Allow TP to provide compile errors/warnings

[rojepp]

Description

Feature suggestion: It would be nice if a TP could contribute compile errors and warnings, with a file and a location in the file. For instance, if say the json parser for a json TP fails to parse and gives a line number in its error, we could propagate that info out to the user, with squigglies in the json file even.

Maybe TypeProviderConfig could have a mechanism to allow adding this info?

[dsyme]

Yes, I agree, providing warnings is important

[smoothdeveloper]

related: fsharp/fslang-suggestions#729

[Thorium]

Warnings would be nice. Then we could really do dependant types as warnings: TypeProviders "compile" information sources to .NET types. However we have more knowledge on the types that what we really want to use: we want to use normal .NET types to make the usability easy. Compiler warnings could solve this.

Concrete example: a varchar(3) has max length 3 but for .NET usability reasons we don't want to create String3-class. So a string-class with compiler warning "You tried to insert "asdf" to varchar(3)" could be a good compromise.