The Deprecation Info API should be updated to check for breaking changes coming in the next major version.

Here is a list created by looking through the breaking changes list in the docs and >breaking PRs. I have not verified each one of these, it will likely be necessary to add and/or remove items from this list.

Cluster

• : is no longer allowed in the cluster name (change in Disallow : in cluster and index/alias names #26247) Deprecation check for : in Cluster/Index name #36185
• [] Shard preferences _primary, _primary_first, _replica, and _replica_first are removed (change in Should search preference _primary take primary relocation target into account? #26335)
  [^^ This is a query-time parameter]
• Cluster-wide shard soft limit (change in Always enforce cluster-wide shard limit #34892)
• Renamed no-master-block setting (changes in Rename no-master-block setting #38350) Deprecation check for No Master Block setting #38383

Indices

• Check for multiple types in indices created in 5.x, as this prevents automatic reindexing (see Implementation tracking for 7.0 types deprecation. #35190) Deprecation check for indices with multiple types #36952
• [] standard token filter removal (does this need a check?) (change in Upgrade to a Lucene 8 snapshot #33310)
  [^^ this does not need a check, as it is special-cased in 7.0 for indices created in 6.x and this token filter is a no-op anyway]
• delimited_payload_filter renamed (changes in Remove delimited_payload_filter #27705) Remove delimited_payload_filter and add to migration assistant #27704
• : is no longer allowed in index name (change in Disallow : in cluster and index/alias names #26247) Deprecation check for : in Cluster/Index name #36185
• index.unassigned.node_left.delayed_timeout may no longer be negative (change in Forbid negative values for index.unassigned.node_left.delayed_timeout #26828) (deprecation info API: negative index.unassigned.node_left.delayed_timeout #36454)
• fix value for index.shard.check_on_startup is removed (change in completely drop index.shard.check_on_startup: fix for 7.0 #33194) (deprecation info API: 'fix' value for index.shard.check_on_startup #36458)
• [] index_options for numeric fields has been removed (change in Reject the index_options parameter for numeric fields #26668)
  [^^ this does not need a check as indices with `index_options` on numeric fields behave fine in 7.0 if they existed prior to upgrade]
• [] Limiting the number of nested json objects (?) (change in Limit the number of nested documents #27405)
  [^^ can't check this without running a query]
• The classic similarity has been removed (change in Improve similarity integration. #29187) Deprecation check for classic similarity #36577
• [] Similarities fail when unsupported options are provided (change in Improve similarity integration. #29187)
  [^^ this does not need a check as indices with unsupported similarity options behave fine in 7.0 if they existed prior to upgrade]
• Deprecated index.percolator.map_unmapped_fields_as_string setting has been removed (changes in remove deprecated percolator map_unmapped_fields_as_string setting #28060) Deprecation check for percolator.map_unmapped_fields_as_string #36460

Nodes

• Azure Repository plugin settings changes
• Google Cloud Storage Repository plugin settings changes
• File-based discovery plugin removed and path changed (changes in Remove discovery-file plugin #33257) Deprecation check for File Discovery plugin #36190
• [] The default for node.name is now the hostname (changes in Core: Default node.name to the hostname #33677)
  [^^ There doesn't appear to be a way to check this one]
• Tribe node has been removed (changes in Remove tribe node support #28443) Deprecation check for tribe node #36240
• Http enabled setting removed (changes in Network: Remove http.enabled setting #29601) Deprecation check for http.enabled setting #36394
• Settings thread_pool.index.size and thread_pool.index.queue_size have been removed (changes in Remove the index thread pool #29556) Deprecation check for index threadpool #36520
• Http pipelining setting removed (changes in Make http pipelining support mandatory #30695) Deprecation check for HTTP pipelining #36521
• Audit logfile local node info settings removed (changes in Logfile auditing settings remove after deprecation  #35205) Deprecation check for audit log prefix settings #36661
• Write threadpool fallback removed (changes in Remove bulk fallback for write thread pool #29609) Deprecation check for renamed bulk threadpool settings #36662
• Security realms type setting removed (changes in Include realm type in Security Realm setting keys #30241) Deprecation check for Auth realm setting structure #36664
• Discovery configuration is required in production (changes in [Zen2] Best-effort cluster formation if unconfigured #36215) Deprecation check for discovery configuration #36666
• Watcher Notifications Account "unsecure" settings removed (changes in Remove Watcher Account "unsecure" settings #36736 and Watcher deprecate notification service settings #36403) Watcher notification settings Upgrade checks #36907
• SSL setting fallback removed (Changes in Security: remove SSL settings fallback #36846) Add deprecation warnings for ssl config fallback #36847
• TLS 1.0 removed from default protocols list (Changes in Remove TLS 1.0 as a default SSL protocol #37512) Add TLS version changes to deprecation checks #37793
• User-Agent ingest plugin alignment with ECS (changes in Add ECS schema for user-agent ingest processor #37727) Dep. check for ECS changes to User Agent processor #38362
• Security is no longer implicitly enabled on trial licenses Deprecate implicit security on trial licenses #38295