Format all Markdown files with dprint (#1157)

This is the result of running `dprint fmt` after removing `src/` from
the list of excluded directories.

This also reformats the Rust code: we might want to tweak this a bit in
the future since some of the changes removes the hand-formatting. Of
course, this formatting can be seen as a mis-feature, so maybe this is
good overall.

Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged
after this, meaning that all existing translations remain valid! A few
messages were changed because of stray whitespace characters:

     msgid ""
     "Slices always borrow from another object. In this example, `a` has to remain "
    -"'alive' (in scope) for at least as long as our slice. "
    +"'alive' (in scope) for at least as long as our slice."
     msgstr ""

The formatting is enforced in CI and we will have to see how annoying
this is in practice for the many contributors. If it becomes annoying,
we should look into fixing dprint/check#11 so that `dprint` can annotate
the lines that need fixing directly, then I think we can consider more
strict formatting checks.

I added more customization to `rustfmt.toml`. This is to better emulate
the dense style used in the course:

- `max_width = 85` allows lines to take up the full width available in
our code blocks (when taking margins and the line numbers into account).
- `wrap_comments = true` ensures that we don't show very long comments
in the code examples. I edited some comments to shorten them and avoid
unnecessary line breaks — please trim other unnecessarily long comments
when you see them! Remember we're writing code for slides 😄
- `use_small_heuristics = "Max"` allows for things like struct literals
and if-statements to take up the full line width configured above.

The formatting settings apply to all our Rust code right now — I think
we could improve this with https://github.com/dprint/dprint/issues/711
which lets us add per-directory `dprint` configuration files. However,
the `inherit: true` setting is not yet implemented (as far as I can
tell), so a nested configuration file will have to copy most or all of
the top-level file.

src/concurrency/channels.md

@@ -23,9 +23,10 @@ fn main() {
 
 <details>
 
-* `mpsc` stands for Multi-Producer, Single-Consumer. `Sender` and `SyncSender` implement `Clone` (so
-  you can make multiple producers) but `Receiver` does not.
-* `send()` and `recv()` return `Result`. If they return `Err`, it means the counterpart `Sender` or
-  `Receiver` is dropped and the channel is closed.
+- `mpsc` stands for Multi-Producer, Single-Consumer. `Sender` and `SyncSender`
+  implement `Clone` (so you can make multiple producers) but `Receiver` does
+  not.
+- `send()` and `recv()` return `Result`. If they return `Err`, it means the
+  counterpart `Sender` or `Receiver` is dropped and the channel is closed.
 
 </details>

src/concurrency/channels/bounded.md

@@ -27,9 +27,13 @@ fn main() {
 ```
 
 <details>
-    
-* Calling `send` will block the current thread until there is space in the channel for the new message. The thread can be blocked indefinitely if there is nobody who reads from the channel.
-* A call to `send` will abort with an error (that is why it returns `Result`) if the channel is closed. A channel is closed when the receiver is dropped.
-* A bounded channel with a size of zero is called a "rendezvous channel". Every send will block the current thread until another thread calls `read`.
-    
+
+- Calling `send` will block the current thread until there is space in the
+  channel for the new message. The thread can be blocked indefinitely if there
+  is nobody who reads from the channel.
+- A call to `send` will abort with an error (that is why it returns `Result`) if
+  the channel is closed. A channel is closed when the receiver is dropped.
+- A bounded channel with a size of zero is called a "rendezvous channel". Every
+  send will block the current thread until another thread calls `read`.
+
 </details>

src/concurrency/scoped-threads.md

@@ -36,8 +36,10 @@ fn main() {
 [1]: https://doc.rust-lang.org/std/thread/fn.scope.html
 
 <details>
-    
-* The reason for that is that when the `thread::scope` function completes, all the threads are guaranteed to be joined, so they can return borrowed data.
-* Normal Rust borrowing rules apply: you can either borrow mutably by one thread, or immutably by any number of threads.
-    
+
+- The reason for that is that when the `thread::scope` function completes, all
+  the threads are guaranteed to be joined, so they can return borrowed data.
+- Normal Rust borrowing rules apply: you can either borrow mutably by one
+  thread, or immutably by any number of threads.
+
 </details>

src/concurrency/send-sync.md

@@ -1,15 +1,16 @@
 # `Send` and `Sync`
 
-How does Rust know to forbid shared access across threads? The answer is in two traits:
+How does Rust know to forbid shared access across threads? The answer is in two
+traits:
 
-* [`Send`][1]: a type `T` is `Send` if it is safe to move a `T` across a thread
+- [`Send`][1]: a type `T` is `Send` if it is safe to move a `T` across a thread
   boundary.
-* [`Sync`][2]: a type `T` is `Sync` if it is safe to move a `&T` across a thread
+- [`Sync`][2]: a type `T` is `Sync` if it is safe to move a `&T` across a thread
   boundary.
 
-`Send` and `Sync` are [unsafe traits][3]. The compiler will automatically derive them for your types
-as long as they only contain `Send` and `Sync` types. You can also implement them manually when you
-know it is valid.
+`Send` and `Sync` are [unsafe traits][3]. The compiler will automatically derive
+them for your types as long as they only contain `Send` and `Sync` types. You
+can also implement them manually when you know it is valid.
 
 [1]: https://doc.rust-lang.org/std/marker/trait.Send.html
 [2]: https://doc.rust-lang.org/std/marker/trait.Sync.html
@@ -17,7 +18,8 @@ know it is valid.
 
 <details>
 
-* One can think of these traits as markers that the type has certain thread-safety properties.
-* They can be used in the generic constraints as normal traits.
-  
+- One can think of these traits as markers that the type has certain
+  thread-safety properties.
+- They can be used in the generic constraints as normal traits.
+
 </details>

src/concurrency/send-sync/examples.md

@@ -4,12 +4,12 @@
 
 Most types you come across are `Send + Sync`:
 
-* `i8`, `f32`, `bool`, `char`, `&str`, ...
-* `(T1, T2)`, `[T; N]`, `&[T]`, `struct { x: T }`, ...
-* `String`, `Option<T>`, `Vec<T>`, `Box<T>`, ...
-* `Arc<T>`: Explicitly thread-safe via atomic reference count.
-* `Mutex<T>`: Explicitly thread-safe via internal locking.
-* `AtomicBool`, `AtomicU8`, ...: Uses special atomic instructions.
+- `i8`, `f32`, `bool`, `char`, `&str`, ...
+- `(T1, T2)`, `[T; N]`, `&[T]`, `struct { x: T }`, ...
+- `String`, `Option<T>`, `Vec<T>`, `Box<T>`, ...
+- `Arc<T>`: Explicitly thread-safe via atomic reference count.
+- `Mutex<T>`: Explicitly thread-safe via internal locking.
+- `AtomicBool`, `AtomicU8`, ...: Uses special atomic instructions.
 
 The generic types are typically `Send + Sync` when the type parameters are
 `Send + Sync`.
@@ -19,23 +19,23 @@ The generic types are typically `Send + Sync` when the type parameters are
 These types can be moved to other threads, but they're not thread-safe.
 Typically because of interior mutability:
 
-* `mpsc::Sender<T>`
-* `mpsc::Receiver<T>`
-* `Cell<T>`
-* `RefCell<T>`
+- `mpsc::Sender<T>`
+- `mpsc::Receiver<T>`
+- `Cell<T>`
+- `RefCell<T>`
 
 ## `!Send + Sync`
 
 These types are thread-safe, but they cannot be moved to another thread:
 
-* `MutexGuard<T: Sync>`: Uses OS level primitives which must be deallocated on the
-  thread which created them.
+- `MutexGuard<T: Sync>`: Uses OS level primitives which must be deallocated on
+  the thread which created them.
 
 ## `!Send + !Sync`
 
 These types are not thread-safe and cannot be moved to other threads:
 
-* `Rc<T>`: each `Rc<T>` has a reference to an `RcBox<T>`, which contains a
+- `Rc<T>`: each `Rc<T>` has a reference to an `RcBox<T>`, which contains a
   non-atomic reference count.
-* `*const T`, `*mut T`: Rust assumes raw pointers may have special
-  concurrency considerations.
+- `*const T`, `*mut T`: Rust assumes raw pointers may have special concurrency
+  considerations.

src/concurrency/send-sync/sync.md

@@ -11,8 +11,14 @@ More precisely, the definition is:
 
 <details>
 
-This statement is essentially a shorthand way of saying that if a type is thread-safe for shared use, it is also thread-safe to pass references of it across threads.
+This statement is essentially a shorthand way of saying that if a type is
+thread-safe for shared use, it is also thread-safe to pass references of it
+across threads.
 
-This is because if a type is Sync it means that it can be shared across multiple threads without the risk of data races or other synchronization issues, so it is safe to move it to another thread. A reference to the type is also safe to move to another thread, because the data it references can be accessed from any thread safely.
+This is because if a type is Sync it means that it can be shared across multiple
+threads without the risk of data races or other synchronization issues, so it is
+safe to move it to another thread. A reference to the type is also safe to move
+to another thread, because the data it references can be accessed from any
+thread safely.
 
 </details>

src/concurrency/shared_state.md

@@ -3,9 +3,9 @@
 Rust uses the type system to enforce synchronization of shared data. This is
 primarily done via two types:
 
-* [`Arc<T>`][1], atomic reference counted `T`: handles sharing between threads and
-  takes care to deallocate `T` when the last reference is dropped,
-* [`Mutex<T>`][2]: ensures mutually exclusive access to the `T` value.
+- [`Arc<T>`][1], atomic reference counted `T`: handles sharing between threads
+  and takes care to deallocate `T` when the last reference is dropped,
+- [`Mutex<T>`][2]: ensures mutually exclusive access to the `T` value.
 
 [1]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 [2]: https://doc.rust-lang.org/std/sync/struct.Mutex.html

src/concurrency/shared_state/arc.md

@@ -3,8 +3,8 @@
 [`Arc<T>`][1] allows shared read-only access via `Arc::clone`:
 
 ```rust,editable
-use std::thread;
 use std::sync::Arc;
+use std::thread;
 
 fn main() {
     let v = Arc::new(vec![10, 20, 30]);
@@ -26,13 +26,14 @@ fn main() {
 
 <details>
 
-* `Arc` stands for "Atomic Reference Counted", a thread safe version of `Rc` that uses atomic
-  operations.
-* `Arc<T>` implements `Clone` whether or not `T` does. It implements `Send` and `Sync` if
-  and only if `T` implements them both.
-* `Arc::clone()` has the cost of atomic operations that get executed, but after that the use of the
-  `T` is free.
-* Beware of reference cycles, `Arc` does not use a garbage collector to detect them.
-    * `std::sync::Weak` can help.
+- `Arc` stands for "Atomic Reference Counted", a thread safe version of `Rc`
+  that uses atomic operations.
+- `Arc<T>` implements `Clone` whether or not `T` does. It implements `Send` and
+  `Sync` if and only if `T` implements them both.
+- `Arc::clone()` has the cost of atomic operations that get executed, but after
+  that the use of the `T` is free.
+- Beware of reference cycles, `Arc` does not use a garbage collector to detect
+  them.
+  - `std::sync::Weak` can help.
 
 </details>

src/concurrency/shared_state/example.md

@@ -21,7 +21,7 @@ fn main() {
 <details>
 
 Possible solution:
-    
+
 ```rust,editable
 use std::sync::{Arc, Mutex};
 use std::thread;
@@ -45,12 +45,16 @@ fn main() {
     println!("v: {v:?}");
 }
 ```
-    
+
 Notable parts:
 
-* `v` is wrapped in both `Arc` and `Mutex`, because their concerns are orthogonal.
-  * Wrapping a `Mutex` in an `Arc` is a common pattern to share mutable state between threads.
-* `v: Arc<_>` needs to be cloned as `v2` before it can be moved into another thread. Note `move` was added to the lambda signature.
-* Blocks are introduced to narrow the scope of the `LockGuard` as much as possible.
+- `v` is wrapped in both `Arc` and `Mutex`, because their concerns are
+  orthogonal.
+  - Wrapping a `Mutex` in an `Arc` is a common pattern to share mutable state
+    between threads.
+- `v: Arc<_>` needs to be cloned as `v2` before it can be moved into another
+  thread. Note `move` was added to the lambda signature.
+- Blocks are introduced to narrow the scope of the `LockGuard` as much as
+  possible.
 
 </details>

src/concurrency/shared_state/mutex.md

@@ -27,19 +27,22 @@ implementation.
 [3]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 
 <details>
-    
-* `Mutex` in Rust looks like a collection with just one element --- the protected data.
-    * It is not possible to forget to acquire the mutex before accessing the protected data.
-* You can get an `&mut T` from an `&Mutex<T>` by taking the lock. The `MutexGuard` ensures that the
-  `&mut T` doesn't outlive the lock being held.
-* `Mutex<T>` implements both `Send` and `Sync` iff (if and only if) `T` implements `Send`.
-* A read-write lock counterpart: `RwLock`.
-* Why does `lock()` return a `Result`? 
-    * If the thread that held the `Mutex` panicked, the `Mutex` becomes "poisoned" to signal that
-      the data it protected might be in an inconsistent state. Calling `lock()` on a poisoned mutex
-      fails with a [`PoisonError`]. You can call `into_inner()` on the error to recover the data
-      regardless.
 
-[`PoisonError`]: https://doc.rust-lang.org/std/sync/struct.PoisonError.html  
-    
+- `Mutex` in Rust looks like a collection with just one element --- the
+  protected data.
+  - It is not possible to forget to acquire the mutex before accessing the
+    protected data.
+- You can get an `&mut T` from an `&Mutex<T>` by taking the lock. The
+  `MutexGuard` ensures that the `&mut T` doesn't outlive the lock being held.
+- `Mutex<T>` implements both `Send` and `Sync` iff (if and only if) `T`
+  implements `Send`.
+- A read-write lock counterpart: `RwLock`.
+- Why does `lock()` return a `Result`?
+  - If the thread that held the `Mutex` panicked, the `Mutex` becomes "poisoned"
+    to signal that the data it protected might be in an inconsistent state.
+    Calling `lock()` on a poisoned mutex fails with a [`PoisonError`]. You can
+    call `into_inner()` on the error to recover the data regardless.
+
+[`PoisonError`]: https://doc.rust-lang.org/std/sync/struct.PoisonError.html
+
 </details>

src/concurrency/threads.md

@@ -21,23 +21,23 @@ fn main() {
 }
 ```
 
-* Threads are all daemon threads, the main thread does not wait for them.
-* Thread panics are independent of each other.
-  * Panics can carry a payload, which can be unpacked with `downcast_ref`.
+- Threads are all daemon threads, the main thread does not wait for them.
+- Thread panics are independent of each other.
+  - Panics can carry a payload, which can be unpacked with `downcast_ref`.
 
 <details>
 
 Key points:
 
-* Notice that the thread is stopped before it reaches 10 --- the main thread is
+- Notice that the thread is stopped before it reaches 10 --- the main thread is
   not waiting.
 
-* Use `let handle = thread::spawn(...)` and later `handle.join()` to wait for
+- Use `let handle = thread::spawn(...)` and later `handle.join()` to wait for
   the thread to finish.
 
-* Trigger a panic in the thread, notice how this doesn't affect `main`.
+- Trigger a panic in the thread, notice how this doesn't affect `main`.
 
-* Use the `Result` return value from `handle.join()` to get access to the panic
+- Use the `Result` return value from `handle.join()` to get access to the panic
   payload. This is a good time to talk about [`Any`].
 
 [`Any`]: https://doc.rust-lang.org/std/any/index.html