Generate script: Don't write .cc or .h files if unchanged

[smith-kyle]

The generation script now checks whether the file has changed before writing it to /src or /include. This is to improve compilation time when testing changes to generated code.

It works by creating a /temp directory, writing the generated code to /temp/src and /temp/include, then syncing those folders with /src and /include by deleting files that no longer exist and copying files that have changed or been added since the last code generation. Finally the /temp directory is deleted

If /src and /include don't exist (i.e. it's the first time the generation script has been run), /temp/src will be copied to /src and /temp/include will be copied to /include.

[maxkorp]

You realize that using node-gyp build instead of node-gyp rebuild already takes care of this, right?

[implausible]

@maxkorp i think this fixes the issue where you make a change to the templates / add definition / add supplement, and you need to run generate, again. This stops the generate script from overwriting unchanged files. That way if you run node-gyp build, it will only build the files that have changed, rather than compile everything @smith-kyle am I right here?

[maxkorp]

Ah interesting, my bad. Lemme play with it a bit, that could be useful then 👍.

[maxkorp]

So, the overall recompile time without this is still fairly small, the bulk of the overall compile time is openssl and that isn't affected in this case (and the second largest is libgit2, which is also unaffected).

That said, if this is a big deal to you guys I'm cool with it. Any reason we don't use os.tmpdir though?

[smith-kyle]

Still relatively small but compilation is going from ~90 seconds to < 5 seconds if you've only changed a couple generated files.

This is the first I'm hearing about os.tmpdir. I don't know much about temp dir etiquette but this seems like a good use for it. Thanks for the suggestion @maxkorp I'll switch it over.

[maxkorp]

Awesome. Thanks a pretty big change, so I can dig it 👍

[smith-kyle]

@maxkorp I've (finally) moved this to use os.tempdir. It's ready for review. Not sure why appveryor is dying

[maxkorp]

I don't have push access to your repo to rebase this, so you gotta rebase this, but it's G2G man.

[smith-kyle]

Rebased 👍

[johnhaley81]

Tested. Looks good, works good. Thanks @smith-kyle!