fix: handle untyped constant expressions in append()

gnovm/pkg/gnolang/preprocess.go

@@ -1006,6 +1006,23 @@
 								n.Args[1] = args1
 							}
 						}
+						// Another special case for append: adding untyped constants.
+						// They must be converted to the array type for consistency.
+						for i, arg := range n.Args[1:] {
+							if _, ok := arg.(*ConstExpr); !ok {
+								// Consider only constant expressions.
+								continue
+							}
+							if t1 := evalStaticTypeOf(store, last, arg); t1 != nil && !isUntyped(t1) {
+								// Consider only untyped values (including nil).
+								continue
+							}
+							// Get the array type from the first argument and convert to it.
+							s0 := evalStaticTypeOf(store, last, n.Args[0])
+							tx := constType(arg, s0.Elem())
+							var arg1 Expr = Call(tx, arg)
+							n.Args[i+1] = Preprocess(nil, last, arg1).(Expr)
+						}
 					} else if fv.PkgPath == uversePkgPath && fv.Name == "copy" {
 						if len(n.Args) == 2 {
 							// If the second argument is a string,

gnovm/tests/files/append5.gno

@@ -0,0 +1,10 @@
+package main
+
+func main() {
+	var errors []error
+	errors = append(errors, nil, nil)
+	println(len(errors))
+}
+
+// Output:
+// 2

gnovm/tests/files/append6.gno

@@ -0,0 +1,12 @@
+package main
+
+func main() {
+	const x = 118999
+	y := 11
+	p := []int{}
+	p = append(p, x, y)
+	println(p[0] + p[1])
+}
+
+// Output:
+// 119010