Fix error message on missing interface, bug985.

Changes

@@ -39,6 +39,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ****  Fix crash in commandArgsPlusMatch, bug987. [Jamie Iles]
 
+****  Fix error message on missing interface, bug985. [Todd Strader]
+
 
 * Verilator 3.876 2015-08-12
 

src/V3LinkDot.cpp

@@ -372,7 +372,14 @@ public:
 	    UINFO(9, "  insAllIface se"<<(void*)varSymp<<" "<<varp<<endl);
 	    AstIfaceRefDType* ifacerefp = varp->subDTypep()->castIfaceRefDType();
 	    if (!ifacerefp) varp->v3fatalSrc("Non-ifacerefs on list!");
-	    if (!ifacerefp->ifaceViaCellp()) ifacerefp->v3fatalSrc("Unlinked interface");
+	    if (!ifacerefp->ifaceViaCellp()) {
+		if (!ifacerefp->cellp()) {  // Probably a NotFoundModule, or a normal module if made mistake
+		    ifacerefp->v3error("Cannot find file containing interface: "<<AstNode::prettyName(ifacerefp->ifaceName()));
+		    continue;
+		} else {
+		    ifacerefp->v3fatalSrc("Unlinked interface");
+		}
+	    }
 	    VSymEnt* ifaceSymp = getNodeSym(ifacerefp->ifaceViaCellp());
 	    VSymEnt* ifOrPortSymp = ifaceSymp;
 	    // Link Modport names to the Modport Node under the Interface

test_regress/t/t_interface_missing_bad.pl

@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+compile (
+	fails=>1,
+	expect=>
+qr{%Error: t/t_interface_missing_bad.v:\d+: Cannot find file containing interface: foo_intf
+.*},
+    );
+
+ok(1);
+1;

test_regress/t/t_interface_missing_bad.v

@@ -0,0 +1,33 @@
+// DESCRIPTION: Verilator: Missing interface test
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2015 by Todd Strader.
+
+// Interface intentionally not defined
+//interface foo_intf;
+//   logic a;
+//endinterface
+
+module foo_mod
+  (
+   foo_intf foo
+   );
+endmodule
+
+module t (/*AUTOARG*/);
+
+   foo_intf the_foo ();
+
+   foo_mod
+     foo_mod
+       (
+	.foo (the_foo)
+	);
+
+   initial begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+
+endmodule
+