The Supreme Court ruled on Thursday that California may not require charities soliciting contributions in the state to report the identities of their major donors. The vote was 6 to 3, with the court’s three liberal members in dissent... The disputed measure requires charities to file with the state a copy of an Internal Revenue Service form that identifies major donors. Under federal law, the I.R.S. must keep the form confidential. California also promised to keep the forms secret, but it has not always done so. According to court papers, the challengers discovered in 2015 that the state had displayed about 1,800 forms on its website. State officials said that the disclosures were inadvertent and promptly corrected and that the state had imposed new security measures.