Rollup merge of #62772 - estebank:trait-bound, r=matthewjasper
Suggest trait bound on type parameter when it is unconstrained
Given
```
trait Foo { fn method(&self) {} }
fn call_method<T>(x: &T) {
x.method()
}
```
suggest constraining `T` with `Foo`.
Fix #21673, fix #41030.
This commit is contained in:
Mazdak Farrokhzad
GitHub
commit
e933f54793
@ -643,13 +643,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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}
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}
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fn suggest_traits_to_import<'b>(&self,
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err: &mut DiagnosticBuilder<'_>,
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span: Span,
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rcvr_ty: Ty<'tcx>,
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item_name: ast::Ident,
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source: SelfSource<'b>,
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valid_out_of_scope_traits: Vec<DefId>) {
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fn suggest_traits_to_import<'b>(
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&self,
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err: &mut DiagnosticBuilder<'_>,
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span: Span,
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rcvr_ty: Ty<'tcx>,
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item_name: ast::Ident,
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source: SelfSource<'b>,
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valid_out_of_scope_traits: Vec<DefId>,
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) {
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if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
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return;
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}
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@ -683,30 +685,96 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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candidates.sort_by(|a, b| a.cmp(b).reverse());
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candidates.dedup();
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// FIXME #21673: this help message could be tuned to the case
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// of a type parameter: suggest adding a trait bound rather
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// than implementing.
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err.help("items from traits can only be used if the trait is implemented and in scope");
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let mut msg = format!("the following {traits_define} an item `{name}`, \
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perhaps you need to implement {one_of_them}:",
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traits_define = if candidates.len() == 1 {
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"trait defines"
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} else {
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"traits define"
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},
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one_of_them = if candidates.len() == 1 {
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"it"
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} else {
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"one of them"
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},
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name = item_name);
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let param_type = match rcvr_ty.sty {
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ty::Param(param) => Some(param),
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ty::Ref(_, ty, _) => match ty.sty {
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ty::Param(param) => Some(param),
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_ => None,
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}
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_ => None,
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};
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err.help(if param_type.is_some() {
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"items from traits can only be used if the type parameter is bounded by the trait"
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} else {
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"items from traits can only be used if the trait is implemented and in scope"
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});
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let mut msg = format!(
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"the following {traits_define} an item `{name}`, perhaps you need to {action} \
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{one_of_them}:",
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traits_define = if candidates.len() == 1 {
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"trait defines"
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} else {
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"traits define"
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},
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action = if let Some(param) = param_type {
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format!("restrict type parameter `{}` with", param)
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} else {
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"implement".to_string()
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},
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one_of_them = if candidates.len() == 1 {
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"it"
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} else {
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"one of them"
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},
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name = item_name,
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);
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// Obtain the span for `param` and use it for a structured suggestion.
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let mut suggested = false;
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if let (Some(ref param), Some(ref table)) = (param_type, self.in_progress_tables) {
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let table = table.borrow();
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if let Some(did) = table.local_id_root {
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let generics = self.tcx.generics_of(did);
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let type_param = generics.type_param(param, self.tcx);
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let hir = &self.tcx.hir();
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if let Some(id) = hir.as_local_hir_id(type_param.def_id) {
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// Get the `hir::Param` to verify whether it already has any bounds.
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// We do this to avoid suggesting code that ends up as `T: FooBar`,
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// instead we suggest `T: Foo + Bar` in that case.
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let mut has_bounds = false;
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if let Node::GenericParam(ref param) = hir.get(id) {
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has_bounds = !param.bounds.is_empty();
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}
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let sp = hir.span(id);
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// `sp` only covers `T`, change it so that it covers
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// `T:` when appropriate
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let sp = if has_bounds {
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sp.to(self.tcx
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.sess
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.source_map()
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.next_point(self.tcx.sess.source_map().next_point(sp)))
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} else {
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sp
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};
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for (i, trait_info) in candidates.iter().enumerate() {
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msg.push_str(&format!("\ncandidate #{}: `{}`",
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i + 1,
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self.tcx.def_path_str(trait_info.def_id)));
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// FIXME: contrast `t.def_id` against `param.bounds` to not suggest traits
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// already there. That can happen when the cause is that we're in a const
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// scope or associated function used as a method.
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err.span_suggestions(
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sp,
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&msg[..],
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candidates.iter().map(|t| format!(
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"{}: {}{}",
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param,
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self.tcx.def_path_str(t.def_id),
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if has_bounds { " +"} else { "" },
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)),
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Applicability::MaybeIncorrect,
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);
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suggested = true;
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}
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};
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}
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if !suggested {
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for (i, trait_info) in candidates.iter().enumerate() {
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msg.push_str(&format!(
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"\ncandidate #{}: `{}`",
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i + 1,
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self.tcx.def_path_str(trait_info.def_id),
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));
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}
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err.note(&msg[..]);
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}
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err.note(&msg[..]);
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}
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}
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@ -4,9 +4,11 @@ error[E0599]: no function or associated item named `dim` found for type `D` in t
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LL | entries: [T; D::dim()],
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| ^^^ function or associated item not found in `D`
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= help: items from traits can only be used if the trait is implemented and in scope
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= note: the following trait defines an item `dim`, perhaps you need to implement it:
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candidate #1: `Dim`
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= help: items from traits can only be used if the type parameter is bounded by the trait
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help: the following trait defines an item `dim`, perhaps you need to restrict type parameter `D` with it:
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LL | pub struct Vector<T, D: Dim + Dim> {
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| ^^^^^^^^
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error: aborting due to previous error
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@ -61,9 +61,11 @@ note: the candidate is defined in the trait `ManyImplTrait`
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LL | fn is_str() -> bool {
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| ^^^^^^^^^^^^^^^^^^^
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= help: to disambiguate the method call, write `ManyImplTrait::is_str(t)` instead
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= help: items from traits can only be used if the trait is implemented and in scope
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= note: the following trait defines an item `is_str`, perhaps you need to implement it:
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candidate #1: `ManyImplTrait`
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= help: items from traits can only be used if the type parameter is bounded by the trait
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help: the following trait defines an item `is_str`, perhaps you need to restrict type parameter `T` with it:
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LL | fn param_bound<T: ManyImplTrait + ManyImplTrait>(t: T) -> bool {
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| ^^^^^^^^^^^^^^^^^^
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error: aborting due to 3 previous errors
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13
src/test/ui/suggestions/issue-21673.rs
Normal file
13
src/test/ui/suggestions/issue-21673.rs
Normal file
@ -0,0 +1,13 @@
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trait Foo {
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fn method(&self) {}
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}
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fn call_method<T: std::fmt::Debug>(x: &T) {
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x.method() //~ ERROR E0599
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}
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fn call_method_2<T>(x: T) {
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x.method() //~ ERROR E0599
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}
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fn main() {}
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27
src/test/ui/suggestions/issue-21673.stderr
Normal file
27
src/test/ui/suggestions/issue-21673.stderr
Normal file
@ -0,0 +1,27 @@
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error[E0599]: no method named `method` found for type `&T` in the current scope
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--> $DIR/issue-21673.rs:6:7
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LL | x.method()
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| ^^^^^^
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= help: items from traits can only be used if the type parameter is bounded by the trait
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help: the following trait defines an item `method`, perhaps you need to restrict type parameter `T` with it:
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LL | fn call_method<T: Foo + std::fmt::Debug>(x: &T) {
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| ^^^^^^^^
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error[E0599]: no method named `method` found for type `T` in the current scope
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--> $DIR/issue-21673.rs:10:7
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LL | x.method()
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| ^^^^^^
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= help: items from traits can only be used if the type parameter is bounded by the trait
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help: the following trait defines an item `method`, perhaps you need to restrict type parameter `T` with it:
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LL | fn call_method_2<T: Foo>(x: T) {
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| ^^^^^^
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0599`.
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