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New lint [filter_map_bool_then] #11115

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1 change: 1 addition & 0 deletions CHANGELOG.md
Original file line number Diff line number Diff line change
Expand Up @@ -4844,6 +4844,7 @@ Released 2018-09-13
[`field_reassign_with_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#field_reassign_with_default
[`filetype_is_file`]: https://rust-lang.github.io/rust-clippy/master/index.html#filetype_is_file
[`filter_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_map
[`filter_map_bool_then`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_map_bool_then
[`filter_map_identity`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_map_identity
[`filter_map_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_map_next
[`filter_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_next
Expand Down
1 change: 1 addition & 0 deletions clippy_lints/src/declared_lints.rs
Original file line number Diff line number Diff line change
Expand Up @@ -337,6 +337,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
crate::methods::EXPECT_USED_INFO,
crate::methods::EXTEND_WITH_DRAIN_INFO,
crate::methods::FILETYPE_IS_FILE_INFO,
crate::methods::FILTER_MAP_BOOL_THEN_INFO,
crate::methods::FILTER_MAP_IDENTITY_INFO,
crate::methods::FILTER_MAP_NEXT_INFO,
crate::methods::FILTER_NEXT_INFO,
Expand Down
45 changes: 45 additions & 0 deletions clippy_lints/src/methods/filter_map_bool_then.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::paths::BOOL_THEN;
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::is_copy;
use clippy_utils::{is_from_proc_macro, is_trait_method, match_def_path, peel_blocks};
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_span::{sym, Span};

use super::FILTER_MAP_BOOL_THEN;

pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, arg: &Expr<'_>, call_span: Span) {
if !in_external_macro(cx.sess(), expr.span)
&& is_trait_method(cx, expr, sym::Iterator)
&& let ExprKind::Closure(closure) = arg.kind
&& let body = cx.tcx.hir().body(closure.body)
&& let value = peel_blocks(body.value)
// Indexing should be fine as `filter_map` always has 1 input, we unfortunately need both
// `inputs` and `params` here as we need both the type and the span
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&& let param_ty = closure.fn_decl.inputs[0]
&& let param = body.params[0]
&& is_copy(cx, cx.typeck_results().node_type(param_ty.hir_id).peel_refs())
&& let ExprKind::MethodCall(_, recv, [then_arg], _) = value.kind
&& let ExprKind::Closure(then_closure) = then_arg.kind
&& let then_body = peel_blocks(cx.tcx.hir().body(then_closure.body).value)
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(value.hir_id)
&& match_def_path(cx, def_id, &BOOL_THEN)
&& !is_from_proc_macro(cx, expr)
&& let Some(param_snippet) = snippet_opt(cx, param.span)
&& let Some(filter) = snippet_opt(cx, recv.span)
&& let Some(map) = snippet_opt(cx, then_body.span)
{
span_lint_and_sugg(
cx,
FILTER_MAP_BOOL_THEN,
call_span,
"usage of `bool::then` in `filter_map`",
"use `filter` then `map` instead",
format!("filter(|&{param_snippet}| {filter}).map(|{param_snippet}| {map})"),
Applicability::MachineApplicable,
);
}
}
34 changes: 34 additions & 0 deletions clippy_lints/src/methods/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ mod expect_used;
mod extend_with_drain;
mod filetype_is_file;
mod filter_map;
mod filter_map_bool_then;
mod filter_map_identity;
mod filter_map_next;
mod filter_next;
Expand Down Expand Up @@ -3475,6 +3476,37 @@ declare_clippy_lint! {
"disallows `.skip(0)`"
}

declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `bool::then` in `Iterator::filter_map`.
///
/// ### Why is this bad?
/// This can be written with `filter` then `map` instead, which would reduce nesting and
/// separates the filtering from the transformation phase. This comes with no cost to
/// performance and is just cleaner.
///
/// ### Limitations
/// Does not lint `bool::then_some`, as it eagerly evaluates its arguments rather than lazily.
/// This can create differing behavior, so better safe than sorry.
///
/// ### Example
/// ```rust
/// # fn really_expensive_fn(i: i32) -> i32 { i }
/// # let v = vec![];
/// _ = v.into_iter().filter_map(|i| (i % 2 == 0).then(|| really_expensive_fn(i)));
/// ```
/// Use instead:
/// ```rust
/// # fn really_expensive_fn(i: i32) -> i32 { i }
/// # let v = vec![];
/// _ = v.into_iter().filter(|i| i % 2 == 0).map(|i| really_expensive_fn(i));
/// ```
#[clippy::version = "1.72.0"]
pub FILTER_MAP_BOOL_THEN,
style,
"checks for usage of `bool::then` in `Iterator::filter_map`"
}

pub struct Methods {
avoid_breaking_exported_api: bool,
msrv: Msrv,
Expand Down Expand Up @@ -3612,6 +3644,7 @@ impl_lint_pass!(Methods => [
FORMAT_COLLECT,
STRING_LIT_CHARS_ANY,
ITER_SKIP_ZERO,
FILTER_MAP_BOOL_THEN,
]);

/// Extracts a method call name, args, and `Span` of the method name.
Expand Down Expand Up @@ -3889,6 +3922,7 @@ impl Methods {
},
("filter_map", [arg]) => {
unnecessary_filter_map::check(cx, expr, arg, name);
filter_map_bool_then::check(cx, expr, arg, call_span);
filter_map_identity::check(cx, expr, arg, span);
},
("find_map", [arg]) => {
Expand Down
2 changes: 2 additions & 0 deletions clippy_utils/src/paths.rs
Original file line number Diff line number Diff line change
Expand Up @@ -163,3 +163,5 @@ pub const OPTION_EXPECT: [&str; 4] = ["core", "option", "Option", "expect"];
pub const FORMATTER: [&str; 3] = ["core", "fmt", "Formatter"];
pub const DEBUG_STRUCT: [&str; 4] = ["core", "fmt", "builders", "DebugStruct"];
pub const ORD_CMP: [&str; 4] = ["core", "cmp", "Ord", "cmp"];
#[expect(clippy::invalid_paths)] // not sure why it thinks this, it works so
pub const BOOL_THEN: [&str; 4] = ["core", "bool", "<impl bool>", "then"];
44 changes: 44 additions & 0 deletions tests/ui/filter_map_bool_then.fixed
Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
//@run-rustfix
//@aux-build:proc_macros.rs:proc-macro
#![allow(
clippy::clone_on_copy,
clippy::map_identity,
clippy::unnecessary_lazy_evaluations,
unused
)]
#![warn(clippy::filter_map_bool_then)]

#[macro_use]
extern crate proc_macros;

#[derive(Clone, PartialEq)]
struct NonCopy;

fn main() {
let v = vec![1, 2, 3, 4, 5, 6];
v.clone().iter().filter(|&i| (i % 2 == 0)).map(|i| i + 1);
v.clone().into_iter().filter(|&i| (i % 2 == 0)).map(|i| i + 1);
v.clone()
.into_iter()
.filter(|&i| (i % 2 == 0)).map(|i| i + 1);
v.clone()
.into_iter()
.filter(|&i| i != 1000)
.filter(|&i| (i % 2 == 0)).map(|i| i + 1);
v.iter()
.copied()
.filter(|&i| i != 1000)
.filter(|&i| (i.clone() % 2 == 0)).map(|i| i + 1);
// Do not lint
let v = vec![NonCopy, NonCopy];
v.clone().iter().filter_map(|i| (i == &NonCopy).then(|| i));
external! {
let v = vec![1, 2, 3, 4, 5, 6];
v.clone().into_iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
}
with_span! {
span
let v = vec![1, 2, 3, 4, 5, 6];
v.clone().into_iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
}
}
44 changes: 44 additions & 0 deletions tests/ui/filter_map_bool_then.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
//@run-rustfix
//@aux-build:proc_macros.rs:proc-macro
#![allow(
clippy::clone_on_copy,
clippy::map_identity,
clippy::unnecessary_lazy_evaluations,
unused
)]
#![warn(clippy::filter_map_bool_then)]

#[macro_use]
extern crate proc_macros;

#[derive(Clone, PartialEq)]
struct NonCopy;

fn main() {
let v = vec![1, 2, 3, 4, 5, 6];
v.clone().iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
v.clone().into_iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
v.clone()
.into_iter()
.filter_map(|i| -> Option<_> { (i % 2 == 0).then(|| i + 1) });
v.clone()
.into_iter()
.filter(|&i| i != 1000)
.filter_map(|i| (i % 2 == 0).then(|| i + 1));
v.iter()
.copied()
.filter(|&i| i != 1000)
.filter_map(|i| (i.clone() % 2 == 0).then(|| i + 1));
// Do not lint
let v = vec![NonCopy, NonCopy];
v.clone().iter().filter_map(|i| (i == &NonCopy).then(|| i));
external! {
let v = vec![1, 2, 3, 4, 5, 6];
v.clone().into_iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
}
with_span! {
span
let v = vec![1, 2, 3, 4, 5, 6];
v.clone().into_iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
}
}
34 changes: 34 additions & 0 deletions tests/ui/filter_map_bool_then.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
error: usage of `bool::then` in `filter_map`
--> $DIR/filter_map_bool_then.rs:19:22
|
LL | v.clone().iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `filter` then `map` instead: `filter(|&i| (i % 2 == 0)).map(|i| i + 1)`
|
= note: `-D clippy::filter-map-bool-then` implied by `-D warnings`

error: usage of `bool::then` in `filter_map`
--> $DIR/filter_map_bool_then.rs:20:27
|
LL | v.clone().into_iter().filter_map(|i| (i % 2 == 0).then(|| i + 1));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `filter` then `map` instead: `filter(|&i| (i % 2 == 0)).map(|i| i + 1)`

error: usage of `bool::then` in `filter_map`
--> $DIR/filter_map_bool_then.rs:23:10
|
LL | .filter_map(|i| -> Option<_> { (i % 2 == 0).then(|| i + 1) });
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `filter` then `map` instead: `filter(|&i| (i % 2 == 0)).map(|i| i + 1)`

error: usage of `bool::then` in `filter_map`
--> $DIR/filter_map_bool_then.rs:27:10
|
LL | .filter_map(|i| (i % 2 == 0).then(|| i + 1));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `filter` then `map` instead: `filter(|&i| (i % 2 == 0)).map(|i| i + 1)`

error: usage of `bool::then` in `filter_map`
--> $DIR/filter_map_bool_then.rs:31:10
|
LL | .filter_map(|i| (i.clone() % 2 == 0).then(|| i + 1));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `filter` then `map` instead: `filter(|&i| (i.clone() % 2 == 0)).map(|i| i + 1)`

error: aborting due to 5 previous errors