fix: typed const conversion validation (gnolang#3117)

During preprocessing, validates if typed constants are convertible.
Fixes [issue](gnolang#2681)

Typed constants are convertible only in a lossless way.
That means that we can convert floats to integers if the fractional part
of the float is 0.

gnovm/pkg/gnolang/gno_test.go

@@ -129,6 +129,136 @@ func TestBuiltinIdentifiersShadowing(t *testing.T) {
 	}
 }
 
+func TestConvertTo(t *testing.T) {
+	t.Parallel()
+
+	testFunc := func(source, msg string) {
+		defer func() {
+			if len(msg) == 0 {
+				return
+			}
+
+			r := recover()
+
+			if r == nil {
+				t.Fail()
+			}
+
+			err := r.(*PreprocessError)
+			c := strings.Contains(err.Error(), msg)
+			if !c {
+				t.Fatalf(`expected "%s", got "%s"`, msg, r)
+			}
+		}()
+
+		m := NewMachine("test", nil)
+
+		n := MustParseFile("main.go", source)
+		m.RunFiles(n)
+		m.RunMain()
+	}
+
+	type cases struct {
+		source string
+		msg    string
+	}
+
+	tests := []cases{
+		{
+			`package test
+
+func main() {
+	const a int = -1
+    println(uint(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type IntKind to UintKind`,
+		},
+		{
+			`package test
+
+func main() {
+	const a int = -1
+    println(uint8(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type IntKind to Uint8Kind`,
+		},
+		{
+			`package test
+
+func main() {
+	const a int = -1
+    println(uint16(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type IntKind to Uint16Kind`,
+		},
+		{
+			`package test
+
+func main() {
+	const a int = -1
+    println(uint32(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type IntKind to Uint32Kind`,
+		},
+		{
+			`package test
+
+func main() {
+	const a int = -1
+    println(uint64(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type IntKind to Uint64Kind`,
+		},
+		{
+			`package test
+
+func main() {
+	const a float32 = 1.5
+    println(int32(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type Float32Kind to Int32Kind`,
+		},
+		{
+			`package test
+
+func main() {
+    println(int32(1.5))
+}`,
+			`test/main.go:4:13: cannot convert (const (1.5 <untyped> bigdec)) to integer type`,
+		},
+		{
+			`package test
+
+func main() {
+	const a float64 = 1.5
+    println(int64(a))
+}`,
+			`test/main.go:5:13: cannot convert constant of type Float64Kind to Int64Kind`,
+		},
+		{
+			`package test
+
+func main() {
+    println(int64(1.5))
+}`,
+			`test/main.go:4:13: cannot convert (const (1.5 <untyped> bigdec)) to integer type`,
+		},
+		{
+			`package test
+		
+		func main() {
+			const f = float64(1.0)
+		   println(int64(f))
+		}`,
+			``,
+		},
+	}
+
+	for _, tc := range tests {
+		testFunc(tc.source, tc.msg)
+	}
+}
+
 // run empty main().
 func TestRunEmptyMain(t *testing.T) {
 	t.Parallel()

gnovm/pkg/gnolang/op_expressions.go

@@ -800,6 +800,6 @@ func (m *Machine) doOpFuncLit() {
 func (m *Machine) doOpConvert() {
 	xv := m.PopValue()
 	t := m.PopValue().GetType()
-	ConvertTo(m.Alloc, m.Store, xv, t)
+	ConvertTo(m.Alloc, m.Store, xv, t, false)
 	m.PushValue(*xv)
 }

gnovm/pkg/gnolang/preprocess.go

@@ -3656,7 +3656,7 @@ func convertConst(store Store, last BlockNode, cx *ConstExpr, t Type) {
 		setConstAttrs(cx)
 	} else if t != nil {
 		// e.g. a named type or uint8 type to int for indexing.
-		ConvertTo(nilAllocator, store, &cx.TypedValue, t)
+		ConvertTo(nilAllocator, store, &cx.TypedValue, t, true)
 		setConstAttrs(cx)
 	}
 }

gnovm/pkg/gnolang/values.go

@@ -1207,7 +1207,7 @@ func (tv *TypedValue) SetInt(n int) {
 
 func (tv *TypedValue) ConvertGetInt() int {
 	var store Store = nil // not used
-	ConvertTo(nilAllocator, store, tv, IntType)
+	ConvertTo(nilAllocator, store, tv, IntType, false)
 	return tv.GetInt()
 }