Add ui test for missing_transmute_annotation

Author: GuillaumeGomez

tests/ui/missing_transmute_annotations.fixed

@@ -0,0 +1,25 @@
+#![warn(clippy::missing_transmute_annotations)]
+
+macro_rules! bad_transmute {
+    ($e:expr) => {
+        std::mem::transmute::<[u16; 2], i32>($e)
+    }
+}
+
+fn main() {
+    unsafe {
+        let x: i32 = std::mem::transmute::<[u16; 2], i32>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x: i32 = std::mem::transmute::<[u16; 2], i32>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x = std::mem::transmute::<[u16; 2], i32>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x: i32 = std::mem::transmute::<[u16; 2], i32>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x: i32 = bad_transmute!([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+
+        // Should not warn.
+        let x = std::mem::transmute::<[u16; 2], i32>([1u16, 2u16]);
+    }
+}

tests/ui/missing_transmute_annotations.rs

@@ -0,0 +1,25 @@
+#![warn(clippy::missing_transmute_annotation)]
+
+macro_rules! bad_transmute {
+    ($e:expr) => {
+        std::mem::transmute($e)
+    };
+}
+
+fn main() {
+    unsafe {
+        let x: i32 = std::mem::transmute([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x: i32 = std::mem::transmute::<_, _>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x = std::mem::transmute::<_, i32>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x: i32 = std::mem::transmute::<[u16; 2], _>([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+        let x: i32 = bad_transmute!([1u16, 2u16]);
+        //~^ ERROR: transmute used without annotations
+
+        // Should not warn.
+        let x = std::mem::transmute::<[u16; 2], i32>([1u16, 2u16]);
+    }
+}

tests/ui/missing_transmute_annotations.stderr

@@ -0,0 +1,40 @@
+error: transmute used without annotations
+  --> $DIR/missing_transmute_annotations.rs:11:32
+   |
+LL |         let x: i32 = std::mem::transmute([1u16, 2u16]);
+   |                                ^^^^^^^^^ help: consider adding missing annotations: `transmute::<[u16; 2], i32>`
+   |
+   = note: `-D clippy::missing-transmute-annotation` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::missing_transmute_annotation)]`
+
+error: transmute used without annotations
+  --> $DIR/missing_transmute_annotations.rs:13:32
+   |
+LL |         let x: i32 = std::mem::transmute::<_, _>([1u16, 2u16]);
+   |                                ^^^^^^^^^^^^^^^^^ help: consider adding missing annotations: `transmute::<[u16; 2], i32>`
+
+error: transmute used without annotations
+  --> $DIR/missing_transmute_annotations.rs:15:27
+   |
+LL |         let x = std::mem::transmute::<_, i32>([1u16, 2u16]);
+   |                           ^^^^^^^^^^^^^^^^^^^ help: consider adding missing annotations: `transmute::<[u16; 2], i32>`
+
+error: transmute used without annotations
+  --> $DIR/missing_transmute_annotations.rs:17:32
+   |
+LL |         let x: i32 = std::mem::transmute::<[u16; 2], _>([1u16, 2u16]);
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider adding missing annotations: `transmute::<[u16; 2], i32>`
+
+error: transmute used without annotations
+  --> $DIR/missing_transmute_annotations.rs:5:19
+   |
+LL |         std::mem::transmute($e)
+   |                   ^^^^^^^^^ help: consider adding missing annotations: `transmute::<[u16; 2], i32>`
+...
+LL |         let x: i32 = bad_transmute!([1u16, 2u16]);
+   |                      ---------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `bad_transmute` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 5 previous errors
+