automatically comment preprocessor conditionals

[fangism]

Summary

This request captures features from a script that lived outside of Verible, but some developers found useful.
The script (by @jonmayergoogle ) would automatically add comments after ifdef elsif else endif directives that reflected the condition under which the section was active, and served as a readability aid.

Test cases and examples

/* Hello, world. */
alpha
`ifdef FOO
/*
beta
`ifndef BAR
*/
luke
`ifdef BUM  // is BUM defined
wookie
`endif  // this comment gets removed
r2d2
`endif
wedge

would automatically become annotated like:

/* Hello, world. */
alpha
`ifdef FOO  // FOO
/*
beta
`ifndef BAR
*/
luke
`ifdef BUM  // FOO && BUM
wookie
`endif  // FOO && BUM
r2d2
`endif  // FOO
wedge

Proposal

The implementation for this would be based on an unpreprocessed token stream. No syntactic validation is needed, as this is purely a transformation based on preprocessing tokens. The simplicity of this task means that we don't need a full syntax tree transformation/rewriting framework.

Additional context

cl/629042737 (Google)

[kuku929]

hello, this seems interesting. In which file should I put the code for the feature?

[Bhavin-umatiya]

@fangism Hello
please check any further change so u can guide me i'll try

[fangism]

@fangism Hello please check any further change so u can guide me i'll try

Got your message. I'm a little occupied over the holidays but will try to take a look at #2314.