Ch. 17 §03: support code for motivating Pin

- Rexport `tokio::fs::read_to_string` as `trpl::read_to_string`.
- Add a no-listing example for the mutable borrow example. This will
  keep us honest that the code there itself compiles just fine!

listings/ch17-async-await/no-listing-borrow-mutable-vec/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "async_await"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+trpl = { path = "../../../packages/trpl" }

listings/ch17-async-await/no-listing-borrow-mutable-vec/src/main.rs

@@ -0,0 +1,18 @@
+fn main() {
+    trpl::block_on({
+        // ANCHOR: here
+        async {
+            let mut strings = vec![];
+
+            let a = trpl::read_to_string("test-data/hello.txt").await.unwrap();
+            strings.push(a.trim());
+
+            let b = trpl::read_to_string("test-data/world.txt").await.unwrap();
+            strings.push(b.trim());
+
+            let combined = strings.join(" ");
+            println!("{combined}");
+        }
+        // ANCHOR_END: here
+    });
+}

listings/ch17-async-await/no-listing-borrow-mutable-vec/test-data/hello.txt

@@ -0,0 +1 @@
+Hello

listings/ch17-async-await/no-listing-borrow-mutable-vec/test-data/punct.txt

@@ -0,0 +1 @@
+!

listings/ch17-async-await/no-listing-borrow-mutable-vec/test-data/world.txt

@@ -0,0 +1 @@
+World

packages/trpl/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 [dependencies]
 futures = "0.3.30"
 tokio = { version = "1", default-features = false, features = [
+    "fs",
     "rt-multi-thread",
     "sync",
     "time",

packages/trpl/src/lib.rs

@@ -20,6 +20,7 @@ pub use futures::{
     join,
 };
 pub use tokio::{
+    fs::read_to_string,
     runtime::Runtime,
     // We use the `unbounded` variants because they most closely match the APIs
     // from `std::sync::mpsc::channel`. Tokio's API choices are interesting:

packages/trpl/tests/integration/main.rs

@@ -188,3 +188,14 @@ fn yield_now() {
 
     assert_eq!(result, "done");
 }
+
+#[test]
+fn read_to_string() {
+    let result = trpl::block_on(async {
+        trpl::read_to_string("tests/integration/to-read.txt")
+            .await
+            .unwrap()
+    });
+
+    assert_eq!(result, String::from("This is some text!\n"));
+}

packages/trpl/tests/integration/to-read.txt

@@ -0,0 +1 @@
+This is some text!