Fix auto-application of associated generic functions with placeholders

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -14,11 +14,17 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{ExprKind, Node, QPath};
-use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc_infer::infer::{
+    type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
+    RegionVariableOrigin,
+};
+use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::traits::util::supertraits;
 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
 use rustc_middle::ty::print::with_crate_prefix;
-use rustc_middle::ty::{self, DefIdTree, ToPredicate, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{
+    self, DefIdTree, GenericArg, GenericArgKind, ToPredicate, Ty, TyCtxt, TypeVisitable,
+};
 use rustc_middle::ty::{IsSuggestable, ToPolyTraitRef};
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Symbol;
@@ -279,7 +285,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ) {
                     return None;
                 }
-
                 span = item_name.span;
 
                 // Don't show generic arguments when the method can't be found in any implementation (#81576).
@@ -392,28 +397,118 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     custom_span_label = true;
                 }
                 if static_candidates.len() == 1 {
-                    let ty_str =
-                        if let Some(CandidateSource::Impl(impl_did)) = static_candidates.get(0) {
-                            // When the "method" is resolved through dereferencing, we really want the
-                            // original type that has the associated function for accurate suggestions.
-                            // (#61411)
-                            let ty = tcx.at(span).type_of(*impl_did);
-                            match (&ty.peel_refs().kind(), &actual.peel_refs().kind()) {
-                                (ty::Adt(def, _), ty::Adt(def_actual, _)) if def == def_actual => {
-                                    // Use `actual` as it will have more `substs` filled in.
-                                    self.ty_to_value_string(actual.peel_refs())
+                    let mut has_unsuggestable_args = false;
+                    let ty_str = if let Some(CandidateSource::Impl(impl_did)) =
+                        static_candidates.get(0)
+                    {
+                        // When the "method" is resolved through dereferencing, we really want the
+                        // original type that has the associated function for accurate suggestions.
+                        // (#61411)
+                        let ty = tcx.at(span).type_of(*impl_did);
+                        match (&ty.peel_refs().kind(), &actual.peel_refs().kind()) {
+                            (ty::Adt(def, _), ty::Adt(def_actual, substs)) if def == def_actual => {
+                                // If there are any inferred arguments, (`{integer}`), we should replace
+                                // them with underscores to allow the compiler to infer them
+                                let infer_substs: Vec<GenericArg<'_>> = substs
+                                    .into_iter()
+                                    .map(|arg| {
+                                        if !arg.is_suggestable(tcx, true) {
+                                            has_unsuggestable_args = true;
+                                            match arg.unpack() {
+                                            GenericArgKind::Lifetime(_) => self
+                                                .next_region_var(RegionVariableOrigin::MiscVariable(
+                                                    rustc_span::DUMMY_SP,
+                                                ))
+                                                .into(),
+                                            GenericArgKind::Type(_) => self
+                                                .next_ty_var(TypeVariableOrigin {
+                                                    span: rustc_span::DUMMY_SP,
+                                                    kind: TypeVariableOriginKind::MiscVariable,
+                                                })
+                                                .into(),
+                                            GenericArgKind::Const(arg) => self
+                                                .next_const_var(
+                                                    arg.ty(),
+                                                    ConstVariableOrigin {
+                                                        span: rustc_span::DUMMY_SP,
+                                                        kind: ConstVariableOriginKind::MiscVariable,
+                                                    },
+                                                )
+                                                .into(),
+                                            }
+                                        } else {
+                                            arg
+                                        }
+                                    })
+                                    .collect::<Vec<_>>();
+
+                                tcx.value_path_str_with_substs(
+                                    def_actual.did(),
+                                    tcx.intern_substs(&infer_substs),
+                                )
+                            }
+                            _ => self.ty_to_value_string(ty.peel_refs()),
+                        }
+                    } else {
+                        self.ty_to_value_string(actual.peel_refs())
+                    };
+                    if let SelfSource::MethodCall(_) = source {
+                        let first_arg = if let Some(CandidateSource::Impl(impl_did)) = static_candidates.get(0) &&
+                            let Some(assoc) = self.associated_value(*impl_did, item_name) {
+                            let sig = self.tcx.fn_sig(assoc.def_id);
+                            if let Some(first) = sig.inputs().skip_binder().get(0) {
+                                if first.peel_refs() == rcvr_ty.peel_refs() {
+                                    None
+                                } else {
+                                    Some(if first.is_region_ptr() {
+                                        if first.is_mutable_ptr() { "&mut " } else { "&" }
+                                    } else {
+                                        ""
+                                    })
                                 }
-                                _ => self.ty_to_value_string(ty.peel_refs()),
+                            } else {
+                                None
                             }
                         } else {
-                            self.ty_to_value_string(actual.peel_refs())
+                            None
+                        };
+                        let mut applicability = Applicability::MachineApplicable;
+                        let args = if let Some((receiver, args)) = args {
+                            // The first arg is the same kind as the receiver
+                            let explicit_args = if first_arg.is_some() {
+                                std::iter::once(receiver).chain(args.iter()).collect::<Vec<_>>()
+                            } else {
+                                // There is no `Self` kind to infer the arguments from
+                                if has_unsuggestable_args {
+                                    applicability = Applicability::HasPlaceholders;
+                                }
+                                args.iter().collect()
+                            };
+                            format!(
+                                "({}{})",
+                                first_arg.unwrap_or(""),
+                                explicit_args
+                                    .iter()
+                                    .map(|arg| tcx
+                                        .sess
+                                        .source_map()
+                                        .span_to_snippet(arg.span)
+                                        .unwrap_or_else(|_| {
+                                            applicability = Applicability::HasPlaceholders;
+                                            "_".to_owned()
+                                        }))
+                                    .collect::<Vec<_>>()
+                                    .join(", "),
+                            )
+                        } else {
+                            applicability = Applicability::HasPlaceholders;
+                            "(...)".to_owned()
                         };
-                    if let SelfSource::MethodCall(expr) = source {
                         err.span_suggestion(
-                            expr.span.to(span),
+                            sugg_span,
                             "use associated function syntax instead",
-                            format!("{}::{}", ty_str, item_name),
-                            Applicability::MachineApplicable,
+                            format!("{}::{}{}", ty_str, item_name, args),
+                            applicability,
                         );
                     } else {
                         err.help(&format!("try with `{}::{}`", ty_str, item_name,));
@@ -1826,7 +1921,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Print out the type for use in value namespace.
     fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
         match ty.kind() {
-            ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did(), substs)),
+            ty::Adt(def, substs) => self.tcx.def_path_str_with_substs(def.did(), substs),
             _ => self.ty_to_string(ty),
         }
     }

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -1659,6 +1659,12 @@ impl<'t> TyCtxt<'t> {
         debug!("def_path_str: def_id={:?}, ns={:?}", def_id, ns);
         FmtPrinter::new(self, ns).print_def_path(def_id, substs).unwrap().into_buffer()
     }
+
+    pub fn value_path_str_with_substs(self, def_id: DefId, substs: &'t [GenericArg<'t>]) -> String {
+        let ns = guess_def_namespace(self, def_id);
+        debug!("value_path_str: def_id={:?}, ns={:?}", def_id, ns);
+        FmtPrinter::new(self, ns).print_value_path(def_id, substs).unwrap().into_buffer()
+    }
 }
 
 impl fmt::Write for FmtPrinter<'_, '_> {

src/test/ui/issues/issue-3707.stderr

@@ -2,10 +2,10 @@ error[E0599]: no method named `boom` found for reference `&Obj` in the current s
   --> $DIR/issue-3707.rs:10:14
    |
 LL |         self.boom();
-   |         -----^^^^
+   |         -----^^^^--
    |         |    |
    |         |    this is an associated function, not a method
-   |         help: use associated function syntax instead: `Obj::boom`
+   |         help: use associated function syntax instead: `Obj::boom()`
    |
    = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
 note: the candidate is defined in an impl for the type `Obj`

src/test/ui/suggestions/inner_type2.rs

@@ -22,5 +22,5 @@ fn main() {
     let item = std::mem::MaybeUninit::new(Struct { p: 42_u32 });
     item.method();
     //~^ ERROR no method named `method` found for union `MaybeUninit` in the current scope [E0599]
-    //~| HELP if this `MaybeUninit::<Struct<u32>>` has been initialized, use one of the `assume_init` methods to access the inner value
+    //~| HELP if this `MaybeUninit<Struct<u32>>` has been initialized, use one of the `assume_init` methods to access the inner value
 }

src/test/ui/suggestions/inner_type2.stderr

@@ -17,7 +17,7 @@ error[E0599]: no method named `method` found for union `MaybeUninit` in the curr
 LL |     item.method();
    |          ^^^^^^ method not found in `MaybeUninit<Struct<u32>>`
    |
-   = help: if this `MaybeUninit::<Struct<u32>>` has been initialized, use one of the `assume_init` methods to access the inner value
+   = help: if this `MaybeUninit<Struct<u32>>` has been initialized, use one of the `assume_init` methods to access the inner value
 note: the method `method` exists on the type `Struct<u32>`
   --> $DIR/inner_type2.rs:6:5
    |

src/test/ui/suggestions/issue-102354.stderr

@@ -13,7 +13,7 @@ LL |     fn func() {}
 help: use associated function syntax instead
    |
 LL |     i32::func();
-   |     ~~~~~~~~~
+   |     ~~~~~~~~~~~
 help: disambiguate the associated function for the candidate
    |
 LL |     <i32 as Trait>::func(x);

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish-placeholder.rs

@@ -0,0 +1,11 @@
+struct GenericAssocMethod<T>(T);
+
+impl<T> GenericAssocMethod<T> {
+    fn default_hello() {}
+}
+
+fn main() {
+    let x = GenericAssocMethod(33);
+    x.default_hello();
+    //~^ ERROR no method named `default_hello` found
+}

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish-placeholder.stderr

@@ -0,0 +1,22 @@
+error[E0599]: no method named `default_hello` found for struct `GenericAssocMethod<{integer}>` in the current scope
+  --> $DIR/suggest-assoc-fn-call-with-turbofish-placeholder.rs:9:7
+   |
+LL | struct GenericAssocMethod<T>(T);
+   | ---------------------------- method `default_hello` not found for this struct
+...
+LL |     x.default_hello();
+   |     --^^^^^^^^^^^^^--
+   |     | |
+   |     | this is an associated function, not a method
+   |     help: use associated function syntax instead: `GenericAssocMethod::<_>::default_hello()`
+   |
+   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
+note: the candidate is defined in an impl for the type `GenericAssocMethod<T>`
+  --> $DIR/suggest-assoc-fn-call-with-turbofish-placeholder.rs:4:5
+   |
+LL |     fn default_hello() {}
+   |     ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish-through-deref.stderr

@@ -2,10 +2,10 @@ error[E0599]: no method named `hello` found for struct `RefMut<'_, HasAssocMetho
   --> $DIR/suggest-assoc-fn-call-with-turbofish-through-deref.rs:11:11
    |
 LL |     state.hello();
-   |     ------^^^^^
+   |     ------^^^^^--
    |     |     |
    |     |     this is an associated function, not a method
-   |     help: use associated function syntax instead: `HasAssocMethod::hello`
+   |     help: use associated function syntax instead: `HasAssocMethod::hello()`
    |
    = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
 note: the candidate is defined in an impl for the type `HasAssocMethod`

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.fixed

@@ -0,0 +1,26 @@
+// run-rustfix
+
+struct GenericAssocMethod<T>(T);
+
+impl<T> GenericAssocMethod<T> {
+    fn default_hello() {}
+    fn self_ty_hello(_: Self) {}
+    fn self_ty_ref_hello(_: &Self) {}
+}
+
+fn main() {
+    // Test for inferred types
+    let x = GenericAssocMethod(33);
+    GenericAssocMethod::<_>::self_ty_ref_hello(&x);
+    //~^ ERROR no method named `self_ty_ref_hello` found
+    GenericAssocMethod::<_>::self_ty_hello(x);
+    //~^ ERROR no method named `self_ty_hello` found
+    // Test for known types
+    let y = GenericAssocMethod(33i32);
+    GenericAssocMethod::<i32>::default_hello();
+    //~^ ERROR no method named `default_hello` found
+    GenericAssocMethod::<i32>::self_ty_ref_hello(&y);
+    //~^ ERROR no method named `self_ty_ref_hello` found
+    GenericAssocMethod::<i32>::self_ty_hello(y);
+    //~^ ERROR no method named `self_ty_hello` found
+}

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.rs

@@ -1,11 +1,26 @@
+// run-rustfix
+
 struct GenericAssocMethod<T>(T);
 
 impl<T> GenericAssocMethod<T> {
     fn default_hello() {}
+    fn self_ty_hello(_: Self) {}
+    fn self_ty_ref_hello(_: &Self) {}
 }
 
 fn main() {
-    let x = GenericAssocMethod(33i32);
-    x.default_hello();
+    // Test for inferred types
+    let x = GenericAssocMethod(33);
+    x.self_ty_ref_hello();
+    //~^ ERROR no method named `self_ty_ref_hello` found
+    x.self_ty_hello();
+    //~^ ERROR no method named `self_ty_hello` found
+    // Test for known types
+    let y = GenericAssocMethod(33i32);
+    y.default_hello();
     //~^ ERROR no method named `default_hello` found
+    y.self_ty_ref_hello();
+    //~^ ERROR no method named `self_ty_ref_hello` found
+    y.self_ty_hello();
+    //~^ ERROR no method named `self_ty_hello` found
 }