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Suggest moving redundant generic args of an assoc fn to its trait #100838

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Original file line number Diff line number Diff line change
Expand Up @@ -524,6 +524,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
if self.not_enough_args_provided() {
self.suggest_adding_args(err);
} else if self.too_many_args_provided() {
self.suggest_moving_args_from_assoc_fn_to_trait(err);
self.suggest_removing_args_or_generics(err);
} else {
unreachable!();
Expand Down Expand Up @@ -654,6 +655,123 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
}
}

/// Suggests moving redundant argument(s) of an associate function to the
/// trait it belongs to.
///
/// ```compile_fail
/// Into::into::<Option<_>>(42) // suggests considering `Into::<Option<_>>::into(42)`
/// ```
fn suggest_moving_args_from_assoc_fn_to_trait(&self, err: &mut Diagnostic) {
let trait_ = match self.tcx.trait_of_item(self.def_id) {
Some(def_id) => def_id,
None => return,
};

// Skip suggestion when the associated function is itself generic, it is unclear
// how to split the provided parameters between those to suggest to the trait and
// those to remain on the associated type.
let num_assoc_fn_expected_args =
self.num_expected_type_or_const_args() + self.num_expected_lifetime_args();
if num_assoc_fn_expected_args > 0 {
return;
}

let num_assoc_fn_excess_args =
self.num_excess_type_or_const_args() + self.num_excess_lifetime_args();

let trait_generics = self.tcx.generics_of(trait_);
let num_trait_generics_except_self =
trait_generics.count() - if trait_generics.has_self { 1 } else { 0 };

let msg = format!(
"consider moving {these} generic argument{s} to the `{name}` trait, which takes up to {num} argument{s}",
these = pluralize!("this", num_assoc_fn_excess_args),
s = pluralize!(num_assoc_fn_excess_args),
name = self.tcx.item_name(trait_),
num = num_trait_generics_except_self,
);

if let Some(hir_id) = self.path_segment.hir_id
&& let Some(parent_node) = self.tcx.hir().find_parent_node(hir_id)
&& let Some(parent_node) = self.tcx.hir().find(parent_node)
&& let hir::Node::Expr(expr) = parent_node {
match expr.kind {
hir::ExprKind::Path(ref qpath) => {
self.suggest_moving_args_from_assoc_fn_to_trait_for_qualified_path(
err,
qpath,
msg,
num_assoc_fn_excess_args,
num_trait_generics_except_self
)
},
hir::ExprKind::MethodCall(..) => {
self.suggest_moving_args_from_assoc_fn_to_trait_for_method_call(
err,
trait_,
expr,
msg,
num_assoc_fn_excess_args,
num_trait_generics_except_self
)
},
_ => return,
}
}
}

fn suggest_moving_args_from_assoc_fn_to_trait_for_qualified_path(
&self,
err: &mut Diagnostic,
qpath: &'tcx hir::QPath<'tcx>,
msg: String,
num_assoc_fn_excess_args: usize,
num_trait_generics_except_self: usize,
) {
if let hir::QPath::Resolved(_, path) = qpath
&& let Some(trait_path_segment) = path.segments.get(0) {
let num_generic_args_supplied_to_trait = trait_path_segment.args().num_generic_params();

if num_assoc_fn_excess_args == num_trait_generics_except_self - num_generic_args_supplied_to_trait {
if let Some(span) = self.gen_args.span_ext()
&& let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
let sugg = vec![
(self.path_segment.ident.span, format!("{}::{}", snippet, self.path_segment.ident)),
(span.with_lo(self.path_segment.ident.span.hi()), "".to_owned())
];

err.multipart_suggestion(
msg,
sugg,
Applicability::MaybeIncorrect
);
}
}
}
}

fn suggest_moving_args_from_assoc_fn_to_trait_for_method_call(
&self,
err: &mut Diagnostic,
trait_: DefId,
expr: &'tcx hir::Expr<'tcx>,
msg: String,
num_assoc_fn_excess_args: usize,
num_trait_generics_except_self: usize,
) {
if let hir::ExprKind::MethodCall(_, args, _) = expr.kind {
assert_eq!(args.len(), 1);
if num_assoc_fn_excess_args == num_trait_generics_except_self {
if let Some(gen_args) = self.gen_args.span_ext()
&& let Ok(gen_args) = self.tcx.sess.source_map().span_to_snippet(gen_args)
&& let Ok(args) = self.tcx.sess.source_map().span_to_snippet(args[0].span) {
let sugg = format!("{}::{}::{}({})", self.tcx.item_name(trait_), gen_args, self.tcx.item_name(self.def_id), args);
err.span_suggestion(expr.span, msg, sugg, Applicability::MaybeIncorrect);
}
}
}
}

/// Suggests to remove redundant argument(s):
///
/// ```text
Expand Down
13 changes: 10 additions & 3 deletions src/test/ui/const-generics/invalid-const-arg-for-type-param.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -2,15 +2,22 @@ error[E0107]: this associated function takes 0 generic arguments but 1 generic a
--> $DIR/invalid-const-arg-for-type-param.rs:6:23
|
LL | let _: u32 = 5i32.try_into::<32>().unwrap();
| ^^^^^^^^------ help: remove these generics
| |
| expected 0 generic arguments
| ^^^^^^^^ expected 0 generic arguments
|
note: associated function defined here, with 0 generic parameters
--> $SRC_DIR/core/src/convert/mod.rs:LL:COL
|
LL | fn try_into(self) -> Result<T, Self::Error>;
| ^^^^^^^^
help: consider moving this generic argument to the `TryInto` trait, which takes up to 1 argument
|
LL | let _: u32 = TryInto::<32>::try_into(5i32).unwrap();
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
help: remove these generics
|
LL - let _: u32 = 5i32.try_into::<32>().unwrap();
LL + let _: u32 = 5i32.try_into().unwrap();
|

error[E0599]: no method named `f` found for struct `S` in the current scope
--> $DIR/invalid-const-arg-for-type-param.rs:9:7
Expand Down
35 changes: 35 additions & 0 deletions src/test/ui/suggestions/issue-89064.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
use std::convert::TryInto;

trait A<T> {
fn foo() {}
}

trait B<T, U> {
fn bar() {}
}

struct S;

impl<T> A<T> for S {}
impl<T, U> B<T, U> for S {}

fn main() {
let _ = A::foo::<S>();
//~^ ERROR
//~| HELP remove these generics
//~| HELP consider moving this generic argument

let _ = B::bar::<S, S>();
//~^ ERROR
//~| HELP remove these generics
//~| HELP consider moving these generic arguments

let _ = A::<S>::foo::<S>();
//~^ ERROR
//~| HELP remove these generics

let _ = 42.into::<Option<_>>();
//~^ ERROR
//~| HELP remove these generics
//~| HELP consider moving this generic argument
}
82 changes: 82 additions & 0 deletions src/test/ui/suggestions/issue-89064.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,82 @@
error[E0107]: this associated function takes 0 generic arguments but 1 generic argument was supplied
--> $DIR/issue-89064.rs:17:16
|
LL | let _ = A::foo::<S>();
| ^^^ expected 0 generic arguments
|
note: associated function defined here, with 0 generic parameters
--> $DIR/issue-89064.rs:4:8
|
LL | fn foo() {}
| ^^^
help: consider moving this generic argument to the `A` trait, which takes up to 1 argument
|
LL - let _ = A::foo::<S>();
LL + let _ = A::<S>::foo();
|
help: remove these generics
|
LL - let _ = A::foo::<S>();
LL + let _ = A::foo();
|

error[E0107]: this associated function takes 0 generic arguments but 2 generic arguments were supplied
--> $DIR/issue-89064.rs:22:16
|
LL | let _ = B::bar::<S, S>();
| ^^^ expected 0 generic arguments
|
note: associated function defined here, with 0 generic parameters
--> $DIR/issue-89064.rs:8:8
|
LL | fn bar() {}
| ^^^
help: consider moving these generic arguments to the `B` trait, which takes up to 2 arguments
|
LL - let _ = B::bar::<S, S>();
LL + let _ = B::<S, S>::bar();
|
help: remove these generics
|
LL - let _ = B::bar::<S, S>();
LL + let _ = B::bar();
|

error[E0107]: this associated function takes 0 generic arguments but 1 generic argument was supplied
--> $DIR/issue-89064.rs:27:21
|
LL | let _ = A::<S>::foo::<S>();
| ^^^----- help: remove these generics
| |
| expected 0 generic arguments
|
note: associated function defined here, with 0 generic parameters
--> $DIR/issue-89064.rs:4:8
|
LL | fn foo() {}
| ^^^

error[E0107]: this associated function takes 0 generic arguments but 1 generic argument was supplied
--> $DIR/issue-89064.rs:31:16
|
LL | let _ = 42.into::<Option<_>>();
| ^^^^ expected 0 generic arguments
|
note: associated function defined here, with 0 generic parameters
--> $SRC_DIR/core/src/convert/mod.rs:LL:COL
|
LL | fn into(self) -> T;
| ^^^^
help: consider moving this generic argument to the `Into` trait, which takes up to 1 argument
|
LL | let _ = Into::<Option<_>>::into(42);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~
help: remove these generics
|
LL - let _ = 42.into::<Option<_>>();
LL + let _ = 42.into();
|

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0107`.