Likely to cause new Flow errors:

• Fixes to object spread. Seehttps://medium.com/flow-type/spreads-common-errors-fixes-9701012e9d58

New features:

• Introduced an experimental flag (experimental.minimal_merge) that speeds up rechecks when the experimental types-first mode is in use. This flag will be turned on by default and then removed in future releases.
• Turned onexperimental.allow_skip_direct_dependents by default. The flag will be removed next release. This flag speeds up rechecks when the experimental types-first mode is in use.

Notable bug fixes:

• Fixed a bug where the ocaml representation of union types caused crashes in rare scenarios
• Fixed a bug in node module resolution which allowedmodule.system.node.resolve_dirname=.. For those who relied on this bug to import modules using root-relative paths, you can now usemodule.system.node.allow_root_relative=true. See#8156 for more details.

Misc:

• Add getElementById to DocumentFragment
• Add missing methods to Blob (thanks@lyleunderwood!)
• Allow clients offlow status,flow check, etc. to choose character offset style
• Support length refinement on tuples (thanks@ilya-bobyr)

Parser:

• Allow => in objects in return types of arrow functions