Substrate uses a lot of macros to make it easier to write runtime modules:
construct_runtime!decl_module!decl_storage!decl_event!However, it is hard to understand what these macros actually do and what the final code looks like. How can I dig deeper into these macros and expansions?
To me, the most comfortable solution is to use cargo expand
https://github.com/dtolnay/cargo-expand
cargo install cargo-expand
then just call it from your crate
cargo expand
If you wanted to take a look at the final generated code for a crate, you can run the following:
cargo +nightly rustc --profile=check --package <crate-name> --lib -- -Zunstable-options --pretty=expanded > <output-file>
Note there are two variables here: <crate-name> and <output-file>.
Thus, if you wanted to look at your final runtime from the substrate-node-template, you would run:
cargo +nightly rustc --profile=check --package node-template-runtime --lib -- -Zunstable-options --pretty=expanded > substrate-node-template-runtime.rs
Or if you wanted to look at just the expansion of a single module like the Sudo module, you could do:
cargo +nightly rustc --profile=check --package srml-sudo --lib -- -Zunstable-options --pretty=expanded > sudo-module.rs
These would produce files with all the expanded code that look like this: https://gist.github.com/shawntabrizi/b4a1952dbd3af113e8a3498418e52741