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Fixes manual_flatten removes the useless if let (#14861)

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Closes rust-lang/rust-clippy#14692

The suggestion of `manual_flatten` does not includes the replacement of
`if let` so far despite of `.flatten()` suggestion.
This PR eliminates a redundant `if let`.

changelog: [`manual_flatten`] the suggestion removes `if let`
This commit is contained in:
Samuel Tardieu 2025-06-12 23:20:25 +00:00 • committed by GitHub
commit ce8d263874
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GPG key ID: B5690EEEBB952194
4 changed files with 307 additions and 57 deletions
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38
clippy_lints/src/loops/manual_flatten.rs
View file

@ -2,8 +2,9 @@ use super::MANUAL_FLATTEN;
use super::utils::make_iterator_snippet;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::source::{HasSession, indent_of, reindent_multiline, snippet_with_applicability};
use clippy_utils::visitors::is_local_used;
use clippy_utils::{higher, is_refutable, path_to_local_id, peel_blocks_with_stmt};
use clippy_utils::{higher, is_refutable, path_to_local_id, peel_blocks_with_stmt, span_contains_comment};
use rustc_errors::Applicability;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::{Expr, Pat, PatKind};
@ -39,13 +40,20 @@ pub(super) fn check<'tcx>(
&& msrv.meets(cx, msrvs::ITER_FLATTEN)
&& !is_refutable(cx, inner_pat)
{
if arg.span.from_expansion() || if_then.span.from_expansion() {
return;
}
let if_let_type = if some_ctor { "Some" } else { "Ok" };
// Prepare the error message
let msg =
format!("unnecessary `if let` since only the `{if_let_type}` variant of the iterator element is used");
// Prepare the help message
let mut applicability = Applicability::MaybeIncorrect;
let mut applicability = if span_contains_comment(cx.sess().source_map(), body.span) {
Applicability::MaybeIncorrect
} else {
Applicability::MachineApplicable
};
let arg_snippet = make_iterator_snippet(cx, arg, &mut applicability);
let copied = match cx.typeck_results().expr_ty(let_expr).kind() {
ty::Ref(_, inner, _) => match inner.kind() {
@ -55,20 +63,26 @@ pub(super) fn check<'tcx>(
_ => "",
};
let sugg = format!("{arg_snippet}{copied}.flatten()");
let help_msg = "try `.flatten()` and remove the `if let` statement in the for loop";
// If suggestion is not a one-liner, it won't be shown inline within the error message. In that
// case, it will be shown in the extra `help` message at the end, which is why the first
// `help_msg` needs to refer to the correct relative position of the suggestion.
let help_msg = if sugg.contains('\n') {
"remove the `if let` statement in the for loop and then..."
} else {
"...and remove the `if let` statement in the for loop"
};
let pat_snippet =
snippet_with_applicability(cx, inner_pat.span.source_callsite(), "_", &mut applicability).to_string();
let body_snippet =
snippet_with_applicability(cx, if_then.span.source_callsite(), "[body]", &mut applicability).to_string();
let suggestions = vec![
// flatten the iterator
(arg.span, format!("{arg_snippet}{copied}.flatten()")),
(pat.span, pat_snippet),
// remove the `if let` statement
(
body.span,
reindent_multiline(&body_snippet, true, indent_of(cx, body.span)),
),
];
span_lint_and_then(cx, MANUAL_FLATTEN, span, msg, |diag| {
diag.span_suggestion(arg.span, "try", sugg, applicability);
diag.span_help(inner_expr.span, help_msg);
diag.multipart_suggestion("try", suggestions, applicability);
});
}
}

148
tests/ui/manual_flatten.fixed Normal file
View file

@ -0,0 +1,148 @@
#![warn(clippy::manual_flatten)]
#![allow(clippy::useless_vec, clippy::uninlined_format_args)]
fn main() {
// Test for loop over implicitly adjusted `Iterator` with `if let` expression
let x = vec![Some(1), Some(2), Some(3)];
for y in x.into_iter().flatten() {
println!("{}", y);
}
// Test for loop over implicitly adjusted `Iterator` with `if let` statement
let y: Vec<Result<i32, i32>> = vec![];
for n in y.clone().into_iter().flatten() {
println!("{}", n);
}
// Test for loop over by reference
for n in y.iter().flatten() {
println!("{}", n);
}
// Test for loop over an implicit reference
let z = &y;
for n in z.iter().flatten() {
println!("{}", n);
}
// Test for loop over `Iterator` with `if let` expression
let z = vec![Some(1), Some(2), Some(3)];
let z = z.iter();
for m in z.flatten() {
println!("{}", m);
}
// Using the `None` variant should not trigger the lint
// Note: for an autofixable suggestion, the binding in the for loop has to take the
// name of the binding in the `if let`
let z = vec![Some(1), Some(2), Some(3)];
for n in z {
if n.is_none() {
println!("Nada.");
}
}
// Using the `Err` variant should not trigger the lint
for n in y.clone() {
if let Err(e) = n {
println!("Oops: {}!", e);
}
}
// Having an else clause should not trigger the lint
for n in y.clone() {
if let Ok(n) = n {
println!("{}", n);
} else {
println!("Oops!");
}
}
let vec_of_ref = vec![&Some(1)];
for n in vec_of_ref.iter().copied().flatten() {
println!("{:?}", n);
}
let vec_of_ref = &vec_of_ref;
for n in vec_of_ref.iter().copied().flatten() {
println!("{:?}", n);
}
let slice_of_ref = &[&Some(1)];
for n in slice_of_ref.iter().copied().flatten() {
println!("{:?}", n);
}
struct Test {
a: usize,
}
let mut vec_of_struct = [Some(Test { a: 1 }), None];
// Usage of `if let` expression should not trigger lint
for n in vec_of_struct.iter_mut() {
if let Some(z) = n {
*n = None;
}
}
// Using manual flatten should not trigger the lint
for n in vec![Some(1), Some(2), Some(3)].iter().flatten() {
println!("{}", n);
}
// Using nested `Some` pattern should not trigger the lint
for n in vec![Some((1, Some(2)))] {
if let Some((_, Some(n))) = n {
println!("{}", n);
}
}
macro_rules! inner {
($id:ident / $new:pat => $action:expr) => {
if let Some($new) = $id {
$action;
}
};
}
// Usage of `if let` expression with macro should not trigger lint
for ab in [Some((1, 2)), Some((3, 4))] {
inner!(ab / (c, d) => println!("{c}-{d}"));
}
macro_rules! args {
($($arg:expr),*) => {
vec![$(Some($arg)),*]
};
}
// Usage of `if let` expression with macro should not trigger lint
for n in args!(1, 2, 3) {
if let Some(n) = n {
println!("{:?}", n);
}
}
// This should trigger the lint, but the applicability is `MaybeIncorrect`
let z = vec![Some(1), Some(2), Some(3)];
for n in z.into_iter().flatten() {
println!("{:?}", n);
}
run_unformatted_tests();
}
#[rustfmt::skip]
fn run_unformatted_tests() {
// Skip rustfmt here on purpose so the suggestion does not fit in one line
for n in vec![
//~^ manual_flatten
Some(1),
Some(2),
Some(3)
].iter().flatten() {
println!("{:?}", n);
}
}

39
tests/ui/manual_flatten.rs
View file

@ -1,6 +1,6 @@
#![warn(clippy::manual_flatten)]
#![allow(clippy::useless_vec, clippy::uninlined_format_args)]
//@no-rustfix
fn main() {
// Test for loop over implicitly adjusted `Iterator` with `if let` expression
let x = vec![Some(1), Some(2), Some(3)];
@ -130,6 +130,43 @@ fn main() {
}
}
macro_rules! inner {
($id:ident / $new:pat => $action:expr) => {
if let Some($new) = $id {
$action;
}
};
}
// Usage of `if let` expression with macro should not trigger lint
for ab in [Some((1, 2)), Some((3, 4))] {
inner!(ab / (c, d) => println!("{c}-{d}"));
}
macro_rules! args {
($($arg:expr),*) => {
vec![$(Some($arg)),*]
};
}
// Usage of `if let` expression with macro should not trigger lint
for n in args!(1, 2, 3) {
if let Some(n) = n {
println!("{:?}", n);
}
}
// This should trigger the lint, but the applicability is `MaybeIncorrect`
let z = vec![Some(1), Some(2), Some(3)];
for n in z {
//~^ manual_flatten
if let Some(n) = n {
println!("{:?}", n);
}
// foo
}
run_unformatted_tests();
}

139
tests/ui/manual_flatten.stderr
View file

@ -1,10 +1,7 @@
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:7:5
|
LL | for n in x {
| ^ - help: try: `x.into_iter().flatten()`
| _____|
| |
LL | / for n in x {
LL | |
LL | |
LL | | if let Some(y) = n {
@ -12,7 +9,7 @@ LL | | if let Some(y) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:10:9
|
LL | / if let Some(y) = n {
@ -21,14 +18,17 @@ LL | | }
| |_________^
= note: `-D clippy::manual-flatten` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::manual_flatten)]`
help: try
|
LL ~ for y in x.into_iter().flatten() {
LL + println!("{}", y);
LL + }
|
error: unnecessary `if let` since only the `Ok` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:17:5
|
LL | for n in y.clone() {
| ^ --------- help: try: `y.clone().into_iter().flatten()`
| _____|
| |
LL | / for n in y.clone() {
LL | |
LL | |
LL | | if let Ok(n) = n {
@ -37,21 +37,24 @@ LL | | };
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:20:9
|
LL | / if let Ok(n) = n {
LL | | println!("{}", n);
LL | | };
| |_________^
help: try
|
LL ~ for n in y.clone().into_iter().flatten() {
LL + println!("{}", n);
LL + }
|
error: unnecessary `if let` since only the `Ok` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:26:5
|
LL | for n in &y {
| ^ -- help: try: `y.iter().flatten()`
| _____|
| |
LL | / for n in &y {
LL | |
LL | |
LL | | if let Ok(n) = n {
@ -59,21 +62,24 @@ LL | | if let Ok(n) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:29:9
|
LL | / if let Ok(n) = n {
LL | | println!("{}", n);
LL | | }
| |_________^
help: try
|
LL ~ for n in y.iter().flatten() {
LL + println!("{}", n);
LL + }
|
error: unnecessary `if let` since only the `Ok` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:36:5
|
LL | for n in z {
| ^ - help: try: `z.iter().flatten()`
| _____|
| |
LL | / for n in z {
LL | |
LL | |
LL | | if let Ok(n) = n {
@ -81,21 +87,24 @@ LL | | if let Ok(n) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:39:9
|
LL | / if let Ok(n) = n {
LL | | println!("{}", n);
LL | | }
| |_________^
help: try
|
LL ~ for n in z.iter().flatten() {
LL + println!("{}", n);
LL + }
|
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:47:5
|
LL | for n in z {
| ^ - help: try: `z.flatten()`
| _____|
| |
LL | / for n in z {
LL | |
LL | |
LL | | if let Some(m) = n {
@ -103,21 +112,24 @@ LL | | if let Some(m) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:50:9
|
LL | / if let Some(m) = n {
LL | | println!("{}", m);
LL | | }
| |_________^
help: try
|
LL ~ for m in z.flatten() {
LL + println!("{}", m);
LL + }
|
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:82:5
|
LL | for n in &vec_of_ref {
| ^ ----------- help: try: `vec_of_ref.iter().copied().flatten()`
| _____|
| |
LL | / for n in &vec_of_ref {
LL | |
LL | |
LL | | if let Some(n) = n {
@ -125,21 +137,24 @@ LL | | if let Some(n) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:85:9
|
LL | / if let Some(n) = n {
LL | | println!("{:?}", n);
LL | | }
| |_________^
help: try
|
LL ~ for n in vec_of_ref.iter().copied().flatten() {
LL + println!("{:?}", n);
LL + }
|
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:91:5
|
LL | for n in vec_of_ref {
| ^ ---------- help: try: `vec_of_ref.iter().copied().flatten()`
| _____|
| |
LL | / for n in vec_of_ref {
LL | |
LL | |
LL | | if let Some(n) = n {
@ -147,21 +162,24 @@ LL | | if let Some(n) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:94:9
|
LL | / if let Some(n) = n {
LL | | println!("{:?}", n);
LL | | }
| |_________^
help: try
|
LL ~ for n in vec_of_ref.iter().copied().flatten() {
LL + println!("{:?}", n);
LL + }
|
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:100:5
|
LL | for n in slice_of_ref {
| ^ ------------ help: try: `slice_of_ref.iter().copied().flatten()`
| _____|
| |
LL | / for n in slice_of_ref {
LL | |
LL | |
LL | | if let Some(n) = n {
@ -169,16 +187,47 @@ LL | | if let Some(n) = n {
LL | | }
| |_____^
|
help: ...and remove the `if let` statement in the for loop
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:103:9
|
LL | / if let Some(n) = n {
LL | | println!("{:?}", n);
LL | | }
| |_________^
help: try
|
LL ~ for n in slice_of_ref.iter().copied().flatten() {
LL + println!("{:?}", n);
LL + }
|
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:139:5
--> tests/ui/manual_flatten.rs:161:5
|
LL | / for n in z {
LL | |
LL | |
LL | | if let Some(n) = n {
... |
LL | | }
| |_____^
|
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:164:9
|
LL | / if let Some(n) = n {
LL | | println!("{:?}", n);
LL | | }
| |_________^
help: try
|
LL ~ for n in z.into_iter().flatten() {
LL + println!("{:?}", n);
LL + }
|
error: unnecessary `if let` since only the `Some` variant of the iterator element is used
--> tests/ui/manual_flatten.rs:176:5
|
LL | / for n in vec![
LL | |
@ -188,8 +237,8 @@ LL | | Some(1),
LL | | }
| |_____^
|
help: remove the `if let` statement in the for loop and then...
--> tests/ui/manual_flatten.rs:146:9
help: try `.flatten()` and remove the `if let` statement in the for loop
--> tests/ui/manual_flatten.rs:183:9
|
LL | / if let Some(n) = n {
LL | | println!("{:?}", n);
@ -201,7 +250,9 @@ LL | for n in vec![
...
LL | Some(3)
LL ~ ].iter().flatten() {
LL + println!("{:?}", n);
LL + }
|
error: aborting due to 9 previous errors
error: aborting due to 10 previous errors