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Add tests to assert current behavior of large future sizes
Based on a couple of sources: - https://swatinem.de/blog/future-size/ - rust-lang#62958
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‎tests/ui/future-sizes/future-as-arg.rs

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// edition: 2021
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// run-pass
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async fn test(_arg: [u8; 8192]) {}
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async fn use_future(fut: impl std::future::Future<Output = ()>) {
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fut.await
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}
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fn main() {
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let n = std::mem::size_of_val(&use_future(use_future(use_future(use_future(use_future(
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use_future(use_future(use_future(use_future(use_future(test(
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[0; 8192]
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))))))
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))))));
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println!("size is: {n}");
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// Not putting an exact number in case it slightly changes over different commits
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assert!(n > 8000000);
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}

‎tests/ui/future-sizes/large-arg.rs

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// compile-flags: -Z print-type-sizes --crate-type=lib
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// edition: 2021
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// build-pass
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pub async fn test() {
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let _ = a([0u8; 1024]).await;
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}
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pub async fn a<T>(t: T) -> T {
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b(t).await
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}
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async fn b<T>(t: T) -> T {
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c(t).await
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}
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async fn c<T>(t: T) -> T {
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t
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}

‎tests/ui/future-sizes/large-arg.stdout

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print-type-size type: `[async fn body@$DIR/large-arg.rs:5:21: 7:2]`: 3076 bytes, alignment: 1 bytes
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print-type-size discriminant: 1 bytes
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print-type-size variant `Suspend0`: 3075 bytes
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print-type-size field `.__awaitee`: 3075 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Unresumed`: 0 bytes
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print-type-size variant `Returned`: 0 bytes
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print-type-size variant `Panicked`: 0 bytes
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print-type-size type: `[async fn body@$DIR/large-arg.rs:9:30: 11:2]`: 3075 bytes, alignment: 1 bytes
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print-type-size discriminant: 1 bytes
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print-type-size variant `Suspend0`: 3074 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size field `.__awaitee`: 2050 bytes
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print-type-size variant `Unresumed`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Returned`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Panicked`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size type: `std::mem::ManuallyDrop<[async fn body@$DIR/large-arg.rs:9:30: 11:2]>`: 3075 bytes, alignment: 1 bytes
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print-type-size field `.value`: 3075 bytes
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print-type-size type: `std::mem::MaybeUninit<[async fn body@$DIR/large-arg.rs:9:30: 11:2]>`: 3075 bytes, alignment: 1 bytes
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print-type-size variant `MaybeUninit`: 3075 bytes
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print-type-size field `.uninit`: 0 bytes
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print-type-size field `.value`: 3075 bytes
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print-type-size type: `[async fn body@$DIR/large-arg.rs:12:26: 14:2]`: 2050 bytes, alignment: 1 bytes
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print-type-size discriminant: 1 bytes
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print-type-size variant `Suspend0`: 2049 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size field `.__awaitee`: 1025 bytes
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print-type-size variant `Unresumed`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Returned`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Panicked`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size type: `std::mem::ManuallyDrop<[async fn body@$DIR/large-arg.rs:12:26: 14:2]>`: 2050 bytes, alignment: 1 bytes
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print-type-size field `.value`: 2050 bytes
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print-type-size type: `std::mem::MaybeUninit<[async fn body@$DIR/large-arg.rs:12:26: 14:2]>`: 2050 bytes, alignment: 1 bytes
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print-type-size variant `MaybeUninit`: 2050 bytes
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print-type-size field `.uninit`: 0 bytes
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print-type-size field `.value`: 2050 bytes
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print-type-size type: `[async fn body@$DIR/large-arg.rs:15:26: 17:2]`: 1025 bytes, alignment: 1 bytes
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print-type-size discriminant: 1 bytes
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print-type-size variant `Unresumed`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Returned`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size variant `Panicked`: 1024 bytes
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print-type-size field `.t`: 1024 bytes, offset: 0 bytes, alignment: 1 bytes
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print-type-size type: `std::mem::ManuallyDrop<[async fn body@$DIR/large-arg.rs:15:26: 17:2]>`: 1025 bytes, alignment: 1 bytes
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print-type-size field `.value`: 1025 bytes
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print-type-size type: `std::mem::MaybeUninit<[async fn body@$DIR/large-arg.rs:15:26: 17:2]>`: 1025 bytes, alignment: 1 bytes
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print-type-size variant `MaybeUninit`: 1025 bytes
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print-type-size field `.uninit`: 0 bytes
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print-type-size field `.value`: 1025 bytes
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print-type-size type: `std::task::Poll<[u8; 1024]>`: 1025 bytes, alignment: 1 bytes
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print-type-size discriminant: 1 bytes
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print-type-size variant `Ready`: 1024 bytes
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print-type-size field `.0`: 1024 bytes
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print-type-size variant `Pending`: 0 bytes

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