Code change:
The following example code yields an error: It's unclear from this error message how to proceed - I'm not sure of the syntax, location, or where I should be putting the "GetString" trait bound. It should be shown with a better example or link when this error is presented, as the current message is not sufficient for a resolution to be arrived at.
cc
Fixing in . To fix your code write:
Thanks!

Related discussion:
text: // Get the `hir::Param` to verify whether it already has any bounds. // We do this to avoid suggesting code that ends up as `T: FooBar`, // instead we suggest `T: Foo + Bar` in that case. <del> let mut has_bounds = None; let mut impl_trait = false; if let Node::GenericParam(ref param) = hir.get(id) { let kind = &param.kind; if let hir::GenericParamKind::Type { synthetic: Some(_), .. } = kind { // We've found `fn foo(x: impl Trait)` instead of // `fn foo<T>(x: T)`. We want to suggest the correct // `fn foo(x: impl Trait + TraitBound)` instead of // `fn foo<T: TraitBound>(x: T)`. (See #63706.) impl_trait = true; has_bounds = param.bounds.get(1); } else { has_bounds = param.bounds.get(0); </del> <ins> match hir.get(id) { Node::GenericParam(ref param) => { let mut impl_trait = false; let has_bounds = if let hir::GenericParamKind::Type { synthetic: Some(_), .. } = &param.kind { // We've found `fn foo(x: impl Trait)` instead of // `fn foo<T>(x: T)`. We want to suggest the correct // `fn foo(x: impl Trait + TraitBound)` instead of // `fn foo<T: TraitBound>(x: T)`. (#63706) impl_trait = true; param.bounds.get(1) } else { param.bounds.get(0) }; let sp = hir.span(id); let sp = if let Some(first_bound) = has_bounds { // `sp` only covers `T`, change it so that it covers // `T:` when appropriate sp.until(first_bound.span()) } else { sp }; // FIXME: contrast `t.def_id` against `param.bounds` to not suggest // traits already there. That can happen when the cause is that // we're in a const scope or associated function used as a method. err.span_suggestions( sp, &message(format!( "restrict type parameter `{}` with", param.name.ident().as_str(), )), candidates.iter().map(|t| format!( "{}{} {}{}", param.name.ident().as_str(), if impl_trait { " +" } else { ":" }, self.tcx.def_path_str(t.def_id), if has_bounds.is_some() { " + "} else { "" }, )), Applicability::MaybeIncorrect, ); suggested = true; } Node::Item(hir::Item { kind: hir::ItemKind::Trait(.., bounds, _), ident, .. }) => { let (sp, sep, article) = if bounds.is_empty() { (ident.span.shrink_to_hi(), ":", "a") } else { (bounds.last().unwrap().span().shrink_to_hi(), " +", "another") }; err.span_suggestions( sp, &message(format!("add {} supertrait for", article)), candidates.iter().map(|t| format!( "{} {}", sep, self.tcx.def_path_str(t.def_id), )), Applicability::MaybeIncorrect, ); suggested = true; </ins> } <ins> _ => {} </ins> } <del> let sp = hir.span(id); // `sp` only covers `T`, change it so that it covers `T:` when appropriate. let sp = if let Some(first_bound) = has_bounds { sp.until(first_bound.span()) } else { sp }; // FIXME: contrast `t.def_id` against `param.bounds` to not suggest traits // already there. That can happen when the cause is that we're in a const // scope or associated function used as a method. err.span_suggestions( sp, &msg[..], candidates.iter().map(|t| format!( "{}{} {}{}", param, if impl_trait { " +" } else { ":" }, self.tcx.def_path_str(t.def_id), if has_bounds.is_some() { " + " } else { "" }, )), Applicability::MaybeIncorrect, ); suggested = true; </del> } }; } if !suggested { <ins> let mut msg = message(if let Some(param) = param_type { format!("restrict type parameter `{}` with", param) } else { "implement".to_string() }); </ins> for (i, trait_info) in candidates.iter().enumerate() { msg.push_str(&format!( "ncandidate #{}: `{}`",