Merge pull request #2814 from VKlayd/fn_to_int

WIP: Add lint on cast Fn to all numerical except usize.

tests/ui/types_fn_to_int.rs

@@ -0,0 +1,22 @@
+enum Foo {
+    A(usize),
+    B
+}
+
+fn bar() -> i32 {
+    0i32
+}
+
+fn main() {
+    let x = Foo::A;
+    let _y = x as i32;
+    let _y1 = Foo::A as i32;
+    let _y = x as u32;
+    let _z = bar as u32;
+    let _y = bar as i64;
+    let _y = bar as u64;
+    let _z = Foo::A as i128;
+    let _z = Foo::A as u128;
+    let _z = bar as i128;
+    let _z = bar as u128;
+}

tests/ui/types_fn_to_int.stderr

@@ -0,0 +1,66 @@
+error: casting a `fn(usize) -> Foo {Foo::A}` to `i32` may truncate the function address value.
+  --> $DIR/types_fn_to_int.rs:12:14
+   |
+12 |     let _y = x as i32;
+   |              ^^^^^^^^ help: if you need the address of the function, consider: `x as usize`
+   |
+   = note: #[deny(fn_to_numeric_cast_with_truncation)] on by default
+
+error: casting a `fn(usize) -> Foo {Foo::A}` to `i32` may truncate the function address value.
+  --> $DIR/types_fn_to_int.rs:13:15
+   |
+13 |     let _y1 = Foo::A as i32;
+   |               ^^^^^^^^^^^^^ help: if you need the address of the function, consider: `Foo::A as usize`
+
+error: casting a `fn(usize) -> Foo {Foo::A}` to `u32` may truncate the function address value.
+  --> $DIR/types_fn_to_int.rs:14:14
+   |
+14 |     let _y = x as u32;
+   |              ^^^^^^^^ help: if you need the address of the function, consider: `x as usize`
+
+error: casting a `fn() -> i32 {bar}` to `u32` may truncate the function address value.
+  --> $DIR/types_fn_to_int.rs:15:14
+   |
+15 |     let _z = bar as u32;
+   |              ^^^^^^^^^^ help: if you need the address of the function, consider: `bar as usize`
+
+error: casting a `fn() -> i32 {bar}` to `i64` may truncate the function address value.
+  --> $DIR/types_fn_to_int.rs:16:14
+   |
+16 |     let _y = bar as i64;
+   |              ^^^^^^^^^^ help: if you need the address of the function, consider: `bar as usize`
+
+error: casting a `fn() -> i32 {bar}` to `u64` is bad style.
+  --> $DIR/types_fn_to_int.rs:17:14
+   |
+17 |     let _y = bar as u64;
+   |              ^^^^^^^^^^ help: if you need the address of the function, consider: `bar as usize`
+   |
+   = note: `-D fn-to-numeric-cast` implied by `-D warnings`
+
+error: casting a `fn(usize) -> Foo {Foo::A}` to `i128` is bad style.
+  --> $DIR/types_fn_to_int.rs:18:14
+   |
+18 |     let _z = Foo::A as i128;
+   |              ^^^^^^^^^^^^^^ help: if you need the address of the function, consider: `Foo::A as usize`
+
+error: casting a `fn(usize) -> Foo {Foo::A}` to `u128` is bad style.
+  --> $DIR/types_fn_to_int.rs:19:14
+   |
+19 |     let _z = Foo::A as u128;
+   |              ^^^^^^^^^^^^^^ help: if you need the address of the function, consider: `Foo::A as usize`
+
+error: casting a `fn() -> i32 {bar}` to `i128` is bad style.
+  --> $DIR/types_fn_to_int.rs:20:14
+   |
+20 |     let _z = bar as i128;
+   |              ^^^^^^^^^^^ help: if you need the address of the function, consider: `bar as usize`
+
+error: casting a `fn() -> i32 {bar}` to `u128` is bad style.
+  --> $DIR/types_fn_to_int.rs:21:14
+   |
+21 |     let _z = bar as u128;
+   |              ^^^^^^^^^^^ help: if you need the address of the function, consider: `bar as usize`
+
+error: aborting due to 10 previous errors
+