{"action":"created","issue":{"url":"https://api.github.com/repos/Microsoft/TypeScript/issues/30059","repository_url":"https://api.github.com/repos/Microsoft/TypeScript","labels_url":"https://api.github.com/repos/Microsoft/TypeScript/issues/30059/labels{/name}","comments_url":"https://api.github.com/repos/Microsoft/TypeScript/issues/30059/comments","events_url":"https://api.github.com/repos/Microsoft/TypeScript/issues/30059/events","html_url":"https://github.com/Microsoft/TypeScript/pull/30059","id":413611067,"node_id":"MDExOlB1bGxSZXF1ZXN0MjU1NTU4MjMx","number":30059,"title":"Retain substitution types through instantiation if possible","user":{"login":"weswigham","id":2932786,"node_id":"MDQ6VXNlcjI5MzI3ODY=","avatar_url":"https://avatars3.githubusercontent.com/u/2932786?v=4","gravatar_id":"","url":"https://api.github.com/users/weswigham","html_url":"https://github.com/weswigham","followers_url":"https://api.github.com/users/weswigham/followers","following_url":"https://api.github.com/users/weswigham/following{/other_user}","gists_url":"https://api.github.com/users/weswigham/gists{/gist_id}","starred_url":"https://api.github.com/users/weswigham/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/weswigham/subscriptions","organizations_url":"https://api.github.com/users/weswigham/orgs","repos_url":"https://api.github.com/users/weswigham/repos","events_url":"https://api.github.com/users/weswigham/events{/privacy}","received_events_url":"https://api.github.com/users/weswigham/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2019-02-22T22:55:08Z","updated_at":"2019-02-23T00:37:03Z","closed_at":null,"author_association":"MEMBER","pull_request":{"url":"https://api.github.com/repos/Microsoft/TypeScript/pulls/30059","html_url":"https://github.com/Microsoft/TypeScript/pull/30059","diff_url":"https://github.com/Microsoft/TypeScript/pull/30059.diff","patch_url":"https://github.com/Microsoft/TypeScript/pull/30059.patch"},"body":"Fixes #29677\r\n\r\nThe alias lacked the correct constraint because the constraint was implied by the substitution type, which disappeared when the type alias was instantiated with the outer type parameters. The correct behavior is to retain substitution types through instantiation if their type variable is still a type variable upon instantiation.\r\n\r\nThis required correctly handling substitution types on the target side in inference (other tests needed the change to continue to work as expected), naturally, since, eg, an `Extract<K, string>`'s true branch is now going to look like a substitution of `K` instead of `K` directly."},"comment":{"url":"https://api.github.com/repos/Microsoft/TypeScript/issues/comments/466595508","html_url":"https://github.com/Microsoft/TypeScript/pull/30059#issuecomment-466595508","issue_url":"https://api.github.com/repos/Microsoft/TypeScript/issues/30059","id":466595508,"node_id":"MDEyOklzc3VlQ29tbWVudDQ2NjU5NTUwOA==","user":{"login":"weswigham","id":2932786,"node_id":"MDQ6VXNlcjI5MzI3ODY=","avatar_url":"https://avatars3.githubusercontent.com/u/2932786?v=4","gravatar_id":"","url":"https://api.github.com/users/weswigham","html_url":"https://github.com/weswigham","followers_url":"https://api.github.com/users/weswigham/followers","following_url":"https://api.github.com/users/weswigham/following{/other_user}","gists_url":"https://api.github.com/users/weswigham/gists{/gist_id}","starred_url":"https://api.github.com/users/weswigham/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/weswigham/subscriptions","organizations_url":"https://api.github.com/users/weswigham/orgs","repos_url":"https://api.github.com/users/weswigham/repos","events_url":"https://api.github.com/users/weswigham/events{/privacy}","received_events_url":"https://api.github.com/users/weswigham/received_events","type":"User","site_admin":false},"created_at":"2019-02-23T00:37:03Z","updated_at":"2019-02-23T00:37:03Z","author_association":"MEMBER","body":"@typescript-bot test this & @typescript-bot run dt"}}
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