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Fix suggestion from incorrect move async to async move. #63699

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merged 1 commit into from
Aug 20, 2019
Merged

Fix suggestion from incorrect move async to async move. #63699

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11 changes: 10 additions & 1 deletion src/librustc_mir/borrow_check/conflict_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1190,7 +1190,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
);

let suggestion = match tcx.sess.source_map().span_to_snippet(args_span) {
Ok(string) => format!("move {}", string),
Ok(mut string) => {
if string.starts_with("async ") {
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@jakubadamw jakubadamw Aug 20, 2019 •
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This is a rather error-prone way of checking this that will fail with:

async
|x| {}

or

async\t|x|

I don't think this should be looking at the code snippet but rather trace with self.tcx whether this closure was an async one before lowering. I sadly cannot tell you off the top of my head how to do it and cannot look at the code at this very moment but maybe someone else can chim in. @estebank?

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That is true. Ideally you'd want to get the original node, but I don't think you can. An alternative that keeps operating on the string (less than ideal, as already established) would be to use string.split_whitespace().next() which would yield Some("async") for the cases we care about in a pretty foolproof way.

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String operations for these checks is not ideal, but sometimes we have no way around them unless we track more things from the AST onwards.

string.insert_str(6, "move ");
} else if string.starts_with("async|") {
string.insert_str(5, " move");
} else {
string.insert_str(0, "move ");
};
string
},
Err(_) => "move |<args>| <body>".to_string()
};

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10 changes: 10 additions & 0 deletions src/test/ui/async-await/async-borrowck-escaping-closure-error.rs
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@@ -0,0 +1,10 @@
// edition:2018
#![feature(async_closure,async_await)]
fn foo() -> Box<dyn std::future::Future<Output = u32>> {
let x = 0u32;
Box::new((async || x)())
//~^ ERROR E0373
}

fn main() {
}
21 changes: 21 additions & 0 deletions src/test/ui/async-await/async-borrowck-escaping-closure-error.stderr
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@@ -0,0 +1,21 @@
error[E0373]: closure may outlive the current function, but it borrows `x`, which is owned by the current function
--> $DIR/async-borrowck-escaping-closure-error.rs:5:15
|
LL | Box::new((async || x)())
| ^^^^^^^^ - `x` is borrowed here
| |
| may outlive borrowed value `x`
|
note: closure is returned here
--> $DIR/async-borrowck-escaping-closure-error.rs:5:5
|
LL | Box::new((async || x)())
| ^^^^^^^^^^^^^^^^^^^^^^^^
help: to force the closure to take ownership of `x` (and any other referenced variables), use the `move` keyword
|
LL | Box::new((async move || x)())
| ^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0373`.