Rollup of 5 pull requests

src/libcore/convert.rs

@@ -463,11 +463,11 @@ impl<T, U> TryInto<U> for T where U: TryFrom<T>
 // Infallible conversions are semantically equivalent to fallible conversions
 // with an uninhabited error type.
 #[unstable(feature = "try_from", issue = "33417")]
-impl<T, U> TryFrom<U> for T where T: From<U> {
+impl<T, U> TryFrom<U> for T where U: Into<T> {
     type Error = !;
 
     fn try_from(value: U) -> Result<Self, Self::Error> {
-        Ok(T::from(value))
+        Ok(U::into(value))
     }
 }
 

src/librustc/hir/lowering.rs

@@ -31,6 +31,7 @@
 //! in the HIR, especially for multiple identifiers.
 
 use dep_graph::DepGraph;
+use errors::Applicability;
 use hir::{self, ParamName};
 use hir::HirVec;
 use hir::map::{DefKey, DefPathData, Definitions};
@@ -1806,7 +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)
@@ -1823,10 +1824,25 @@ impl<'a> LoweringContext<'a> {
                         (hir::GenericArgs::none(), true)
                     }
                     ParenthesizedGenericArgs::Err => {
-                        struct_span_err!(self.sess, data.span, E0214, "{}", msg)
-                            .span_label(data.span, "only traits may use parentheses")
-                            .emit();
-                        (hir::GenericArgs::none(), true)
+                        let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
+                        err.span_label(data.span, "only `Fn` traits may use parentheses");
+                        if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
+                            // 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(
+                            &data.as_angle_bracketed_args(),
+                            param_mode,
+                            itctx).0,
+                         false)
                     }
                 },
             }

src/librustc/infer/error_reporting/mod.rs

@@ -485,12 +485,29 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
-    fn note_error_origin(&self, err: &mut DiagnosticBuilder<'tcx>, cause: &ObligationCause<'tcx>) {
+    fn note_error_origin(
+        &self,
+        err: &mut DiagnosticBuilder<'tcx>,
+        cause: &ObligationCause<'tcx>,
+        exp_found: Option<ty::error::ExpectedFound<Ty<'tcx>>>,
+    ) {
         match cause.code {
             ObligationCauseCode::MatchExpressionArmPattern { span, ty } => {
                 if ty.is_suggestable() {  // don't show type `_`
                     err.span_label(span, format!("this match expression has type `{}`", ty));
                 }
+                if let Some(ty::error::ExpectedFound { found, .. }) = exp_found {
+                    if ty.is_box() && ty.boxed_ty() == found {
+                        if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
+                            err.span_suggestion_with_applicability(
+                                span,
+                                "consider dereferencing the boxed value",
+                                format!("*{}", snippet),
+                                Applicability::MachineApplicable,
+                            );
+                        }
+                    }
+                }
             }
             ObligationCauseCode::MatchExpressionArm { arm_span, source } => match source {
                 hir::MatchSource::IfLetDesugar { .. } => {
@@ -1013,7 +1030,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         // It reads better to have the error origin as the final
         // thing.
-        self.note_error_origin(diag, &cause);
+        self.note_error_origin(diag, &cause, exp_found);
     }
 
     /// When encountering a case where `.as_ref()` on a `Result` or `Option` would be appropriate,

src/librustc_typeck/check/demand.rs

@@ -454,12 +454,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         false
     }
 
-    pub fn check_for_cast(&self,
-                      err: &mut DiagnosticBuilder<'tcx>,
-                      expr: &hir::Expr,
-                      checked_ty: Ty<'tcx>,
-                      expected_ty: Ty<'tcx>)
-                      -> bool {
+    pub fn check_for_cast(
+        &self,
+        err: &mut DiagnosticBuilder<'tcx>,
+        expr: &hir::Expr,
+        checked_ty: Ty<'tcx>,
+        expected_ty: Ty<'tcx>,
+    ) -> bool {
         let parent_id = self.tcx.hir().get_parent_node(expr.id);
         if let Some(parent) = self.tcx.hir().find(parent_id) {
             // Shouldn't suggest `.into()` on `const`s.
@@ -487,17 +488,40 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         // For now, don't suggest casting with `as`.
         let can_cast = false;
 
+        let mut prefix = String::new();
+        if let Some(hir::Node::Expr(hir::Expr {
+            node: hir::ExprKind::Struct(_, fields, _),
+            ..
+        })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.id)) {
+            // `expr` is a literal field for a struct, only suggest if appropriate
+            for field in fields {
+                if field.expr.id == expr.id && field.is_shorthand {
+                    // This is a field literal
+                    prefix = format!("{}: ", field.ident);
+                    break;
+                }
+            }
+            if &prefix == "" {
+                // Likely a field was meant, but this field wasn't found. Do not suggest anything.
+                return false;
+            }
+        }
+
         let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);
 
         if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
             let msg = format!("you can cast an `{}` to `{}`", checked_ty, expected_ty);
-            let cast_suggestion = format!("{}{}{} as {}",
-                                          if needs_paren { "(" } else { "" },
-                                          src,
-                                          if needs_paren { ")" } else { "" },
-                                          expected_ty);
+            let cast_suggestion = format!(
+                "{}{}{}{} as {}",
+                prefix,
+                if needs_paren { "(" } else { "" },
+                src,
+                if needs_paren { ")" } else { "" },
+                expected_ty,
+            );
             let into_suggestion = format!(
-                "{}{}{}.into()",
+                "{}{}{}{}.into()",
+                prefix,
                 if needs_paren { "(" } else { "" },
                 src,
                 if needs_paren { ")" } else { "" },

src/libsyntax/ast.rs

@@ -192,6 +192,16 @@ pub struct ParenthesisedArgs {
     pub output: Option<P<Ty>>,
 }
 
+impl ParenthesisedArgs {
+    pub fn as_angle_bracketed_args(&self) -> AngleBracketedArgs {
+        AngleBracketedArgs {
+            span: self.span,
+            args: self.inputs.iter().cloned().map(|input| GenericArg::Type(input)).collect(),
+            bindings: vec![],
+        }
+    }
+}
+
 // hack to ensure that we don't try to access the private parts of `NodeId` in this module
 mod node_id_inner {
     use rustc_data_structures::indexed_vec::Idx;

src/libsyntax/parse/parser.rs

@@ -2176,11 +2176,11 @@ impl<'a> Parser<'a> {
               style != PathStyle::Mod && self.check(&token::ModSep)
                                       && self.look_ahead(1, |t| is_args_start(t)) {
             // Generic arguments are found - `<`, `(`, `::<` or `::(`.
-            let lo = self.span;
             if self.eat(&token::ModSep) && style == PathStyle::Type && enable_warning {
                 self.diagnostic().struct_span_warn(self.prev_span, "unnecessary path disambiguator")
                                  .span_label(self.prev_span, "try removing `::`").emit();
             }
+            let lo = self.span;
 
             let args = if self.eat_lt() {
                 // `<'a, T, A = U>`
@@ -4483,13 +4483,17 @@ impl<'a> Parser<'a> {
     }
 
     /// Emit an expected item after attributes error.
-    fn expected_item_err(&self, attrs: &[Attribute]) {
+    fn expected_item_err(&mut self, attrs: &[Attribute]) -> PResult<'a,  ()> {
         let message = match attrs.last() {
             Some(&Attribute { is_sugared_doc: true, .. }) => "expected item after doc comment",
             _ => "expected item after attributes",
         };
 
-        self.span_err(self.prev_span, message);
+        let mut err = self.diagnostic().struct_span_err(self.prev_span, message);
+        if attrs.last().unwrap().is_sugared_doc {
+            err.span_label(self.prev_span, "this doc comment doesn't document anything");
+        }
+        Err(err)
     }
 
     /// Parse a statement. This stops just before trailing semicolons on everything but items.
@@ -7636,7 +7640,7 @@ impl<'a> Parser<'a> {
             }
             None => {
                 if !attrs.is_empty()  {
-                    self.expected_item_err(&attrs);
+                    self.expected_item_err(&attrs)?;
                 }
 
                 self.unexpected()
@@ -7699,7 +7703,7 @@ impl<'a> Parser<'a> {
         }
 
         if !attributes_allowed && !attrs.is_empty() {
-            self.expected_item_err(&attrs);
+            self.expected_item_err(&attrs)?;
         }
         Ok(None)
     }

src/test/run-pass/try_from.rs

@@ -0,0 +1,37 @@
+// This test relies on `TryFrom` being blanket impl for all `T: Into`
+// and `TryInto` being blanket impl for all `U: TryFrom`
+
+// This test was added to show the motivation for doing this
+// over `TryFrom` being blanket impl for all `T: From`
+
+#![feature(try_from, never_type)]
+
+use std::convert::TryInto;
+
+struct Foo<T> {
+    t: T,
+}
+
+// This fails to compile due to coherence restrictions
+// as of Rust version 1.32.x, therefore it could not be used
+// instead of the `Into` version of the impl, and serves as
+// motivation for a blanket impl for all `T: Into`, instead
+// of a blanket impl for all `T: From`
+/*
+impl<T> From<Foo<T>> for Box<T> {
+    fn from(foo: Foo<T>) -> Box<T> {
+        Box::new(foo.t)
+    }
+}
+*/
+
+impl<T> Into<Vec<T>> for Foo<T> {
+    fn into(self) -> Vec<T> {
+        vec![self.t]
+    }
+}
+
+pub fn main() {
+    let _: Result<Vec<i32>, !> = Foo { t: 10 }.try_into();
+}
+

src/test/ui/e0119/conflict-with-std.stderr

@@ -25,7 +25,7 @@ LL | impl TryFrom<X> for X { //~ ERROR conflicting implementations
    |
    = note: conflicting implementation in crate `core`:
            - impl<T, U> std::convert::TryFrom<U> for T
-             where T: std::convert::From<U>;
+             where U: std::convert::Into<T>;
 
 error: aborting due to 3 previous errors
 

src/test/ui/error-codes/E0214.stderr

@@ -1,8 +1,11 @@
-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
 

src/test/ui/issues/issue-23589.rs

@@ -1,4 +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
 }

src/test/ui/issues/issue-23589.stderr

@@ -1,9 +1,22 @@
-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: aborting due to previous error
+error[E0308]: mismatched types
+  --> $DIR/issue-23589.rs:2:29
+   |
+LL |     let v: Vec(&str) = vec!['1', '2'];
+   |                             ^^^ expected &str, found char
+   |
+   = note: expected type `&str`
+              found type `char`
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0214`.
+Some errors occurred: E0214, E0308.
+For more information about an error, try `rustc --explain E0214`.

src/test/ui/issues/issue-32995-2.rs

@@ -2,17 +2,17 @@
 
 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
 }
 
 #[derive(Clone)]
 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

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 {}