are you using IItem elsewhere?
If no - then this is not a false-positive.
Self referencing things are not considered a usage - or else you'll get isolated, unused islands of things.

This is the same behaviour that you get for self-referencing functions

@bradzacher yes，I declare IItem and some other interface as global interface in definition file，so i can access them in other files in my project.But only the IItem interface got warnings.

please provide the full code sample so I can repro it appropriately.

@bradzacher try this repo, please

The bug is that we're doing an explicit report for interfaces that self-reference, but that circumvents the checks we do for ambient declarations.

@bradzacher would this solve the issue?

        const isOnlySelfReferenced = variable.references.every(ref => {
          if (
            ref.identifier.range[0] >= node.range[0] &&
-             ref.identifier.range[1] <= node.range[1]
+            ref.identifier.range[1] <= node.range[1] &&
+            !util.isDefinitionFile(filename)
          ) {
            return true;
          }
          return false;
        });

that's in the right direction! But we should be able simplify this (I believe)

When the rule runs over a declaration file, it calls markDeclarationChildAsUsed to manually mark the variables (using a standard ESLint property - eslintUsed).

So instead we could express this clearer as:

 const isOnlySelfReferenced = variable.references.every(ref => { 
   if ( 
     ref.identifier.range[0] >= node.range[0] && 
     ref.identifier.range[1] <= node.range[1] 
   ) { 
     return true; 
   } 
   return false; 
 }); 
-if (isOnlySelfReferenced) {
+if (isOnlySelfReferenced && variable.eslintUsed !== true) {

@bradzacher is it possible to create a test case for this? To test variable.eslintUsed we need two files: .d.ts and .ts.

yes - you can use the filename prop in the test case.