fix: add special case error when a parameter/index overflows int (goo…

…gle#305)

starlark/eval.go

@@ -1163,7 +1163,7 @@ func slice(x, lo, hi, step_ Value) (Value, error) {
 		var err error
 		step, err = AsInt32(step_)
 		if err != nil {
-			return nil, fmt.Errorf("got %s for slice step, want int", step_.Type())
+			return nil, fmt.Errorf("invalid slice step: %s", err)
 		}
 		if step == 0 {
 			return nil, fmt.Errorf("zero is not a valid slice step")
@@ -1257,7 +1257,7 @@ func asIndex(v Value, len int, result *int) error {
 		var err error
 		*result, err = AsInt32(v)
 		if err != nil {
-			return fmt.Errorf("got %s, want int", v.Type())
+			return err
 		}
 		if *result < 0 {
 			*result += len

starlark/library.go

@@ -207,7 +207,7 @@ func chr(thread *Thread, _ *Builtin, args Tuple, kwargs []Tuple) (Value, error)
 	}
 	i, err := AsInt32(args[0])
 	if err != nil {
-		return nil, fmt.Errorf("chr: got %s, want int", args[0].Type())
+		return nil, fmt.Errorf("chr: %s", err)
 	}
 	if i < 0 {
 		return nil, fmt.Errorf("chr: Unicode code point %d out of range (<0)", i)

starlark/testdata/string.star

@@ -128,7 +128,7 @@ assert.eq("banana"[::-1], "ananab")
 assert.eq("banana"[None:None:-2], "aaa")
 assert.fails(lambda: "banana"[1.0::], "invalid start index: got float, want int")
 assert.fails(lambda: "banana"[:"":], "invalid end index: got string, want int")
-assert.fails(lambda: "banana"[:"":True], "got bool for slice step, want int")
+assert.fails(lambda: "banana"[:"":True], "invalid slice step: got bool, want int")
 
 # in, not in
 assert.true("oo" in "food")