Account for generics when suggesting bound

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -286,21 +286,32 @@ fn suggest_restriction(
  );
  } else {
  // Trivial case: `T` needs an extra bound: `T: Bound`.
- let (sp, suggestion) = match super_traits {
- None => predicate_constraint(
+ let (sp, suggestion) = match (
+ generics
+ .params
+ .iter()
+ .filter(
+ |p| !matches!(p.kind, hir::GenericParamKind::Type { synthetic: Some(_), ..}),
+ )
+ .next(),
+ super_traits,
+ ) {
+ (_, None) => predicate_constraint(
  generics,
  trait_ref.without_const().to_predicate(tcx).to_string(),
  ),
- Some((ident, bounds)) => match bounds {
- [.., bound] => (
- bound.span().shrink_to_hi(),
- format!(" + {}", trait_ref.print_only_trait_path().to_string()),
- ),
- [] => (
- ident.span.shrink_to_hi(),
- format!(": {}", trait_ref.print_only_trait_path().to_string()),
- ),
- },
+ (None, Some((ident, []))) => (
+ ident.span.shrink_to_hi(),
+ format!(": {}", trait_ref.print_only_trait_path().to_string()),
+ ),
+ (_, Some((_, [.., bounds]))) => (
+ bounds.span().shrink_to_hi(),
+ format!(" + {}", trait_ref.print_only_trait_path().to_string()),
+ ),
+ (Some(_), Some((_, []))) => (
+ generics.span.shrink_to_hi(),
+ format!(": {}", trait_ref.print_only_trait_path().to_string()),
+ ),
  };
 
  err.span_suggestion_verbose(

src/test/ui/bound-suggestions.fixed

@@ -40,4 +40,29 @@ fn test_many_bounds_where<X>(x: X) where X: Sized, X: Sized, X: Debug {
  //~^ ERROR doesn't implement
 }
 
-pub fn main() { }
+trait Foo<T>: Sized {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Bar: std::fmt::Display + Sized {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Baz: Sized where Self: std::fmt::Display {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Qux<T>: Sized where Self: std::fmt::Display {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Bat<T>: std::fmt::Display + Sized {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+fn main() { }

src/test/ui/bound-suggestions.rs

@@ -40,4 +40,29 @@ fn test_many_bounds_where<X>(x: X) where X: Sized, X: Sized {
  //~^ ERROR doesn't implement
 }
 
-pub fn main() { }
+trait Foo<T> {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Bar: std::fmt::Display {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Baz where Self: std::fmt::Display {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Qux<T> where Self: std::fmt::Display {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+trait Bat<T>: std::fmt::Display {
+ const SIZE: usize = core::mem::size_of::<Self>();
+ //~^ ERROR the size for values of type `Self` cannot be known at compilation time
+}
+
+fn main() { }

src/test/ui/bound-suggestions.stderr

@@ -76,6 +76,86 @@ help: consider further restricting type parameter `X`
 LL | fn test_many_bounds_where<X>(x: X) where X: Sized, X: Sized, X: Debug {
  | ^^^^^^^^^^
 
-error: aborting due to 6 previous errors
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
+ --> $DIR/bound-suggestions.rs:44:46
+ |
+LL | const SIZE: usize = core::mem::size_of::<Self>();
+ | ^^^^ doesn't have a size known at compile-time
+ | 
+ ::: $SRC_DIR/core/src/mem/mod.rs:LL:COL
+ |
+LL | pub const fn size_of<T>() -> usize {
+ | - required by this bound in `std::mem::size_of`
+ |
+help: consider further restricting `Self`
+ |
+LL | trait Foo<T>: Sized {
+ | ^^^^^^^
+
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
+ --> $DIR/bound-suggestions.rs:49:46
+ |
+LL | const SIZE: usize = core::mem::size_of::<Self>();
+ | ^^^^ doesn't have a size known at compile-time
+ | 
+ ::: $SRC_DIR/core/src/mem/mod.rs:LL:COL
+ |
+LL | pub const fn size_of<T>() -> usize {
+ | - required by this bound in `std::mem::size_of`
+ |
+help: consider further restricting `Self`
+ |
+LL | trait Bar: std::fmt::Display + Sized {
+ | ^^^^^^^
+
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
+ --> $DIR/bound-suggestions.rs:54:46
+ |
+LL | const SIZE: usize = core::mem::size_of::<Self>();
+ | ^^^^ doesn't have a size known at compile-time
+ | 
+ ::: $SRC_DIR/core/src/mem/mod.rs:LL:COL
+ |
+LL | pub const fn size_of<T>() -> usize {
+ | - required by this bound in `std::mem::size_of`
+ |
+help: consider further restricting `Self`
+ |
+LL | trait Baz: Sized where Self: std::fmt::Display {
+ | ^^^^^^^
+
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
+ --> $DIR/bound-suggestions.rs:59:46
+ |
+LL | const SIZE: usize = core::mem::size_of::<Self>();
+ | ^^^^ doesn't have a size known at compile-time
+ | 
+ ::: $SRC_DIR/core/src/mem/mod.rs:LL:COL
+ |
+LL | pub const fn size_of<T>() -> usize {
+ | - required by this bound in `std::mem::size_of`
+ |
+help: consider further restricting `Self`
+ |
+LL | trait Qux<T>: Sized where Self: std::fmt::Display {
+ | ^^^^^^^
+
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
+ --> $DIR/bound-suggestions.rs:64:46
+ |
+LL | const SIZE: usize = core::mem::size_of::<Self>();
+ | ^^^^ doesn't have a size known at compile-time
+ | 
+ ::: $SRC_DIR/core/src/mem/mod.rs:LL:COL
+ |
+LL | pub const fn size_of<T>() -> usize {
+ | - required by this bound in `std::mem::size_of`
+ |
+help: consider further restricting `Self`
+ |
+LL | trait Bat<T>: std::fmt::Display + Sized {
+ | ^^^^^^^
+
+error: aborting due to 11 previous errors
 
 For more information about this error, try `rustc --explain E0277`.