Attempt to fix arguments of associated functions

6 files changed, 126 insertions, 61 deletions

diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 52099102dc2..7ec3d453660 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -13,7 +13,7 @@ use rustc_hir as hir;
 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_hir::{Expr, ExprKind, Node, QPath};
 use rustc_infer::infer::{
     type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
     RegionVariableOrigin,
@@ -397,6 +397,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     custom_span_label = true;
                 }
                 if static_candidates.len() == 1 {
+                    let mut has_unsuggestable_args = false;
                     let ty_str = if let Some(CandidateSource::Impl(impl_did)) =
                     static_candidates.get(0)
                     {
@@ -412,6 +413,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                     .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(
@@ -450,12 +452,62 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     } else {
                         self.ty_to_value_string(actual.peel_refs())
                     };
-                    if let SelfSource::MethodCall(expr) = source {
+                    if let SelfSource::MethodCall(_) = source {
+                        let first_arg = if let Some(CandidateSource::Impl(impl_did)) = static_sources.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 {
+                                        ""
+                                    })
+                                }
+                            } else {
+                                None
+                            }
+                        } else {
+                            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 it = if first_arg.is_some() {
+                                Box::new(std::iter::once(receiver).chain(args.iter()))
+                                    as Box<dyn Iterator<Item = &Expr<'_>>>
+                            } else {
+                                // There is no `Self` kind to infer the arguments from
+                                if has_unsuggestable_args {
+                                    applicability = Applicability::HasPlaceholders;
+                                }
+                                Box::new(args.iter()) as _
+                            };
+                            format!(
+                                "({}{})",
+                                first_arg.unwrap_or(""),
+                                it.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()
+                        };
                         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,));
diff --git a/src/test/ui/issues/issue-3707.stderr b/src/test/ui/issues/issue-3707.stderr
index 6ca2deee377..07c8101cbc6 100644
--- a/src/test/ui/issues/issue-3707.stderr
+++ b/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`
diff --git a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish-through-deref.stderr b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish-through-deref.stderr
index 996d5773118..7c9f0b6c212 100644
--- a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish-through-deref.stderr
+++ b/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`
diff --git a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.fixed b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.fixed
new file mode 100644
index 00000000000..0398c510fea
--- /dev/null
+++ b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.fixed
@@ -0,0 +1,29 @@
+// 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);
+    // This particular case is unfixable without more information by the user,
+    // but `cargo fix --broken-code` reports a bug if
+    // x.default_hello();
+    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
+}
diff --git a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.rs b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.rs
index 213d1c72f9a..8bafc83bdd0 100644
--- a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.rs
+++ b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.rs
@@ -1,16 +1,19 @@
+// run-rustfix
+
 struct GenericAssocMethod<T>(T);
 
 impl<T> GenericAssocMethod<T> {
     fn default_hello() {}
-    fn self_ty_hello(_: T) {}
-    fn self_ty_ref_hello(_: &T) {}
+    fn self_ty_hello(_: Self) {}
+    fn self_ty_ref_hello(_: &Self) {}
 }
 
 fn main() {
     // Test for inferred types
     let x = GenericAssocMethod(33);
-    x.default_hello();
-    //~^ ERROR no method named `default_hello` found
+    // This particular case is unfixable without more information by the user,
+    // but `cargo fix --broken-code` reports a bug if
+    // x.default_hello();
     x.self_ty_ref_hello();
     //~^ ERROR no method named `self_ty_ref_hello` found
     x.self_ty_hello();
diff --git a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.stderr b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.stderr
index c6d9122228a..e2f2d46b9e8 100644
--- a/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.stderr
+++ b/src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.stderr
@@ -1,117 +1,98 @@
-error[E0599]: no method named `default_hello` found for struct `GenericAssocMethod<{integer}>` in the current scope
-  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:12:7
-   |
-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.rs:4:5
-   |
-LL |     fn default_hello() {}
-   |     ^^^^^^^^^^^^^^^^^^
-
 error[E0599]: no method named `self_ty_ref_hello` found for struct `GenericAssocMethod<{integer}>` in the current scope
-  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:14:7
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:17:7
    |
 LL | struct GenericAssocMethod<T>(T);
    | ---------------------------- method `self_ty_ref_hello` not found for this struct
 ...
 LL |     x.self_ty_ref_hello();
-   |     --^^^^^^^^^^^^^^^^^
+   |     --^^^^^^^^^^^^^^^^^--
    |     | |
    |     | this is an associated function, not a method
-   |     help: use associated function syntax instead: `GenericAssocMethod::<_>::self_ty_ref_hello`
+   |     help: use associated function syntax instead: `GenericAssocMethod::<_>::self_ty_ref_hello(&x)`
    |
    = 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.rs:6:5
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:8:5
    |
-LL |     fn self_ty_ref_hello(_: &T) {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     fn self_ty_ref_hello(_: &Self) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0599]: no method named `self_ty_hello` found for struct `GenericAssocMethod<{integer}>` in the current scope
-  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:16:7
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:19:7
    |
 LL | struct GenericAssocMethod<T>(T);
    | ---------------------------- method `self_ty_hello` not found for this struct
 ...
 LL |     x.self_ty_hello();
-   |     --^^^^^^^^^^^^^
+   |     --^^^^^^^^^^^^^--
    |     | |
    |     | this is an associated function, not a method
-   |     help: use associated function syntax instead: `GenericAssocMethod::<_>::self_ty_hello`
+   |     help: use associated function syntax instead: `GenericAssocMethod::<_>::self_ty_hello(x)`
    |
    = 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.rs:5:5
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:7:5
    |
-LL |     fn self_ty_hello(_: T) {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^
+LL |     fn self_ty_hello(_: Self) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0599]: no method named `default_hello` found for struct `GenericAssocMethod<i32>` in the current scope
-  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:20:7
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:23:7
    |
 LL | struct GenericAssocMethod<T>(T);
    | ---------------------------- method `default_hello` not found for this struct
 ...
 LL |     y.default_hello();
-   |     --^^^^^^^^^^^^^
+   |     --^^^^^^^^^^^^^--
    |     | |
    |     | this is an associated function, not a method
-   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::default_hello`
+   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::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.rs:4:5
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:6:5
    |
 LL |     fn default_hello() {}
    |     ^^^^^^^^^^^^^^^^^^
 
 error[E0599]: no method named `self_ty_ref_hello` found for struct `GenericAssocMethod<i32>` in the current scope
-  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:22:7
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:25:7
    |
 LL | struct GenericAssocMethod<T>(T);
    | ---------------------------- method `self_ty_ref_hello` not found for this struct
 ...
 LL |     y.self_ty_ref_hello();
-   |     --^^^^^^^^^^^^^^^^^
+   |     --^^^^^^^^^^^^^^^^^--
    |     | |
    |     | this is an associated function, not a method
-   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::self_ty_ref_hello`
+   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::self_ty_ref_hello(&y)`
    |
    = 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.rs:6:5
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:8:5
    |
-LL |     fn self_ty_ref_hello(_: &T) {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     fn self_ty_ref_hello(_: &Self) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0599]: no method named `self_ty_hello` found for struct `GenericAssocMethod<i32>` in the current scope
-  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:24:7
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:27:7
    |
 LL | struct GenericAssocMethod<T>(T);
    | ---------------------------- method `self_ty_hello` not found for this struct
 ...
 LL |     y.self_ty_hello();
-   |     --^^^^^^^^^^^^^
+   |     --^^^^^^^^^^^^^--
    |     | |
    |     | this is an associated function, not a method
-   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::self_ty_hello`
+   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::self_ty_hello(y)`
    |
    = 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.rs:5:5
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:7:5
    |
-LL |     fn self_ty_hello(_: T) {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^
+LL |     fn self_ty_hello(_: Self) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0599`.