Extend suggestion support for traits and foreign items

src/librustc_typeck/check/mod.rs

@@ -3858,11 +3858,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     Some(Node::Item(hir::Item {
                         node: ItemKind::Fn(.., body_id),
                         ..
+                    })) |
+                    Some(Node::ImplItem(hir::ImplItem {
+                        node: hir::ImplItemKind::Method(_, body_id),
+                        ..
+                    })) |
+                    Some(Node::TraitItem(hir::TraitItem {
+                        node: hir::TraitItemKind::Method(.., hir::TraitMethod::Provided(body_id)),
+                        ..
                     })) => {
                         let body = hir.body(*body_id);
                         sugg_call = body.arguments.iter()
                             .map(|arg| match &arg.pat.node {
-                                hir::PatKind::Binding(_, _, ident, None) => ident.to_string(),
+                                hir::PatKind::Binding(_, _, ident, None)
+                                if ident.name != kw::SelfLower => ident.to_string(),
                                 _ => "_".to_string(),
                             }).collect::<Vec<_>>().join(", ");
                     }
@@ -3878,6 +3887,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             _ => {}
                         }
                     }
+                    Some(Node::ForeignItem(hir::ForeignItem {
+                        node: hir::ForeignItemKind::Fn(_, idents, _),
+                        ..
+                    })) |
+                    Some(Node::TraitItem(hir::TraitItem {
+                        node: hir::TraitItemKind::Method(.., hir::TraitMethod::Required(idents)),
+                        ..
+                    })) => sugg_call = idents.iter()
+                            .map(|ident| if ident.name != kw::SelfLower {
+                                ident.to_string()
+                            } else {
+                                "_".to_string()
+                            }).collect::<Vec<_>>()
+                            .join(", "),
                     _ => {}
                 }
             };

src/test/ui/suggestions/fn-or-tuple-struct-without-args.rs

@@ -11,7 +11,18 @@ struct V();
 
 trait T {
     fn baz(x: usize, y: usize) -> usize { x }
-    fn bat() -> usize { 42 }
+    fn bat(x: usize) -> usize { 42 }
+    fn bax(x: usize) -> usize { 42 }
+    fn bach(x: usize) -> usize;
+    fn ban(&self) -> usize { 42 }
+    fn bal(&self) -> usize;
+}
+
+struct X;
+
+impl T for X {
+    fn bach(x: usize) -> usize { 42 }
+    fn bal(&self) -> usize { 42 }
 }
 
 fn main() {
@@ -23,4 +34,12 @@ fn main() {
     let _: usize = T::bat; //~ ERROR mismatched types
     let _: E = E::A; //~ ERROR mismatched types
     let _: E = E::B; //~ ERROR expected value, found struct variant `E::B`
+    let _: usize = X::baz; //~ ERROR mismatched types
+    let _: usize = X::bat; //~ ERROR mismatched types
+    let _: usize = X::bax; //~ ERROR mismatched types
+    let _: usize = X::bach; //~ ERROR mismatched types
+    let _: usize = X::ban; //~ ERROR mismatched types
+    let _: usize = X::bal; //~ ERROR mismatched types
+    let _: usize = X.ban; //~ ERROR attempted to take value of method
+    let _: usize = X.bal; //~ ERROR attempted to take value of method
 }

src/test/ui/suggestions/fn-or-tuple-struct-without-args.stderr

@@ -1,5 +1,5 @@
 error[E0423]: expected value, found struct variant `E::B`
-  --> $DIR/fn-or-tuple-struct-without-args.rs:25:16
+  --> $DIR/fn-or-tuple-struct-without-args.rs:36:16
    |
 LL |     let _: E = E::B;
    |                ^^^-
@@ -8,7 +8,7 @@ LL |     let _: E = E::B;
    |                did you mean `E::B { /* fields */ }`?
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:18:20
+  --> $DIR/fn-or-tuple-struct-without-args.rs:29:20
    |
 LL | fn foo(a: usize, b: usize) -> usize { a }
    | ----------------------------------- fn(usize, usize) -> usize {foo} defined here
@@ -23,7 +23,7 @@ LL |     let _: usize = foo;
               found type `fn(usize, usize) -> usize {foo}`
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:19:16
+  --> $DIR/fn-or-tuple-struct-without-args.rs:30:16
    |
 LL | struct S(usize, usize);
    | ----------------------- fn(usize, usize) -> S {S} defined here
@@ -38,7 +38,7 @@ LL |     let _: S = S;
               found type `fn(usize, usize) -> S {S}`
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:20:20
+  --> $DIR/fn-or-tuple-struct-without-args.rs:31:20
    |
 LL | fn bar() -> usize { 42 }
    | ----------------- fn() -> usize {bar} defined here
@@ -53,7 +53,7 @@ LL |     let _: usize = bar;
               found type `fn() -> usize {bar}`
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:21:16
+  --> $DIR/fn-or-tuple-struct-without-args.rs:32:16
    |
 LL | struct V();
    | ----------- fn() -> V {V} defined here
@@ -68,7 +68,7 @@ LL |     let _: V = V;
               found type `fn() -> V {V}`
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:22:20
+  --> $DIR/fn-or-tuple-struct-without-args.rs:33:20
    |
 LL |     fn baz(x: usize, y: usize) -> usize { x }
    |     ----------------------------------- fn(usize, usize) -> usize {<_ as T>::baz} defined here
@@ -77,28 +77,28 @@ LL |     let _: usize = T::baz;
    |                    ^^^^^^
    |                    |
    |                    expected usize, found fn item
-   |                    help: use parentheses to call this function: `T::baz(...)`
+   |                    help: use parentheses to call this function: `T::baz(x, y)`
    |
    = note: expected type `usize`
               found type `fn(usize, usize) -> usize {<_ as T>::baz}`
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:23:20
+  --> $DIR/fn-or-tuple-struct-without-args.rs:34:20
    |
-LL |     fn bat() -> usize { 42 }
-   |     ----------------- fn() -> usize {<_ as T>::bat} defined here
+LL |     fn bat(x: usize) -> usize { 42 }
+   |     ------------------------- fn(usize) -> usize {<_ as T>::bat} defined here
 ...
 LL |     let _: usize = T::bat;
    |                    ^^^^^^
    |                    |
    |                    expected usize, found fn item
-   |                    help: use parentheses to call this function: `T::bat()`
+   |                    help: use parentheses to call this function: `T::bat(x)`
    |
    = note: expected type `usize`
-              found type `fn() -> usize {<_ as T>::bat}`
+              found type `fn(usize) -> usize {<_ as T>::bat}`
 
 error[E0308]: mismatched types
-  --> $DIR/fn-or-tuple-struct-without-args.rs:24:16
+  --> $DIR/fn-or-tuple-struct-without-args.rs:35:16
    |
 LL |     A(usize),
    |     -------- fn(usize) -> E {E::A} defined here
@@ -112,7 +112,109 @@ LL |     let _: E = E::A;
    = note: expected type `E`
               found type `fn(usize) -> E {E::A}`
 
-error: aborting due to 8 previous errors
+error[E0308]: mismatched types
+  --> $DIR/fn-or-tuple-struct-without-args.rs:37:20
+   |
+LL |     fn baz(x: usize, y: usize) -> usize { x }
+   |     ----------------------------------- fn(usize, usize) -> usize {<X as T>::baz} defined here
+...
+LL |     let _: usize = X::baz;
+   |                    ^^^^^^
+   |                    |
+   |                    expected usize, found fn item
+   |                    help: use parentheses to call this function: `X::baz(x, y)`
+   |
+   = note: expected type `usize`
+              found type `fn(usize, usize) -> usize {<X as T>::baz}`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-or-tuple-struct-without-args.rs:38:20
+   |
+LL |     fn bat(x: usize) -> usize { 42 }
+   |     ------------------------- fn(usize) -> usize {<X as T>::bat} defined here
+...
+LL |     let _: usize = X::bat;
+   |                    ^^^^^^
+   |                    |
+   |                    expected usize, found fn item
+   |                    help: use parentheses to call this function: `X::bat(x)`
+   |
+   = note: expected type `usize`
+              found type `fn(usize) -> usize {<X as T>::bat}`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-or-tuple-struct-without-args.rs:39:20
+   |
+LL |     fn bax(x: usize) -> usize { 42 }
+   |     ------------------------- fn(usize) -> usize {<X as T>::bax} defined here
+...
+LL |     let _: usize = X::bax;
+   |                    ^^^^^^
+   |                    |
+   |                    expected usize, found fn item
+   |                    help: use parentheses to call this function: `X::bax(x)`
+   |
+   = note: expected type `usize`
+              found type `fn(usize) -> usize {<X as T>::bax}`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-or-tuple-struct-without-args.rs:40:20
+   |
+LL |     fn bach(x: usize) -> usize;
+   |     --------------------------- fn(usize) -> usize {<X as T>::bach} defined here
+...
+LL |     let _: usize = X::bach;
+   |                    ^^^^^^^
+   |                    |
+   |                    expected usize, found fn item
+   |                    help: use parentheses to call this function: `X::bach(x)`
+   |
+   = note: expected type `usize`
+              found type `fn(usize) -> usize {<X as T>::bach}`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-or-tuple-struct-without-args.rs:41:20
+   |
+LL |     fn ban(&self) -> usize { 42 }
+   |     ---------------------- for<'r> fn(&'r X) -> usize {<X as T>::ban} defined here
+...
+LL |     let _: usize = X::ban;
+   |                    ^^^^^^
+   |                    |
+   |                    expected usize, found fn item
+   |                    help: use parentheses to call this function: `X::ban(_)`
+   |
+   = note: expected type `usize`
+              found type `for<'r> fn(&'r X) -> usize {<X as T>::ban}`
+
+error[E0308]: mismatched types
+  --> $DIR/fn-or-tuple-struct-without-args.rs:42:20
+   |
+LL |     fn bal(&self) -> usize;
+   |     ----------------------- for<'r> fn(&'r X) -> usize {<X as T>::bal} defined here
+...
+LL |     let _: usize = X::bal;
+   |                    ^^^^^^
+   |                    |
+   |                    expected usize, found fn item
+   |                    help: use parentheses to call this function: `X::bal(_)`
+   |
+   = note: expected type `usize`
+              found type `for<'r> fn(&'r X) -> usize {<X as T>::bal}`
+
+error[E0615]: attempted to take value of method `ban` on type `X`
+  --> $DIR/fn-or-tuple-struct-without-args.rs:43:22
+   |
+LL |     let _: usize = X.ban;
+   |                      ^^^ help: use parentheses to call the method: `ban()`
+
+error[E0615]: attempted to take value of method `bal` on type `X`
+  --> $DIR/fn-or-tuple-struct-without-args.rs:44:22
+   |
+LL |     let _: usize = X.bal;
+   |                      ^^^ help: use parentheses to call the method: `bal()`
+
+error: aborting due to 16 previous errors
 
-Some errors have detailed explanations: E0308, E0423.
+Some errors have detailed explanations: E0308, E0423, E0615.
 For more information about an error, try `rustc --explain E0308`.