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
|
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::macros::{find_format_arg_expr, find_format_args, root_macro_call_first_node};
use clippy_utils::source::{snippet_opt, snippet_with_context};
use clippy_utils::sugg::Sugg;
use rustc_ast::{FormatArgsPiece, FormatOptions, FormatTrait};
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::declare_lint_pass;
use rustc_span::{sym, Span};
declare_clippy_lint! {
/// ### What it does
/// Checks for the use of `format!("string literal with no
/// argument")` and `format!("{}", foo)` where `foo` is a string.
///
/// ### Why is this bad?
/// There is no point of doing that. `format!("foo")` can
/// be replaced by `"foo".to_owned()` if you really need a `String`. The even
/// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
/// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
/// if `foo: &str`.
///
/// ### Examples
/// ```no_run
/// let foo = "foo";
/// format!("{}", foo);
/// ```
///
/// Use instead:
/// ```no_run
/// let foo = "foo";
/// foo.to_owned();
/// ```
#[clippy::version = "pre 1.29.0"]
pub USELESS_FORMAT,
complexity,
"useless use of `format!`"
}
declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
impl<'tcx> LateLintPass<'tcx> for UselessFormat {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let Some(macro_call) = root_macro_call_first_node(cx, expr)
&& cx.tcx.is_diagnostic_item(sym::format_macro, macro_call.def_id)
&& let Some(format_args) = find_format_args(cx, expr, macro_call.expn)
{
let mut applicability = Applicability::MachineApplicable;
let call_site = macro_call.span;
match (format_args.arguments.all_args(), &format_args.template[..]) {
([], []) => span_useless_format_empty(cx, call_site, "String::new()".to_owned(), applicability),
([], [_]) => {
// Simulate macro expansion, converting {{ and }} to { and }.
let Some(snippet) = snippet_opt(cx, format_args.span) else {
return;
};
let s_expand = snippet.replace("{{", "{").replace("}}", "}");
let sugg = format!("{s_expand}.to_string()");
span_useless_format(cx, call_site, sugg, applicability);
},
([arg], [piece]) => {
if let Ok(value) = find_format_arg_expr(expr, arg)
&& let FormatArgsPiece::Placeholder(placeholder) = piece
&& placeholder.format_trait == FormatTrait::Display
&& placeholder.format_options == FormatOptions::default()
&& match cx.typeck_results().expr_ty(value).peel_refs().kind() {
ty::Adt(adt, _) => Some(adt.did()) == cx.tcx.lang_items().string(),
ty::Str => true,
_ => false,
}
{
let is_new_string = match value.kind {
ExprKind::Binary(..) => true,
ExprKind::MethodCall(path, ..) => path.ident.name == sym::to_string,
_ => false,
};
let sugg = if is_new_string {
snippet_with_context(cx, value.span, call_site.ctxt(), "..", &mut applicability)
.0
.into_owned()
} else {
let sugg = Sugg::hir_with_context(cx, value, call_site.ctxt(), "<arg>", &mut applicability);
format!("{}.to_string()", sugg.maybe_par())
};
span_useless_format(cx, call_site, sugg, applicability);
}
},
_ => {},
}
}
}
}
fn span_useless_format_empty(cx: &LateContext<'_>, span: Span, sugg: String, applicability: Applicability) {
span_lint_and_sugg(
cx,
USELESS_FORMAT,
span,
"useless use of `format!`",
"consider using `String::new()`",
sugg,
applicability,
);
}
fn span_useless_format(cx: &LateContext<'_>, span: Span, sugg: String, applicability: Applicability) {
span_lint_and_sugg(
cx,
USELESS_FORMAT,
span,
"useless use of `format!`",
"consider using `.to_string()`",
sugg,
applicability,
);
}
|
