Feature Request: Improved detection of 'already instrumented' files

[coreyfarrell]

Per @jdalton request on #73.

One possible mitigation might be to have the instrumenter insert an /* istanbul ignore file */ comment.

[jdalton]

You might also be able to use a custom pragma:

"use istanbul";

These are easy to sniff for, don't interfere with other pragmas (like "use strict"), and won't be removed as easily as comments.

[coreyfarrell]

@jdalton could you point me to an example of where this is a problem? istanbul should already detect that files are already instrumented.. the only exception is if you have multiple major versions of istanbul-lib-instrument for example if 2.x instruments first then 3.x won't detect the existing coverage.

If you are getting the error Cannot read property 'fileCoverage' of undefined then I think this should get fixed by #470.