improve rustc-driver.md

minor addition and adding links

Update rustc-driver.md

removing parens for functions

reorganized directory

reorganized directory

minor edits

src/SUMMARY.md

@@ -90,9 +90,9 @@
 
 - [Prologue](./part-3-intro.md)
 - [Command-line arguments](./cli.md)
-- [rustc_driver and rustc_interface](./rustc-driver.md)
-    - [Example: Type checking](./rustc-driver-interacting-with-the-ast.md)
-    - [Example: Getting diagnostics](./rustc-driver-getting-diagnostics.md)
+- [rustc_driver and rustc_interface](./rustc-driver/intro.md)
+    - [Example: Type checking](./rustc-driver/interacting-with-the-ast.md)
+    - [Example: Getting diagnostics](./rustc-driver/getting-diagnostics.md)
 - [Syntax and the AST](./syntax-intro.md)
     - [Lexing and Parsing](./the-parser.md)
     - [Macro expansion](./macro-expansion.md)

src/rustc-driver-getting-diagnostics.md → src/rustc-driver/getting-diagnostics.md

@@ -7,8 +7,8 @@ otherwise be printed to stderr.
 
 To get diagnostics from the compiler,
 configure [`rustc_interface::Config`] to output diagnostic to a buffer,
-and run [`TyCtxt.analysis`]. The following was tested
-with <!-- date-check: september 2024 --> `nightly-2024-09-16`:
+and run [`TyCtxt.analysis`].
+The following was tested with <!-- date-check: september 2024 --> `nightly-2024-09-16`:
 
 ```rust
 {{#include ../examples/rustc-driver-getting-diagnostics.rs}}

src/rustc-driver/intro.md

@@ -0,0 +1,50 @@
+# `rustc_driver` and `rustc_interface`
+
+The [`rustc_driver`] is essentially `rustc`'s `main` function.
+It acts as the glue for running the various phases of the compiler in the correct order,
+using the interface defined in the [`rustc_interface`] crate.
+
+Generally the [`rustc_interface`] crate provides external users with an (unstable) API
+for running code at particular times during the compilation process, allowing
+third parties to effectively use `rustc`'s internals as a library for
+analyzing a crate or for ad hoc emulating of the compiler (i.e. `rustdoc`
+compiling code and serving output).
+
+More specifically the [`rustc_interface::run_compiler`][i_rc] function is the
+main entrypoint for using [`nightly-rustc`] as a library.
+Initially [`run_compiler`][i_rc] takes a configuration variable for the compiler
+and a `closure` taking a yet unresolved [`Compiler`].
+Operationally [`run_compiler`][i_rc] creates a `Compiler` from the configuration and passes
+it to the `closure`. Inside the `closure` you can use the `Compiler` to drive
+queries to compile a crate and get the results.
+Providing results about the internal state of the compiler what the [`rustc_driver`] does too.
+You can see a minimal example of how to use [`rustc_interface`] [here][example].
+
+You can see what queries are currently available in the [`Compiler`] rustdocs.
+You can see an example of how to use the queries by looking at the `rustc_driver` implementation,
+specifically [`rustc_driver::run_compiler`][rd_rc]
+(not to be confused with [`rustc_interface::run_compiler`][i_rc]).
+Generally [`rustc_driver::run_compiler`][i_rc] takes a bunch of command-line args
+and some other configurations and drives the compilation to completion.
+
+Finally [`rustc_driver::run_compiler`][rd_rc] also takes a [`Callbacks`][cb],
+which is a `trait` that allows for custom compiler configuration,
+as well as allowing custom code to run after different phases of the compilation.
+
+> **Warning:** By its very nature, the internal compiler APIs are always going
+> to be unstable. That said, we do try not to break things unnecessarily.
+
+
+[`Compiler`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/interface/struct.Compiler.html
+[`rustc_driver`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/
+[`rustc_interface`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/index.html
+[`Session`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_session/struct.Session.html
+[`SourceMap`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/source_map/struct.SourceMap.html
+[`TyCtxt`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html
+[Appendix A]: appendix/stupid-stats.html
+[cb]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/trait.Callbacks.html
+[example]: https://github.com/rust-lang/rustc-dev-guide/blob/master/examples/rustc-driver-example.rs
+[i_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/interface/fn.run_compiler.html
+[rd_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver_impl/fn.run_compiler.html
+[stupid-stats]: https://github.com/nrc/stupid-stats
+[`nightly-rustc`]: https://doc.rust-lang.org/nightly/nightly-rustc/