The compiler does not do emit based on semantic information in most cases. this allows us to provide an api for transpiling a module that does not require typecheck or full program information. just single file syntactic transformation.
This can be helpful in multiple scenarios, including: typescript-simple (https://github.com/teppeis/typescript-simple), JSPM (#2233), es6-module-loader and as atom extensions.

A new compiler flag (--singeFileTranspilation or --disableFullProgramOptimizations for instance) that will make cases that break single file-transpilation an error namely: 1.Const enums defined in ambient modules and 2.Re-exporting types-only constructs when targeting ES6