Add regression tests for `$unit::` reference order

Check separately that `$unit::` references to a variable, named event, and
parameter declared later in the compilation unit are rejected.

Also check that preceding compilation-unit items remain visible and that a
later function name remains visible as permitted by the LRM section 3.12.1
exception.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

ivtest/ivltests/sv_unit_order_event_fail.v

@@ -0,0 +1,9 @@
+// Check that $unit:: does not allow a forward named event reference.
+
+module test;
+
+  initial -> $unit::value;
+
+endmodule
+
+event value;

ivtest/ivltests/sv_unit_order_parameter_fail.v

@@ -0,0 +1,9 @@
+// Check that $unit:: does not allow a forward parameter reference.
+
+module test;
+
+  localparam integer result = $unit::value;
+
+endmodule
+
+parameter integer value = 42;

ivtest/ivltests/sv_unit_order_valid.v

@@ -0,0 +1,44 @@
+// Check legal $unit:: references and a forward function reference.
+
+parameter integer parameter_value = 17;
+integer variable_value = 42;
+event event_value;
+
+module test;
+
+  reg event_seen;
+  reg failed;
+
+  `define check(val, exp) \
+    if (val !== exp) begin \
+      $display("FAILED(%0d). '%s' expected %b, got %b", `__LINE__, \
+               `"val`", exp, val); \
+      failed = 1'b1; \
+    end
+
+  always @($unit::event_value)
+    event_seen = 1'b1;
+
+  initial begin
+    failed = 1'b0;
+    event_seen = 1'b0;
+
+    #1;
+    -> $unit::event_value;
+    #1;
+
+    `check($unit::parameter_value, 17);
+    `check($unit::variable_value, 42);
+    `check(event_seen, 1'b1);
+    `check($unit::function_value(), 23);
+
+    if (!failed) begin
+      $display("PASSED");
+    end
+  end
+
+endmodule
+
+function integer function_value;
+  function_value = 23;
+endfunction

ivtest/ivltests/sv_unit_order_variable_fail.v

@@ -0,0 +1,9 @@
+// Check that $unit:: does not allow a forward variable reference.
+
+module test;
+
+  initial $display("%0d", $unit::value);
+
+endmodule
+
+integer value;

ivtest/regress-vvp.list

@@ -505,6 +505,10 @@ sv_type_param_restrict_union1	vvp_tests/sv_type_param_restrict_union1.json
 sv_type_param_restrict_union2	vvp_tests/sv_type_param_restrict_union2.json
 sv_type_param_restrict_union_fail1	vvp_tests/sv_type_param_restrict_union_fail1.json
 sv_type_param_restrict_union_fail2	vvp_tests/sv_type_param_restrict_union_fail2.json
+sv_unit_order_event_fail	vvp_tests/sv_unit_order_event_fail.json
+sv_unit_order_parameter_fail	vvp_tests/sv_unit_order_parameter_fail.json
+sv_unit_order_valid		vvp_tests/sv_unit_order_valid.json
+sv_unit_order_variable_fail	vvp_tests/sv_unit_order_variable_fail.json
 sv_wildcard_import8		vvp_tests/sv_wildcard_import8.json
 sv_wildcard_port_order		vvp_tests/sv_wildcard_port_order.json
 sv_wildcard_port_order_relaxed	vvp_tests/sv_wildcard_port_order_relaxed.json

ivtest/vvp_tests/sv_unit_order_event_fail.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "CE",
+    "source"        : "sv_unit_order_event_fail.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

ivtest/vvp_tests/sv_unit_order_parameter_fail.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "CE",
+    "source"        : "sv_unit_order_parameter_fail.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

ivtest/vvp_tests/sv_unit_order_valid.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "normal",
+    "source"        : "sv_unit_order_valid.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}

ivtest/vvp_tests/sv_unit_order_variable_fail.json

@@ -0,0 +1,5 @@
+{
+    "type"          : "CE",
+    "source"        : "sv_unit_order_variable_fail.v",
+    "iverilog-args" : [ "-g2005-sv" ]
+}