How to annotate a symbol outside the location of definition?

[juj]

When developing Closure minification support to Emscripten compiler, there is a need to annotate some symbols with e.g. @suppress {undefinedVars} or @suppress {duplicate}.

If I use an --externs file to specify an annotation, e.g. --externs externs.js, with

/**
 * @suppress {duplicate}
 */
var foo;

then not only does Closure take in the annotation, but it also then will no longer minify foo, because it is being specified in an externs file.

If I use a --js file before the main JS file to specify an annotation, e.g. --js annotation.js --js main.js, with

/**
 * @suppress {duplicate}
 */
var foo;

then Closure will want to add (in some scenarios, not quite sure when this occurs) a top level global dummy variable var a; in the beginning of the Closured output file, that takes up redundant space and bloats the final output.

What I'd like to do is specify a --annotations annotations.js file that would not prevent minification like externs does, but neither will cause dummy symbols being defined to the build output, like --js does. Is this possible somehow with current Closure?

[EatingW]

To confirm, you are trying to annotate symbols that are used in main.js?

Was there a particular reason you can't annotate them directly in main.js?

[EatingW]

Created internal Google issue b/122736136

[juj]

Was there a particular reason you can't annotate them directly in main.js?

The trouble with this in context of Emscripten is that there is no good simple main.js where symbols could be annotated. That JS code is emitted as part of compiler codegen, and JS linking and DCE passes, and programmatically carrying and emitting Closure/JSDoc annotations through the compilation pipeline would be a significant body of work for little practical use. It has been simpler to use a separate annotations file mechanism, where different annotations would be passed, but historically Emscripten has used --externs for this purpose, which caused missed minification opportunities.

In some cases the symbols that are being annotated do not exist in the generated main.js and we'd like to add a @suppress {undefinedVars} annotation, in other cases they do, and we'd like to add an annotation @suppress {duplicate}. It would be useful to be able to annotate these symbols independent of whether they will appear in the Emscripten generated main.js file.

[EatingW]

As far as I know, we don't have support for this currently. I'll leave this open as a feature request.