Do not suggest angle brackets when there are no type arguments

14 files changed, 45 insertions, 48 deletions

diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
index 9d3438289a0..f7af135bc76 100644
--- a/src/librustc/hir/lowering.rs
+++ b/src/librustc/hir/lowering.rs
@@ -1807,7 +1807,7 @@ impl<'a> LoweringContext<'a> {
         explicit_owner: Option<NodeId>,
     ) -> hir::PathSegment {
         let (mut generic_args, infer_types) = if let Some(ref generic_args) = segment.args {
-            let msg = "parenthesized parameters may only be used with a trait";
+            let msg = "parenthesized type parameters may only be used with a `Fn` trait";
             match **generic_args {
                 GenericArgs::AngleBracketed(ref data) => {
                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
@@ -1825,14 +1825,17 @@ impl<'a> LoweringContext<'a> {
                     }
                     ParenthesizedGenericArgs::Err => {
                         let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
-                        err.span_label(data.span, "only traits may use parentheses");
+                        err.span_label(data.span, "only `Fn` traits may use parentheses");
                         if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
-                            err.span_suggestion_with_applicability(
-                                data.span,
-                                "use angle brackets instead",
-                                format!("<{}>", &snippet[1..snippet.len() - 1]),
-                                Applicability::MaybeIncorrect,
-                            );
+                            // Do not suggest going from `Trait()` to `Trait<>`
+                            if data.inputs.len() > 0 {
+                                err.span_suggestion_with_applicability(
+                                    data.span,
+                                    "use angle brackets instead",
+                                    format!("<{}>", &snippet[1..snippet.len() - 1]),
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
                         };
                         err.emit();
                         (self.lower_angle_bracketed_parameter_data(
diff --git a/src/test/ui/error-codes/E0214.stderr b/src/test/ui/error-codes/E0214.stderr
index 0172dc706ac..a10f2c00578 100644
--- a/src/test/ui/error-codes/E0214.stderr
+++ b/src/test/ui/error-codes/E0214.stderr
@@ -1,10 +1,10 @@
-error[E0214]: parenthesized parameters may only be used with a trait
+error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/E0214.rs:2:15
    |
 LL |     let v: Vec(&str) = vec!["foo"];
    |               ^^^^^^
    |               |
-   |               only traits may use parentheses
+   |               only `Fn` traits may use parentheses
    |               help: use angle brackets instead: `<&str>`
 
 error: aborting due to previous error
diff --git a/src/test/ui/issues/issue-23589.rs b/src/test/ui/issues/issue-23589.rs
index fb765e453dc..1c640af8d02 100644
--- a/src/test/ui/issues/issue-23589.rs
+++ b/src/test/ui/issues/issue-23589.rs
@@ -1,5 +1,5 @@
 fn main() {
     let v: Vec(&str) = vec!['1', '2'];
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| ERROR mismatched types
 }
diff --git a/src/test/ui/issues/issue-23589.stderr b/src/test/ui/issues/issue-23589.stderr
index 932e8eedad1..bc2007ba39c 100644
--- a/src/test/ui/issues/issue-23589.stderr
+++ b/src/test/ui/issues/issue-23589.stderr
@@ -1,10 +1,10 @@
-error[E0214]: parenthesized parameters may only be used with a trait
+error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-23589.rs:2:15
    |
 LL |     let v: Vec(&str) = vec!['1', '2'];
    |               ^^^^^^
    |               |
-   |               only traits may use parentheses
+   |               only `Fn` traits may use parentheses
    |               help: use angle brackets instead: `<&str>`
 
 error[E0308]: mismatched types
diff --git a/src/test/ui/issues/issue-32995-2.rs b/src/test/ui/issues/issue-32995-2.rs
index a4e333ec20a..2234f68f246 100644
--- a/src/test/ui/issues/issue-32995-2.rs
+++ b/src/test/ui/issues/issue-32995-2.rs
@@ -2,11 +2,11 @@
 
 fn main() {
     { fn f<X: ::std::marker()::Send>() {} }
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 
     { fn f() -> impl ::std::marker()::Send { } }
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 }
 
@@ -14,5 +14,5 @@ fn main() {
 struct X;
 
 impl ::std::marker()::Copy for X {}
-//~^ ERROR parenthesized parameters may only be used with a trait
+//~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
 //~| WARN previously accepted
diff --git a/src/test/ui/issues/issue-32995-2.stderr b/src/test/ui/issues/issue-32995-2.stderr
index 0ac12b78d38..104b76cba2d 100644
--- a/src/test/ui/issues/issue-32995-2.stderr
+++ b/src/test/ui/issues/issue-32995-2.stderr
@@ -1,4 +1,4 @@
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995-2.rs:4:28
    |
 LL |     { fn f<X: ::std::marker()::Send>() {} }
@@ -8,7 +8,7 @@ LL |     { fn f<X: ::std::marker()::Send>() {} }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995-2.rs:8:35
    |
 LL |     { fn f() -> impl ::std::marker()::Send { } }
@@ -17,7 +17,7 @@ LL |     { fn f() -> impl ::std::marker()::Send { } }
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995-2.rs:16:19
    |
 LL | impl ::std::marker()::Copy for X {}
diff --git a/src/test/ui/issues/issue-32995.rs b/src/test/ui/issues/issue-32995.rs
index 726cc85d3f4..c32fb63f1e5 100644
--- a/src/test/ui/issues/issue-32995.rs
+++ b/src/test/ui/issues/issue-32995.rs
@@ -2,32 +2,32 @@
 
 fn main() {
     let x: usize() = 1;
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 
     let b: ::std::boxed()::Box<_> = Box::new(1);
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 
     let p = ::std::str::()::from_utf8(b"foo").unwrap();
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 
     let p = ::std::str::from_utf8::()(b"foo").unwrap();
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 
     let o : Box<::std::marker()::Send> = Box::new(1);
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 
     let o : Box<Send + ::std::marker()::Sync> = Box::new(1);
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 }
 
 fn foo<X:Default>() {
     let d : X() = Default::default();
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| WARN previously accepted
 }
diff --git a/src/test/ui/issues/issue-32995.stderr b/src/test/ui/issues/issue-32995.stderr
index e27f2d9553a..97b4b7fa76c 100644
--- a/src/test/ui/issues/issue-32995.stderr
+++ b/src/test/ui/issues/issue-32995.stderr
@@ -1,4 +1,4 @@
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:4:17
    |
 LL |     let x: usize() = 1;
@@ -8,7 +8,7 @@ LL |     let x: usize() = 1;
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:8:24
    |
 LL |     let b: ::std::boxed()::Box<_> = Box::new(1);
@@ -17,7 +17,7 @@ LL |     let b: ::std::boxed()::Box<_> = Box::new(1);
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:12:25
    |
 LL |     let p = ::std::str::()::from_utf8(b"foo").unwrap();
@@ -26,7 +26,7 @@ LL |     let p = ::std::str::()::from_utf8(b"foo").unwrap();
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:16:36
    |
 LL |     let p = ::std::str::from_utf8::()(b"foo").unwrap();
@@ -35,7 +35,7 @@ LL |     let p = ::std::str::from_utf8::()(b"foo").unwrap();
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:20:30
    |
 LL |     let o : Box<::std::marker()::Send> = Box::new(1);
@@ -44,7 +44,7 @@ LL |     let o : Box<::std::marker()::Send> = Box::new(1);
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:24:37
    |
 LL |     let o : Box<Send + ::std::marker()::Sync> = Box::new(1);
@@ -53,7 +53,7 @@ LL |     let o : Box<Send + ::std::marker()::Sync> = Box::new(1);
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error: parenthesized parameters may only be used with a trait
+error: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/issue-32995.rs:30:14
    |
 LL |     let d : X() = Default::default();
diff --git a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.rs b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.rs
index 2827e6eead5..c96a6fa8b6c 100644
--- a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.rs
+++ b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.rs
@@ -6,7 +6,7 @@ struct Bar<A> {
 
 fn bar() {
     let x: Box<Bar()> = panic!();
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| ERROR wrong number of type arguments: expected 1, found 0
 }
 
diff --git a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.stderr b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.stderr
index 87832d839b9..fa52e66fb03 100644
--- a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.stderr
+++ b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-1.stderr
@@ -1,11 +1,8 @@
-error[E0214]: parenthesized parameters may only be used with a trait
+error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/unboxed-closure-sugar-used-on-struct-1.rs:8:19
    |
 LL |     let x: Box<Bar()> = panic!();
-   |                   ^^
-   |                   |
-   |                   only traits may use parentheses
-   |                   help: use angle brackets instead: `<>`
+   |                   ^^ only `Fn` traits may use parentheses
 
 error[E0107]: wrong number of type arguments: expected 1, found 0
   --> $DIR/unboxed-closure-sugar-used-on-struct-1.rs:8:16
diff --git a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.rs b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.rs
index 3cada322b1e..79ced1ecfb1 100644
--- a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.rs
+++ b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.rs
@@ -12,7 +12,7 @@ fn bar() {
     let b = Bar::<isize, usize>::new(); // OK
 
     let b = Bar::(isize, usize)::new(); // OK too (for the parser)
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
 }
 
 fn main() {}
diff --git a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.stderr b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.stderr
index c9cc60717a6..7d05ca55ffd 100644
--- a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.stderr
+++ b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct-3.stderr
@@ -1,10 +1,10 @@
-error[E0214]: parenthesized parameters may only be used with a trait
+error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/unboxed-closure-sugar-used-on-struct-3.rs:14:18
    |
 LL |     let b = Bar::(isize, usize)::new(); // OK too (for the parser)
    |                  ^^^^^^^^^^^^^^
    |                  |
-   |                  only traits may use parentheses
+   |                  only `Fn` traits may use parentheses
    |                  help: use angle brackets instead: `<isize, usize>`
 
 error: aborting due to previous error
diff --git a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.rs b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.rs
index 6da53585c9c..1af7f55674c 100644
--- a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.rs
+++ b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.rs
@@ -5,7 +5,7 @@ struct Bar<A> {
 }
 
 fn foo(b: Box<Bar()>) {
-    //~^ ERROR parenthesized parameters may only be used with a trait
+    //~^ ERROR parenthesized type parameters may only be used with a `Fn` trait
     //~| ERROR wrong number of type arguments: expected 1, found 0
 }
 
diff --git a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.stderr b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.stderr
index a09c2b75386..b34237937ee 100644
--- a/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.stderr
+++ b/src/test/ui/unboxed-closures/unboxed-closure-sugar-used-on-struct.stderr
@@ -1,11 +1,8 @@
-error[E0214]: parenthesized parameters may only be used with a trait
+error[E0214]: parenthesized type parameters may only be used with a `Fn` trait
   --> $DIR/unboxed-closure-sugar-used-on-struct.rs:7:18
    |
 LL | fn foo(b: Box<Bar()>) {
-   |                  ^^
-   |                  |
-   |                  only traits may use parentheses
-   |                  help: use angle brackets instead: `<>`
+   |                  ^^ only `Fn` traits may use parentheses
 
 error[E0107]: wrong number of type arguments: expected 1, found 0
   --> $DIR/unboxed-closure-sugar-used-on-struct.rs:7:15