cargo inspect
What is Rust doing behind the scenes?
There are only two ways to live your life.
One is as though nothing is a miracle. The other is as though everything is a miracle. -- Albert Einstein
Installation
You need Rust nightly and rustfmt
to get started.
You can install those via rustup:
rustup install nightly
rustup component add rustfmt-preview
All set? Let's get cracking!
cargo install cargo-inspect
Usage
Call it on any Rust file:
cargo inspect main.rs
Configuration
USAGE:
cargo inspect [OPTIONS] <INPUT_FILE>
FLAGS:
-h, --help Prints help information
-V, --version Prints version information
OPTIONS:
--theme <theme> Theme for syntax highlighting. See syntex documentation for options [default: base16-
ocean.dark]
--unpretty <unpretty> rustc "unpretty" parameters [default: hir]
ARGS:
<INPUT_FILE> Input file
Background
Rust allows for a lot of syntactic sugar, that makes it a pleasure to write. It is sometimes hard, however, to look behind the curtain and see what the compiler is really doing with our code.
To quote @tshepang, "It is good to know what these conveniences are, to avoid being mystified by what's going on under the hood... the less magical thinking we have of the world, the better."
- lifetime elisions
- type inference
- syntactic sugar
- implicit dereferencing
- type coercions
- hidden code (e.g. the prelude)
I was always interested in how programming languages work in the background, how my code was unrolled to the compiler backend easier to maintain.
The goal is to make the compiler more approachable for mere-mortals.
Mystery! Exploration! Discovery!
Code Examples
If-let
gets desugared into match
Consider the following code snippet:
When you compile it, the first thing Rust does is desugar it. To see what the code looks like after this step, run
cargo inspect examples/if_let.rs
This produces the following output:
use *;
extern crate std;
You can see that the if let
was desugared into a match
statement.
More examples
Please find more examples in the examples
folder. You can also contribute more.
The Magic Sauce
The best things in the world are assembled from simple building blocks. This tool stands on the shoulders of giants. To work its magic, it runs the following commands:
rustc -Zinspect=hir
, for retrieving the HIR.rustfmt
, for formatting the output.syntect
, for syntax-highlighting.
Contributing
This is a young project, which has downsides and upsides.
- Everything is in flux and things can break at any time. 😫
- There's plenty of opportunity to shape and form the project. 😊
Thus, become a contributor today!
Known issues
As of now, this is a very fragile tool. If it fails, it might will produce
horrible error messages.
You have been warned.
License
Licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.