Type Checking with rustc

1st chunk of `src/rustc-driver/interacting-with-the-ast.md`

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# Example: Type checking through `rustc_driver`

[`rustc_driver`] allows you to interact with Rust code at various stages of compilation.

## Getting the type of an expression

To get the type of an expression, use the [`after_analysis`] callback to get a [`TyCtxt`].

```rust
{{#include ../../examples/rustc-driver-interacting-with-the-ast.rs}}
```

Title: Type Checking with rustc_driver

Summary

The `rustc_driver` crate allows interaction with Rust code during compilation. To obtain the type of an expression, the `after_analysis` callback can be used to access a `TyCtxt`.