Suppress VARHIDDEN on dpi import arguments.

Changes

@@ -4,6 +4,11 @@ The contributors that suggested a given feature are shown in [].  [by ...]
 indicates the contributor was also the author of the fix; Thanks!
 
 
+* Verilator 3.831****
+
+****  Suppress VARHIDDEN on dpi import arguments.  [Ruben Diez]
+
+
 * Verilator 3.830 2011/11/27
 
 **   With "--language VAMS" support a touch of Verilog AMS.  [Holger Waechtler]

src/V3Link.cpp

@@ -319,7 +319,8 @@ private:
 		    }
 		} else {
 		    // User can disable the message at either point
-		    if (!nodep->fileline()->warnIsOff(V3ErrorCode::VARHIDDEN)
+		    if (!(m_ftaskp && m_ftaskp->dpiImport())
+			&& !nodep->fileline()->warnIsOff(V3ErrorCode::VARHIDDEN)
 			&& !foundp->fileline()->warnIsOff(V3ErrorCode::VARHIDDEN)) {
 			nodep->v3warn(VARHIDDEN,"Declaration of signal hides declaration in upper scope: "<<nodep->name());
 			foundp->v3warn(VARHIDDEN,"... Location of original declaration");

test_regress/t/t_var_bad_hide2.v

@@ -5,6 +5,11 @@
 
 module t;
 
+   // Arguable, but we won't throw a hidden warning on tcp_port
+   parameter tcp_port  = 5678;
+   import "DPI-C" function int dpii_func ( input integer  tcp_port,
+                                           output longint obj );
+   // 't' is hidden:
    integer t;
 
 endmodule