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

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

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

In GitLab EE, a GitLab instance can be read-only (e.g. when it's a Geo
secondary node). But in GitLab CE it also might be useful to have the
"read-only" idea around. So port it back to GitLab CE.

Also having the principle of read-only in GitLab CE would hopefully
lead to less errors introduced, doing write operations when there
aren't allowed for read-only calls.

Closes gitlab-org/gitlab-ce#37534.

MergeRequest#create_merge_request_diff and MergeRequest#reload_diff are
the only places where we generate a new MR diff so that's where we
should fetch the ref.

This also ensures that the ref is not fetched when we call
merge_request.merge_request_diffs.create in
Github::Import#fetch_pull_requests.

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

In this particular case the use of UNION ALL leads to a better query
plan compared to using 1 big query that uses an OR statement to combine
different data sources.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/38508 for more
information.

This ensures the open issues/MR count caches are refreshed properly when
creating new issues or MRs. This MR also includes a change to the cache
keys to ensure all caches are rebuilt on the fly.

This particular problem was not caught in the test suite due to a null
cache being used, resulting in all calls that would use a cache using
the underlying data directly. In production the code would fail because
a newly saved record returns an empty hash in #changes meaning checks
such as `state_changed? || confidential_changed?` would return false for
new rows, thus never updating the counters.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/38061

also fix some code styling issues

 - only show in merge-requests
 - show as a little glyph

This ensures the issues/MR cache of the sidebar is only updated when the
state or confidential flags changes, instead of changing this for every
update.

Our state machine shall have enough knowledge to not allow states other
than locked from transitioning to opened (e.g. MergeRequest#unlock_mr).

So that whenever we want to reserve more, we're aware,
and don't mess it up.

Every project page displays a navigation menu that in turn displays the
number of open issues and merge requests. This means that for every
project page we run two COUNT(*) queries, each taking up roughly 30
milliseconds on GitLab.com. By caching these numbers and refreshing them
whenever necessary we can reduce loading times of all these pages by up
to roughly 60 milliseconds.

The number of open issues does not include confidential issues. This is
a trade-off to keep the code simple and to ensure refreshing the data
only needs 2 COUNT(*) queries instead of 3. A downside is that if a
project only has 5 confidential issues the counter will be set to 0.

Because we now have 3 similar counting service classes the code
previously used in Projects::ForksCountService has mostly been moved to
Projects::CountService, which in turn is reused by the various service
classes.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/36622

So that we could limit the access to Repository#fetch_ref
See: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13416#note_37487433

Also fix a few tests

so that we don't have to fetch it for non-forks

Having two states that essentially mean the same thing is very much like
having a boolean "true" and boolean "mostly-true": it's rather silly.
This commit merges the "reopened" state into the "opened" state while
taking care of system notes still showing messages along the lines of
"Alice reopened this issue".

A big benefit from having only two states (opened and closed) is that
indexing and querying becomes simpler and more performant. For example,
to get all the opened queries we no longer have to query both states:

    SELECT *
    FROM issues
    WHERE project_id = 2
    AND state IN ('opened', 'reopened');

Instead we can query a single state directly, which can be much faster:

    SELECT *
    FROM issues
    WHERE project_id = 2
    AND state = 'opened';

Further, only having two states makes indexing easier as we will only
ever filter (and thus scan an index) using a single value. Partial
indexes could help but aren't supported on MySQL, complicating the
development process and not being helpful for MySQL.

Identified via `ENABLE_BULLET=1 bundle exec rspec spec/requests/api/merge_requests_spec.rb:34`

Improves speed of #34159