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I do not think you have this information on the script side. we do not know if lib.d.ts is really a user file, or has been injected into the context by VS. the only one who has this information is VS, and in the genral case, the language service Host.
how the question, should we even do that? or just let the host do that for us? i.e. just return the rename info, and the host will compian if it cannot apply them. alternatively, we can ask the host, if this is trully a library file or not.
if you want to still do this check, i would do something like

ts.getBaseFileName(ts.normalizePath(fileName)) === getDefaultLibFileName(options);

Thanks for the comments.
@mhegazy - made the changes we discussed . I was going to add the typeof check for getDefaultLibFileName to ensure it is backward compatible with the previous lower-cased version (getDefaultLibFilename). Case does not appear to matter for the shimHost though as both work (they return typeof "unknown"). Using a completely different method that isn't on shimHost would return typeof "undefined".
I have another change that I'll send a CR out for on the host side if @CyrusNajmabadi and @JsonFreeman are good with this change.

👍