Improved error message.

[SebastienCaunes]

Inspired by this issue
#4534
And adding the tip that this message arise when forgetting parenthesis on a decorator. Frequent error when using Angular :

@Input
myVar:MyVar;

[msftclas]

Hi @SebastienCaunes, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, MSBOT;

[SebastienCaunes]

Another one experiencing angular problem with decorators
http://stackoverflow.com/questions/40083195/angular-2-service-error-cannot-find-cause

[RyanCavanaugh]

When you change diagnosticMessages.json, you need to run the generate-diagnostics task and also commit the changes to the .generated.js file (as well as update any compiler sources which reference the error)

[mhegazy]

I would say this is not the right place to fix this issue. in checker.ts in resolveDecorator we can check if the signatures did not match, and the decorator node is not a call expression (i.e. @dec vs @dec(..)) we can add an explanation message to say something like have you forgot to call it?.

[mhegazy]

Closing for now. feel free to create a new PR with the proposed changes.