add a bunch of ui tests

Cargo.toml

@@ -7,4 +7,12 @@ license = "MIT OR Apache-2.0"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[[test]]
+name = "ui-tests"
+path = "tests/ui/test.rs"
+
 [dependencies]
+
+[dev-dependencies]
+trybuild = "1"
+futures = { version = "0.3", features = ["executor"] }

README.md

@@ -4,7 +4,7 @@ The main codes are copy from [lru-rs](https://github.com/jeromefroe/lru-rs), ver
 
 The main motivation for implementing this project is that `LRUCache` should allow multiple immutable references obtained through `get` method.
 
-The main idea is separating the value operating permissions from the data structure itself. I'll give an elaboration in my blog post later.
+The main idea is separating the value operating permissions from the data structure itself. I'll give an elaboration in my blog post later. You can also take a look at [uitest](./tests/ui/test.rs), which explains the API design goals.
 
 ## Example
 

tests/ui/concurrent-use-refs.rs

@@ -0,0 +1,31 @@
+use ref_stable_lru::LruCache;
+use std::num::NonZeroUsize;
+
+fn main() {
+    let mut cache: LruCache<&'static str, String> = LruCache::new(NonZeroUsize::new(3).unwrap());
+
+    let out = cache.scope(|mut handle, mut perm| {
+        handle.put("a", "bb".to_string(), &mut perm);
+        handle.put("b", "cc".to_string(), &mut perm);
+        handle.put("c", "dd".to_string(), &mut perm);
+
+        let futs = ["a", "b", "c"].iter().map(|k| {
+            let v = handle.get(k, &perm).unwrap();
+
+            async {
+                // Assert v is a reference.
+                let v: &String = v;
+                v.get(..1).unwrap().to_string()
+            }
+        });
+
+        let fut = async {
+            let out = futures::future::join_all(futs).await;
+            out.join(" ")
+        };
+
+        futures::executor::block_on(fut)
+    });
+
+    assert_eq!(out, "b c d".to_string());
+}

tests/ui/double-get-in-scope.rs

@@ -0,0 +1,20 @@
+use ref_stable_lru::LruCache;
+use std::num::NonZeroUsize;
+
+fn main() {
+    let mut cache: LruCache<&'static str, String> = LruCache::new(NonZeroUsize::new(3).unwrap());
+
+    let out = cache.scope(|mut handle, mut perm| {
+        handle.put("a", "b".to_string(), &mut perm);
+        handle.put("b", "c".to_string(), &mut perm);
+        handle.put("c", "d".to_string(), &mut perm);
+
+        // Success here, since `x`, `y` and `z` actually borrowed `perm` instead of `handle`.
+        let x = handle.get(&"a", &perm).unwrap().as_str();
+        let y = handle.get(&"b", &perm).unwrap().as_str();
+        let z = handle.get(&"c", &perm).unwrap().as_str();
+        [x, y, z].join(" ")
+    });
+
+    assert_eq!(out, "b c d".to_string());
+}

tests/ui/double-get-without-scope.rs

@@ -0,0 +1,12 @@
+use ref_stable_lru::LruCache;
+use std::num::NonZeroUsize;
+
+fn main() {
+    let mut cache: LruCache<&'static str, String> = LruCache::new(NonZeroUsize::new(2).unwrap());
+
+    let x = cache.get(&"a").unwrap().as_str();
+    // Should failed here, since `x` already mutually borrowed cache.
+    let y = cache.get(&"b").unwrap().as_str();
+    let z = cache.get(&"c").unwrap().as_str();
+    [x, y, z].join(" ");
+}

tests/ui/double-get-without-scope.stderr

@@ -0,0 +1,22 @@
+error[E0499]: cannot borrow `cache` as mutable more than once at a time
+  --> tests/ui/double-get-without-scope.rs:9:13
+   |
+7  |     let x = cache.get(&"a").unwrap().as_str();
+   |             ----- first mutable borrow occurs here
+8  |     // Should failed here, since `x` already mutually borrowed cache.
+9  |     let y = cache.get(&"b").unwrap().as_str();
+   |             ^^^^^ second mutable borrow occurs here
+10 |     let z = cache.get(&"c").unwrap().as_str();
+11 |     [x, y, z].join(" ");
+   |      - first borrow later used here
+
+error[E0499]: cannot borrow `cache` as mutable more than once at a time
+  --> tests/ui/double-get-without-scope.rs:10:13
+   |
+7  |     let x = cache.get(&"a").unwrap().as_str();
+   |             ----- first mutable borrow occurs here
+...
+10 |     let z = cache.get(&"c").unwrap().as_str();
+   |             ^^^^^ second mutable borrow occurs here
+11 |     [x, y, z].join(" ");
+   |      - first borrow later used here