Add splat formatting regression tests

tests/target/splat.rs

@@ -0,0 +1,111 @@
+/// Tests that the `#[rustc_splat]` attribute is preserved by rustfmt.
+/// This attribute is currently unstable, and its syntax might change in future.
+/// It currently uses the default formatting for attributes.
+
+// These snippets are mainly from rust/tests/ui/splat
+
+// Rejected by rustc, but still needs to be formatted correctly
+
+// Can't have rust-call and splat on the same function
+trait Trait: Tuple + Sized {
+    extern "rust-call" fn method(#[rustc_splat] self: Self);
+}
+
+extern "rust-call" fn f(#[rustc_splat] _: ());
+
+fn wrong_type(#[rustc_splat] _x: u32) {}
+
+// Can't have multiple splats in the same function
+fn multi_splat_bad(#[rustc_splat] (_a, _b): (u32, i8), #[rustc_splat] (_c, _d): (u32, i8)) {}
+
+// Multiple splats on the same argument are redundant
+fn multisplat_arg_bad(
+    #[rustc_splat]
+    #[rustc_splat]
+    (_a, _b): (u32, i8),
+) {
+}
+
+fn multisplat_arg_fn_bad(
+    #[rustc_splat]
+    #[rustc_splat]
+    (_a, _b): (u32, i8),
+    #[rustc_splat] (_c, _d): (u32, i8),
+) {
+}
+
+// Can't have variadic and splat on the same function
+unsafe extern "C" fn splat_variadic(#[rustc_splat] (_a, _b): (u32, i8), varargs: ...) {}
+unsafe extern "C" fn splat_variadic2(varargs: ..., #[rustc_splat] (_a, _b): (u32, i8)) {}
+
+// Accepted by rustc
+struct Foo;
+
+impl Foo {
+    fn method(&self, #[rustc_splat] args: impl MethodArgs) -> String {}
+    fn tuple_1(#[rustc_splat] (_a,): (u32,)) {}
+    fn tuple_3(#[rustc_splat] (_a, _b, _c): (u32, i32, i8)) {}
+}
+
+fn generic<T: Tuple + Debug>(#[rustc_splat] a: T) -> String {
+    String::new()
+}
+
+fn splat_non_terminal_arg(#[rustc_splat] (a, b): (u32, i8), c: f64) -> (i8, f64, u32) {
+    (a, b, c)
+}
+
+const X: fn(#[rustc_splat] (f32,)) = None.unwrap();
+
+fn main() {
+    struct Type<T: ?Sized>(T);
+
+    // Rejected by rustc, but still needs to be formatted correctly
+    // Closures
+    (|#[rustc_splat] x: i32| {})(1);
+
+    // Function pointer types
+
+    // Rust-call and splat aren't allowed in the same function
+    let f_: extern "rust-call" fn(#[rustc_splat] ()) = f;
+
+    let wrong_type_: fn(#[rustc_splat] _x: u32) = wrong_type;
+
+    let multi_splat_bad_: fn(#[rustc_splat] (u32, i8), #[rustc_splat] (u32, i8)) = multi_splat_bad;
+    let multisplat_arg_bad_: fn(
+        #[rustc_splat]
+        #[rustc_splat]
+        (u32, i8),
+    ) = multisplat_arg_bad;
+    let multisplat_arg_fn_bad_: fn(
+        #[rustc_splat]
+        #[rustc_splat]
+        (u32, i8),
+        #[rustc_splat] (u32, i8),
+    ) = multisplat_arg_fn_bad;
+
+    // Splat and variadic aren't allowed in the same function
+    let splat_variadic_: unsafe extern "C" fn(#[rustc_splat] (u32, i8), ...) = splat_variadic;
+    let splat_variadic2_: unsafe extern "C" fn(..., #[rustc_splat] (u32, i8)) = splat_variadic2;
+
+    // Accepted by rustc
+    // Function pointer types
+
+    // Only one splatted arg
+    let fn_ptr: fn(#[rustc_splat] (u32, i8)) -> String =
+        generic as fn(#[rustc_splat] (u32, i8)) -> String;
+    impl Type<fn(#[rustc_splat] (u8, u32))> {}
+
+    // Leading splatted arg
+    let fn_pp: *const fn(#[rustc_splat] (u32, i8), f64) -> (i8, f64, u32) =
+        &(splat_non_terminal_arg as fn(#[rustc_splat] (u32, i8), f64) -> (i8, f64, u32));
+
+    // Trailing splatted arg
+    impl Type<*mut fn(u32, i8, #[rustc_splat] (f64,))> {}
+
+    // Middle splatted arg
+    impl Type<&fn(u32, #[rustc_splat] (i8, f32, usize), f64)> {}
+
+    // Splats within splats
+    impl Type<Box<fn(u32, #[rustc_splat] (fn(#[rustc_splat] ()), i8), f64)>> {}
+}