Expr: Handle TYPE_VOID in SizeExpr and AssignExpr::Typecheck()

@vpax reported surprising behavior when working with "void values".
While these are not exposed to script land, plumb the places he
pointed out are causing confusing behavior.

Closes #3640.

src/Expr.cc

@@ -1313,7 +1313,9 @@ SizeExpr::SizeExpr(ExprPtr arg_op) : UnaryExpr(EXPR_SIZE, std::move(arg_op)) {
 
     auto& t = op->GetType();
 
-    if ( t->Tag() == TYPE_ANY )
+    if ( t->Tag() == TYPE_VOID )
+        SetError("cannot take size of void");
+    else if ( t->Tag() == TYPE_ANY )
         SetType(base_type(TYPE_ANY));
     else if ( t->Tag() == TYPE_FILE || t->Tag() == TYPE_SUBNET || t->InternalType() == TYPE_INTERNAL_DOUBLE )
         SetType(base_type(TYPE_DOUBLE));
@@ -2204,6 +2206,11 @@ bool AssignExpr::TypeCheck(const AttributesPtr& attrs) {
     TypeTag bt1 = op1->GetType()->Tag();
     TypeTag bt2 = op2->GetType()->Tag();
 
+    if ( bt2 == TYPE_VOID ) {
+        ExprError("can't assign void value");
+        return false;
+    }
+
     if ( bt1 == TYPE_LIST && bt2 == TYPE_ANY )
         // This is ok because we cannot explicitly declare lists on
         // the script level.
@@ -2241,7 +2248,7 @@ bool AssignExpr::TypeCheck(const AttributesPtr& attrs) {
         }
     }
 
-    if ( op1->GetType()->Tag() == TYPE_RECORD && op2->GetType()->Tag() == TYPE_RECORD ) {
+    if ( bt1 == TYPE_RECORD && bt2 == TYPE_RECORD ) {
         if ( same_type(op1->GetType(), op2->GetType()) )
             return true;
 

testing/btest/Baseline/language.void-errors-2/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 2: identifier not defined: void

testing/btest/Baseline/language.void-errors-3/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 1: identifier not defined: void

testing/btest/Baseline/language.void-errors-4/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 2: return statement cannot have an expression (return (a))

testing/btest/Baseline/language.void-errors-5/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 4: cannot take size of void (sizeofx[3.4.5.6])

testing/btest/Baseline/language.void-errors-6/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 2: can't assign void value (y = x[3])

testing/btest/Baseline/language.void-errors-7/output

@@ -0,0 +1,4 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 5: can't assign void value (z = x())
+error in <...>/void-errors.zeek, line 6: value of type void illegal (print x())
+error in <...>/void-errors.zeek, line 7: cannot take size of void (sizeofx())

testing/btest/Baseline/language.void-errors/output

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+error in <...>/void-errors.zeek, line 7: identifier not defined: void

testing/btest/language/void-errors.zeek

@@ -0,0 +1,43 @@
+# @TEST-DOC: Zeek does not have a script land void type, but internally it does exist (indexing a set, or a function returning no result). Regression test #3640.
+#
+# @TEST-EXEC-FAIL: zeek -b %INPUT >output 2>&1
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff output
+
+# identifier void not defined...
+global x: void = 1;
+
+# @TEST-START-NEXT
+type R: record {
+	x: void;
+};
+
+
+# @TEST-START-NEXT
+function x(): void {
+	return "a";
+};
+
+# @TEST-START-NEXT
+function x() {
+	return "a";
+};
+
+# @TEST-START-NEXT
+
+global x = set(3.4.5.6, 9.8.7.6);
+print |x|;
+print |x[3.4.5.6]|;
+
+# @TEST-START-NEXT
+local x = set(5, 3);
+local y: any = x[3];
+print y;
+
+# @TEST-START-NEXT
+function x() {
+	print "x()";
+}
+
+global z: any = x();
+print x();
+print |x()|;