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E0229: Suggest Moving Type Constraints to Type Parameter Declaration #126054

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Jun 14, 2024
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E0229: Suggest Moving Type Constraints to Type Parameter Declaration #126054

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6d19ac3
Update Tests
veera-sivarajan Jun 5, 2024
5da1b41
E0229: Suggest Moving Type Constraints to Type Parameter Declaration
veera-sivarajan Jun 6, 2024
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24 changes: 24 additions & 0 deletions compiler/rustc_hir/src/hir.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2456,6 +2456,15 @@ pub enum AssocItemConstraintKind<'hir> {
Bound { bounds: &'hir [GenericBound<'hir>] },
}

impl<'hir> AssocItemConstraintKind<'hir> {
pub fn descr(&self) -> &'static str {
match self {
AssocItemConstraintKind::Equality { .. } => "binding",
AssocItemConstraintKind::Bound { .. } => "constraint",
}
}
}

#[derive(Debug, Clone, Copy, HashStable_Generic)]
pub struct Ty<'hir> {
pub hir_id: HirId,
Expand Down Expand Up @@ -3735,6 +3744,21 @@ impl<'hir> Node<'hir> {
}
}

/// Get a `hir::Impl` if the node is an impl block for the given `trait_def_id`.
pub fn impl_block_of_trait(self, trait_def_id: DefId) -> Option<&'hir Impl<'hir>> {
match self {
Node::Item(Item { kind: ItemKind::Impl(impl_block), .. })
if impl_block
.of_trait
.and_then(|trait_ref| trait_ref.trait_def_id())
.is_some_and(|trait_id| trait_id == trait_def_id) =>
{
Some(impl_block)
}
_ => None,
}
}

pub fn fn_sig(self) -> Option<&'hir FnSig<'hir>> {
match self {
Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(fn_sig, _), .. })
Expand Down
71 changes: 62 additions & 9 deletions compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1217,7 +1217,6 @@ pub fn prohibit_assoc_item_constraint(
// otherwise suggest the removal of the binding.
if let Some((def_id, segment, _)) = segment
&& segment.args().parenthesized == hir::GenericArgsParentheses::No
&& let hir::AssocItemConstraintKind::Equality { term } = constraint.kind
{
// Suggests removal of the offending binding
let suggest_removal = |e: &mut Diag<'_>| {
Expand Down Expand Up @@ -1263,7 +1262,7 @@ pub fn prohibit_assoc_item_constraint(
if let Ok(suggestion) = tcx.sess.source_map().span_to_snippet(removal_span) {
e.span_suggestion_verbose(
removal_span,
"consider removing this associated item binding",
format!("consider removing this associated item {}", constraint.kind.descr()),
suggestion,
Applicability::MaybeIncorrect,
);
Expand All @@ -1286,19 +1285,73 @@ pub fn prohibit_assoc_item_constraint(
// Check if the type has a generic param with the same name
// as the assoc type name in the associated item binding.
let generics = tcx.generics_of(def_id);
let matching_param =
generics.own_params.iter().find(|p| p.name.as_str() == constraint.ident.as_str());
let matching_param = generics.own_params.iter().find(|p| p.name == constraint.ident.name);
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Also, changed this because comparing interned strings is more efficient


// Now emit the appropriate suggestion
if let Some(matching_param) = matching_param {
match (&matching_param.kind, term) {
(GenericParamDefKind::Type { .. }, hir::Term::Ty(ty)) => {
suggest_direct_use(&mut err, ty.span);
}
(GenericParamDefKind::Const { .. }, hir::Term::Const(c)) => {
match (constraint.kind, &matching_param.kind) {
(
hir::AssocItemConstraintKind::Equality { term: hir::Term::Ty(ty) },
GenericParamDefKind::Type { .. },
) => suggest_direct_use(&mut err, ty.span),
(
hir::AssocItemConstraintKind::Equality { term: hir::Term::Const(c) },
GenericParamDefKind::Const { .. },
) => {
let span = tcx.hir().span(c.hir_id);
suggest_direct_use(&mut err, span);
}
(hir::AssocItemConstraintKind::Bound { bounds }, _) => {
// Suggest `impl<T: Bound> Trait<T> for Foo` when finding
// `impl Trait<T: Bound> for Foo`

// Get the parent impl block based on the binding we have
// and the trait DefId
let impl_block = tcx
.hir()
.parent_iter(constraint.hir_id)
.find_map(|(_, node)| node.impl_block_of_trait(def_id));

let type_with_constraints =
tcx.sess.source_map().span_to_snippet(constraint.span);

if let Some(impl_block) = impl_block
&& let Ok(type_with_constraints) = type_with_constraints
{
// Filter out the lifetime parameters because
// they should be declared before the type parameter
let lifetimes: String = bounds
.iter()
.filter_map(|bound| {
if let hir::GenericBound::Outlives(lifetime) = bound {
Some(format!("{lifetime}, "))
} else {
None
}
})
.collect();
// Figure out a span and suggestion string based on
// whether there are any existing parameters
let param_decl = if let Some(param_span) =
impl_block.generics.span_for_param_suggestion()
{
(param_span, format!(", {lifetimes}{type_with_constraints}"))
} else {
(
impl_block.generics.span.shrink_to_lo(),
format!("<{lifetimes}{type_with_constraints}>"),
)
};
let suggestions =
vec![param_decl, (constraint.span, format!("{}", matching_param.name))];

err.multipart_suggestion_verbose(
format!("declare the type parameter right after the `impl` keyword"),
suggestions,
Applicability::MaybeIncorrect,
);
}
}
_ => suggest_removal(&mut err),
}
} else {
Expand Down
17 changes: 16 additions & 1 deletion compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -531,6 +531,7 @@ pub(crate) fn check_generic_arg_count(

let num_default_params = expected_max - expected_min;

let mut all_params_are_binded = false;
let gen_args_info = if provided > expected_max {
invalid_args.extend((expected_max..provided).map(|i| i + args_offset));
let num_redundant_args = provided - expected_max;
Expand All @@ -547,6 +548,20 @@ pub(crate) fn check_generic_arg_count(
} else {
let num_missing_args = expected_max - provided;

let constraint_names: Vec<_> =
gen_args.constraints.iter().map(|b| b.ident.name).collect();
let param_names: Vec<_> = gen_params
.own_params
.iter()
.filter(|param| !has_self || param.index != 0) // Assumes `Self` will always be the first parameter
.map(|param| param.name)
.collect();
if constraint_names == param_names {
// We set this to true and delay emitting `WrongNumberOfGenericArgs`
// to provide a succinct error for cases like issue #113073
all_params_are_binded = true;
};

GenericArgsInfo::MissingTypesOrConsts {
num_missing_args,
num_default_params,
Expand All @@ -567,7 +582,7 @@ pub(crate) fn check_generic_arg_count(
def_id,
)
.diagnostic()
.emit()
.emit_unless(all_params_are_binded)
});

Err(reported)
Expand Down
1 change: 1 addition & 0 deletions tests/ui/associated-type-bounds/no-gat-position.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ pub trait Iter {

fn next<'a>(&'a mut self) -> Option<Self::Item<'a, As1: Copy>>;
//~^ ERROR associated item constraints are not allowed here
//~| HELP consider removing this associated item constraint
}

impl Iter for () {
Expand Down
5 changes: 5 additions & 0 deletions tests/ui/associated-type-bounds/no-gat-position.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,11 @@ error[E0229]: associated item constraints are not allowed here
|
LL | fn next<'a>(&'a mut self) -> Option<Self::Item<'a, As1: Copy>>;
| ^^^^^^^^^ associated item constraint not allowed here
|
help: consider removing this associated item constraint
|
LL | fn next<'a>(&'a mut self) -> Option<Self::Item<'a, As1: Copy>>;
| ~~~~~~~~~~~

error: aborting due to 1 previous error

Expand Down
2 changes: 0 additions & 2 deletions tests/ui/associated-types/associated-types-eq-2.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,6 @@ trait Tr3<const N: i32, T2, T3> {
impl Tr3<N
//~^ ERROR associated item constraints are not allowed here
//~| ERROR associated const equality is incomplete
//~| ERROR trait takes 3 generic arguments but 0 generic arguments were supplied
= 42, T2 = Qux, T3 = usize> for Bar {
}

Expand All @@ -92,7 +91,6 @@ impl Tr3<n = 42, T2 = Qux, T3 = usize> for Qux {
// matches the const param ident but the constraint is a type arg
impl Tr3<N = u32, T2 = Qux, T3 = usize> for Bar {
//~^ ERROR associated item constraints are not allowed here
//~| ERROR trait takes 3 generic arguments but 0 generic arguments were supplied
}

// Test for when equality constraint's ident
Expand Down
62 changes: 14 additions & 48 deletions tests/ui/associated-types/associated-types-eq-2.stderr
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Expand Up @@ -5,7 +5,6 @@ LL | impl Tr3<N
| __________^
LL | |
LL | |
LL | |
LL | | = 42, T2 = Qux, T3 = usize> for Bar {
| |____^
|
Expand All @@ -14,7 +13,7 @@ LL | | = 42, T2 = Qux, T3 = usize> for Bar {
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: associated const equality is incomplete
--> $DIR/associated-types-eq-2.rs:85:10
--> $DIR/associated-types-eq-2.rs:84:10
|
LL | impl Tr3<n = 42, T2 = Qux, T3 = usize> for Qux {
| ^^^^^^
Expand All @@ -24,7 +23,7 @@ LL | impl Tr3<n = 42, T2 = Qux, T3 = usize> for Qux {
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: associated const equality is incomplete
--> $DIR/associated-types-eq-2.rs:100:14
--> $DIR/associated-types-eq-2.rs:98:14
|
LL | impl Tr3<42, T2 = 42, T3 = usize> for Bar {
| ^^^^^^^
Expand All @@ -34,7 +33,7 @@ LL | impl Tr3<42, T2 = 42, T3 = usize> for Bar {
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: associated const equality is incomplete
--> $DIR/associated-types-eq-2.rs:108:10
--> $DIR/associated-types-eq-2.rs:106:10
|
LL | impl Tr3<X = 42, Y = Qux, Z = usize> for Bar {
| ^^^^^^
Expand Down Expand Up @@ -190,30 +189,13 @@ help: to use `GenericTerm<i32>` as a generic argument specify it directly
LL | impl Tr2<i32, Qux, GenericTerm<i32>> for Bar {
| ~~~~~~~~~~~~~~~~

error[E0107]: trait takes 3 generic arguments but 0 generic arguments were supplied
--> $DIR/associated-types-eq-2.rs:76:6
|
LL | impl Tr3<N
| ^^^ expected 3 generic arguments
|
note: trait defined here, with 3 generic parameters: `N`, `T2`, `T3`
--> $DIR/associated-types-eq-2.rs:69:7
|
LL | trait Tr3<const N: i32, T2, T3> {
| ^^^ ------------ -- --
help: add missing generic arguments
|
LL | impl Tr3<N, T2, T3, N
| ++++++++++

error[E0229]: associated item constraints are not allowed here
--> $DIR/associated-types-eq-2.rs:76:10
|
LL | impl Tr3<N
| __________^
LL | |
LL | |
LL | |
LL | | = 42, T2 = Qux, T3 = usize> for Bar {
| |____^ associated item constraint not allowed here
|
Expand All @@ -223,7 +205,7 @@ LL | impl Tr3<42, T2 = Qux, T3 = usize> for Bar {
| ~~

error[E0107]: trait takes 3 generic arguments but 0 generic arguments were supplied
--> $DIR/associated-types-eq-2.rs:85:6
--> $DIR/associated-types-eq-2.rs:84:6
|
LL | impl Tr3<n = 42, T2 = Qux, T3 = usize> for Qux {
| ^^^ expected 3 generic arguments
Expand All @@ -239,7 +221,7 @@ LL | impl Tr3<N, T2, T3, n = 42, T2 = Qux, T3 = usize> for Qux {
| ++++++++++

error[E0229]: associated item constraints are not allowed here
--> $DIR/associated-types-eq-2.rs:85:10
--> $DIR/associated-types-eq-2.rs:84:10
|
LL | impl Tr3<n = 42, T2 = Qux, T3 = usize> for Qux {
| ^^^^^^ associated item constraint not allowed here
Expand All @@ -249,24 +231,8 @@ help: consider removing this associated item binding
LL | impl Tr3<n = 42, T2 = Qux, T3 = usize> for Qux {
| ~~~~~~~

error[E0107]: trait takes 3 generic arguments but 0 generic arguments were supplied
--> $DIR/associated-types-eq-2.rs:93:6
|
LL | impl Tr3<N = u32, T2 = Qux, T3 = usize> for Bar {
| ^^^ expected 3 generic arguments
|
note: trait defined here, with 3 generic parameters: `N`, `T2`, `T3`
--> $DIR/associated-types-eq-2.rs:69:7
|
LL | trait Tr3<const N: i32, T2, T3> {
| ^^^ ------------ -- --
help: add missing generic arguments
|
LL | impl Tr3<N, T2, T3, N = u32, T2 = Qux, T3 = usize> for Bar {
| ++++++++++

error[E0229]: associated item constraints are not allowed here
--> $DIR/associated-types-eq-2.rs:93:10
--> $DIR/associated-types-eq-2.rs:92:10
|
LL | impl Tr3<N = u32, T2 = Qux, T3 = usize> for Bar {
| ^^^^^^^ associated item constraint not allowed here
Expand All @@ -277,7 +243,7 @@ LL | impl Tr3<N = u32, T2 = Qux, T3 = usize> for Bar {
| ~~~~~~~~

error[E0107]: trait takes 3 generic arguments but 1 generic argument was supplied
--> $DIR/associated-types-eq-2.rs:100:6
--> $DIR/associated-types-eq-2.rs:98:6
|
LL | impl Tr3<42, T2 = 42, T3 = usize> for Bar {
| ^^^ -- supplied 1 generic argument
Expand All @@ -295,7 +261,7 @@ LL | impl Tr3<42, T2, T3, T2 = 42, T3 = usize> for Bar {
| ++++++++

error[E0229]: associated item constraints are not allowed here
--> $DIR/associated-types-eq-2.rs:100:14
--> $DIR/associated-types-eq-2.rs:98:14
|
LL | impl Tr3<42, T2 = 42, T3 = usize> for Bar {
| ^^^^^^^ associated item constraint not allowed here
Expand All @@ -306,7 +272,7 @@ LL | impl Tr3<42, T2 = 42, T3 = usize> for Bar {
| ~~~~~~~~~

error[E0107]: trait takes 3 generic arguments but 0 generic arguments were supplied
--> $DIR/associated-types-eq-2.rs:108:6
--> $DIR/associated-types-eq-2.rs:106:6
|
LL | impl Tr3<X = 42, Y = Qux, Z = usize> for Bar {
| ^^^ expected 3 generic arguments
Expand All @@ -322,7 +288,7 @@ LL | impl Tr3<N, T2, T3, X = 42, Y = Qux, Z = usize> for Bar {
| ++++++++++

error[E0229]: associated item constraints are not allowed here
--> $DIR/associated-types-eq-2.rs:108:10
--> $DIR/associated-types-eq-2.rs:106:10
|
LL | impl Tr3<X = 42, Y = Qux, Z = usize> for Bar {
| ^^^^^^ associated item constraint not allowed here
Expand All @@ -333,13 +299,13 @@ LL | impl Tr3<X = 42, Y = Qux, Z = usize> for Bar {
| ~~~~~~~

error[E0107]: struct takes 1 generic argument but 0 generic arguments were supplied
--> $DIR/associated-types-eq-2.rs:119:13
--> $DIR/associated-types-eq-2.rs:117:13
|
LL | impl<'a, T> St<'a , T = Qux> {
| ^^ expected 1 generic argument
|
note: struct defined here, with 1 generic parameter: `T`
--> $DIR/associated-types-eq-2.rs:117:8
--> $DIR/associated-types-eq-2.rs:115:8
|
LL | struct St<'a, T> { v: &'a T }
| ^^ -
Expand All @@ -349,7 +315,7 @@ LL | impl<'a, T> St<'a, T , T = Qux> {
| +++

error[E0229]: associated item constraints are not allowed here
--> $DIR/associated-types-eq-2.rs:119:21
--> $DIR/associated-types-eq-2.rs:117:21
|
LL | impl<'a, T> St<'a , T = Qux> {
| ^^^^^^^ associated item constraint not allowed here
Expand All @@ -359,7 +325,7 @@ help: to use `Qux` as a generic argument specify it directly
LL | impl<'a, T> St<'a , Qux> {
| ~~~

error: aborting due to 27 previous errors
error: aborting due to 25 previous errors

Some errors have detailed explanations: E0046, E0107, E0229, E0658.
For more information about an error, try `rustc --explain E0046`.
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