Allow configuration to skip the execute_inline! call

[nevinera]

Purpose

Since updating to lhm-shopify, we had a recurring issue where people would write a migration using LHM (we have it in our generator templates), but fill it with normal calls to migration methods like add_column(:tablename, :colname, :string).

Before the upgrade, these calls would get caught immediately, because the schema file wouldn't get the intended changes, and any staging stack based on that branch would not have the column present. But after the upgrade, these calls worked fine locally, and since our staging stacks are based on the schema file (not by running migrations from scratch), we only end up catching these problems in production.

When we realized what was happening, we tracked it to here - the explanations on the change make total sense, but in our case we'd much rather exclude development from inlining, so this problem will get caught locally. (You should probably consider dropping the development? condition entirely - I expect other people are getting surprised here occasionally as well).

Implementation

• Fix a typo I noticed in the docs while setting up for specs (bundle exec rake specs to run all specs)
• Update the README to note the new configuration option, without going into much detail about why you'd care
• Add Lhm.disallow_inline! and Lhm.inline_allowed? to the base module for configuration purposes
• Add an extra check against Lhm.inline_allowed? to the Railtie. Didn't see any tests on this thing, but I'm happy to go learn how to make one if you'd like.

Verification

Confirmed locally that with the setting not supplied migrations run inline, and with Lhm.disallow_inline! called, they do not.

Note

If you'd rather drop the 'auto-inline in development' part, that's a smaller change, and I'd be happy to update the PR :-)

[nevinera]

Let me know if you think more explanation (of why it does that, or why you might want to opt out of it) is warranted here.

[nevinera]

Any chance of a review? I'd be happy to make other changes, but this repo feels somewhat forgotten :-/

[fmichaut-diff]

This has definitively tripped us a dozen times, but for a different reason

LHM does not support virtual columns / foreign keys, and if we forget to temporarily remove the foreign keys at the beginning of the migration, the migration will pass on Dev, but fail on Prod.

We would also like to be able to not run LHM inline on Dev because of theses difference of behavior, and catch errors early instead of catching them when they reach Prod...