Add ui test for incompatible_msrv lint

tests/ui-toml/min_rust_version/min_rust_version.fixed

@@ -1,4 +1,4 @@
-#![allow(clippy::redundant_clone, clippy::unnecessary_operation)]
+#![allow(clippy::redundant_clone, clippy::unnecessary_operation, clippy::incompatible_msrv)]
 #![warn(clippy::manual_non_exhaustive, clippy::borrow_as_ptr, clippy::manual_bits)]
 
 use std::mem::{size_of, size_of_val};

tests/ui-toml/min_rust_version/min_rust_version.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::redundant_clone, clippy::unnecessary_operation)]
+#![allow(clippy::redundant_clone, clippy::unnecessary_operation, clippy::incompatible_msrv)]
 #![warn(clippy::manual_non_exhaustive, clippy::borrow_as_ptr, clippy::manual_bits)]
 
 use std::mem::{size_of, size_of_val};

tests/ui/incompatible_msrv.rs

@@ -0,0 +1,23 @@
+#![warn(clippy::incompatible_msrv)]
+#![feature(custom_inner_attributes)]
+#![clippy::msrv = "1.3.0"]
+
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::thread::sleep;
+use std::time::Duration;
+
+fn foo() {
+    let mut map: HashMap<&str, u32> = HashMap::new();
+    // Stable since 1.10, so should not warn.
+    assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    if let Entry::Vacant(v) = map.entry("poneyland") {
+        v.into_key();
+        //~^ ERROR:  MSRV is `1.3.0` but this item is stable since `1.12.0`
+    }
+    // Should warn for `sleep` but not for `Duration` (which was added in `1.3.0`).
+    sleep(Duration::new(1, 0));
+    //~^ ERROR:  MSRV is `1.3.0` but this item is stable since `1.4.0`
+}
+
+fn main() {}

tests/ui/incompatible_msrv.stderr

@@ -0,0 +1,23 @@
+error: current MSRV is `1.3.0` but this item is stable since `1.10.0`
+  --> $DIR/incompatible_msrv.rs:13:39
+   |
+LL |     assert_eq!(map.entry("poneyland").key(), &"poneyland");
+   |                                       ^^^^^
+   |
+   = note: `-D clippy::incompatible-msrv` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::incompatible_msrv)]`
+
+error: current MSRV is `1.3.0` but this item is stable since `1.12.0`
+  --> $DIR/incompatible_msrv.rs:15:11
+   |
+LL |         v.into_key();
+   |           ^^^^^^^^^^
+
+error: current MSRV is `1.3.0` but this item is stable since `1.4.0`
+  --> $DIR/incompatible_msrv.rs:19:5
+   |
+LL |     sleep(Duration::new(1, 0));
+   |     ^^^^^
+
+error: aborting due to 3 previous errors
+