You don't need to change Location.report to have sub-messages without a (displayed) location: you can do that by setting the sub-message location to Location.none.

@Armael I reverted and use Location.none. This added 2 spaces at the beginning of the line, what do you think of my last commit ?

@Armael I finally reverted all my changes to location.ml.

Thanks for the review !

#2319 may not be merged because my PRs are adding code that should not be in the type checker. Do you think moving error-reporting code to another module is feasible or is a good solution ?

Let's not mix this PR and #2319 . And note that in the current situation, creating new modules in the compiler is a bit delicate, since they pollute the global namespace for anyone linking against compiler-libs...