Add an API for writing inline annotations that apply to a subset of queries

[mattyoho]

Marginalia's request-level or job-level annotations are great, but in some cases it's valuable to add annotations to a specific subset of queries issued during a request or other context.

Since Marginalia is already hooked into annotating the SQL string passed into the database adapter level, it provides a good chokepoint for that functionality as well.

This patch implements a new API to add that ability. The following code:

Marginalia.with_annotation("foo") do
  Account.where(queenbee_id: 1234567890).first
end

will issue this query:

Account Load (0.3ms)  SELECT `accounts`.* FROM `accounts`
WHERE `accounts`.`queenbee_id` = 1234567890
LIMIT 1
/*application:BCX,controller:project_imports,action:show*/ /*foo*/

Any queries issues inside the with_annotation block will include the inline comment.

Nesting with_annotation blocks will concatenate the comment strings.

Marginalia.with_annotation("foo") do
  Marginalia.with_annotation("-bar") do
    Account.where(queenbee_id: 1234567890).first
  end
end

yields:

Account Load (0.3ms)  SELECT `accounts`.* FROM `accounts`
WHERE `accounts`.`queenbee_id` = 1234567890
LIMIT 1
/*application:BCX,controller:project_imports,action:show*/ /*foo-bar*/

/cc @arthurnn

[mattyoho]

Note: the current build failures appear to be in the test setup itself, and are occurring on master as well.

[eileencodes]

Hey @mattyoho can you rebase with master? I fixed the Travis tests to run and to test against 5.2 additionally.

[mattyoho]

@eileencodes Awesome, thank you! Rebased. 👍

[arthurnn]

This looks good to me, i am ready to merge it when you are

[arthurnn]

👍 for escaping it

[mattyoho]

i am ready to merge it when you are

Awesome. I think this diff is ready. 👍

[arthurnn]

new version released also https://rubygems.org/gems/marginalia/versions/1.7.0

[mattyoho]

Great, thanks!