When a two-word phrase forms an adjective, both AP and Chicago recommend hyphenating. Thus, "an open-source product" vs. "the product is open source".

I have always followed what @creachadair said. Is there some reason why you prefer "open source", @aileenrose?

My primary argument for hyphenating multi-word phrases when used as adjectives is to make it easier for non-native readers of English (https://about.sourcegraph.com/handbook/communication/style_guide#clarity) to parse the phrase boundaries in our sentences.

Also, if we standardize on "open source" (no hyphens), then we would need to change a lot of other things, right? Such as (from some of our recent blog posts):

• "all-remote company" -> "all remote company"
• "enterprise-wide deployment" -> "enterprise wide deployment"
• "code-aware search" -> "code aware search"
• "high-level health monitoring" -> "high level health monitoring"
• "cross-repository search" -> "cross repository search"
• "precise LSIF-based code intelligence" -> "precise LSIF based code intelligence"

In all of those cases above, we use hyphens. I believe hyphens improve clarity in all these cases, and the fact that we've use hyphens in cases like these suggests it will be difficult to (re)train everyone to not use hyphens.

I think the key point is adopting a style. Since we use serial commas, should we respect Chicago style? Here's a table of hyphen usage:
https://ophi.org.uk/wp-content/uploads/CMS_list.pdf
If we use it as an adjective, yes it should be hyphenated, but if otherwise i.e. noun not.
Then we just need to be more diligent in copywriting.

In other web discussions, I also found that there is a 'popular' adoption of non-hyphen open source.
apache/openwhisk-website#120
https://dzone.com/articles/blogging-programmers < the latter a random article with non-scientific web searching. (i prefer not to jump off bridges with the mass - XKCD)

But if we really want to respect the OSI, then there's no hyphen.
https://opensource.org/
They are the "the stewards of the Open Source Definition (OSD)".

cc @adamfrankl2015 @vanesa @ryan-blunden wdyt?

Adopting a style makes sense. The only caution I would advise is against trying to mix styles: Each org tends to have its own pattern of style conventions and exceptions that deviate from the base style. Combining them almost always introduces inconsistencies.

I think the most important role of style is to promote clarity for the reader, and we should choose rules based on that. Second to that, style should be reasonably self-consistent. Being consistent with other style guides (outside whatever we use as our base) is not that valuable (IMO) unless there is a preponderance of consensus.

To ensure we stick to our own rules, I find it's helpful if the rules we choose are fairly intuitive to remember as well.

(I am not the decider here; these are only my opinions as someone who cares a lot about language)

Thanks for the Trend data.

Putting aside the style, I vote for aligning with the stewards of open source, this includes the Linux Foundation.

It really seems like "open source" is an exception to the general rule, which is strange. For example, from https://www.linuxfoundation.org/about/:

But it does seem that's most common, so that's fine with me (I mean, it will be painful, but I will get used to it 😄).

Separately, do you agree all the bullet examples in #508 (comment) should have hyphens?

Anyway, just document what the rule is in our style guide (and if "open source" is an exception to the general rule).

This rule has been documented in #584.