Better input framework error messages for unset non-optionals

The input framework currently gives a rather opaque error message when
encountering a line in which a required value is not provided. This
change updates this behavior; the error message now provides the record
element (or the name or the index element) which was not set in the
input data, even though it is required to be set by the underlying Zeek
type.

testing/btest/scripts/base/frameworks/input/invalidtable.zeek

@@ -0,0 +1,72 @@
+# @TEST-EXEC: btest-bg-run zeek zeek -b %INPUT
+# @TEST-EXEC: btest-bg-wait 10
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-sort btest-diff out
+# @TEST-EXEC: sed 1d .stderr > .stderrwithoutfirstline
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff .stderrwithoutfirstline
+
+@TEST-START-FILE input.log
+#separator \x09
+#fields	i	y	s
+name	-	127.0.0.1
+name	name2	127.0.0.1
+@TEST-END-FILE
+
+redef exit_only_after_terminate = T;
+redef InputAscii::fail_on_invalid_lines = T;
+
+global outfile: file;
+
+module A;
+
+type Idx: record {
+	i: string;
+	y: string;
+};
+
+type Val: record {
+	s: set[addr];
+};
+
+global endcount: count = 0;
+
+global servers: table[string, string] of Val = table();
+
+event handle_our_errors(desc: Input::TableDescription, msg: string, level: Reporter::Level)
+	{
+	print outfile, "TableErrorEvent", msg, level;
+	}
+
+event handle_our_errors_event(desc: Input::EventDescription, msg: string, level: Reporter::Level)
+	{
+	print outfile, "EventErrorEvent", msg, level;
+	}
+
+event line(description: Input::EventDescription, tpe: Input::Event, v: Val)
+	{
+	print outfile, "Event", v;
+	}
+
+event zeek_init()
+	{
+	outfile = open("../out");
+	# first read in the old stuff into the table...
+	Input::add_table([$source="../input.log", $name="ssh", $error_ev=handle_our_errors, $idx=Idx, $val=Val, $destination=servers]);
+	}
+
+event Input::end_of_data(name: string, source:string)
+	{
+	++endcount;
+
+	# ... and when we're done, move to reading via events.
+	# This makes the reads sequential, avoiding races in the output.
+	if ( endcount == 1 )
+		{
+		Input::add_event([$source="../input.log", $name="sshevent", $error_ev=handle_our_errors_event, $fields=Val, $want_record=T, $ev=line]);
+		}
+
+	if ( endcount == 2 )
+		{
+		print outfile, servers;
+		terminate();
+		}
+	}