Fix redef of table index from clearing table. Addresses #1013.

`redef foo["x"] = 1` now acts like `redef foo += { ["x"] = 1 }`
instead of `redef foo = { ["x"] = 1 }`.

src/Var.cc

@@ -156,6 +156,12 @@ static void make_var(ID* id, BroType* t, init_class c, Expr* init,
 
 	if ( do_init )
 		{
+		if ( c == INIT_NONE && dt == VAR_REDEF && t->IsTable() &&
+		     init && init->Tag() == EXPR_ASSIGN )
+			// e.g. 'redef foo["x"] = 1' is missing an init class, but the
+			// intention clearly isn't to overwrite entire existing table val.
+			c = INIT_EXTRA;
+
 		if ( (c == INIT_EXTRA && id->FindAttr(ATTR_ADD_FUNC)) ||
 		     (c == INIT_REMOVE && id->FindAttr(ATTR_DEL_FUNC)) )
 			// Just apply the function.

testing/btest/Baseline/language.table-redef/out

@@ -0,0 +1,6 @@
+{
+[def] = 99.0,
+[neat] = 1.0,
+[cool] = 28.0,
+[abc] = 8.0
+}

testing/btest/language/table-redef.bro

@@ -0,0 +1,26 @@
+# @TEST-EXEC: bro -b %INPUT > out
+# @TEST-EXEC: btest-diff out
+
+const foo: table[string] of double &redef;
+
+# full (re)initialization
+redef foo = { ["nope"] = 37.0 };
+
+# full (re)initialization, discards "nope" index
+redef foo = { ["abc"] = 42.0 };
+
+# add elements
+redef foo += { ["def"] = -42.0, ["ghi"] = 7.0 };
+
+# remove elements from LHS based on indices shared with RHS
+redef foo -= { ["ghi"] = 0.0 };
+
+# RHS can be a table value
+redef foo += table(["cool"] = 5.0, ["neat"] = 1.0);
+
+# Redef at a single index is allowed, same as += when RHS has overlapping index
+redef foo["cool"] = 28.0;
+redef foo["abc"] = 8.0;
+redef foo += { ["def"] = 99.0 };
+
+print foo;