Document that HAL's RelationLinkManager(Interface) also supports registered link relation types

I'm not sure I understand this issue. In #2300979: Hal _links are not conform hal rfc I expected these IANA link relations for HAL.

Is this issue only about code cleanup or also for output JSON and HAL+JSON ?

I think this is saying \Drupal\rest\LinkManager\RelationLinkManagerInterface::getRelationUri() is technically incorrect, it should actually have been \Drupal\rest\LinkManager\RelationLinkManagerInterface::getRelation(), because it doesn't have to be a URI, it can also be something like edit-form or canonical or version-history.

But for that, it's too late. That'd be a BC break. What we can do is updating the existing documentation.

I checked https://www.drupal.org/core/d8-allowed-changes#patch
And I think this can still go in 8.1.x since "API documentation improvements" are allowed.

@markdorison Thanks for looking at this issue.

Adding some more information about what you do when you do a review helps the committers and future reviewers.
(https://www.drupal.org/patch/review)

I looked at the patch, also applied in to look at it in more context and noticed:

1. +++ b/core/modules/rest/src/LinkManager/RelationLinkManagerInterface.php
   @@ -26,7 +26,9 @@
   +   *   The corresponding URI or IANA link relation for the field.
   
   @@ -34,7 +36,7 @@ public function getRelationUri($entity_type, $bundle, $field_name, $context = ar
   +   *   Relation URI (or IANA link relation) to transform into internal IDs.
   

   these two changes can be more consistent with each other (either use the parenthesis or not).

   adding the dot at the end of the sentence is a good standards improvement, cause that line is already being changed by the purpose of this issue.

2. +++ b/core/modules/rest/src/LinkManager/RelationLinkManagerInterface.php
   @@ -26,7 +26,9 @@
   +   * @see \Drupal\rest\LinkManager\RelationLinkManagerInterface::getRelationUri
       */
      public function getRelationUri($entity_type, $bundle, $field_name, $context = array());
   

   Maybe this @see was supposed to go on the hunk below for the
   \Drupal\rest\LinkManager\RelationLinkManagerInterface::getRelationInternalIds
   (or reference getRelationInternalIds, or maybe reference somewhere else)

   Cause, where the @see is now, it is referencing itself.

Update the doc with the mentions in #6

This looks great, thanks! :) But let's postpone this on #2758897: Move rest module's "link manager" services to serialization module (which will move it) and #2113345: Define a mechanism for custom link relationships (which may require this to change).

#2758897: Move rest module's "link manager" services to serialization module and #2113345: Define a mechanism for custom link relationships have landed since I posted #10. Yay! :)

This interface now lives in the hal module, so changing the component.

1. Rebased #9
2. Minor change: changed "IANA link relation" to "IANA link relation type" per #2113345: Define a mechanism for custom link relationships
3. RTBC'd — thanks! :)

Given that this is clearly a trivial/minor docs-only change, demoting to Minor priority.

Thanks all, committed to both 8.4.x and 8.3.x given that patch releases allow API docs updates as per https://www.drupal.org/core/d8-allowed-changes#patch.