This should have an explicit return type annotation, to associate it with the definition of SourceMapSource in types.ts.

Leaving the result untyped avoids a catch-22 caused by https://github.com/Microsoft/TypeScript/blob/v2.3.4/src/services/types.ts#L70-L72.

I added return type and as any which I don't really like but there is no good way I found around this. Including services/types.ts (e.g. when building tsserer.js) requires this literal have getLineAndCharacterOfPosition() but not include services/types.ts (e.g. when building tsc.js) requires it not have it. This is caused indirectly because SourceMapSource needs to extend SourceFileLIke (which I changed to be more clear by explicitly extending the interface).

Out of curiosity, why must it extend SourceFileLike? Could you not use a union in the places where this matters in either sourcemap.ts or utilities.ts?

sourcemap.ts calls getLineAndCharacterOfPosition() from scanner.ts with a SourceMapSource which then requires SourceFileSource to be SourceFileLike.

I don't want to infect scanner.ts with SourceMapSource as SourceFileLike is intended to be the minimal specification of a content and cached lines. The fact it is extended to include getLineAndCharacterOfPosition() in services/types.ts seems troubling and unnecessary.

@chuckjaz The constructor for a SourceFile is actually created by the objectAllocator. This allows us to keep nodes relatively light for the commandline compiler, but also allows us to create richer nodes for the language service.

You could consider adding a constructor factory for SourceMapSource to the object allocator, and hook in the getLineAndCharacterOfPosition method with a separate constructor in services.

To make this clean I believe there are three options:

1. Remove the extension of SourceFileLike in service/types.ts and fix all calls to the method getLineAndCharacterofPosition() to call the function getLineAndCharacterOfPosition().
2. Introduce a new sub-type of SourceFileLIke in service/types.ts, such as ServiceSource, that extends SourceFileLIke and move all references to SourceFileLIke in services to use ServiceSource.
3. Introduce a new type in compiler/types.ts called something like SourceWithLines that SourceFileLike extends from and change all other references to SourceFileLike in compiler to SourceWithLines.

I like the first one best. It is faster than using a method and I could not find any cases in service that overrides getCharacterAndLineOfPosition in a source file that would required either (2) or (3).

@rbuckton Sorry. I was writing my last response before I saw yours. I will update the PR to your recommendation.

Please note that this method is also used in src/harness/typeWriter.ts. Please also note that while SourceFileLike and SourceFileLike#getLineAndCharacterOfPosition are public, the computeLineAndCharacterOfPosition function is internal.

I think my comment above stands as the best approach at this point.

Done

To cut down on lookups, consider changing the above to:

const range = emitNode && emitNode.sourceMapRange;
const { pos, end } = range || node;
let source = range && range.source;

Done

line maps are internal only.

Fixed.

You lost the default for skipTrivia with this change. Previously you had pos => pos. Was this intended?

Fixed.

getLineAndCharacterOfPosition is generally public.

This was intentional to prevent getLineAndCharacterOfPosition from being written to typescript.d.ts as part of SourceMapSource and making supplying a getLineAndCharacerOfPosition() required when creating a SourceMapRange for calls to setSourceMapRange().

source is optional on SourceMapRange and a SourceMapSource should always be created by calling createSourceMapSource in factory.ts. Marking it internal here means that SourceMapSource can't be used as a SourceFileLike in the public API, only in the compiler.

SourceFileLike isn't really used in the public API anyways so maybe this doesn't matter.

Removing /* @internal */ since removing it then it will essentially force calling createSoruceMapSource() which is, as you point out, a good thing.