originalPositionFor returns null if sourcemap does not contains the exact line.

[yoshiokatsuneo]

originalPositionFor returns null if sourcemap does not contains the exact line.
It cause the issue with typescript(ts-node) that may not create source map for all the lines,
especially when the source contains multi-line chained function call like below.

let obj:any = null;
obj
.map();

In this case, the error happens on the last line. But, sourcemap does not have information on the line. So, the following code assume the mapping does not found and return null.

source-map/lib/source-map-consumer.js

Line 616 in 75663e0

if (mapping.generatedLine === needle.generatedLine) {

It is much better to return the nearest source map position, instead of just return null.

[yoshiokatsuneo]

Related to:
TypeStrong/ts-node#325

[tromey]

Over in #220 the proposal is to remove "fuzzy mapping" from another API. It would be funny to change that one to be more strict while changing this one to be less so -- but maybe that's even the best thing to do.

[tromey]

I see now that originalPositionFor is documented as returning the nearest mapping.

[Snipx]

For Kotlin the issue is even more important because the mapping is fuzzier in Kotlin than in TypeScript I believe. See istanbuljs/nyc#818

[ericmorand]

Any news about this one? The bias property only works with columns. line still has to match exactly for the function to return a position.

[TimHambourger]

This one would greatly help SourceMapGenerator.prototype.applySourceMap. I'll file a separate issue describing what I'm hitting there, b/c it concerns behaviors in applySourceMap and not just originalPositionFor.

But one suggestion I'll make here is that as in #220, this could work well as an optional argument. It makes sense to me that some cases might call for strict matching and others fuzzy. I don't have strong feelings about what the default should be -- I personally would be fine keeping strict as the default for backwards compatibility. My main interest is to see applySourceMap move to fuzzy matching, for reasons I'll explain in my separate issue.