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Add E0788 for improper #[no_coverage] usage
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‎compiler/rustc_error_codes/src/error_codes.rs‎

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@@ -491,6 +491,7 @@ E0784: include_str!("./error_codes/E0784.md"),
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E0785: include_str!("./error_codes/E0785.md"),
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E0786: include_str!("./error_codes/E0786.md"),
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E0787: include_str!("./error_codes/E0787.md"),
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E0788: include_str!("./error_codes/E0788.md"),
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;
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// E0006, // merged with E0005
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// E0008, // cannot bind by-move into a pattern guard

‎compiler/rustc_error_codes/src/error_codes/E0788.md‎

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A `#[no_coverage]` attribute was incorrectly placed on something that couldn't
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be covered.
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Example of erroneous code:
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```compile_fail,E0788
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#[no_coverage]
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struct Foo;
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#[no_coverage]
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const FOO: Foo = Foo;
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```
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`#[no_coverage]` tells the compiler to not generate coverage instrumentation for
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a piece of code when the `-C instrument-coverage` flag is passed. Things like
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structs and consts are not coverable code, and thus cannot do anything with this
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attribute.
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If you wish to apply this attribute to all methods in an impl or module,
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manually annotate each method; it is not possible to annotate the entire impl
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with a `#[no_coverage]` attribute.

‎compiler/rustc_passes/src/check_attr.rs‎

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@@ -76,6 +76,7 @@ impl CheckAttrVisitor<'_> {
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for attr in attrs {
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let attr_is_valid = match attr.name_or_empty() {
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sym::inline => self.check_inline(hir_id, attr, span, target),
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sym::no_coverage => self.check_no_coverage(hir_id, attr, span, target),
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sym::non_exhaustive => self.check_non_exhaustive(hir_id, attr, span, target),
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sym::marker => self.check_marker(hir_id, attr, span, target),
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sym::rustc_must_implement_one_of => {
@@ -292,6 +293,56 @@ impl CheckAttrVisitor<'_> {
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}
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}
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/// Checks if a `#[no_coverage]` is applied directly to a function
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fn check_no_coverage(
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&self,
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hir_id: HirId,
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attr: &Attribute,
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span: Span,
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target: Target,
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) -> bool {
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match target {
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// no_coverage on function is fine
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Target::Fn
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| Target::Closure
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| Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => true,
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// function prototypes can't be covered
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Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
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self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
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lint.build("`#[no_coverage]` is ignored on function prototypes").emit();
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});
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true
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}
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Target::Mod | Target::ForeignMod | Target::Impl | Target::Trait => {
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self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
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lint.build("`#[no_coverage]` cannot be done recursively and must be applied to functions directly").emit();
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});
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true
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}
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Target::Expression | Target::Statement | Target::Arm => {
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self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, attr.span, |lint| {
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lint.build("`#[no_coverage]` can only be applied at the function level, not on code directly").emit();
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});
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true
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}
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_ => {
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struct_span_err!(
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self.tcx.sess,
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attr.span,
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E0788,
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"`#[no_coverage]` must be applied to coverable code",
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)
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.span_label(span, "not coverable code")
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.emit();
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false
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}
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}
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}
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fn check_generic_attr(
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&self,
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hir_id: HirId,

‎src/test/ui/lint/no-coverage.rs‎

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#![feature(extern_types)]
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#![feature(no_coverage)]
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#![feature(type_alias_impl_trait)]
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#![warn(unused_attributes)]
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trait Trait {
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#[no_coverage] //~ ERROR `#[no_coverage]` must be applied to coverable code
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const X: u32;
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#[no_coverage] //~ ERROR `#[no_coverage]` must be applied to coverable code
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type T;
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type U;
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}
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impl Trait for () {
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const X: u32 = 0;
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#[no_coverage] //~ ERROR `#[no_coverage]` must be applied to coverable code
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type T = Self;
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#[no_coverage] //~ ERROR `#[no_coverage]` must be applied to coverable code
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type U = impl Trait; //~ ERROR unconstrained opaque type
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}
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extern "C" {
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#[no_coverage] //~ ERROR `#[no_coverage]` must be applied to coverable code
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static X: u32;
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#[no_coverage] //~ ERROR `#[no_coverage]` must be applied to coverable code
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type T;
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}
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#[no_coverage]
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fn main() {
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#[no_coverage] //~ WARN `#[no_coverage]` can only be applied at the function level, not on code directly
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let _ = ();
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match () {
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#[no_coverage] //~ WARN `#[no_coverage]` can only be applied at the function level, not on code directly
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() => (),
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}
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#[no_coverage] //~ WARN `#[no_coverage]` can only be applied at the function level, not on code directly
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return ();
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}

‎src/test/ui/lint/no-coverage.stderr‎

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warning: `#[no_coverage]` can only be applied at the function level, not on code directly
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--> $DIR/no-coverage.rs:36:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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|
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note: the lint level is defined here
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--> $DIR/no-coverage.rs:4:9
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|
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LL | #![warn(unused_attributes)]
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| ^^^^^^^^^^^^^^^^^
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warning: `#[no_coverage]` can only be applied at the function level, not on code directly
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--> $DIR/no-coverage.rs:40:9
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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warning: `#[no_coverage]` can only be applied at the function level, not on code directly
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--> $DIR/no-coverage.rs:44:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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error[E0788]: `#[no_coverage]` must be applied to coverable code
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--> $DIR/no-coverage.rs:7:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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LL | const X: u32;
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| ------------- not coverable code
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error[E0788]: `#[no_coverage]` must be applied to coverable code
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--> $DIR/no-coverage.rs:10:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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LL | type T;
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| ------- not coverable code
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error[E0788]: `#[no_coverage]` must be applied to coverable code
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--> $DIR/no-coverage.rs:19:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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LL | type T = Self;
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| -------------- not coverable code
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error[E0788]: `#[no_coverage]` must be applied to coverable code
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--> $DIR/no-coverage.rs:22:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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LL | type U = impl Trait;
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| -------------------- not coverable code
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error[E0788]: `#[no_coverage]` must be applied to coverable code
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--> $DIR/no-coverage.rs:27:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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LL | static X: u32;
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| -------------- not coverable code
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error[E0788]: `#[no_coverage]` must be applied to coverable code
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--> $DIR/no-coverage.rs:30:5
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|
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LL | #[no_coverage]
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| ^^^^^^^^^^^^^^
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LL | type T;
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| ------- not coverable code
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error: unconstrained opaque type
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--> $DIR/no-coverage.rs:23:14
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|
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LL | type U = impl Trait;
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| ^^^^^^^^^^
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|
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= note: `U` must be used in combination with a concrete type within the same module
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error: aborting due to 7 previous errors; 3 warnings emitted
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For more information about this error, try `rustc --explain E0788`.

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