Use hugo.IsProduction instead of checking HUGO_ENV

[chalin]

• Reapplies Use hugo.isProduction for production environment checks #413, which was removed by mistake in Accessibility and SEO improvements #540. For details, see https://github.com/google/docsy/pull/540/files#r685339766
• Closes Changes introducing hugo.IsProduction were overwritten #652

[chalin]

@LisaFC - given that this essentially fixes a "regression" (a previous change that was overwritten by mistake), can it be merged soon? /cc @nate-double-u

[LisaFC]

Yep, I'm just looking at it now - the main thing is that it needs to be documented and announced because it's a breaking change with regard to whether your site is indexed.

(which I didn't think the original change was because I hadn't fully explored the mysterious ways of how the relevant environment variable and the current Hugo environment are not the same thing, as I did in #611)

[chalin]

Thanks. AFAICT, hugo.IsProduction will be true if HUGO_ENV=production is set, so it might not be a breaking change.

[LisaFC]

I think that's true but I need to check, I remember finding some unintuitive behaviour when I explored it in #611

We also need to document for the case where HUGO_ENV=production is not set and the user expects their site not to be indexed - if we make this change it will be indexed unless they explicitly specify that this is a non-production build.

[LisaFC]

Thanks. AFAICT, hugo.IsProduction will be true if HUGO_ENV=production is set, so it might not be a breaking change.

Annoyingly, I just checked, and it isn't (or at least HUGO_ENV=production in your Netlify setup doesn't override setting an environment in your hugo command with -e) - though it shouldn't be a problem anyway for existing sites as users will get a production build by default.

[chalin]

Right, production is the default for the build command. It makes sense that -e takes precedence.

Btw, let me know if there is anything I can do to help.