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handle another type of collapsible if-statement #15104

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a10ab29
Handle another type of collapsible if-statement.
Arc8ne Jun 22, 2025
8b9f3ee
Remove an unnecessary comment that was accidentally introduced by the…
Arc8ne Jun 23, 2025
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67 changes: 64 additions & 3 deletions clippy_lints/src/collapsible_if.rs
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@
use clippy_config::Conf;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
use clippy_utils::higher::If;
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::source::{IntoSpan as _, SpanRangeExt, snippet, snippet_block_with_applicability};
use clippy_utils::{span_contains_non_whitespace, tokenize_with_text};
use clippy_utils::sugg::{Sugg, make_binop, make_unop};
use clippy_utils::{SpanlessEq, span_contains_non_whitespace, tokenize_with_text};
use rustc_ast::BinOpKind;
use rustc_errors::Applicability;
use rustc_hir::{Block, Expr, ExprKind, Stmt, StmtKind};
use rustc_hir::{Block, Expr, ExprKind, Stmt, StmtKind, UnOp};
use rustc_lexer::TokenKind;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::impl_lint_pass;
Expand Down Expand Up @@ -209,6 +211,64 @@ impl CollapsibleIf {
!matches!(cond.kind, ExprKind::Let(..))
|| (cx.tcx.sess.edition().at_least_rust_2024() && self.msrv.meets(cx, msrvs::LET_CHAINS))
}

fn check_collapsible_if_nested_if_else(&self, cx: &LateContext<'_>, if_expr: &Expr<'_>) {
if let Some(If {
cond,
then: Expr {
kind: ExprKind::Block(then_block, ..),
..
},
r#else: Some(else_expr),
}) = If::hir(if_expr)
&& let Some(inner_if_expr) = expr_block(then_block)
&& let Expr {
kind: ExprKind::If(inner_cond, inner_then, ..),
..
} = inner_if_expr
&& !block_starts_with_significant_tokens(cx, then_block, inner_if_expr, self.lint_commented_code)
&& SpanlessEq::new(cx).eq_expr(inner_then, else_expr)
{
let mut app = Applicability::MachineApplicable;

let first_cond_sugg = match cond.kind {
ExprKind::Binary(bin_op, lhs, rhs) => {
let new_bin_op = if let BinOpKind::Ne = bin_op.node {
BinOpKind::Eq
} else {
BinOpKind::Ne
};
Comment on lines +236 to +240
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What about other binary operations? Right now, the following

    let a = 10;
    let b = 20;

    if a < 20 {
        if b < 30 {
            println!("Hello");
        }
    } else {
        println!("world!");
    }

will be transformed into the (non equivalent)

    if a != 20 || b < 30 {
        println!("Hello world!");
    }

You should look at the ! operator for Sugg and let it invert the operation, it might be beneficial.


make_binop(
new_bin_op,
&Sugg::hir_with_applicability(cx, lhs, "_", &mut app),
&Sugg::hir_with_applicability(cx, rhs, "_", &mut app),
)
},
ExprKind::Unary(UnOp::Not, expr) => Sugg::hir_with_applicability(cx, expr, "_", &mut app),
ExprKind::Path(_) => make_unop("!", Sugg::hir_with_applicability(cx, cond, "_", &mut app)),
_ => Sugg::hir_with_applicability(cx, cond, "_", &mut app),
};

span_lint_and_sugg(
cx,
COLLAPSIBLE_IF,
if_expr.span,
"this `if` statement can be collapsed",
"collapse else and nested if blocks",
format!(
"if {} {}",
make_binop(
BinOpKind::Or,
&first_cond_sugg,
&Sugg::hir_with_applicability(cx, inner_cond, "_", &mut app)
),
Sugg::hir_with_applicability(cx, else_expr, "_", &mut app)
),
app,
);
}
}
}

impl_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
Expand All @@ -222,6 +282,7 @@ impl LateLintPass<'_> for CollapsibleIf {
&& let ExprKind::Block(else_, None) = else_.kind
{
self.check_collapsible_else_if(cx, then.span, else_);
self.check_collapsible_if_nested_if_else(cx, expr);
} else if else_.is_none()
&& self.eligible_condition(cx, cond)
&& let ExprKind::Block(then, None) = then.kind
Expand Down
33 changes: 33 additions & 0 deletions tests/ui/collapsible_if.fixed
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Original file line number Diff line number Diff line change
Expand Up @@ -132,6 +132,39 @@ fn main() {
println!("Hello world!");
}
}

let a = false;

let b = false;

if !a || b {
println!("Hello world!");
}
//~^^^^^^^^ collapsible_if

if !a || b {
println!("Hello world!");
}

if a {
// A comment that should not be removed.
if b {
println!("Hello world!");
}
} else {
println!("Hello world!");
}

let s = "foo";

if s == "foobar" || a {
println!("Hello world!");
}
//~^^^^^^^^ collapsible_if

if s == "foobar" || a {
println!("Hello world!");
}
}

#[rustfmt::skip]
Expand Down
43 changes: 43 additions & 0 deletions tests/ui/collapsible_if.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,49 @@ fn main() {
println!("Hello world!");
}
}

let a = false;

let b = false;

if a {
if b {
println!("Hello world!");
}
}
else {
println!("Hello world!");
}
//~^^^^^^^^ collapsible_if

if !a || b {
println!("Hello world!");
}

if a {
// A comment that should not be removed.
if b {
println!("Hello world!");
}
} else {
println!("Hello world!");
}

let s = "foo";

if s != "foobar" {
if a {
println!("Hello world!");
}
}
else {
println!("Hello world!");
}
//~^^^^^^^^ collapsible_if

if s == "foobar" || a {
println!("Hello world!");
}
}

#[rustfmt::skip]
Expand Down
40 changes: 38 additions & 2 deletions tests/ui/collapsible_if.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -173,7 +173,43 @@ LL ~ }
|

error: this `if` statement can be collapsed
--> tests/ui/collapsible_if.rs:149:5
--> tests/ui/collapsible_if.rs:150:5
|
LL | / if a {
LL | | if b {
LL | | println!("Hello world!");
... |
LL | | println!("Hello world!");
LL | | }
| |_____^
|
help: collapse else and nested if blocks
|
LL ~ if !a || b {
LL + println!("Hello world!");
LL + }
|

error: this `if` statement can be collapsed
--> tests/ui/collapsible_if.rs:175:5
|
LL | / if s != "foobar" {
LL | | if a {
LL | | println!("Hello world!");
... |
LL | | println!("Hello world!");
LL | | }
| |_____^
|
help: collapse else and nested if blocks
|
LL ~ if s == "foobar" || a {
LL + println!("Hello world!");
LL + }
|

error: this `if` statement can be collapsed
--> tests/ui/collapsible_if.rs:192:5
|
LL | / if true {
LL | | if true {
Expand All @@ -190,5 +226,5 @@ LL | // This is a comment, do not collapse code to it
LL ~ ; 3
|

error: aborting due to 11 previous errors
error: aborting due to 13 previous errors