By importing this Ruby code into gitlab-rails (and gitaly-ruby), we avoid
200ms of startup time for each gitlab_projects subprocess we are eliminating.

By not having a gitlab_projects subprocess between gitlab-rails / sidekiq and
any git subprocesses (e.g. for fork_project, fetch_remote, etc, calls), we can
also manage these git processes more cleanly, and avoid sending SIGKILL to them

This allows us to avoid relying on telnet / netcat being installed

i.e.
Using compare and swap we update the expires_at value.
The thread that actually is able to update this value will also set
the cache holding method_call enabled state

Signed-off-by: NRémy Coutable <remy@rymai.me>

The Gitaly CommitService is being hammered by n + 1 calls, mostly when
finding commits. This leads to this gRPC being turned of on production:
https://gitlab.com/gitlab-org/gitaly/issues/514#note_48991378

Hunting down where it came from, most of them were due to
MergeRequest#show. To prove this, I set a script to request the
MergeRequest#show page 50 times. The GDK was being scraped by
Prometheus, where we have metrics on controller#action and their Gitaly
calls performed. On both occations I've restarted the full GDK so all
caches had to be rebuild.

Current master, 806a68a8, needed 435 requests
After this commit, 154 requests

Instead of using the factories. Since the factories might be using
columns that aren't available in the schema at version the particular
spec is running in.

When a merge request is created from email, use message body
as merge request description. If message body is empty then
merge request description is still created from the source
branch commit (if there is only single commit in the merge
request).

If message body is empty and there are multiple commits in
the source branch, then merge request description is left empty.

Closes #40968

On GitLab.com, InfluxSampler#sample_objects appears to take 1.2 s or so to
iterate through 1059 objects. This had led to delays of a couple hundred
milliseconds in processing in the main thread. Remove this code since it's not
really being used.

Closes gitlab-com/infrastructure#3250

If the source import directory were different from the destination directory,
GitLab would first create a blank repository and then erroneously move the
original one into a subdirectory. Adding an import type prevents this the project
from being initialized in the first place. It was accidentally removed in
1f917cbd49.

Closes #40765

TableOfContents filter generates hrefs for each header in markdown,
if the header text consists from digits and redacted symbols only,
e.g. "123" or "1.0 then the auto-generated href has the same format
as issue references.

If the generated id contains only digits, then 'anchor-' prefix is
prepended to the id.

Closes #38473

Moving the check out of the general requests, makes sure we don't have
any slowdown in the regular requests.

To keep the process performing this checks small, the check is still
performed inside a unicorn. But that is called from a process running
on the same server.

Because the checks are now done outside normal request, we can have a
simpler failure strategy:

The check is now performed in the background every
`circuitbreaker_check_interval`. Failures are logged in redis. The
failures are reset when the check succeeds. Per check we will try
`circuitbreaker_access_retries` times within
`circuitbreaker_storage_timeout` seconds.

When the number of failures exceeds
`circuitbreaker_failure_count_threshold`, we will block access to the
storage.

After `failure_reset_time` of no checks, we will clear the stored
failures. This could happen when the process that performs the checks
is not running.

create_merge_request_handler_spec needs a repository for some tests but
this repository lasts on disk by default which causes failures of other
tests. TestEnv.clean_test_path is used to get rid of the repository
after each test.

Closes #40900

- handle unchanged empty lines in inline diff

This also allows us to simplify the naming since we can make some
fetching methods private.

Later migrations added fields to the EE DB which were used by factories which were used in these specs.

And in CE on MySQL, a single appearance row is enforced.

The migration and migration specs should not depend on the codebase staying the same.

Use Class.new(StandardError) instead of custom extended error class. Bring back specified_dependencies?.