address Zoxc's comments

src/appendix/stupid-stats.md

@@ -4,7 +4,9 @@
 > a copy of the code on the GitHub repository.
 >
 > Due to the compiler's constantly evolving nature, the `rustc_driver`
-> mechanisms described in this chapter have been replaced by a new
+> mechanisms described in this chapter have changed. In particular, the
+> `CompilerCalls` and `CompileController` types have been replaced by
+> [`Callbacks`][cb].  Also, there is a new query-based interface in the
 > [`rustc_interface`] crate. See [The Rustc Driver and Interface] for more
 > information.
 
@@ -409,6 +411,7 @@ analysis, rather than doing its own analysis). Other parts of the compiler
 internally (I already changed save-analysis to use `CompilerController`). I've
 been experimenting with a prototype rustfmt which also uses these APIs.
 
+[cb]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/trait.Callbacks.html
 [stupid-stats]: https://github.com/nrc/stupid-stats
 [`rustc_interface`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/index.html
 [The Rustc Driver and Interface]: ../rustc-driver.html

src/rustc-driver.md

@@ -21,6 +21,13 @@ specifically the [`rustc_driver::run_compiler` function][rd_rc] (not to be confu
 `interface::run_compiler`). The `rustc_driver::run_compiler` function takes a bunch of
 command-line args and some other configurations and drives the compilation to completion.
 
+`rustc_driver::run_compiler` also takes a [`Callbacks`][cb]. In the past, when
+the `rustc_driver::run_compiler` was the primary way to use the compiler as a
+library, these callbacks were used to have some custom code run after different
+phases of the compilation. If you read [Appendix A], you may notice the use of the
+types `CompilerCalls` and `CompileController`, which no longer exist. `Callbacks`
+replaces this functionality.
+
 > **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.
 
@@ -38,6 +45,7 @@ duplication while also preventing a lot of the ergonomic issues due to many
 pervasive lifetimes. The `rustc::ty::tls` module is used to access these
 thread-locals, although you should rarely need to touch it.
 
+[cb]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/trait.Callbacks.html
 [rd_rc]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/fn.run_compiler.html
 [`rustc_interface`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_interface/index.html
 [`rustc_driver`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/