New Delhi, Jan. 20 -- India just rewrote tax rules for foreign investors. Sadly, it isn't clear what they are. That's the subtext of the Supreme Court's 15 January ruling against Tiger Global. The verdict itself is unambiguous: the private equity (PE) firm must pay capital gains tax on its $1.6 billion Flipkart stake sale to Walmart in 2018, despite routing the transaction through Mauritius, a country with which India has a tax treaty specifically designed to avoid double taxation. The court ruled that having a registered entity in Mauritius and holding a Tax Residency Certificate wasn't enough when the real control sat in New York.

If this were just another tax dispute that went against a global firm, it would be the end of the story. B...