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[map_identity]: respect match ergonomics #11792

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Merged
merged 1 commit into from
Nov 11, 2023
Merged

[map_identity]: respect match ergonomics #11792

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12 changes: 12 additions & 0 deletions clippy_utils/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2034,6 +2034,18 @@ pub fn is_must_use_func_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
/// Consider calling [`is_expr_untyped_identity_function`] or [`is_expr_identity_function`] instead.
fn is_body_identity_function(cx: &LateContext<'_>, func: &Body<'_>) -> bool {
fn check_pat(cx: &LateContext<'_>, pat: &Pat<'_>, expr: &Expr<'_>) -> bool {
if cx
.typeck_results()
.pat_binding_modes()
.get(pat.hir_id)
.is_some_and(|mode| matches!(mode, BindingMode::BindByReference(_)))
{
// If a tuple `(x, y)` is of type `&(i32, i32)`, then due to match ergonomics,
// the inner patterns become references. Don't consider this the identity function
// as that changes types.
return false;
}

match (pat.kind, expr.kind) {
(PatKind::Binding(_, id, _, _), _) => {
path_to_local_id(expr, id) && cx.typeck_results().expr_adjustments(expr).is_empty()
Expand Down
42 changes: 27 additions & 15 deletions tests/ui/map_identity.fixed
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Expand Up @@ -24,28 +24,40 @@ fn main() {

fn issue7189() {
// should lint
let x = [(1, 2), (3, 4)];
let _ = x.iter();
let _ = x.iter();
let _ = x.iter();
let x = [(1, 2), (3, 4)].iter().copied();
let _ = x.clone();
let _ = x.clone();
let _ = x.clone();

let y = [(1, 2, (3, (4,))), (5, 6, (7, (8,)))];
let _ = y.iter();
let y = [(1, 2, (3, (4,))), (5, 6, (7, (8,)))].iter().copied();
let _ = y.clone();

// should not lint
let _ = x.iter().map(|(x, y)| (x, y, y));
let _ = x.iter().map(|(x, _y)| (x,));
let _ = x.iter().map(|(x, _)| (x,));
let _ = x.iter().map(|(x, ..)| (x,));
let _ = y.iter().map(|(x, y, (z, _))| (x, y, (z, z)));
let _ = x.clone().map(|(x, y)| (x, y, y));
let _ = x.clone().map(|(x, _y)| (x,));
let _ = x.clone().map(|(x, _)| (x,));
let _ = x.clone().map(|(x, ..)| (x,));
let _ = y.clone().map(|(x, y, (z, _))| (x, y, (z, z)));
let _ = y
.iter()
.map(|(x, y, (z, _)): &(i32, i32, (i32, (i32,)))| (x, y, (z, z)));
.clone()
.map(|(x, y, (z, _)): (i32, i32, (i32, (i32,)))| (x, y, (z, z)));
let _ = y
.iter()
.map(|(x, y, (z, (w,))): &(i32, i32, (i32, (i32,)))| (x, y, (z, (w,))));
.clone()
.map(|(x, y, (z, (w,))): (i32, i32, (i32, (i32,)))| (x, y, (z, (w,))));
}

fn not_identity(x: &u16) -> u16 {
*x
}

fn issue11764() {
let x = [(1, 2), (3, 4)];
// don't lint: this is an `Iterator<Item = &(i32, i32)>`
// match ergonomics makes the binding patterns into references
// so that its type changes to `Iterator<Item = (&i32, &i32)>`
let _ = x.iter().map(|(x, y)| (x, y));
let _ = x.iter().map(|x| (x.0,)).map(|(x,)| x);

// no match ergonomics for `(i32, i32)`
let _ = x.iter().copied();
}
42 changes: 27 additions & 15 deletions tests/ui/map_identity.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,30 +26,42 @@ fn main() {

fn issue7189() {
// should lint
let x = [(1, 2), (3, 4)];
let _ = x.iter().map(|(x, y)| (x, y));
let _ = x.iter().map(|(x, y)| {
let x = [(1, 2), (3, 4)].iter().copied();
let _ = x.clone().map(|(x, y)| (x, y));
let _ = x.clone().map(|(x, y)| {
return (x, y);
});
let _ = x.iter().map(|(x, y)| return (x, y));
let _ = x.clone().map(|(x, y)| return (x, y));

let y = [(1, 2, (3, (4,))), (5, 6, (7, (8,)))];
let _ = y.iter().map(|(x, y, (z, (w,)))| (x, y, (z, (w,))));
let y = [(1, 2, (3, (4,))), (5, 6, (7, (8,)))].iter().copied();
let _ = y.clone().map(|(x, y, (z, (w,)))| (x, y, (z, (w,))));

// should not lint
let _ = x.iter().map(|(x, y)| (x, y, y));
let _ = x.iter().map(|(x, _y)| (x,));
let _ = x.iter().map(|(x, _)| (x,));
let _ = x.iter().map(|(x, ..)| (x,));
let _ = y.iter().map(|(x, y, (z, _))| (x, y, (z, z)));
let _ = x.clone().map(|(x, y)| (x, y, y));
let _ = x.clone().map(|(x, _y)| (x,));
let _ = x.clone().map(|(x, _)| (x,));
let _ = x.clone().map(|(x, ..)| (x,));
let _ = y.clone().map(|(x, y, (z, _))| (x, y, (z, z)));
let _ = y
.iter()
.map(|(x, y, (z, _)): &(i32, i32, (i32, (i32,)))| (x, y, (z, z)));
.clone()
.map(|(x, y, (z, _)): (i32, i32, (i32, (i32,)))| (x, y, (z, z)));
let _ = y
.iter()
.map(|(x, y, (z, (w,))): &(i32, i32, (i32, (i32,)))| (x, y, (z, (w,))));
.clone()
.map(|(x, y, (z, (w,))): (i32, i32, (i32, (i32,)))| (x, y, (z, (w,))));
}

fn not_identity(x: &u16) -> u16 {
*x
}

fn issue11764() {
let x = [(1, 2), (3, 4)];
// don't lint: this is an `Iterator<Item = &(i32, i32)>`
// match ergonomics makes the binding patterns into references
// so that its type changes to `Iterator<Item = (&i32, &i32)>`
let _ = x.iter().map(|(x, y)| (x, y));
let _ = x.iter().map(|x| (x.0,)).map(|(x,)| x);

// no match ergonomics for `(i32, i32)`
let _ = x.iter().copied().map(|(x, y)| (x, y));
}
32 changes: 19 additions & 13 deletions tests/ui/map_identity.stderr
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Expand Up @@ -41,31 +41,37 @@ LL | let _: Result<u32, u32> = Ok(1).map_err(|a| a);
| ^^^^^^^^^^^^^^^ help: remove the call to `map_err`

error: unnecessary map of the identity function
--> $DIR/map_identity.rs:30:21
--> $DIR/map_identity.rs:30:22
|
LL | let _ = x.iter().map(|(x, y)| (x, y));
| ^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`
LL | let _ = x.clone().map(|(x, y)| (x, y));
| ^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`

error: unnecessary map of the identity function
--> $DIR/map_identity.rs:31:21
--> $DIR/map_identity.rs:31:22
|
LL | let _ = x.iter().map(|(x, y)| {
| _____________________^
LL | let _ = x.clone().map(|(x, y)| {
| ______________________^
LL | | return (x, y);
LL | | });
| |______^ help: remove the call to `map`

error: unnecessary map of the identity function
--> $DIR/map_identity.rs:34:21
--> $DIR/map_identity.rs:34:22
|
LL | let _ = x.iter().map(|(x, y)| return (x, y));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`
LL | let _ = x.clone().map(|(x, y)| return (x, y));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`

error: unnecessary map of the identity function
--> $DIR/map_identity.rs:37:21
--> $DIR/map_identity.rs:37:22
|
LL | let _ = y.iter().map(|(x, y, (z, (w,)))| (x, y, (z, (w,))));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`
LL | let _ = y.clone().map(|(x, y, (z, (w,)))| (x, y, (z, (w,))));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`

error: aborting due to 10 previous errors
error: unnecessary map of the identity function
--> $DIR/map_identity.rs:66:30
|
LL | let _ = x.iter().copied().map(|(x, y)| (x, y));
| ^^^^^^^^^^^^^^^^^^^^^ help: remove the call to `map`

error: aborting due to 11 previous errors