During profiling looking up topic users popped up as a hot path, this
change more than halved the amount of work it does
It reduces object allocations and method calls and avoids repeate translation
of common terms
This adds support for DISCOURSE_ENABLE_PERFORMANCE_HTTP_HEADERS
when set to `true` this will turn on performance related headers
```text
X-Redis-Calls: 10 # number of redis calls
X-Redis-Time: 1.02 # redis time in seconds
X-Sql-Commands: 102 # number of SQL commands
X-Sql-Time: 1.02 # duration in SQL in seconds
X-Queue-Time: 1.01 # time the request sat in queue (depends on NGINX)
```
To get queue time NGINX must provide: HTTP_X_REQUEST_START
We do not recommend you enable this without thinking, it exposes information
about what your page is doing, usually you would only enable this if you
intend to strip off the headers further down the stream in a proxy
Previously as soon as any override was defined we would regress to the slow
path for locale lookups. Additionally if `raise: true` was specified which
rails likes to add in views we would bypass the cache
The new design manages to use the fast path for many more cases
Before the locking here was added, replying to a post and liking a post
at roughly the same time could cause a deadlock.
Liking a post grabs an update lock on the post and then on the topic (to
update like counts).
We now lock the replied to post before getting the topic lock so that we
can update the replied to post later without causing a deadlock.
This was a fairly serious regression on sites with large (mega) topics,
however it was limited to staff.
The issue here is the query was using filtered_post_ids which I'd
assumed was already windowed to the current page, when in fact it was
all the ids in the topic. This fix corrects it by using the correct
windowed collection.
You can now add javascript files under `/javascripts/*` in a theme, and they will be loaded as if they were included in core, or a plugin. If you give something the same name as a core/plugin file, it will be overridden. Support file extensions are `.js.es6`, `.hbs` and `.raw.hbs`.
Previously theme setting descriptions were defined in the `settings.yml` file like this:
```
setting_name:
default: "My Default Value"
description:
en: "English description"
fr: "French description"
```
This commit allows developers to store the localised descriptions in the theme locale files instead:
```
en:
theme_metadata:
description: Theme Description
settings:
setting_name: "The localised description for setting_name"
```
