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Auto merge of #4190 - projedi:fix-eta, r=flip1995
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Fixing eta with respect to lazy evaluation.

This fixes #4187

changelog: `redundant_closure`: stop linting on expressions returning a function, which is then directly used by the closure
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bors committed Jun 10, 2019
2 parents c0dbd34 + 41a4ce5 commit ba1702a
Showing 4 changed files with 19 additions and 15 deletions.
2 changes: 2 additions & 0 deletions clippy_lints/src/eta_reduction.rs
Original file line number Diff line number Diff line change
@@ -82,6 +82,8 @@ fn check_closure(cx: &LateContext<'_, '_>, expr: &Expr) {
if_chain!(
if let ExprKind::Call(ref caller, ref args) = ex.node;

if let ExprKind::Path(_) = caller.node;

// Not the same number of arguments, there is no way the closure is the same as the function return;
if args.len() == decl.inputs.len();

11 changes: 9 additions & 2 deletions tests/ui/eta.fixed
Original file line number Diff line number Diff line change
@@ -20,7 +20,7 @@ use std::path::PathBuf;
fn main() {
let a = Some(1u8).map(foo);
meta(foo);
let c = Some(1u8).map({1+2; foo});
let c = Some(1u8).map(|a| {1+2; foo}(a));
let d = Some(1u8).map(|a| foo((|b| foo2(b))(a))); //is adjusted?
all(&[1, 2, 3], &2, |x, y| below(x, y)); //is adjusted
unsafe {
@@ -105,7 +105,7 @@ fn test_redundant_closures_containing_method_calls() {

let mut some = Some(|x| x * x);
let arr = [Ok(1), Err(2)];
let _: Vec<_> = arr.iter().map(|x| x.map_err(some.take().unwrap())).collect();
let _: Vec<_> = arr.iter().map(|x| x.map_err(|e| some.take().unwrap()(e))).collect();
}

struct Thunk<T>(Box<dyn FnMut() -> T>);
@@ -177,3 +177,10 @@ fn test_redundant_closure_with_another_closure() {
let closure = |a| println!("{}", a);
let a = Some(1u8).map(closure);
}

fn make_lazy(f: impl Fn() -> fn(u8) -> u8) -> impl Fn(u8) -> u8 {
// Currently f is called when result of make_lazy is called.
// If the closure is removed, f will be called when make_lazy itself is
// called. This changes semantics, so the closure must stay.
Box::new(move |x| f()(x))
}
7 changes: 7 additions & 0 deletions tests/ui/eta.rs
Original file line number Diff line number Diff line change
@@ -177,3 +177,10 @@ fn test_redundant_closure_with_another_closure() {
let closure = |a| println!("{}", a);
let a = Some(1u8).map(|a| closure(a));
}

fn make_lazy(f: impl Fn() -> fn(u8) -> u8) -> impl Fn(u8) -> u8 {
// Currently f is called when result of make_lazy is called.
// If the closure is removed, f will be called when make_lazy itself is
// called. This changes semantics, so the closure must stay.
Box::new(move |x| f()(x))
}
14 changes: 1 addition & 13 deletions tests/ui/eta.stderr
Original file line number Diff line number Diff line change
@@ -12,12 +12,6 @@ error: redundant closure found
LL | meta(|a| foo(a));
| ^^^^^^^^^^ help: remove closure as shown: `foo`

error: redundant closure found
--> $DIR/eta.rs:23:27
|
LL | let c = Some(1u8).map(|a| {1+2; foo}(a));
| ^^^^^^^^^^^^^^^^^ help: remove closure as shown: `{1+2; foo}`

error: this expression borrows a reference that is immediately dereferenced by the compiler
--> $DIR/eta.rs:25:21
|
@@ -70,12 +64,6 @@ error: redundant closure found
LL | let e: std::vec::Vec<char> = vec!['a', 'b', 'c'].iter().map(|c| c.to_ascii_uppercase()).collect();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove closure as shown: `char::to_ascii_uppercase`

error: redundant closure found
--> $DIR/eta.rs:108:50
|
LL | let _: Vec<_> = arr.iter().map(|x| x.map_err(|e| some.take().unwrap()(e))).collect();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove closure as shown: `some.take().unwrap()`

error: redundant closure found
--> $DIR/eta.rs:173:27
|
@@ -88,5 +76,5 @@ error: redundant closure found
LL | let a = Some(1u8).map(|a| closure(a));
| ^^^^^^^^^^^^^^ help: remove closure as shown: `closure`

error: aborting due to 14 previous errors
error: aborting due to 12 previous errors

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