fix: verify type is ok

gnovm/pkg/gnolang/preprocess.go

@@ -1857,7 +1857,10 @@ func Preprocess(store Store, ctx BlockNode, n Node) Node {
 				tvs := make([]TypedValue, numNames)
 				if numNames > 1 && len(n.Values) == 1 {
 					// special case if `var a, b, c T? = f()` form.
-					cx := n.Values[0].(*CallExpr)
+					cx, ok := n.Values[0].(*CallExpr)
+					if !ok {
+						panic("should not happen")
+					}
 					tt := evalStaticTypeOfRaw(store, last, cx).(*tupleType)
 					if len(tt.Elts) != numNames {
 						panic("should not happen")

gnovm/tests/files/var18.gno

@@ -0,0 +1,11 @@
+package main
+
+func main() {
+	var a, b = 1
+}
+
+// Error:
+// main/files/var18.gno:3: should not happen:
+// --- preprocess stack ---
+// stack 0: func main() { var a<VPBlock(1,0)>, b<VPBlock(1,1)> = (const (1 <untyped> bigint)) }
+// ------------------------

gnovm/tests/files/var19.gno

@@ -0,0 +1,11 @@
+package main
+
+func main() {
+	var a, b, c = 1, a+1
+	println(a)
+	println(b)
+	println(c)
+}
+
+// Error:
+// main/files/var19.gno:3: constant definition loop with a

gnovm/tests/files/var20.gno

@@ -0,0 +1,15 @@
+package main
+
+func r() int {
+	return 1
+}
+
+func main() {
+	var a, b, c = r()
+}
+
+// Error:
+// main/files/var20.gno:7: should not happen:
+// --- preprocess stack ---
+// stack 0: func main() { var a<VPBlock(1,0)>, b<VPBlock(1,1)>, c<VPBlock(1,2)> = r<VPBlock(3,0)>() }
+// ------------------------