fix: boolean operations must have boolean operands

gnovm/pkg/gnolang/preprocess.go

@@ -755,6 +755,13 @@
 					resn := Preprocess(store, last, n2)
 					return resn, TRANS_CONTINUE
 				}
+
+				// Left and right hand expressions must evaluate to a boolean typed value if
+				// the operation is a logical AND or OR.
+				if (n.Op == LAND || n.Op == LOR) && (lt.Kind() != BoolKind || rt.Kind() != BoolKind) {
+					panic("operands of boolean operators must evaluate to boolean typed values")
+				}
+
 				// General case.
 				lcx, lic := n.Left.(*ConstExpr)
 				rcx, ric := n.Right.(*ConstExpr)

gnovm/tests/files/bool6.gno

@@ -0,0 +1,12 @@
+package main
+
+func main() {
+	println(X())
+}
+
+func X() string {
+	return "hello" || "world"
+}
+
+// Error:
+// main/files/bool6.gno:8: operands of boolean operators must evaluate to boolean typed values

gnovm/tests/files/bool7.gno

@@ -0,0 +1,16 @@
+package main
+
+// Ensure, when comparing evaluated boolean operand types, that the kinds produced
+// are the same when one operand is typed and the other is untyped.
+func main() {
+	println(boolAndTrue(true))
+	println(boolAndTrue(false))
+}
+
+func boolAndTrue(b bool) bool {
+	return b && true
+}
+
+// Output:
+// true
+// false