No compiler error for script with decorators when target ES3

[PFight]

TypeScript Version: 1.7-2.0.3

Code

https://jsfiddle.net/PFight/vLfnpqk0/

Expected behavior:

Minimum target version for decorators is ES5 (that says documentation). When compiling code with target: 0 (ES3), expected to get diagnostics message, that decorators not supported for specified target.

... or decorators for ES3 should work without differences with ES5, and documentation should be fixed.

Actual behavior:

In TypeScript 1.7.0 were added support of decorators for ES3, and compiler error TS1205: Decorators are only available when targeting ECMAScript 5 and higher were removed. But, there is two differences in generated code for ES3:

1. Method and property decorators do not receive third parameter - descriptor
2. Return value of method and property decorators is ignored

For example, code work fine in playground, but fails in JSFiddle without meaningfull error, because JSFiddle uses target ES3.

[mhegazy]

@rbuckton can you take a look

[rbuckton]

We should update the documentation, because this is how we decided to support decorators for ES3 (i.e. no descriptor for methods), which is the same as how we support decorators for fields in ES3 and up.

[RyanCavanaugh]

This doesn't seem to come up often enough to warrant documentation