1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::higher::VecArgs;
use clippy_utils::source::snippet;
use clippy_utils::visitors::for_each_expr_without_closures;
use rustc_ast::LitKind;
use rustc_data_structures::packed::Pu128;
use rustc_errors::Applicability;
use rustc_hir::{ConstArgKind, ExprKind, Node};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::Ty;
use rustc_session::declare_lint_pass;
use rustc_span::Span;
declare_clippy_lint! {
/// ### What it does
/// Checks for array or vec initializations which call a function or method,
/// but which have a repeat count of zero.
///
/// ### Why is this bad?
/// Such an initialization, despite having a repeat length of 0, will still call the inner function.
/// This may not be obvious and as such there may be unintended side effects in code.
///
/// ### Example
/// ```no_run
/// fn side_effect() -> i32 {
/// println!("side effect");
/// 10
/// }
/// let a = [side_effect(); 0];
/// ```
/// Use instead:
/// ```no_run
/// fn side_effect() -> i32 {
/// println!("side effect");
/// 10
/// }
/// side_effect();
/// let a: [i32; 0] = [];
/// ```
#[clippy::version = "1.79.0"]
pub ZERO_REPEAT_SIDE_EFFECTS,
suspicious,
"usage of zero-sized initializations of arrays or vecs causing side effects"
}
declare_lint_pass!(ZeroRepeatSideEffects => [ZERO_REPEAT_SIDE_EFFECTS]);
impl LateLintPass<'_> for ZeroRepeatSideEffects {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &rustc_hir::Expr<'_>) {
if let Some(args) = VecArgs::hir(cx, expr)
&& let VecArgs::Repeat(inner_expr, len) = args
&& let ExprKind::Lit(l) = len.kind
&& let LitKind::Int(Pu128(0), _) = l.node
{
inner_check(cx, expr, inner_expr, true);
}
// Lint only if the length is a literal zero, and not a path to any constants.
// NOTE(@y21): When reading `[f(); LEN]`, I intuitively expect that the function is called and it
// doesn't seem as confusing as `[f(); 0]`. It would also have false positives when eg.
// the const item depends on `#[cfg]s` and has different values in different compilation
// sessions).
else if let ExprKind::Repeat(inner_expr, const_arg) = expr.kind
&& let ConstArgKind::Anon(anon_const) = const_arg.kind
&& let length_expr = cx.tcx.hir_body(anon_const.body).value
&& !length_expr.span.from_expansion()
&& let ExprKind::Lit(literal) = length_expr.kind
&& let LitKind::Int(Pu128(0), _) = literal.node
{
inner_check(cx, expr, inner_expr, false);
}
}
}
fn inner_check(cx: &LateContext<'_>, expr: &'_ rustc_hir::Expr<'_>, inner_expr: &'_ rustc_hir::Expr<'_>, is_vec: bool) {
// check if expr is a call or has a call inside it
if for_each_expr_without_closures(inner_expr, |x| {
if let ExprKind::Call(_, _) | ExprKind::MethodCall(_, _, _, _) = x.kind {
std::ops::ControlFlow::Break(())
} else {
std::ops::ControlFlow::Continue(())
}
})
.is_some()
{
let parent_hir_node = cx.tcx.parent_hir_node(expr.hir_id);
let return_type = cx.typeck_results().expr_ty(expr);
if let Node::LetStmt(l) = parent_hir_node {
array_span_lint(
cx,
l.span,
inner_expr.span,
l.pat.span,
Some(return_type),
is_vec,
false,
);
} else if let Node::Expr(x) = parent_hir_node
&& let ExprKind::Assign(l, _, _) = x.kind
{
array_span_lint(cx, x.span, inner_expr.span, l.span, Some(return_type), is_vec, true);
} else {
span_lint_and_sugg(
cx,
ZERO_REPEAT_SIDE_EFFECTS,
expr.span.source_callsite(),
"function or method calls as the initial value in zero-sized array initializers may cause side effects",
"consider using",
format!(
"{{ {}; {}[] as {return_type} }}",
snippet(cx, inner_expr.span.source_callsite(), ".."),
if is_vec { "vec!" } else { "" },
),
Applicability::Unspecified,
);
}
}
}
fn array_span_lint(
cx: &LateContext<'_>,
expr_span: Span,
func_call_span: Span,
variable_name_span: Span,
expr_ty: Option<Ty<'_>>,
is_vec: bool,
is_assign: bool,
) {
let has_ty = expr_ty.is_some();
span_lint_and_sugg(
cx,
ZERO_REPEAT_SIDE_EFFECTS,
expr_span.source_callsite(),
"function or method calls as the initial value in zero-sized array initializers may cause side effects",
"consider using",
format!(
"{}; {}{}{} = {}[]{}{}",
snippet(cx, func_call_span.source_callsite(), ".."),
if has_ty && !is_assign { "let " } else { "" },
snippet(cx, variable_name_span.source_callsite(), ".."),
if let Some(ty) = expr_ty
&& !is_assign
{
format!(": {ty}")
} else {
String::new()
},
if is_vec { "vec!" } else { "" },
if let Some(ty) = expr_ty
&& is_assign
{
format!(" as {ty}")
} else {
String::new()
},
if is_assign { "" } else { ";" }
),
Applicability::Unspecified,
);
}
|
