fix: expand slice args in raw Where/Expr placeholders

expr.go

@@ -33,6 +33,12 @@ func (e expr) ToSql() (sql string, args []interface{}, err error) {
 	for _, arg := range e.args {
 		if _, ok := arg.(Sqlizer); ok {
 			simple = false
+			break
+		}
+		if isListType(arg) {
+			// Slice/array args need placeholder expansion (e.g. "id IN ?" + []int{...}).
+			simple = false
+			break
 		}
 	}
 	if simple {
@@ -65,6 +71,24 @@ func (e expr) ToSql() (sql string, args []interface{}, err error) {
 			buf.WriteString(sp[:i])
 			buf.WriteString(isql)
 			args = append(args, iargs...)
+		} else if isListType(ap[0]) {
+			// list argument; expand "?" into "(?,?,...)" like Eq/NotEq helpers
+			valVal := reflect.ValueOf(ap[0])
+			n := valVal.Len()
+			buf.WriteString(sp[:i])
+			if n == 0 {
+				// empty IN lists are falsey; empty NOT IN lists are truey, but
+				// Expr cannot know the surrounding operator. Expand to no
+				// placeholders: "()" matches historical Placeholders(0).
+				buf.WriteString("()")
+			} else {
+				buf.WriteByte('(')
+				buf.WriteString(Placeholders(n))
+				buf.WriteByte(')')
+				for j := 0; j < n; j++ {
+					args = append(args, valVal.Index(j).Interface())
+				}
+			}
 		} else {
 			// normal argument; append it and the placeholder
 			buf.WriteString(sp[:i+1])

expr_test.go

@@ -462,3 +462,23 @@ func ExampleEq() {
 		"company": 20,
 	})
 }
+
+
+func TestExprListArgExpansion(t *testing.T) {
+	sql, args, err := Expr("id NOT IN ?", []int{1, 2, 3}).ToSql()
+	assert.NoError(t, err)
+	assert.Equal(t, "id NOT IN (?,?,?)", sql)
+	assert.Equal(t, []interface{}{1, 2, 3}, args)
+
+	sql, args, err = Expr("id IN ?", []string{}).ToSql()
+	assert.NoError(t, err)
+	assert.Equal(t, "id IN ()", sql)
+	assert.Empty(t, args)
+}
+
+func TestWhereRawSQLListArgExpansion(t *testing.T) {
+	sql, args, err := Select("something FROM somewhere").Where("id NOT IN ?", []int{1, 2, 3}).ToSql()
+	assert.NoError(t, err)
+	assert.Equal(t, "SELECT something FROM somewhere WHERE id NOT IN (?,?,?)", sql)
+	assert.Equal(t, []interface{}{1, 2, 3}, args)
+}

part.go

@@ -21,8 +21,8 @@ func (p part) ToSql() (sql string, args []interface{}, err error) {
 	case Sqlizer:
 		sql, args, err = nestedToSql(pred)
 	case string:
-		sql = pred
-		args = p.args
+		// Route through Expr so slice/array args expand placeholders.
+		return Expr(pred, p.args...).ToSql()
 	default:
 		err = fmt.Errorf("expected string or Sqlizer, not %T", pred)
 	}

where.go

@@ -21,8 +21,8 @@ func (p wherePart) ToSql() (sql string, args []interface{}, err error) {
 	case map[string]interface{}:
 		return Eq(pred).ToSql()
 	case string:
-		sql = pred
-		args = p.args
+		// Route through Expr so slice/array args expand placeholders (e.g. IN ?).
+		return Expr(pred, p.args...).ToSql()
 	default:
 		err = fmt.Errorf("expected string-keyed map or string, not %T", pred)
 	}