fix: parse "/*/" as an unclosed comment

The comment branch searches for the closing "*/" with
value.indexOf("*/", pos), starting at the same index as the opening
"/*". For the input "/*/" that search matches the "*" of the opening
delimiter plus the following "/", so the parser reports a closed empty
comment and never sets the unclosed flag. On stringify it then emits
"/**/", so the round trip is not lossless.

"/*/" is an unterminated comment, which postcss core also reports as an
unclosed comment. The parser already handles this for other inputs such
as "/*x"; only the slash right after the opener slipped through. Start
the closing search at pos + 2 so the opening "/*" cannot be matched as
its own terminator.

Author: mahirhir

lib/parse.js

@@ -103,7 +103,7 @@ module.exports = function (input) {
 
       // Comments
     } else if (code === slash && value.charCodeAt(pos + 1) === star) {
-      next = value.indexOf("*/", pos);
+      next = value.indexOf("*/", pos + 2);
 
       token = {
         type: "comment",

test/parse.js

@@ -1553,6 +1553,19 @@ const tests = [
       },
     ],
   },
+  {
+    message: "should not treat the opening slash-star as its own terminator",
+    fixture: "/*/",
+    expected: [
+      {
+        type: "comment",
+        sourceIndex: 0,
+        sourceEndIndex: 3,
+        value: "/",
+        unclosed: true,
+      },
+    ],
+  },
   {
     message: "should respect escape character",
     fixture: "Hawaii \\35 -0",