roc/.rules

## Roc snapshot tool

The Roc compiler uses golden snapshots to assist with debugging and verification of the compiler's behavior. The snapshots are generated by running `zig build snapshot`, and individual files can be generated using `zig build snapshot -- <file_path>`. For example, to generate a snapshot for the file `src/snapshots/can_two_decls.md`, run: `zig build snapshot -- src/snapshots/can_two_decls.md`.

Here is an example of a snapshot file for a roc program that prints `Hello world!`:

```txt
# META
~~~ini
description=Hello world
type=file
~~~
# SOURCE
~~~roc
app [main!] { pf: platform "../basic-cli/platform.roc" }

import pf.Stdout

main! = |_| Stdout.line!("Hello, world!")
```

And another which represents a single expression of a list:

```txt
# META
~~~ini
description=List with integer literals
type=expr
~~~
# SOURCE
~~~roc
[1, 2, 3]
```

Once the tool is ran, the compiler will generate human readable sections like problems (compiler errors and other diagnostics) and the intermediate representations using a s-expression text format. For example the Parser AST or the Canonical IR representation of the source code.

Changes can be reviewed manually to verify the correct behavior before committing the new snapshots to the repository.