JSON objects can only have string keys, although HashMaps can have many types of keys. In the case of i32 keys (eg HashMap<i32, i32>), serde_json coerces the stringified integer key (eg "1") into 1i32. However, that fails in the case of bool keys; it raises an error when trying to coerce "true" or "false" into true or false:

Error("invalid type: string \"false\", expected a boolean", line: 0, column: 0)

I'm assuming the coercion behavior in the bool case should be similar to the i32 case.

Playground reproduction is here: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=92d5a43496299513df591ec5a6f2832c