[jingwen]

> The net result is a Bazel (and Blaze) that are less burdened by the baggage of legacy, but the cost is a faster treadmill to keep pace with changes.

(I work on Bazel.)

This is accurate. A few of the biggest breaking change themes are:

1) Converting functionality linked within the Bazel binary into the extensibility mechanism implemented in Starlark. An example includes converting the native Java, C++, Android, Python, Protobuf, Obj-C and packaging rules into rules_java, rules_cc, etc. Many languages now are already implemented exclusively in Starlark. See rules_scala, rules_rust, rules_go and rules_haskell.

2) Starlark and Build API cleanups that accumulated over organic growth and development within Google for the past decade.

3) New build system features to support seamless integration with other build systems and package managers.