update error chapter with v0.23.0 error info (#45)

src/chapter_3/errors.md

@@ -1,9 +1,19 @@
 # Errors
-There are three types of errors in anchor programs. Anchor Internal Errors, Custom Errors, and non-anchor errors.
 
-The autogenerated clients can automatically parse Anchor Internal Errors and Custom Errors so they can display the error code and error message. This is not possible for non-anchor errors where clients just return the raw error returned by the underlying solana client libraries.
+> [`AnchorError` Rust Reference](https://docs.rs/anchor-lang/latest/anchor_lang/error/struct.AnchorError.html)
 
-> (Ultimately, all programs return the same Error: The [`ProgramError`](https://docs.rs/solana-program/latest/solana_program/program_error/enum.ProgramError.html). This Error has a field for a custom error number. This is where Anchor puts its internal and custom error codes. The autogenerated clients read this number and read the IDL (where custom errors' numbers are mapped to their messages) to display the correct error messages (The Anchor internal error number=>message mapping is hardcoded in the clients). Doing it this way means that there is no way to display dynamic custom error messages because all error messages are hardcoded in the IDL. Very soon, anchor will use logs instead of relying only on the returned error code number to emit errors. These logs can also be read by the client and allow dynamic content.)
+> [`AnchorError` Typescript Reference](https://project-serum.github.io/anchor/ts/classes/AnchorError.html)
+
+There are two types of errors in anchor programs. AnchorErrors and non-anchor errors.
+AnchorErrors can be divided into Anchor Internal Errors that the framework returns from inside its own code or
+custom errors which the user (you!) can return. 
+
+- AnchorErrors
+  - Anchor Internal Errors
+  - Custom Errors
+- Non-anchor errors.
+
+[AnchorErrors](https://docs.rs/anchor-lang/latest/anchor_lang/error/struct.AnchorError.html) provide a range of information like the error name and number or the location in the code where the anchor was thrown, or the account that violated a constraint (e.g. a `mut` constraint). Once thrown inside the program, [you can access the error information](https://project-serum.github.io/anchor/ts/classes/AnchorError.html) in the anchor clients like the typescript client. The typescript client also enriches the error with additional information about which program the error was thrown in and the CPI calls (which are explained [here](./CPIs.md) in the book) that led to the program from which the error was thrown from. [The milestone chapter](./milestone_project_tic-tac-toe.md) explores how all of this works together in practice. For now, let's look at how different errors can be returned from inside a program.
 
 ## Anchor Internal Errors
 
@@ -61,3 +71,7 @@ pub enum MyError {
     DataTooLarge
 }
 ```
+
+There are a couple of `require` macros to choose from ([search for require in the docs](https://docs.rs/anchor-lang/latest/anchor_lang/?search=require)). When comparing public keys, it's important to use the `keys` variants of the require statements like `require_keys_eq` instead of `require_eq` because comparing public keys with `require_eq` is very expensive.
+
+> (Ultimately, all programs return the same Error: The [`ProgramError`](https://docs.rs/solana-program/latest/solana_program/program_error/enum.ProgramError.html). This Error has a field for a custom error number. This is where Anchor puts its internal and custom error codes. However, this is just a single number and a single number is only so useful. So in addition, in the case of AnchorErrors, Anchor logs the returned AnchorError and the Anchor clients parse these logs to provide as much information as possible. This is not always possible. For example, there is currently no easy way to get the logs of a `processed` transaction with preflight checks turned off. In addition, non-anchor or old anchor programs might not log AnchorErrors. In these cases, Anchor will fall back to checking whether the returned error number by the transaction matches a an error number defined in the `IDL` or an Anchor internal error code. If so, Anchor will at least enrich the error with the error message. Also, if there are logs available, Anchor will always try to parse the program error stack and return that so you know which program the error was returned from.