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
|
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;
use rustc_ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{ExprKind, Node};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, ConstKind, 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 = "1.75.0"]
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(i, _) = l.node
&& i.0 == 0
{
inner_check(cx, expr, inner_expr, true);
} else if let ExprKind::Repeat(inner_expr, _) = expr.kind
&& let ty::Array(_, cst) = cx.typeck_results().expr_ty(expr).kind()
&& let ConstKind::Value(_, ty::ValTree::Leaf(element_count)) = cst.kind()
&& let Ok(element_count) = element_count.try_to_target_usize(cx.tcx)
&& element_count == 0
{
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(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,
);
}
|
