For all backends (except C), the FIDL compiler operates in two phases. A first phase parses the FIDL file(s) and produces a JSON-based Intermediate Representation (IR). A second phase takes the IR as input, and produces the appropriate language-specific output.
The shape of the JSON IR is described in the schema. All JSON IR files that
are produced during compilation using fx build are validated using this schema.
If you are interested in the JSON IR, you can generate it by running the FIDL compiler.