Ts-morph: Question: what is the difference between "diagnostics" and "preEmitDiagnostics?"

[anurbol]

Couldn't find the answer here: https://dsherret.github.io/ts-simple-ast/setup/diagnostics

In the link there are project.getDiagnostics and project.getPreEmitDiagnostics. They seem identical. Are there any hidden difference e.g. in performance?

[anurbol]

BTW, thanks @dsherret this library saved my life. Default TS compiler API was pain.

[dsherret]

Hey @anurbol, excellent question! This was something I added a little while back and was mostly just trying to mirror functions available in the compiler api. I didn't realize the actual behaviour of getPreEmitDiagnostics, but after looking into it, you're right that these methods are almost identical. I recommend using .getPreEmitDiagnostics() as that will do the following:

export function getPreEmitDiagnostics(program: Program, sourceFile?: SourceFile, cancellationToken?: CancellationToken): Diagnostic[] {
    const diagnostics = [
        ...program.getConfigFileParsingDiagnostics(),
        ...program.getOptionsDiagnostics(cancellationToken),
        ...program.getSyntacticDiagnostics(sourceFile, cancellationToken),
        ...program.getGlobalDiagnostics(cancellationToken),
        ...program.getSemanticDiagnostics(sourceFile, cancellationToken)
    ];

    if (program.getCompilerOptions().declaration) {
        addRange(diagnostics, program.getDeclarationDiagnostics(sourceFile, cancellationToken));
    }

    return sortAndDeduplicateDiagnostics(diagnostics);
}

The current .getDiagnostics() isn't as good as that and I'd rather leave as much functionality with the compiler api. So I'm going to deprecate .getDiagnostics() in #386.

[anurbol]

Thank you for the response! Cool, I am glad I gave you idea on cleaning the library up. I ended up using
getPreEmitDiagnostics(). If I understand correctly, you will just deprecate the other method and add new methods to Diagnostic object item (of Diagnostic[], that is returned from getPreEmitDiagnostics()) so there would be no breaking change to API of getPreEmitDiagnostics() (I hope it would not be broke). Thank you again! Good luck!