fix: handle untyped constant expressions in append()

gnovm/pkg/gnolang/preprocess.go

@@ -1013,6 +1013,23 @@
 								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())
+							arg1 := 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/pkg/gnolang/values_conversions.go

@@ -77,6 +77,10 @@
 	}
 	// special case for undefined/nil source
 	if tv.IsUndefined() {
+		switch t.Kind() {
+		case BoolKind, StringKind, IntKind, Int8Kind, Int16Kind, Int32Kind, Int64Kind, UintKind, Uint8Kind, Uint16Kind, Uint32Kind, Uint64Kind, Float32Kind, Float64Kind, BigintKind, BigdecKind:
+			panic(fmt.Sprintf("cannot convert %v to %v", tv, t))
+		}
 		tv.T = t
 		return
 	}

gnovm/tests/files/append5.gno

@@ -7,4 +7,4 @@ func main() {
 }
 
 // Output:
-// X
+// X

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

gnovm/tests/files/append7.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/convert4.gno

@@ -0,0 +1,7 @@
+package main
+
+func main() {
+	println(int(nil))
+}
+
+// error: cannot convert (undefined) to int

gnovm/tests/files/convert5.gno

@@ -0,0 +1,9 @@
+package main
+
+func main() {
+	var ints []int
+	ints = append(ints, nil, nil)
+	println(ints)
+}
+
+// error: cannot convert (undefined) to int