-tests/test-results/pure2-bugfix-for-unbraced-function-expression.cpp2.output

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

source/parse.h

@@ -3670,6 +3670,9 @@ class parser
                     && curr().type() != lexeme::LeftParen               // not imediatelly called
                     && curr().type() != lexeme::RightParen              // not as a last argument to function
                     && curr().type() != lexeme::Comma                   // not as first or in-the-middle, function argument
+                    && curr().type() != lexeme::RightBracket            // not as the last index argument
+                    && curr().as_string_view() == "is"                  // not as the argument to is
+                    && curr().as_string_view() == "as"                  // not as the argument to as
                 ) {
                     // this is a fix for a short function syntax that should have double semicolon used
                     // (check comment in expression_statement(bool semicolon_required))