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samueltardieusamueltardieu
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feat: add const_is_empty lint
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‎CHANGELOG.md‎

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@@ -5109,6 +5109,7 @@ Released 2018-09-13
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[`collection_is_never_read`]: https://rust-lang.github.io/rust-clippy/master/index.html#collection_is_never_read
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[`comparison_chain`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_chain
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[`comparison_to_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_to_empty
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[`const_is_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#const_is_empty
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[`const_static_lifetime`]: https://rust-lang.github.io/rust-clippy/master/index.html#const_static_lifetime
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[`copy_iterator`]: https://rust-lang.github.io/rust-clippy/master/index.html#copy_iterator
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[`crate_in_macro_def`]: https://rust-lang.github.io/rust-clippy/master/index.html#crate_in_macro_def

‎clippy_lints/src/declared_lints.rs‎

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@@ -350,6 +350,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
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crate::methods::CLONE_ON_COPY_INFO,
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crate::methods::CLONE_ON_REF_PTR_INFO,
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crate::methods::COLLAPSIBLE_STR_REPLACE_INFO,
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crate::methods::CONST_IS_EMPTY_INFO,
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crate::methods::DRAIN_COLLECT_INFO,
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crate::methods::ERR_EXPECT_INFO,
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crate::methods::EXPECT_FUN_CALL_INFO,

‎clippy_lints/src/methods/is_empty.rs‎

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@@ -0,0 +1,40 @@
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use clippy_utils::diagnostics::span_lint_and_note;
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use clippy_utils::expr_or_init;
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use rustc_ast::LitKind;
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use rustc_hir::{Expr, ExprKind};
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use rustc_lint::{LateContext, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_span::source_map::Spanned;
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use super::CONST_IS_EMPTY;
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pub(super) fn check(cx: &LateContext<'_>, expr: &'_ Expr<'_>, receiver: &Expr<'_>) {
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if in_external_macro(cx.sess(), expr.span) || !receiver.span.eq_ctxt(expr.span) {
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return;
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}
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let init_expr = expr_or_init(cx, receiver);
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if let Some(init_is_empty) = is_empty(init_expr)
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&& init_expr.span.eq_ctxt(receiver.span)
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{
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span_lint_and_note(
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cx,
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CONST_IS_EMPTY,
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expr.span,
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&format!("this expression always evaluates to {init_is_empty:?}"),
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Some(init_expr.span),
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"because its initialization value is constant",
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);
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}
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}
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fn is_empty(expr: &'_ rustc_hir::Expr<'_>) -> Option<bool> {
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if let ExprKind::Lit(Spanned { node, .. }) = expr.kind {
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match node {
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LitKind::Str(sym, _) => Some(sym.is_empty()),
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LitKind::ByteStr(value, _) | LitKind::CStr(value, _) => Some(value.is_empty()),
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_ => None,
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}
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} else {
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None
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}
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}

‎clippy_lints/src/methods/mod.rs‎

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@@ -36,6 +36,7 @@ mod inefficient_to_string;
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mod inspect_for_each;
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mod into_iter_on_ref;
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mod is_digit_ascii_radix;
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mod is_empty;
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mod iter_cloned_collect;
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mod iter_count;
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mod iter_filter;
@@ -4041,6 +4042,31 @@ declare_clippy_lint! {
40414042
"calling `.get().is_some()` or `.get().is_none()` instead of `.contains()` or `.contains_key()`"
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}
40434044

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declare_clippy_lint! {
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/// ### What it does
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/// It identifies calls to `.is_empty()` on constant values.
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///
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/// ### Why is this bad?
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/// String literals and constant values are known at compile time. Checking if they
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/// are empty will always return the same value. This might not be the intention of
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/// the expression.
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///
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/// ### Example
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/// ```no_run
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/// let value = "";
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/// if value.is_empty() {
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/// println!("the string is empty");
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/// }
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/// ```
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/// Use instead:
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/// ```no_run
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/// println!("the string is empty");
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/// ```
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#[clippy::version = "1.78.0"]
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pub CONST_IS_EMPTY,
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suspicious,
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"is_empty() called on strings known at compile time"
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}
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pub struct Methods {
40454071
avoid_breaking_exported_api: bool,
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msrv: Msrv,
@@ -4089,6 +4115,7 @@ impl_lint_pass!(Methods => [
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CLONE_ON_COPY,
40904116
CLONE_ON_REF_PTR,
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COLLAPSIBLE_STR_REPLACE,
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CONST_IS_EMPTY,
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ITER_OVEREAGER_CLONED,
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CLONED_INSTEAD_OF_COPIED,
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FLAT_MAP_OPTION,
@@ -4442,7 +4469,7 @@ impl Methods {
44424469
("as_deref" | "as_deref_mut", []) => {
44434470
needless_option_as_deref::check(cx, expr, recv, name);
44444471
},
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("as_bytes" | "is_empty", []) => {
4472+
("as_bytes", []) => {
44464473
if let Some(("as_str", recv, [], as_str_span, _)) = method_call(recv) {
44474474
redundant_as_str::check(cx, expr, recv, as_str_span, span);
44484475
}
@@ -4616,6 +4643,12 @@ impl Methods {
46164643
("hash", [arg]) => {
46174644
unit_hash::check(cx, expr, recv, arg);
46184645
},
4646+
("is_empty", []) => {
4647+
if let Some(("as_str", recv, [], as_str_span, _)) = method_call(recv) {
4648+
redundant_as_str::check(cx, expr, recv, as_str_span, span);
4649+
}
4650+
is_empty::check(cx, expr, recv);
4651+
},
46194652
("is_file", []) => filetype_is_file::check(cx, expr, recv),
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("is_digit", [radix]) => is_digit_ascii_radix::check(cx, expr, recv, radix, &self.msrv),
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("is_none", []) => check_is_some_is_none(cx, expr, recv, call_span, false),

‎tests/ui/const_is_empty.rs‎

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@@ -0,0 +1,52 @@
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#![warn(clippy::const_is_empty)]
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fn test_literal() {
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if "".is_empty() {
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//~^ERROR: this expression always evaluates to true
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}
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if "foobar".is_empty() {
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//~^ERROR: this expression always evaluates to false
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}
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}
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fn test_byte_literal() {
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if b"".is_empty() {
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//~^ERROR: this expression always evaluates to true
15+
}
16+
if b"foobar".is_empty() {
17+
//~^ERROR: this expression always evaluates to false
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}
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}
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fn test_no_mut() {
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let mut empty = "";
23+
if empty.is_empty() {
24+
// No lint because it is mutable
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}
26+
}
27+
28+
fn test_propagated() {
29+
let empty = "";
30+
let non_empty = "foobar";
31+
let empty2 = empty;
32+
let non_empty2 = non_empty;
33+
if empty2.is_empty() {
34+
//~^ERROR: this expression always evaluates to true
35+
}
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if non_empty2.is_empty() {
37+
//~^ERROR: this expression always evaluates to false
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}
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}
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fn main() {
42+
let value = "foobar";
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let _ = value.is_empty();
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//~^ ERROR: this expression always evaluates to false
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let x = value;
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let _ = x.is_empty();
47+
//~^ ERROR: this expression always evaluates to false
48+
let _ = "".is_empty();
49+
//~^ ERROR: this expression always evaluates to true
50+
let _ = b"".is_empty();
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//~^ ERROR: this expression always evaluates to true
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}

‎tests/ui/const_is_empty.stderr‎

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error: this expression always evaluates to true
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--> tests/ui/const_is_empty.rs:4:8
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|
4+
LL | if "".is_empty() {
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| ^^^^^^^^^^^^^
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|
7+
note: because its initialization value is constant
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--> tests/ui/const_is_empty.rs:4:8
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|
10+
LL | if "".is_empty() {
11+
| ^^
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= note: `-D clippy::const-is-empty` implied by `-D warnings`
13+
= help: to override `-D warnings` add `#[allow(clippy::const_is_empty)]`
14+
15+
error: this expression always evaluates to false
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--> tests/ui/const_is_empty.rs:7:8
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|
18+
LL | if "foobar".is_empty() {
19+
| ^^^^^^^^^^^^^^^^^^^
20+
|
21+
note: because its initialization value is constant
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--> tests/ui/const_is_empty.rs:7:8
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|
24+
LL | if "foobar".is_empty() {
25+
| ^^^^^^^^
26+
27+
error: this expression always evaluates to true
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--> tests/ui/const_is_empty.rs:13:8
29+
|
30+
LL | if b"".is_empty() {
31+
| ^^^^^^^^^^^^^^
32+
|
33+
note: because its initialization value is constant
34+
--> tests/ui/const_is_empty.rs:13:8
35+
|
36+
LL | if b"".is_empty() {
37+
| ^^^
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39+
error: this expression always evaluates to false
40+
--> tests/ui/const_is_empty.rs:16:8
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|
42+
LL | if b"foobar".is_empty() {
43+
| ^^^^^^^^^^^^^^^^^^^^
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|
45+
note: because its initialization value is constant
46+
--> tests/ui/const_is_empty.rs:16:8
47+
|
48+
LL | if b"foobar".is_empty() {
49+
| ^^^^^^^^^
50+
51+
error: this expression always evaluates to true
52+
--> tests/ui/const_is_empty.rs:33:8
53+
|
54+
LL | if empty2.is_empty() {
55+
| ^^^^^^^^^^^^^^^^^
56+
|
57+
note: because its initialization value is constant
58+
--> tests/ui/const_is_empty.rs:29:17
59+
|
60+
LL | let empty = "";
61+
| ^^
62+
63+
error: this expression always evaluates to false
64+
--> tests/ui/const_is_empty.rs:36:8
65+
|
66+
LL | if non_empty2.is_empty() {
67+
| ^^^^^^^^^^^^^^^^^^^^^
68+
|
69+
note: because its initialization value is constant
70+
--> tests/ui/const_is_empty.rs:30:21
71+
|
72+
LL | let non_empty = "foobar";
73+
| ^^^^^^^^
74+
75+
error: this expression always evaluates to false
76+
--> tests/ui/const_is_empty.rs:43:13
77+
|
78+
LL | let _ = value.is_empty();
79+
| ^^^^^^^^^^^^^^^^
80+
|
81+
note: because its initialization value is constant
82+
--> tests/ui/const_is_empty.rs:42:17
83+
|
84+
LL | let value = "foobar";
85+
| ^^^^^^^^
86+
87+
error: this expression always evaluates to false
88+
--> tests/ui/const_is_empty.rs:46:13
89+
|
90+
LL | let _ = x.is_empty();
91+
| ^^^^^^^^^^^^
92+
|
93+
note: because its initialization value is constant
94+
--> tests/ui/const_is_empty.rs:42:17
95+
|
96+
LL | let value = "foobar";
97+
| ^^^^^^^^
98+
99+
error: this expression always evaluates to true
100+
--> tests/ui/const_is_empty.rs:48:13
101+
|
102+
LL | let _ = "".is_empty();
103+
| ^^^^^^^^^^^^^
104+
|
105+
note: because its initialization value is constant
106+
--> tests/ui/const_is_empty.rs:48:13
107+
|
108+
LL | let _ = "".is_empty();
109+
| ^^
110+
111+
error: this expression always evaluates to true
112+
--> tests/ui/const_is_empty.rs:50:13
113+
|
114+
LL | let _ = b"".is_empty();
115+
| ^^^^^^^^^^^^^^
116+
|
117+
note: because its initialization value is constant
118+
--> tests/ui/const_is_empty.rs:50:13
119+
|
120+
LL | let _ = b"".is_empty();
121+
| ^^^
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error: aborting due to 10 previous errors
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